CHNG I NGUYN L V K THUT THNG TIN IN THOI I/ NGUYN L THNG TIN IN THOI 1. CC C TUYN V THAM S CA M THANH TING NI. a) Ngun gc m thanh: Ta gy dy n, g vo mt trng... dy n, mt trng s rung ln v pht ra m thanh. S tay vo mng loa, khi loa ang pht ra m thanh ta thy mng loa rung ng. Vy m thanh l do vt th dao ng c hc to nn, m thanh pht ra di dng sng m. b) Bng tn ting ni: Qua nghin cu, ngi ta thy rng ting ni ca con ngi l loi m thanh phc tp, gm nhiu n m to nn c gii hn trong khong tn s t 80Hz 10.000Hz. c) c tuyn nng lng ting ni Nng lng ting ni con ngi phn b khng u trong di tn t 80 10.000Hz m bng thc nghim ngi ta v c c tuyn nng lng ting ni nh sau hnh 1.1: Wa (dB)

10.00 f (Hz) 80 300 8001000 3400 0 Hnh 1.1: c tuyn nng lng ting ni Qua c tuyn nng lng ting ni, ta thy nng lng ting ni hu ht tp trung trong khong tn s t 300 3400Hz, cn ngoi khong tn s nng lng ting ni c phn b rt t. 2. C S LA CHN BNG TN IN THOI a) c tnh tai ngiTrang 1

- Kh nng cm th v bin : Tai ngi c kh nng phn bit c 2500 m trm bng khc nhau, phn bit c 130 mc to nh khc nhau, mi mc cch nhau 1dB. - Kh nng cm th v tn s: Tai ngi c th nghe c nhng m thanh di tn t 16 20.000Hz, cn nhng m thanh di 16Hz gi l h m, trn 20.000Hz gi l siu m th tai ngi u khng c kh nng thu nhn Nh vy tai ngi c kh nng cm th v tn s v cm th v bin . Tai ngi khng ch c kh nng thu nhn ring tng m m cn c kh nng thu c cc m tng hp, phn bit c ging ni ca tng ngi b) c tuyn h ng cong ng m (c tuyn Phone)

Hnh 1.2 : H ng cong ng m miu t c tnh ca tai ngi, ngi ta thng dng c tuyn h ng cong ng m. Trn mt ng cong d tn s v cng khc nhau nhng tai ngi vn c nghe r nh nhau. n v o mc to nh ch quan ca tai ngi gi l "Phone". Cng mt bin th nhng tn hiu c tn s cng dch gn khong tn s t 300 n 3400 Hz th ta nghe cng r. Cng mt tn s th tn hiu no c bin cng ln th ta nghe cng r. H ng cong ng m c biu th trn hnh 1.2. Qua h ng cong chng ta thy rng cc ng cong ng m u vng xung gia. iu ni ln khong tn s t 300 3400Hz tai ngi nghe nhy nht. c) Yu cu ca thng tin in thoi Cht lng ca in thoi c nh gi bng r, hiu v tnh trung thc.Trang 2

- r: L t s phn trm gia s phn t ting ni nhn ng u thu trn tng s ting ni truyn t u pht. V d: Ta ni vo in thoi 50 t m i phng ch nghe c 45 t th r l:45 x100% = 90% 50

- hiu : hiu tu thuc vo r v tnh ch quan ca tng ngi. Thng thng r t 85% th hiu rt tt, nu r gim di 70% th hiu rt km. - Tnh trung thc: L cc ging ni m ngi nghe nhn bit ng khi c truyn t qua in thoi. Song trong thng tin in thoi tnh trung thc yu cu khng cao lm. Theo thng k ting ni ca con ngi truyn qua di bng tn t 500 2000Hz th ngi nghe hon ton nghe r. Song bng tn cng m rng ting ni cng trung thc, cht lng m thanh cng cao song khi yu cu v k thut sn xut my mc, thit b cng phc tp, s lng ng thng ghp c trn mt ng truyn gim nn chi ph cho mt cuc gi in thoi tng ln cao. Cn c vo nhng yu t trn m bng tn truyn dn ca thng tin in thoi hin nay ngi ta chn t 300 3400Hz. 3. KHI NIM V NGUYN L CA THNG TIN IN THOI a) Khi nim : Thng tin in thoi l qu trnh truyn a ting ni t ni ny n ni khc bng tn hiu in thng qua my in thoi. b) Mch in c bn: My in thoi l thit b u cui ca mng thng tin in thoi. Qu trnh truyn thng tin c minh ho nh sau: ( hnh 1.3 ) ng dy b Tx M+ _ E23 19 R2 7 R5 4 C3 5 C3 6 R3 6 R3 5 C3 7

a T Rx

Mch in thoi c bn gm: - ng ni (Tx, M) - ng nghe (T, Rx) - ng dy (a, b) - ngun in (E)

Hnh 1.3 Mch in c bn c) Nguyn l lm vic Khi ta ni trc ng ni ca my in thoi, dao ng m thanh ca ting ni s tc ng vo mng rung ca ng ni v ng ni xut hin mtTrang 3

tn hiu in bin i. Tn hiu in ny c truyn qua ng dy ti ng nghe ca my i phng lm cho mng rung ca ng nghe dao ng, lp khng kh trc mng rung dao ng theo, pht ra m thanh tc ng n tai ngi nghe. Qu trnh truyn dn ngc li cng tng t. II/ CC C KIN TRONG MY IN THOI N PHM 1. CC LOI BIN I IN - THANH (NG NI ) ng ni c nhim v bin dao ng m thanh tc ng vo ng ni thnh tn hiu in c tn s, bin tng ng vi p lc m thanh.

Tx M Tx:Transmitter

M: Micro

Hnh 1.4 K hiu ca ng ni ng ni thng c k hiu trong s nh hnh 1.4: a- ng ni tnh in (loi t) - Cu to Gm 2 tm kim loi lm in cc: 1 tm dao ng t do lm mng rung, 1 tm c nh lm tm . Gia 2 tm kim loi l cht in mi c bit, hnh thnh t in c in dung l C, c kh nng tch gi mt in tch khng i l Q. (h nh 1.5) Mng rung (Cc trc) in mi Tm (Cc sau) a E R

Hnh 1.5: Cu to ca ng ni tnh in (loi t) - Nguyn l lm vic Khi ni trc ng ni, p lc m thanh tc ng vo mng rung, lm cho mng rung dao ng theo tn s v bin ca m thanh.Trang 4

oS . Trong o: a+ X hng s in mi tuyt i, l hng s in mi ca cht in mi. S: din tch bn t, a: khong cch gia 2 bn t; X = xm e jt : l s dao ng ca mng rung khi c p lc m thanh tc ng vo mng rung ( cc trc ); xm:

Gi tr in dung ca t in c xc nh: C =

bin m thanh; j t: gc pha V khong cch gia 2 tm bn cc thay i mt lng l x nn gi tr in dung ca t thay i v c dng in phng, np qua t c tnh theo biu thc:q = c uoiC = dq dt

. Trong q l lng in tch c tch gi trn 2 m t:

Do : iC =

dq dcuo dc = = uo dt dt dt

Dng in ny phn nh bn cht ca ting ni, n c gi tr rt nh do tr khng ca ng ni rt ln. Dng in c a ti u vo b khuch i pht, nng cao mc in, a ln ng dy ti i phng. - c im: ng ni tnh in c tr khng rt ln nn phi hp tr khng ngi ta thng u vo b khuch i pht bng transistor trng v n c tr khng vo ln. b- ng ni p in (ng ni thch anh) - Cu to: Gm: (1) tm tinh th thch anh, barium titanate, polymer bn tinh th. (2) Tm kim loi lm mng rung (cc trc). (3) Tm kim loi lm (cc D sau). (4) V bo v. (5) Np y.(6) cc in cc. (hnh 1.6) 5 2 1 3 4 6

Hnh 1.6: Cu to ng ni p in (ng ni thch anh) - Nguyn l lm vicTrang 5

Khi ta ni trc ng ni, p lc m thanh thng qua cc khe h ca np y tc ng vo mng rung lm mng rung dao ng. Theo tnh cht p in thun ca thch anh, trn b mt ca tm thch anh xut hin mt in p (c tn s v bin ph hp vi p lc m thanh). in p ny c thng qua cc in cc a ti u vo b khuch i pht nng cao mc in a ln ng dy,ti i phng. - c im: ng ni p in c tr khng ln, kch thc tng i nh v nhy kh cao , cht lng m thanh chp nhn c nhng chu chn ng c hc km. c- ng ni in ng (Micro in ng) - Cu to: Gm: (1): Np y, (2): Cc l thng khng kh bn ngoi vi bn trong ng ni, (3): V bo v, (4): Cc in cc vo, (5): Nam chm vnh cu, (6): Cun dy, (7): Mng rung, (8): Khe t, (9): Mng chng m. (hnh 1.7) 2 7 6 N S 9 8 N 3 5 4 (b)

N

S

1

(a)

Hnh 1.7: Cu to ca ng ni in ng (Micro in ng) - Nguyn l lm vic: Khi ta ni trc ng ni, p lc m thanh thng qua cc khe h ca np y tc ng vo mng rung lm cho mng rung dao ng (v mng rung gn cht vi m che bi v cun dy) nn cun dy cng dao ng theo. Mt khc, do cun dy t trong t trng u ca nam chm vnh cu. Theo nh lut cm ng in t th trong cun dy xut hin mt sc in ng cm ng. Sc in ng ny c tn s v bin ph hp vi p lc m thanh v c a ti u vo b khuch i pht, nng cao mc in, a ln ng dy, ti i phng. - c im

Trang 6

ng ni in ng c tr khng nh nn phi hp tr khng ngi ta thng u vo b khuch i pht bng transistor lng cc. ng ni in ng khi lm vic khng cn cp ngun mt chiu. 2. NG NGHE - ng nghe c nhim v bin i dao ng in T, RX thnh dao ng m thanh a n tai ngi nghe. - K hiu: hnh 1.8 a- ng nghe p in - Cu to: hnh 1.6 V nguyn l c cu to hon ton ging ng ni p in nhng kch thc, hnh dng c th ln hn. - Nguyn l lm vic Khi c tn hiu in m thanh t b khuch i thu a ti 2 cc ca ng nghe t vo b mt ca 2 cc thch anh. Theo tnh cht p in ngc ca thch anh, tm tinh th thch anh dao ng lm cho mng rung dao ng, tc ng ti lp khng kh trc mng rung dao ng theo pht ra m thanh a n tai ngi nghe. b- ng nghe in ng (loa) - Cu to: hnh 1.7 V nguyn l c cu to hon ton ging ng ni in ng nhng kch thc v hnh dng c th ln hn v khng c mng chng m. - Nguyn l lm vic Trng thi tnh: khi cha c tn hiu in m thanh ti cun dy th xung quanh cun dy c t trng u ca nam chm vnh cu, ng nghe cha lm vic. Trng thi ng: khi c tn hiu in m thanh ti 2 u cun dy, trn cun dy xut hin dng in m thanh, xung quanh cun dy s c t trng ca dng in m thanh. T trng ca dng in tng tc vi t trng ca nam chm vnh cu to ra t lc tc ng vo cun dy, lm cun dy dao ng, ko mng rung dao ng theo, lp khng kh trc mng rung dao ng pht ra m thanh, a n tai ngi nghe. T: telephone Rx: receive Hnh 1.8: K hiu ca ng nghe

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3. A PHT M a- Nhim v a pht m c nhim v bin dao ng(PIEZO)

Hnh 1.9: K hiu in thnh dao ng m thanh.(ting chung ) a pht m b- K hiu: Hnh 1.9

c- Cu to a pht m c ch to da vo mt s vt liu c tnh cht p in nh thch anh, ceramic, barium titanate, polymer bn tinh th... Ngi ta dng ceramic ch to thnh a mng sau dng keo epoxy dn ln trn mt bng ng thau. Trn a ln c 1 a nh ly tn hiu hi tip.(hnh 1.10) a nh bng ceramc 3 a ln bng Chn ni ra 2 ceramc 1 bng ng thau Keo dn Epoxy

ng cpC pht s tng ng.

d- Nguyn l lm vic Hnh 1.10: cu to a pht m Khi c in p tn hiu m tn a vo hai chn 1 v 2 t ln hai mt a ln, cht keramic s co gin theo s bin i ca in p lm cho a ln b un cong dao ng theo quy lut bin thin ca in p a vo. S dao ng s to ra m thanh. Khi a ln dao ng, a nh gn trn a ln dao ng theo. Theo tnh cht p in thun ca keramic, trn b mt ca a nh xut hin mt in p, in p ny theo dy 2 v 3 a hi tip dng tr v u vo b to dao ng m tn duy tr dao ng. e- Ch

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Thc t trong nhng my c mch to dao ng bng transistor u s dng a pht m c cu to nh trnh by trn, cn cc my in thoi bn, my in thoi v tuyn ko di, my in thoi di ng c mch to dao ng bng IC nn a pht m khng c a nh (ch c hai dy ra 1 v 2). III/ CC PHNG PHP PHT S CA MY IN THOI N PHM 1. CU TO BN PHM S thay i u tin gn lin vi tn gi ca my in thoi n phm chnh l bn phm. Bn phm pht s nh nhng, khng gy ting n, c kh nng thu nh. Bn phm c nhim v nhn tc ng n phm ca ngi s dng kch hot vo IC pht s pht tn hiu chn s ti tng i. a- Cu to ca 1 phm Cc phm c cu to gm 2 loi nh hnh 1.11 bao gm: mt nt n bng nha cng pha trn c ghi s, k hiu tng ng vi v tr ca phm n. Pha di nt n nha l 1 tm cao su c n hi tt, gn pha di cao su l tm than (1 tm hoc 2 tm) (xem hnh v 1.11). i din vi tm than, trn mch in l tip im ci rng lc bng vt liu dn in tt tng tip xc (thng lm bng ng) Nt n bng nha cng trn c ghi s Tm than Cao su c n hi tt Tm than

Ni vi hng

Mch in

Ni vi hng Ni vi ct Hnh 1.11: Cu to ca mt phm

Ni vi ct

Khi n nt, tm than s tip xc ng tip im hng v ct tng ng vi con s va n bo cho mch m ho trong IC pht s bit c phm c n. Khi thi n, nh sc n hi ca cao su, tm than tch ri tip im v trng thi ngh. b- Bn phmTrang 9

Bn phm c 2 loi: 1 loi 4 hng 3 ct & 1 loi 4 hng 4 ct b tr nh hnh 1.12. * Chc nng cc phm : + Cc phm c ghi cc s t 0, 1,...., 9 l cc phm n n pht tn hiu chn s a ch. + Cc phm *, # l cc phm n khai thc cc dch v ca tng i. + Cc phm A, B, C, D l cc phm khai thc cc dch v khc. * Cu to ma trn tip im : hnh 1.13.

ct 1hng 1 2 3 1 hng 4 5 6 2 hng 7 8 9 3 hng * 0 # 4 a. loi 4 hng 3 ct 1 4 7 *

ct 22 5 8 0

ct 33 6 9 #

ct 4A B C D

b. loi 4 hng 4 ct

Hnh: 1.12 Cu to bn phm

Ti chn IC pht s

Hnh 1.13: Ma trn tip im ca bn phm Cc hng v cc ct c ni ti cc chn IC pht s tng ng. 2- PHNG PHP PHT S CH PULSE (dng m thp phn) a) Cu to m thp phn - Hnh 1.14 m t biu thi gian khi n s 32: - di 1 chu k xung T = 100ms Trong :Xung khng dng = 2/3T = 60 67msTrang 10

Xung c dng = 1/3T = 40 33ms - Khong thi gian ngh gia cc s l 1T = 100ms ( c dng )3T 1T

I1T 1T

1T

2T

t t Nhc Thi n s 2 Trng thi n s 3 t hp t/h gian ch m thoi ch ca my ngh gia chung cc s b) Nguyn l gi s thi gian ca xung thp phn khi n s 32 Hnh 1.14: Biu Khi n phm IC pht s lm vic a dng xung thp phn c s chu k xung tng ng vi phm c n ra chn m xung (Dp). V d: n phm s 1 th IC a ra 1 chu k xung,n phm s 2 th IC a ra 2 chu k xung....n phm s 0 th IC a ra 10 chu k xung c) Nhn xt - u im: Cu to m n gin, s dng c c a quay s. S dng c cc loi tng i t ng (in c tng nc, ngang dc, in t analog, in t digital). - Nhc im: Tc pht s chm. V d: khi cn gi s 842270 th dng s pht ti tng i mt 3800ms=3,8s. 3- PHNG PHP PHT S CH TONE ( dng m DTMF) a) Cu to m DTMF Khi n 1 phm bt k, IC pht ra 1 tn hiu gm t hp 2 sng hnh sin m tn c tn s tng ng vi hng v ct ca phm c n c di l 40ms. Khong cch gia cc s l 40ms. V d: khi cn gi s 842270 th dng s pht ti tng i mt 440ms = 0,44s. b) Nguyn l

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- Khi thit k mch pht s ch tone ngi ta gn vi cc hng v cc ct vi cc tn s tng ng. C th nh sau: Gn vi cc hng l nhm tn s thp: Hng 1: f1 = 697Hz, hng 2: f2 = 770Hz, hng 3: f3 = 852Hz, hng 4: f4 = 941Hz. Gn vi cc ct l nhm tn s cao: Ct 1: F1 = 1209Hz, ct 2: F2 = 1336Hz, ct 3: F3 = 1447Hz, ct 4: F4 = 1633Hz. - Khi n phm IC pht s lm vic, a ra chn m dng DTMF ( D t ) l mt tn hiu gm t hp 2 sng hnh sin m tn c tn s tng ng vi hng v ct ca phm c n. V d: khi n phm s 5 th IC pht s a ra chn m D t mt tn hiu gm t hp 2 sng hnh sin m tn c tn s f2 = 770Hz v F2 = 1336Hz. - tng i sau khi nhn c t hp tn hiu ny, n s tin hnh phn tch v gii m xc nh ra con s m thu bao n. c) Nhn xt - u im: tc pht s nhanh - Nhc im: m DTMF ch s dng c tng i in t digital, cn cc loi tng i khc khng s dng c v cc loi tng i khc khng c b phn tch, gii m DTMF. 4- KT LUN tn dng c u im ca cc phng thc gi s v gip ngi s dng thun tin, bo m tnh kinh doanh ca nh sn xut nn trong my in thoi n phm ngi ta thit k c 2 phng thc gi s (dng ch pulse v dng ch tone). Mun s dng phng thc gi s no ngi ta ch cn chuyn kho chn phng thc gi s (P-T) v pha . IV/ CC MCH IN TRONG MY IN THOI N PHM R0 R0 T T T 1. MCH CHNG QU P D1 a/ Mch in: Hnh1.15 Vo Vo ZNR my my D2 R (a) R (b) R(c)

R0Vo my

D

(a) mch chng qu p dng diode Zene (b) mch Trang 12 chng qu p dng SIDAC (c) mch chng qu p dng DIAC Hnh 1.15: Mch chng qu p

b/ Nguyn l lm vic - Khi trn ng dy thu bao c in p - 48V t tng i a n in p ngng ca mch bo v qu p th tr khng ca mch rt ln, l tng Z = nn khng c dng qua mch bo v qu p m ton b c cp cho cc mch in trong my lm vic. - Khi c in p l (st, in lc ...) xm nhp vo ng dy thu bao c in p rt ln hn in p ngng ca mch bo v qu p th diode ZENER, SIDAC, DIAC b nh thng ngn mch u vo. Khi dng in trn ng dy tng ln gy st p trn in tr R 0 rt ln lm cho in tr b chy, h mch u vo, bo v an ton cho cc c kin trong my. 2. MCH CHNG O CC a-Mch chng o cc bng cu diode - Mch in: Hnh 1.16 T ZNR R D4 D3 D1 A D2 Rt

B Hnh 1.16: Mch chng o cc bng cu diode - Nguyn l lm vic Nu in p ngun t tng i a n trn 2 dy T, R c th dy T (+), dy R (-) th D1 v D3 phn cc thun nn thng; D2 v D4 phn cc ngc nn tt. C dng cp cho Rt theo mch: (+) dy T D1 A Rt B D3 dy R (-) gy st p trn tr khng Rt: (+) A v (-) B. Nu in p ngun t tng i a n trn 2 dy T, R c th dy T (-), dy R (+) th D2, D4 c phn cc thun nn thng ; D1 v D3 phn cc ngc nn tt. C dng cp cho ti theo mch: (+) dy R D2 A Rt B D4 dy T (-) gy st p trn tr khng Rt: (+) A v (-) B.Trang 13

- Kt lun: mc d th dy T (+), dy R (-) hoc dy T (-), dy R (+) nhng sau khi qua mch chng o cc th th A lun lun (+) v th B lun lun (-) bo m cc tnh ngun cp cho my khng i (c nh). - Nhn xt + u im: n gin, d lp t v sa cha, gi thnh h. + Nhc im: chim din tch trong my ln, khi lm vic st p trn mi diode ln (0,75V) nh vy st p trn mch l 1,5V, vn ny s gy nh hng ti cht lng ca my i vi nhng my qu xa tng i. b/ Mch chng o cc bng IC - Mch in: Hnh 1.17 Ngi ta chn R sao cho cc Q lm vic ch chuyn mch. (ch D) - Nguyn l lm vic T (+) (-) IC Q4 Q3 R (-) (+) -B Nu in p t tng i a n trn 2 dy T, R c th dy T (+), dy R (-) th Q1, Q3 phn cc thun nn thng ; Q2 v Q4 phn cc ngc nn tt. C dng cp cho my theo mch (+) dy T Q1 A Rt B Q3 dy R (-) gy st p trn tr khng Rt: (+) A v (-) B. Nu dy T (-), dy R (+) th Q2, Q4 phn cc thun nn thng; Q1, Q3 phn cc ngc nn tt. C dng cp cho my theo mch (+) dy R Q2 A Rt B Q4 T (-) gy st p trn tr khng Rt: (+) A v (-) B. R R Q1 +A Q2 Rt

Hnh 1.17: Mch chng o cc bng IC

Trang 14

Kt lun: D th dy T (+) hay (-) v dy R (-) hay (+) nhng sau khi qua mch chng o cc th th A lun lun (+) v th B lun lun (-) bo m cc tnh ngun cp cho my khng i. - Nhn xt + u im: Nh, gn, chim t din tch trong my. Khi lm vic st p trn mi transistor nh (0,2V) nn st p trn ton mch bng 0,4V; Rt thch hp cho cc my t xa tng i. + Nhc im: gi thnh cao v khi hng mt linh kin trong IC l phi thay th c IC. 3. MCH THU CHUNG 3.1. Mch thu chung bng Transistor

a. Mch in: Hnh 1.18 T C1 R1 D2 ZD R2 D1 R C2 R3 C3 R4 Q1 PIEZO

Hnh 1.18: Mch thu chung bng Transistor b. Tc dng linh kin - C1: Ngn dng mt chiu, dn tn hiu chung h tn, ng thi kt hp vi R1 to thnh mch phi hp tr khng gia ng dy v mch thu chung. - D1: Ngn mch na chu k tn hiu chung h tn. - D2: Nn ngun chung h tn thnh ngun mt chiu. - ZD: Chng tn hiu gi gi - C2: T lc ngunTrang 15

- R2, R3: nh thin phn p cho Q1. - PIEZO: a pht m - bin tn hiu chung m tn thnh ting chung. - C3: T thot thnh phn xoay chiu khng cn thit trn R3 Q1 lm vic n nh. -Q1: Transistor khuch i dao ng. c. Nguyn l lm vic Khi c tn hiu chung h tn t tng i a n trn 2 dy tip ring, gi s na chu k u tn hiu chung h tn c th dng dy Ring (R), th m dy Tip (T) th D2 b phn cc mgc nn tt, D1 c phn cc thun nn dn. D1 dn s ni tt u vo ca mch thu chung nn mch thu chung cha lm vic. na chu k sau ca tn hiu chung h tn c th dng dy Tip (T), m dy Ring th D1 b phn cc ngc nn tt, D2 c phn cc thun nn dn. Tn hiu chung h tn thng qua C 1, R1 c D2 nn thnh ngun mt chiu, thng qua ZD, c C2 lc, cp ngun cho Q1 lm vic. Q1 to dao ng chung m tn khuch i tn hiu chung m tn ra 2 u a ln ca a pht m, a pht m pht ra ting chung bo cho ch thu bao bit c cuc gi ti. ng thi khi a ln dao ng th a nh cng dao ng theo. Theo nguyn l p in thun ca thch anh, trn a nh s xut hin mt in p ng pha vi tn hiu pht sinh u vo Q1, a hi tip dng v u vo Q1 duy tr dao ng.

T

Trang 16

C3 C4 R3 7V 22 V TRF Hnh 1.19: S khi ca IC chung dng cho mch c cu nn in TRI TR 3.2. Mch thu chung dng IC S AC dng cho mch c cu nn in bn ngoi a. IC chung 1 AC -Mch in: Hnh 1.19 m t s khi ca IC chung dng cho mch 2 c cu nn inPIE bn ngoi. ZO - Chc nng cc khi TR O + BIAS CKTS: khi t ng iu chnh ngun 1 chiu (DC) cp R R2 cho cc phn t tch cc trong IC. C1 R1 + Threshold Detector: ca vo b tch sng

T

+ + + + -

Tn hiu chung h tn t tng i a n trn hai dy tip-ring (T-R) OUt put thng qua C1- R1 t vo hai u cu nn D1 - D4 c in p khong 30V, buff er c cu nn, nn thnh ngun 1 chiu, c C2 lc, ZD1 n nh, in p 1 War ble chiu khong 21V cp ngun cho cc phn t tch cc trong IC lm vic. B Freq uen to dao ng c cp ngun kt hp vi R3C3 v R4C4 to ra dao ng cy Divi chun c tn s 8KHZ. Dao ng ny ng thi c a ti 2 b chia. B der R 0 Ton chia 8 hoc chiae 10 ly dao ng 1000Hz hoc 800Hz v b chia 640 R D1-D Freq ly dao ng 12,5Hz. Hai ZNR ng ny ng thi 4 c a ti b khuch dao uen cy i m u ra Divi nng cao mc in a ra a pht m (PIEZO) hoc loa. Vo cc mch der a pht m hoc loa pht ra mtCm thanh, botrong my thu bao bit c cho ch 1 cuc gi ti. R1 D5chun bng IC ,c cu nn in bn ngoi, dng a pht D8 b. Mch thu Thre B A shol m ZD1 C d H com 2 -. Mch in nguyn l: Hnh 1.20: Ringer para tor L R5 OFF BIA 8 41 S PIEZO R IC R 3 TRC 3 7 5 6 C 2TRC 1 TRO C2 C1 R1 Hnh1.20: Mch D1 D3

Dio OSC: b de dao ng to ra dao ng c tn s 8KHZ to Brig e 8/10: b chia 8 hoc chia 10 ly dao ng 1000 hoc 800Hz. SCR Tra nsie 640: b chia 640 ly tn hiu 12,5Hz nt OUTPUTcla BUFFER: b khuch i m ra mp Osc Nguyn l lm vic ilat or

C4

R4Trang 17

thu chung dng bng IC, c cu nn in bn ngoi, dng a pht m

R3 C3 TRI C4 R4 TRS TRFOUT PUT

BUF FER

ENA BLE

6 40 OS C 8/ 10 BIA S CK TS

-. Tc dng cc linh kin + R0 v ZNR: Mch chng qu p + D1 D4: Cu chng o cc + C1: Ngn dng 1 chiu v dn tn hiu chung h tn + R1: Gy st p bt dng chung h tn + C1 v R1: phi hp tr khng gia ng dy vi mch thu chung. + D5 D8: cu nn in nn ngun chung h tn thnh ngun 1 chiu. + C2: t lc ngun + ZD1: n nh in p bo v an ton cho IC + R3 - C3 & R4 - C4: tham gia cng mch to dao ng trong IC to ra dao ng chung m tn. + R5: gy st p bt dng chung m tn khi kho Ringer v tr L + Kho Ringer la chn dng chung m tn ra a pht m to hay va hay khng thu chung. + PIEZO: a pht m - Nguyn l lm vic Khi c ngun chung h tn t tng i a n trn hai dy T - R: t dy T a ti 1 u ca cu nn D5 D8 v t dy R qua C1 R1 ti u kia ca cu nn D5 D8. Cu nn D5 D8 nn ngun chung h tn thnhTrang 18

ngun 1 chiu c t C2 lc v ZD1 n nh, cp dng ngun vo chn 1 IC v m ngun vo chn 5 IC. Ngun 1 chiu ny c a vo cp cho cc phn t tch cc trong IC. B to dao ng trong IC c cp ngun kt hp vi R3, C3 & R4 - C4 to ra dao ng chung m tn a ra chn 8 IC kho Ringer a pht m t chn 5 IC kn mch. a pht m pht ra ting chung bo cho ch thu bao bit c cuc gi ti. c. Mch thu chung bng IC, c cu nn in bn ngoi,dng loa. - Mch in nguyn l: Hnh 1.21 -Tc dng cc linh kin + Ro v ZNR: mch chng qu p + D1 D4: cu chng o cc + C1: t ngn dng 1 chiu v dn dng chung h tn. + R1: in tr gy st bt in p dng chung h tn. + C1 kt hp vi R1 to thnh mch phi hp tr khng gia ng dy vi u vo mch thu chung. + D5 D8: cu nn in nn ngun chung h tn c in p cao khong 90 15V v tn s thp khong 50Hz thnh ngun 1 chiu. + ZD1: n nh in p, bo v an ton cho IC. + C2: t lc ngun + IC: phn t to ra dao ng chung m tn + R3 - C3 & R4 - C4: phn t tham gia cng b to dao ng trong IC to ra dao ng chung m tn. + C5: ngn dng 1 chiu v dn tn hiu chung m tn + R5: gy st bt dng chung m tn khi kho Ringer v tr L + Kho Ringer la chn dng chung m tn ra loa to (H) hay va (L) hoc khng thu chung (off). + Bin p m tn phi hp tr khng gia u ra ca b khuch i m tn trong IC vi loa, ngn dng mt chiu qua loa, dn tn hiu chung m tn ra loa. + Loa l ti ca mch thu chung dng bin dng chung m tn thnh ting chung.

Trang 19

R T

R0

ZNR

D1 D4 C1 R1 D5 D8 A C2 C5 Vo cc mch trong my

B

ZD1

R3 C3

8 1 4 IC 6 5 3 7 C4 R4

R5 H L Ringer OFF

Hnh 1.21: Mch thu chung bng IC,c cu nn in bn ngoi, dung loa

- Nguyn l lm vic Khi c ngun chung h tn t tng i a ti trn hai dy T - R: t dy T a ti u B ca cu nn D5 D8 v t dy R qua C1 R1 ti u A ca cu nn D5 D8. Cu nn D5 D8 nn ngun chung h tn thnh ngun 1 chiu c C2 lc v ZD1 n nh, cp dng ngun vo chn 1 IC v m ngun vo chn 5IC. Ngun 1 chiu ny s a vo cp cho cc phn t tch cc trong IC. B to dao ng trong IC c cp ngun kt hp vi R3, C3 v R4, C4 to ra dao ng chung m tn a ra chn 8 IC C5 Ringer cun s cp bin p t chn 5 IC, kn mch. St p trn cun s cp, cm ng sang cun th cp a tn hiu chung m tn ra loa. Loa pht ra ting chung bo hiu cho ch thu bao bit c cuc gi ti. d. IC chung dng cho mch khng cu nn in bn ngoi - S khi: Xem hnh 1.22 - Chc nng cc khi + Khi Diode Brige: cu nn in

Trang 20

+ Khi 6 Diode, Zener 7V, Zener 22V, SCR & R kt hp vi khi Bias (iu chnh t ng) to thnh mch n nh in p v n nh dng in. + Khi Threshold comparator l khi so snh in p vo. + Khi Oscillator l b to dao ng. + Khi Tone Frequency divider khi chia tn s dng tone (chia 8/10). + Khi Warble Frequency divider khi chia tn s (chia 640). + Khi output buffer l b khuch i m ra. + Khi cc linh kin h tr nh: . C2-R2 tham gia vi b to dao ng trong IC to ra dao ng c tn s 8KHZ. . C3 lc ngun sau khi nn. . R3- C4 l cc phn t tng nhy ca mch thu chung.

Trang 21

Hnh1.22: S khi IC chung dng cho mch khng cu nn in bn ngoi - Nguyn l lm vic Tn hiu chung h tn t tng i a n trn hai dy Tip-Ring thng qua C1-R1 t vo 2 chn AC1 v AC2 t vo 2 u cn nn trong IC. Cu nn, nn dng chung h tn thnh dng 1 chiu c C3 lc, dy 6 diode ni tip, diode Zener 7V, diode Zener 22V, SCR v Bias n nh in p v dng in cung cp ngun 1 chiu n nh cho cc phn t tch cc trong IC. Khi c cp ngun, b to dao ng kt hp vi C 2 - R2 to ra dao ng 8KHZ. Dao ng ny c a ti b chia. B chia 8 hoc chia 10 ly ra dao ng c tn s 1000Hz hoc 800Hz v b chia 640 ly ra dao ng c tn s 12,5Hz. Hai dao ng ny trn vo nhau c a ti b khuch i m ra nng cao mc in, ri a ra a pht m (PIEZO). e. Mch thu chung bng IC khng cu nn in bn ngoi, dng a pht m - Mch in nguyn l: Hnh 1.23RT T

R0

ZN R

D1 D4 C1 R1

Hnh 1.23: Mch thu chung bng IC Khng c cu nn in bn ngoi,dng a pht m

1

8

C2 R2

2 3 4

IC

7 6 5

C3 H Ringe r R3 L OFF PIEZ O

- Tc dng cc linh kin + R v ZNR: to thnh mch chng qu p + D1 D4: to thnh cu chng o cc + IC: thu tn hiu chung h tn, nn tn hiu chung h tn thnh ngun 1 chiu cp cho b to dao ng to ra tn hiu chung m tn. + C1: ngn dng 1 chiu v dn tn hiu chung h tnTrang 22

+ R1: gy st bt in p chung h tn + C1 v R1: to thnh mch phi hp tr khng gia ng dy vi mch thu chung. + C2, R2: kt hp vi b to dao ng trong IC to ra tn hiu chung m tn. + C3: t lc ngun + R3: gy st bt in p dng chung m tn khi kho Ringer v tr L. + Kho Ringer la chn dng chung m tn ra a pht m to (H), va L hoc khng thu chung off. + PIEZO: a pht m bin tn hiu chung thnh ting chung. - Nguyn l lm vic Tn hiu chung h tn t tng i a n trn 2 dy T-R. T dy T t vo chn 1 IC v t dy R thng qua C 1 R1 t vo chn 8 IC. IC nn ngun chung h tn thnh ngun 1 chiu, c C 3 lc, cp ngun 1 chiu cho cc phn t tch cc trong IC. B to dao ng trong IC c cp ngun, kt hp vi C2, R2 to ra dao ng chung m tn a ra chn 5 IC kho Ringer a pht m chn 2 IC kn mch. a pht m pht ra ting chung bo cho ch thu bao bit c cuc gi ti. 4. MCH M THOI a- S khi: Hnh 1.24 AR Rx D1 D4 C1 b- Tc dng cc khi SW R1 R2 ZNR + R0 v ZNR: mch chng qu p cho my in thoi. R3 MIC Mch + D1 D4: cu chng o Mch iu cc chnh m xut + Mch iu chnh m lng c nhim v n p v n dng tu theo lng (AGC) m AT chiu di ng dy thu bao, n s cp in iu chnh h 4 s khuch R4 C i ca b khuch i pht (AT) v b khuch i thu AR nng cao r ca cuc m thoi. Hnh 1.24: S khi mch m thoi + Mch xut m: l tng khuch i cng sut ting ni a ra ng dy.R0 0

R

Trang 23

+ R3 ni tip vi R4 song song vi C4 l tr khng cn bng vi tr khng ca ng dy. Mc ch l kh trc m. (Trc m l hin tng ngi ni chuyn in thoi nghe c chnh ting ni ca mnh trong ng nghe, gy cm gic mt mi, kh chu v vy cn phi c mch kh trc m). y mch pht thoi v mch thu thoi nm trn 2 ng cho ca cu sai ng in tr. 4 nhnh ca cu sai ng in tr l: tr khng ng dy (ZL), R1, R2 v tr khng ca mch cn bng (Zb). S tng ng ca mch nh hnh 1.25:

MCH THU THOI C1 R1 ZL R2 Zb

MCH PHT THOI

Hnh 1.26: S tng ng ca mch thu pht thoi c- Nguyn l lm vic - Mch pht thoi Tn hiu ting ni t ng ni (MIC) c a ti u vo ca b khuch i. phi hp tr khng vi b khuch i th:Nu dng ng ni tnh in, ng ni p in th mch khuch i dng transistor trng c tr khng vo cao, nu dng ng ni in ng th mch khuch i dng transistor lng cc. Tn hiu sau khi c khuch i c a ti mch xut m khuch i cng sut nng cao mc in. Sau c a ti b t ng iu chnh m lng (AGC) iu chnh h s khuch i cho thch hp tu theo c ly ng dy t my in thoi ti tng i. Tn hiu sau khi c khuch i iu chnh s c a ln ng dy ti i phng. - Mch thu thoiTrang 24

Tn hiu thoi t i phng hoc cc m hiu t tng i a ti mch t ng iu chnh m lng (AGC) sau c a ti b khuch i thu (AR) nng cao mc in a ti ng nghe. d- Mch in nguyn l - Mch in : Hnh 1.26 R0 D1 D4 ZNR A

SW

Q1

1

4 D5 5 R4 Q2 C1 R3

VR D6

Ti mch thu chung

2 Ti mch pht s 3 R2 R1

R5 C2 Q3 R6

R7

R8 C3

R9 M

Hnh 1.26: Mch in c bn ca mch m thoi - Tc dng cc linh kin + Q1: n ng m mch vng thu bao (ging kho in t) + Bin p: . phi hp tr khng gia ng dy vi mch thu - pht thoi, ngn dng mt chiu qua tai nghe (loa). . Kt hp mng cn bng R2, R1, C1 kh trc m. + D5, D6 to thnh mch hn bin bo v an ton cho loa (tai nghe). + VR: iu chnh m lng dng thu thoi ra loa. + R6: in tr nh thin hi tip m dng in mc ni tip cho Q3 + R4, R3: in tr nh thin phn p cho Q2 + R4: in tr nh thin hi tip m in p mc song song cho Q2. + R9, R7: in tr nh thin phn p cho Q3 + R5: in tr ti ca Q3, dn ngun cp cho Q3 + R8: in tr dn ngun cp cho ng niTrang 25

+ C2, C3: t ni tng ( ngn dng mt chiu gia cc tng, dn tn hiu thoi ) + Q3, Q2: khuch i dng pht thoi . Q2: khuch i cng sut n ch A. . Q3: khuch i in p + M: ng ni bin dao ng m thanh thnh tn hiu in. + T: ng nghe bin dao ng in thnh dao ng m thanh. - Nguyn l lm vic Khi nhc t hp m thoi SW ng mch v Q1 thng ng kn mch vng thu bao.( Q1 thng s c phn tch mc 5. Mch pht s) + Dng cp ngun cho ng ni: Dng ngun t mch chng o cc (A) SW Q1 cun 1-2 R8 ng ni t ti m cu chng o cc, kn mch. + Dng pht thoi: khi ni trc ng ni, p lc m thanh tc ng vo ng ni, ng ni bin dao ng m thanh thnh tn hiu in m thanh c tn s v bin ph hp vi p lc m thanh. Tn hiu m thanh t 1 u ng ni C3 cc b Q3 v t u kia ng ni t R6 cc E Q3. Q3 khuch i nng cao mc in a ra chn E-C ca Q3. T cc C Q3 C2 cc b Q2 v t cc E Q3 R6 t cc E Q2. Q2 khuch i nng cao mc in a dng pht thoi ti i phng theo mch: t cc C Q 2 cun 2-1 Q1 SW mch chng o cc ng dy i phng ng dy mch chng o cc t cc E Q2, kn mch. + Dng thu thoi: Dng thoi t i phng ng dy mch chng o cc SW Q1 cun 1-2 cun 2-3 R2 R1// C1 t t mch chng o cc ng dy i phng, kn mch. St p trn cun 1-2-3 cng chiu cm ng sang cun 4-5 a dng thoi ti tai nghe (u 4 VR u 5 kn mch). ng nghe nhn c dng thoi s bin thnh dao ng m thanh (ting ni) a n tai ngi nghe. + Mch kh trc m: Khi pht thoi dng pht thoi t cc C ca Q2: 1 dng i ti i phng l dng pht thoi ng thi cng c 1 dng i t cc C Q2 cun 2-3 R2 R1// C1 t cc E Q2 kn mch. V tr khng R2 ni tip R1 // C1 cn bng vi tr khng ng dy v cun 1-2 bng cun 2-3 nn 2 dng in ny c gi tr bng nhau nhngTrang 26

chy ngc chiu nhau. St p trn cun 2-1 bng st p trn cun 2-3 v ngc chiu nhau nn t trng do chng sinh ra trit tiu ln nhau, do khng c in p cm ng sang cun 4-5. v vy khng c dng trc m vo tai nghe. Nhng thc t do tr khng ng dy lun lun thay i theo thi gian s dng, thi tit, nhit , di... m tr khng cn bng l mt tr s c nh trong my nn 2 dng in qua cun 2-1 v cun 2-3 khng hon ton bng nhau nn t trng do chng sinh ra khng trit tiu ln nhau ht. V vy mc d c mch kh trc m nhng trong my in thoi vn cn trc m. Trong k thut thng tin in thoi yu cu dng trc m bng 1/40 1/20 dng pht thoi l t yu cu. 5. MCH PHT S a- Mch in : Hnh 1.27 b- Tc dng cc linh kin + Ro, ZNR, D1 D4, SW: c tc dng nh mch thu - pht thoi + R11: dn ngun nui b nh + R17: dn ngun khi ng IC pht s + R19: dn ngun cung cp cho IC pht s lm vic + R15, R20,Q6 to thnh mch nh thin phn p cho Q5 + R20: in tr ti Q6 + + R14 R0ZNRTi mch thu pht thoi

R12, R13: in tr nh thin phn p cho Q4Q7R17 D9D10

D1 D4

R11

R23

R24 Dt VDD

nh thin

Q5 SW R15 R20Q6 R21R19

R14R16

ZD2 C10 C8Ti mch thu chung

PLC

TDP

Bn phm

hi tip m dng Q7 R12 R13 C9

Q4

C13C12

CEOSC1 OSC2

in choCL

VSS

Hnh 1.27: Mch in c bn ca mch pht s

Trang 27

Ti mch dit ting click

+ R16: in tr ti Q4 + R23, R24: in tr nh thin Q7 + D9, D10: khng nh cc tnh ngun nui IC v ngn dng phng 1 chiu ca C10 khi pht s ch pulse, ti thi im c xung khng dng. + C9, C10: t lc ngun + C8: t lc nhiu + ZD2: n nh in p bo v an ton cho IC + C12, C13 v thch anh to dao ng chun cho IC c tn s 3,57945MHz + WA9145: IC pht s + Bn phm nhn tc ng ca ngi s dng a vo IC + Q4: ng mch cm nhn tip im t hp + Q5: ng m mch vng thu bao + Q6: iu khin ng, m Q5 + Q5- Q6: iu khin pht s ch pulse + Q7: khuch i dng DTMF c- Nguyn l lm vic * Mch cp ngun 1 chiu - Dng cp ngun nui b nh: (+) CCC (cu chng o cc) R11 chn VDD IC b nh trong IC chn VSS IC t (-) CCC. - Dng cp ngun khi ng IC: Khi nhc t hp SW ng mch (+) CCC SW R17 D9 chn VDD IC mch in trong IC chn VSS IC t (-) CCC.Trang 28

Khi IC c cp ngun khi ng, IC a mc cao ra chn DP R21 t vo cc b Q6 lm Q6 thng, a mc thp t t Q6 R20 t vo cc b Q5 lm Q5 thng ng kn mch vng thu bao. - Dng cp ngun cho IC pht s lm vic: (+) CCC SW Q5 R19 D10 chn VDD IC mch in trong IC chn VSS IC t (-) CCC. * Mch cho php IC pht s lm vic CCC SW R12 R13 t (-) CCC. St p trn R12, R13 nh thin phn p cho Q4 thng, a mc thp t t Q4 t vo chn CE IC (chn cho php CE). Chn CE xung mc thp cho php IC chu mi tc ng ca bn phm. * Mch pht s ch pulse Chuyn kho chn phng thc gi s v P, a mc cao vo chn la chn. IC pht s xc nh lm vic ch pulse. Khi n phm,IC pht s lm vic, a dng xung thp phn c s chu k xung tng ng vi phm c n ra chn DP IC t vo cc b Q6. + ng vi mc thp Q6 tt nn cc bQ5 ln mc cao Q5 tt h mch vng thu bao, pht ln ng dy ti tng i 1 xung khng dng. + ng vi mc cao Q6 thng nn a mc thp t t Q6 R20 t vo cc bQ5 lm Q5 thng ng kn mch vng thu bao pht ln ng dy ti tng i 1 xung c dng. + Qu trnh c tip tc nh vy cho n ht lot xung th chn DP li ln mc cao R21 t vo cc b Q6 lm cho Q6 thng Q5 thng mch vng thu bao ng kn. * Mch pht s ch tone Chuyn kho chn phng thc gi s v T a mc thp vo chn la chn IC. IC pht s xc nh lm vic ch tone. Khi n phm, IC pht s lm vic, a dng DTMF l t hp 2 sng hnh sin c tn s tng ng vi hng v ct ca phm c n ra chn Dt IC R24 t chn 5 IC kn mch. St p trn R24 thng qua R23 t vo cc BE Q7 c Q7 khuch i nng cao mc in a ra chn EC Q7. C dng DTMF i t C Q7 Q5 SW CCC ng dy tng i ng dy CCC t R14 E Q7 kn mch.Trang 29

V. H THNG CORDLESS PHONE 1./ C S THNG TIN V TUYN. a. S khi h thng thng tin v tuyn Thng tin v tuyn s dng khong khng gian lm mi trng truyn dn. Phng php thng tin l: pha pht bc x cc tn hiu thng tin bng sng in t, pha thu nhn sng in t pha pht qua khng gian v tch ly tn hiu gc. Hnh 1.28 m t cc thnh phn c bn ca mt ng thng tin v tuyn hai chiu.

Anten Tn hiu vo My pht

Dy feeder Circulator

Anten My pht Tn hiu vo

My thu My thu Tn hiu ra Tn hiu ra Hnh 1.28 S khi h thng thng tin v tuyn. b. Qu trnh pht trin ca thng tin v tuyn V lch s ca thng tin v tuyn, vo u th k 20 Marconi thnh cng trong vic lin lc v tuyn qua i Ty dng, Kenelly v Heaviside pht hin mt yu t l tng in ly hin din tng pha trn ca kh quyn c th dng lm vt phn x sng in t. Nhng yu t m ra mt k nguyn thng tin v tuyn cao tn i quy m. Chin tranh Th gii ln th hai l mt bc ngot trong thng tin v tuyn. Thng tin tm nhn thng - lnh vc thng tin s dng bng tn s cc cao (VHF) v c nghin cu lin tc sau chin tranh th gii - tr thnh hin thc nh s pht trin cc linh kin in t dng cho HF v UHF, ch yu l pht trin ngnh Raa. Vi s gia tng khng ngng ca lu lng truyn thng, tn s ca thng tin v tuyn vn ti cc bng tn siu cao (SHF) v cc cao (EHF). Vo nhng nm 1960, phng php chuyn tip qua v tinh c thc hin v phng php chuyn tip bng tn x qua tng i lu ca kh quyn xut hin. Do nhng c tnh uTrang 30

vit ca mnh, chng hn nh dung lng ln, phm vi thu rng, hiu qu kinh t cao. Thng tin v tuyn c s dng rt rng ri trong pht thanh truyn hnh qung b, v tuyn o hng, hng khng, qun s, quan st kh tng, lin lc sng ngn nghip d, thng tin v tinh - v tr v.v... Tuy nhin, can nhiu vi lnh vc thng tin khc l iu khng trnh khi, bi v thng tin v tuyn s dng chung phn khng gian lm mi trng truyn dn. i ph vi vn ny, mt lot cc cuc hi ngh v tuyn Quc t c t chc t nm 1906. Tn s v tuyn hin nay c n nh theo "Quy ch thng tin v tuyn (RR) ti Hi ngh ITU-T Geneva nm 1959. Sau ln lt l hi ngh v phn b li di tn s sng ngn s dng vo nm 1967, hi ngh v b sung quy ch tn s v tuyn cho thng tin v tr vo nm 1971, v hi ngh v phn b li tn s v tuyn ca thng tin di ng hng hi cho mc ch kinh doanh vo nm 1974. Ti hi ngh ca ITU-T nm 1979, di tn s v tuyn phn b c m rng ti 9kHz 400 Ghz, xem xt li v b sung cho quy ch thng tin v tuyn in (RR). gim bt can nhiu ca thng tin v tuyn, ITU-T tip tc nghin cu nhng vn sau y b sung vo s sp xp chnh xc khong cch gia cc sng mang trong quy ch thng tin v tuyn: - Dng cch che chn thch hp trong khi la chn trm. - Ci thin hng tnh ca anten. - Nhn dng bng sng phn cc cho. - Tng cng ghp knh. - Chp nhn s dng phng php iu ch chng li can nhiu. c. Phn loi sng in t v ng dng Trong thng tin v tuyn, c ch truyn sng v tuyn v vic s dng thit b truyn thng ph thuc vo tn s v tuyn s dng. Bng1 trnh by bng tn s v tuyn c phn loi theo tiu chun quc t hin hnh, theo c ch v phng thc s dng sng v tuyn. Bng1. Phn loi, c ch v s dng sng v tuyn Tn s 3KHz~30 KHz 30KHz~300KHz Phn loi C ch truyn bng tn sng v tuyn VLF LF B mt B mtTrang 31

Lnh vc s dng Thng tin o hng Thng tin o hng

300KHz~3MHz 3MHz~30MHz 30MHz~300MH z

MF HF VHF

B mt, sng tri B mt, sng tri Sng tri, Sng khng gian

Pht thanh AM, khng, o hng.

Hng

Pht thanh sng ngn, o hng. Pht thanh FM, truyn hnh, thng tin ng, thng tin v tuyn c nh (viba) Truyn hnh, thng tin ng, thng tin v tuyn c nh (viba), Raar, thng tin v tinh. Thng tin v tinh, thng tin v tuyn c nh, Raar, v tuyn thin vn.

300MHz~3GHz

UHF

Sng tri Sng khng gian Sng thng

3GHz~30GHz

SHF, Viba Sng khng gian Sng thng

30GHz~300GH

EHF, Sng khng Thng tin v tinh, thng tin Milimeter gian Sng thng v tuyn c nh, Raar, v tuyn thin vn.

d. Cc phng thc truyn sng in t Sng v tuyn khng truyn lan theo ng thng khi chng trong khng gian c nh hng ca cc yu t trn mt t v tng i lu. Tuy nhin, khi kho st sng truyn trong khng gian ta cng c th coi l mi trng l tng sng in t truyn theo ng thng. Trong thc t ngi ta phn thnh cc phng thc truyn lan ch yu sau: Sng t, sng tri, sng tn x qua tng i lu v sng thng. -. Sng t Sng t l sng in t chu nh hng ca cc yu t kh hu, a hnh, .v.v. trn b mt t khi truyn t an ten pht n anten thu. Sng t gm 2 loi: Sng b mt v sng khng gian. +. Sng b mt. Sng b mt l sng in t truyn dc theo b mt t. Sng b mt ch yu l cc sng in t tn s thp. S lan truyn c thc hin nhTrang 32

nhiu x sng in t (Hin tng tia sng un cong vt qua vt cn vi suy hao rt t). Do nhiu x t l nghch vi bc sng cho nn tn s s dng cng cao th suy hao ca sng t cng ln, kh nng lan truyn sng t cng yu. Tia sng un cong theo mt t

Anten pht Hnh 1.29: Sng truyn dc theo mt t Hnh 1.29 M t m hnh truyn sng t.

Anten thu

Hin tng nhiu x c mi tng quan cht ch vi dn in v hng s in mi ca t trong ng lan truyn. Hng s in mi ca nc bin nh hn ca t nn c ly truyn sng trn mt bin di hn so vi mt t. Do , sng in t tn s thp c s dng rng ri trong thng tin v tuyn o hng. Bng tn s cc thp c s dng ch yu cho truyn thanh AM, thng tin hng hi v thng tin o hng. +. Sng khng gian Sng khng gian l sng truyn gia 2 anten t cao trong khng gian nh m t hnh 1.30. Anten pht Sng phn x i lu Sng trc tip Sng phn x t Anten thu

Hnh 1.30: Sng truyn gia 2 anten t cao trong khng gian Sng in t n im thu c th : - Trc tip t anten pht: Sng trc tip. - Phn x ti mt t trc khi ti im thu: Sng phn x t.

Trang 33

- Phn x trong tng i lu trc khi ti im thu: Sng phn x tng i lu. Sng trc tip l sng in t pht x trc tip t anten pht n anten thu m khng b phn x u c. Trong iu kin truyn lan bnh thng sng trc tip c bin ln hn tt c cc sng khc cng ti in thu. Sng phn x t l sng truyn t anten pht n anten thu sau khi phn x ti mt t hoc ti cc vt th xung quanh. Do , di ng i ca tia sng phn x t di hn so vi sng trc tip. Nh vy, ti im thu, sng phn x t s c bin v pha khc vi sng trc tip. Nu chnh lch v ng truyn gia sng trc tip v sng phn x t khc nhau mt khong bng s l ln bc sng th ti im thu pha ca hai sng ny khc nhau mt gc 180o, c ngha l ngc pha nhau. Nu khi sng trc tip v sng phn x t c bin bng nhau th chng s trit tiu nhau. Sng phn x tng i lu l cc sng in t bc x ti anten pht b un cong khi truyn trong tng i lu - do h s khc x ca khng kh thay i theo cao - trc khi n anten thu. Cng ging nh trng hp sng phn x t, nu chnh lch v ng truyn gia sng trc tip v sng phn x tng i lu khc nhau mt khong bng s l ln bc sng th ti im thu pha ca hai sng ny khc nhau mt gc 180 o v nu khi sng trc tip v sng phn x tng i lu c bin bng nhau th chng s trit tiu nhau. Sng khng gian c s dng cho cc tn hiu c tn s ln hn VHF. S thay i h s khc x theo cao ca kh quyn gy nh hng n sng khng gian. Kh quyn tiu chun l mt kh quyn l tng c mt t l bin i h s khc x theo cao mt cch u n, bi v n c mt h s thay i c nh ca p sut kh quyn theo cao, nhit v m. V c s bin i h s khc x mt cch lin tc, cho nn ng i thc t ca sng khng gian l khc vi ng trc tip (thng). b li s khc nhau ny, c ly thng tin cc i thc t c tnh ton theo ng trc tip da trn quy nh bn knh hiu qu ca tri t KR (K=4/3 trong kh quyn tiu chun) nh m t Hnh 1.31. ng thc t ng trc tip h1 RTrang 34

h2 h1 KR (b)

h2

(a)

Hnh 1.31 ng i ca sng khng gian : a) iu kin thc t. b) iu kin tng ng ca bn knh tri t c tnh bng R (K=4/3) - Sng tri Sng tri l sng in t b thay i hnh trnh ca mnh ti tng in ly v quay tr v tri t . +. Tng in ly Tng in ly hnh thnh ti cao 100Km - 400Km l do kt qu ca vic ion ho trng thi ca tng i lu bng cc tia cc tm v tia X do mt tri bc x. Tng in ly c phn chia thnh mt vi lp c gi tr mt in t cc i. Mi tng c phn chia thnh cc lp D, E, F theo cao ca n. Lp F li c phn chia thnh lp F1, F2. Hnh 1.32 trnh by mt tnh theo cao ca cc lp ion in hnh. +.Truyn sng trong lp Ion 600 m Ngy Lp F2 Lp F1

400

Lp F

200

Lp E Lp D 102 104 Mt (cm3) 106

0

10

Hnh 1.32 Mt tnh theo cao ca cc lp ion

Trang 35

C th xem lp ion ca tng in ly ging nh mt tm in mi khng l m h s khc x ca n bin i lin tc, v s bin i ca mt ion theo bc sng l khng ng k trong bng tn s cao (bc sng ngn hn). Hnh 1.33a trnh by ng i ca sng v tuyn trong tng in ly. C th gii thch hin tng phn x ti tng in ly nh sau: Ta chia tng in ly thnh cc lp rt mng sao cho trong lp chit sut c th coi l u. Nh vy khi truyn t lp Ion ny sang lp Ion khc th tia sng in t b khc x. Qua nhiu lp Ion nh vy tia sng in t s b un cong v coi nh phn x quay v tri t. Nu t mt my thu im tia sng in t tr v th ta s thu c thng tin pht i t my pht. V c tnh ca tng in ly thay i theo cao nn chng c nh hng khc nhau n qu trnh truyn sng in t. cc sng in t c tn s cao qu s i xuyn thng qua tng in ly (Hnh 1.33b). Sng in t c tn s thp qu th kh nng chuyn ti nng lng yu, s khng n c tng in ly. tng in ly ch phn x sng in t trong bng sng ngn v sng trung. Bng thc nghim ngi ta xc nh c rng: sng ngn phn x ti lp F 1 v F2, sng trung phn x ti lp E, lp D khng gy ra phn x sng in t, ngc li lp D hp th nng lng sng in t trong bng sng trung. Tuy nhin lp D ch xut hin vo ban ngy, v nh vy ban ngy khng th dng sng trung thng tin qua tng in ly c.

nn n4 n3 n2 n1 n0 Tia sng t tri t pht ti tng in ly (a) Tia sng khc x v i ra tng in ly tr v tri t Tng in ly

Tng Bnh lu

Hnh 1.33 aTrang 36

Sng v tuyn xuyn qua tng in ly Tng in ly Mt t Khong nhy (b) Hnh 1.33.- C ch phn x ca tng in ly a. Khc x trong tng in ly b. iu kin ti hn c phn x

Sng v tuyn khc x ti hn

Bng thc nghim ngi ta xc nh c rng, kh nng phn x sng in t ti tng in ly ph thuc vo 3 yu t chnh l: Mt cc ht mang in trong tng in ly, tn s v gc ti ca tia sng in t.

Tng in ly

Tia phn x

0 Tia Gc ti ti Tip tuyn Gc tri t t Mt t

Hnh 1.34

Trang 37

Gi s tia sng in t ti tng in ly vi gc ti (Hnh 1.34), 0 sng in t ny phn x c ti tng in ly th phi tho mn iu 0 kin sau:0 1 80 ,8N f 2

Sin 20 1

80 ,8 N f2

1 Cos

2

0 = 1

80 ,8 N f2

f

9 N Cos 0

0 Khi N=Nmax th tn s ny c gi l tn s ln nht f max ng vi . Tn s ln nht s t c khi N=Nmax v = max. 0 0 0

Khi = max th tia ti chnh l tip tuyn ca tri t. tuy nhin ta 0 0 rt kh c th xc nh chnh xc c gc , bi vy ngi ta tm cch 0 0 tnh tn s (f) thng qua gc , v v quan h vi nhau nh sau: Khi = max th =0, khi =0 th =90o. 0 0 0 Vic tnh tn s (f) thng qua gc c m t hnh 1.35. Trong 0 a l bn knh tri t, h l cao im phn x, : gc ti. : gc t. Ta c: f max () = Khif max ( ) =

80 ,8.N max (1 +

2h ) a 2h Sin 2 + a

= max 0 080 ,8.N max ( a + 2h) 2h

th

=0

nn

0 Sin2 =0.

Suy

ra:

Tng in ly

0 GcTia phn x h ti Tip tuyn tri t

Tia ti Gc t a

Mt t aTrang O 38

Hnh1.35

Phng thc truyn sng qua tng in ly c ng dng trong truyn thanh. Bng cch cho sng in t phn x nhiu ln gia tng in ly v mt t nh m t hnh 1.36 ta c th truyn c sng in t i rt xa. Khi truyn nh vy s c nhng vng khng nhn c sng in t, vng c gi l vng ti. khc phc hin tng ny ngi ta pht ln tng in ly chm sng in t phn k nh m t hnh 1.37.

Tng in ly

Tng in ly

Vng ti

Vng tiTri t Tri t

Khong nhy Hnh 1.36 - Sng tn x qua tng i lu

Hnh 1.37

Vic lan truyn ca sng v tuyn nh hiu ng tn x ca vng kh quyn khng ng nht trong tng i lu c gi l truyn sng tn x qua tng i lu. Phng php ny cho php thng tin lin lc c ly xa cc bng tn VHF, UHF, v SHF. Sng in t b tn x

Vng khng kh khng ng nht Mt t im pht

Trang im thu 39

Hnh 1.38: Truyn sng tn x trong tng i lu

Hnh 1.38 m t bn cht ca vic truyn sng tn x qua tng i lu. Trong tng i lu, cao 10 n 12 Km, thng c vng khng kh khng ng nht. Trong , chit sut gia cc lp khng kh thay i rt ln, nn khi i vo vng ny sng in t b tn x ra nhiu hng khc nhau. Mt s tia b tn x n mc gn nh phn x v quay tr v tri t. Hin tng ny c gii thch nh sau: ( hnh 1.39 ) ta chia vng khng kh khng ng nht thnh cc lp rt mng sao cho trong lp chit sut ca khng kh c th coi l u. Nh vy khi truyn t lp khng kh ny sang lp khng kh khc th tia sng in t b khc x. Qua nhiu lp kh quyn nh vy tia sng in t s b un cong v quay v tri t. Nu t mt my thu im tia sng in t tr v th ta s thu c thng tin pht i t my pht. Phng php ny i hi cng sut pht ln v my thu c nhy cao. nn Mt khc tnh n nh ca h thng thng tin ny khng cao do vng kh Vng kh khng ng nht thng xuyn thay i theo ngy - m, theo ma . . . khng ng -. n Truyn sng thng nht 4 n L 3phng thc truyn sng trong khng gian t do. Phng thc ny ch c n2 trong h thng thng tin v tinh, khi sng in t i ra ngoi tng kh n1 tri t. quyn ca n0 e. Cc phng php iu ch v gii iu ch -Tia sng t tri t bn v iu ch vsng khc ch Cc khi nim c Tia gii iu x v dn dn v quay +pht ti vng kh Tn hiu iu ch khng ng nht tr v tri t L cc tn Khc x trongcn truyn (tn khngs v nhthiu tng t bao hiu tin tc vng kh quyn hiu ng tn Hnh 1.39: gm: Tn hiu thoi, truyn hnh, s liu. . . ) c tn s thp. + Tn hiu sng mang L cc tn hiu in cao tn c th ti (mang) c thng tin. Tn hiu cao tn y mang tnh cht tng i. Mt tn hiu in cao tn c th lm sng mang cho mt tn hiu iu ch ny nhng li khng th lm sngTrang 40

mang cho mt tn hiu iu ch khc v chnh n c khi li tr thnh tn hiu iu ch cho mt sng mang c tn s cao hn. Mt sng mang tiu biu c biu thc ton hc l: U(t) = A sin ( t + ) Trong : - A l bin ca sng mang - = 2 f l tn s gc ca sng mang (f l tn s ca sng mang) - : pha ca sng mang - Cc tham s A, f v u c th mang thng tin. - iu ch iu ch l a tn hiu cn iu ch tc ng vo sng mang lm cho mt hoc nhiu tham s ca sng mang thay i theo quy lut ca tn hiu iu ch. S cn thit ca iu ch Trong thng tin v tuyn: do cc tn hiu tin tc (tn hiu tng t v tn hiu s) thng c tn s thp nn rt kh trc tip bc x thnh sng in t truyn i xa, nu c th bc x c th nng lng bc x cng rt yu v i hi phn t bc x (anten) c kch thc ln. d dng truyn thng tin i xa bng sng in t, ngi ta phi tin hnh iu ch tn hiu thng tin vo sng mang cao tn, ngha l gi tin tc cn truyn vo sng mang sau mi cho sng mang iu ch bc x thnh sng in t truyn i xa. V sng mang c tn s cao nn d bc x thnh sng in t v i hi phn t bc x c kch thc khng ln. Trong ghp knh theo tn s: V cc tn hiu thng tin cng loi u c chung mt bng tn truyn dn (V d: tn hiu thoi c bng tn t 0,3 3,4KHz) nn khi truyn nhiu tn hiu trn mt ng truyn dn th chng s b ln vo nhau lm cho pha thu khng thu c tn hiu. truyn c nhiu tn hiu trn cng mt ng truyn th ngi ta phi iu ch cc tn hiu cn truyn vo cc sng mang khc nhau, mc ch l chuyn ph ca thng tin cn truyn ln cc vng khc nhau sau mi truyn chung trn mt ng truyn dn. Nh s khc nhau v vng ph ca cc tn hiu truyn i m pha thu d dng thu c tn hiu.Trang 41

- Gii iu ch V pha pht tin hnh iu ch nn pha thu mun ly li tn hiu nguyn thy th phi tin hnh tch tn hiu tin tc ra khi sng mang iu ch. Qu trnh tch tn hiu tin tc cn thu ra khi sng mang iu ch bn pht, c gi l gii iu ch. - Phn loi iu ch + Phn loi theo tn hiu a vo iu ch . iu ch tng t: tn hiu iu ch l tn hiu tng t. . iu ch s: tn hiu iu ch l tn hiu s. + Phn loi theo s thay i ca cc tham s sng mang . iu ch bin : l tc ng tn hiu iu ch vo sng mang lm cho bin ca sng mang thay i theo quy lut ca tn hiu iu ch. iu ch bin tng t c gi l AM (Amplitude Modulation). iu ch bin s c gi l ASK (Amplitude Shift Keying). . iu ch tn s: l tc ng tn hiu iu ch vo sng mang lm cho tn s ca sng mang thay i theo quy lut ca tn hiu iu ch. iu ch tn s tng t c gi l FM (Frequency Modulation). iu ch tn s s c gi l FSK (Frequency Shift Keying). . iu ch pha: l tc ng tn hiu iu ch vo sng mang lm cho pha ca sng mang thay i theo quy lut ca tn hiu iu ch. iu ch pha tng t c gi l PM (Phase Modulation). iu ch pha s c gi l PSK (Phase Shift Keying). .iu ch QAM (Quature Amplitude Modulation): l phng php iu ch kt hp c iu ch bin ASK v iu ch pha PSK. Vi iu ch ny th khi tn hiu iu ch tc ng vo sng mang th c bin v pha ca sng mang u thay i theo quy lut ca tn hiu iu ch. *. iu ch bin (AM) T/h iu R 1 ch Sng mang R2 R3 D Tn hiu AM

C

L

Trang 42

HNH 1.40: iu ch AM bng mt diode

C nhiu phng php thc hin iu ch AM. Hnh 1.40 m t mt phng php tng i n gin thc hin iu ch AM. Mch gm mt mng trn tn hiu bng in tr (R1, R2, R3), mt diode nn v mt khung cng hng LC. Tn hiu iu ch ( hnh 1.41a ) c a n u vo R1, tn hiu sng mang ( hnh 1.41b ) c a n u vo R2. Mng in tr R1, R2 v R3 thc hin trn tuyn tnh hai tn hiu vi nhau theo nguyn tc cng s hc. Nu tn hiu iu ch l tn hiu hnh sin th tn hiu sau khi trn (ly trn in tr R3) c dng nh hnh 1.41 (c). Ta thy rng sng mang bin thin trn nn ca tn hiu iu ch, nhng y cha phi l tn hiu iu ch bin . y hai tn hiu mi c cng vi nhau, trong khi iu ch l nhn hai tn hiu vi nhau. Tn hiu sau khi cng c nn qua diode D. Sau khi nn ta thu c mt dy xung dng l tp hp ca cc na chu k dng ca tn hiu tng, bin ca cc xung thay i theo quy lut ca tn hiu iu ch (hnh 1.41d). Cc xung ny c a n kch thch cho mt mch cng hng song song LC. Khung cng hng LC ny tU

c tn s cng hng ring (a

f =

1 2 LC

ng bng tn s ca sng mang. Khi

) c kch thch th khung LC s dao ng vi tn s ng bng tn s sng t U mang, cn bin th ph thuc vo bin ca tn hiu kch thch. Khi xung (b kch thch c bin) ln th dao ng ly ra trn khung c bin ln, khi bin ca xung kch thch nh th dao ng ly ra trn khung c bin t U nh. Nh ni trn, bin ca cc xung kch thch thay i theo quy lut ca tn hiu (c) ch nn dao ng ly ra trn khung LC cng c bin iu bin thin ng theo quy lut ca tn hiu iu ch. y chnh l tn hiu iu ch bin (hnh 1.41 e). Trong iu ch bin , nu gi tin tc cn U t truyn c tn s (d l Vt vi Vt = V . cos t (V l bin cc i ca tn hiu iu ch), sng mang cao tn l V = Vo.cos ot th sau khi iu ch ta ) thu c mt tn hiuUmi: VAM (t) = (Vo + V . cos t).cos ot t (e)

Hnh 1.41: a) Tn hiu iu ch b) Sng mang c) Tn hiu trn in tr R3 Trang 43 d) Dng tn hiu qua diode e) Tn hiu trn khung cng hng

(Vo: bin ln nht ca sng mang). Biu thc trn c th vit:V AM ( t ) = Vo (1 + V cos t ) cos o t = V (1 + m cos ) cos o t t Vo

(biu thc 2.1)

Trong : m = V l h s iu ch v cn c gi l su iu ch. o

V

H s iu ch m phi tha mn iu kin m 1. Nu m > 1 th mch c hin tng qu iu ch gy ra mo tn hiu sau iu ch. Trong thc t, m bo tn hiu khng b mo th m c chn vo khong 0,7 0,8. p dng bin i lng gic cho biu thc 2.1 ta c:V AM (t ) = Vo . cos o t + mV o mV o . cos( o + )t + . cos( o )t 2 2

(biu thc2.2)

T biu thc 2.2 ta thy rng: tn hiu sau khi iu ch bin c 3 thnh phn chnh: sng mang c tn s gc o v bin Vo, hai thnh phn mang tin c tn s gc o

v bin

mV o nh m t hnh 2

1.43b. Nu tn hiu tin tc c di tn t min n max th sau khi iu ch vo sng mang ta s thu c tn hiu c ph nh m t hnh 1.43d. Ngoi sng mang c bin Vo v tn s gc o cn c hai bin tn: bin tn trn c tn s t ( o + min) n ( o + max) v bin tn di c tn s t ( o max) n ( o - min) i xng vi nhau qua sng mang. U U (b) 0 0

U

max min

0 - 0 +

U (d)

0 max

0 + max 0+

min HNH 1.42: a) Ph ca tn hiu iu ch n tn b) Ph ca tn hiu AM iu ch n Tn D c) Ph ca tn hiu iu ch a tn Tn hiu d) Ph ca tn hiu AM iu ch a tn gii *. Gii iu ch bin C1 tng t iu Tn hiu C3 ch C2 R3 AM T1Trang 44

0 - min

0

HNH 1.43: Mch gii iu ch bin

Hnh 1.43 m t mt phng php gii iu ch bin n gin nhng c s dng kh rng ri trong k thut gii iu ch. Mch gm c mt bin p cng hng T1 ghp tn hiu AM vo mch, diode nn D, in tr ti R3 v t lc C3. in p trn cc phn t R3 v C3 chnh l tn hiu gii iu ch. Tn hiu AM c t vo hai u cun s cp ca bin p cng hng T1. Cc t C1 v C2 iu chnh tn s cng hng ca bin p. Tn hiu AM cm ng qua cun th cp v t vo mch nn gm D v R 3. Diode D s dn cc na chu k dng ca tn hiu AM, cn na chu k m th D khng dn. Kt qu l trn ti ta thu c mt dy xung dng m bin ca n thay i theo quy lut ca tn hiu iu ch bn pht. khi phc li tn hiu th phi u song song vi R3 mt t C3. T C3 phi c chn sao cho c tr khng nh i vi tn s sng mang v c tr khng ln i vi tn hiu tin tc. Kt qu l thnh phn sng mang s b ngn mch xung mass, cn thnh phn tin tc s c a ti u ra. Mt cch khc phn tch nguyn l hot ng ca mch l gi s khi diode dn t C3 c np rt nhanh n gi tr nh ca xung. Khi diode tt th t C3 phng in qua R3. Hng s thi gian = R3C3 c chn sao cho ln hn rt nhiu so vi chu k ca sng mang. Kt qu l t phng in, in p trn t gim khng nhiu, khi diode dn th t li c np in tr t li ti gi tr nh. in p trn t gn ging vi tn hiu iu ch bn pht. U in p ny chnh l tn hiu gii iu ch. Do t phng np nn tn hiu khi phc c s c nhng gn sng gy (a) ra mo tn hiu sau gii iu ch. Tuy nhin khi sng mang c tn s ln hn t U rt nhiu ln so vi tn s ca tn hiu iu ch th nhng gn sng ny c th b qua. Hnh 1.44 m t dng sng ca cc tn hiu trong mch gii iu (b) t ch bin . U (c)Trang mch gii iu ch AM dng HNH 1.44: Dng sng ca45 dioden n na sng. a) Tn hiu AM b) Dng qua diode. c) Tn hiu sau gii iu ch

tng hiu qu gii iu ch, ngi ta s dng mch gii iu ch tng t theo kiu nn ton sng nh m t hnh 1.45. D1 Tn hiu gii iu chR3C3

Tn hiu AM

C2 D2

T1 HNH 1.45: Mch gii iu ch bin kiu nn ton sng Hnh 1.46 m t dng sng ca cc tn hiu trong mch gii iu ch bin kiu nn ton sng. tU

(a U (b ) U (cTrang 46

t

t

HNH 1.46: Dng sng ca mch gii iu ch AM dng diodenn ton sng. a) Tn hiu AM b) Dng qua diode. c) Tn hiu sau gii iu ch *. iu ch ASK iu ch ASK l iu ch bin p dng cho tn hiu iu ch l tn hiu s. Hnh 1.47 m t s khi ca mch iu ch ASK. S(t): tn hiu iu ch (tn hiu s) M S(t) A(t).sin t LO HNH 1.47: iu ch ASK LO: mch dao ng to sng mang (Local Ocsilator) A.sin t: sng mang c to ra t mch dao ng LO M: B nhn BPF: b lc thng bng (BPF: Band Pass Filter) S(t).Asin t: sng mang c iu ch bin . Tn hiu iu ch S(t) l tn hiu s c a n u vo th nht ca b nhn M. Sng mang A.sin t to ra t b dao ng LO c a n u vo th hai ca b nhn. B nhn M s nhn tn hiu iu ch S(t) vi tn U hiu sng mang A.sin t. u ra ca b nhn ta thu c thnh phn c (a 0 1 0 0 1 1 0 bn l S(t).Asin t 1 1mt s thnh phn khc (v td A.sin2 t, S(t).A v ) sin3 t ...). Tn hiu ny c a qua b lc thng gii loi b cc thnh U phn khng mong mun. Kt qu u ra ca b lc ta thu c tn hiu (b t iu ch bin (ASK) l S(t).Asin t. Dng sng ra sau iu ch c m ) t hnh 1.48. U (c ) t HNH 1.48: Dng sng ca iu ch ASK Trang 47 a) Tn hiu iu ch. b) Sng mang. c) Sng mang sau iu ch

BPF S(t).Asin t

iu ch ASK c u im l mch in iu ch v gii iu ch u rt n gin. Tuy nhin c nhc im rt ln l kh nng chng nhiu thp v nhiu d dng tc ng vo vng bin (vng mang tin ca sng mang iu ch ASK). *. Gii iu ch ASK Hnh 1.49 m t mt mch gii iu ch ASK tiu biu. D Tn hiu ASK C2 + _ Tn hiu s ra

C1

R2

Uchun T1 HNH 1.49: Gii iu ch ASK

Bin p (T1) kt hp vi t C1 to thnh mt bin p cng hng ghp tn hiu vo mch gii iu ch. D l diode nn cao tn R1 v C2 to thnh ti ca mch gii iu ch. N l b khuch i thut ton hot ng theo kiu so snh. U chun l in p ln hn 0V.Trang 48

Khi khng c sng mang a ti u vo ca bin p cng hng T1 th trn cun th cp ca bin p khng c tn hiu. Lc ny in p t vo chn (+) ca N l 0V lm cho chn (+) m hn in p chn (-) ca N nn ng ra ca N c mc 0. Khi c sng mang a vo u vo ca bin p cng hng th tn hiu ny s c ghp qua cun th cp. Sau tn hiu c diode D nn theo kiu nn na chu k (trong mt s mch gii iu ch ASK, hiu qu hn ngi ta s dng nn c chu k) vi ti l in tr R 2. T C2 thc hin lc san bng v to ra trn in tr ti R2 mt in p tng i bng phng. in p ny c t vo chn (+) ca N lm cho in p chn (+) ca N dng hn in p chn (-) nn ng ra ca N c mc cao. Kt qu l ng ra ca mch so snh N ta thu c cc bit 0, 1 nh a vo iu ch bn pht. biu thi gian m t nguyn l hot ng ca mch c m t hnh 1.50

U (a) U (b) U Uchun t

t

0 1 1 0 1 (c) t HNH 1.50: Biu thi gian m t dng sng ca mch gii iu ch ASK *. iu ch tn s tng t (FM) C nhiu phng php thc hin iu ch tn s FM. +Vcc Co Tn hiu iu ch R1 R2 C2 CDTrang 49

C1

L

Ti mch dao ng

HNH 1.51: Mch iu ch tn s tng t FM

Hnh 1.51 gii thiu mt phng php n gin thc hin iu ch tn s. Mch in y cha c v y m ch trch mt phn mch c bn lin quan n vic iu ch tn s. Trong mch in hnh 1.51: CD l mt diode bin dung R1, R2: to thnh mt mch phn p nh im lm vic cho CD. Co: t dn tn hiu iu ch vo mch C2: mt t dn tn hiu, c tr khng gn nh bng 0 i vi bng tn cng tc nhm m bo cho CD dng nh c mc song song vi khung LC1. Nh vy 3 phn t CD, L v C1 to thnh mt khung cng hng vi tn s cng hng ring:f = 1 2 L(C D + C1 )

Khi cha c tn hiu iu ch a vo mch th trn diode bin dung c mt in p tnh c xc nh bi mch phn p R1 v R2 do diode ny c mt gi tr in dung CD khng i. Lc ny mch dao ng s hot ng vi tn s khng i:f = 1 2 L(C D + C1 )

Khi c tn hiu iu ch a vo mch, nu bin ca tn hiu iu ch tng th in p trn diode bin dung tng, lm cho tr s in dung CD U ca diode gim, dn n tn s dao ng ca mch dao ng tng. Nu bin ca tn hiu iu ch gim th in p trn diode bin dung gim lm cho t (a) in dung CD tng dn n tn s cng tc ca mch dao ng gim. Nh vy, tn s dao ng ca mch dao ng b khng ch bi tn hiu iu ch u vo v bin thin ng theo quy lut ca tn hiu iu ch. ng ra ca mch dao ng ta thu c mt tn hiu ct iu ch tn s. (b) Hnh 1.52 m t dng sng ca mch iu ch tn s. t

(c) Hnh 1.52 Dng sng ca mch iu ch tn s. Trang 50 a) Tn hiu iu ch b) Sng mang c) Tn hiu sau khi iu ch

Trong iu ch tn s, nu tn hiu iu ch l U(t) vi U(t) = U . cos t, tn hiu sng mang l U vi U = Uo . cos ot th sau iu ch ta thu c mt tn hiu iu ch UFM viU FM = U o . cos( o t + . sin t )

Trong : l di tn cc i. H s iu ch mf ca mch iu ch tn s c tnh nh sau:m f = k. U =

, k: h s t l ph thuc vo c im ca tng mch iu

ch. T biu thc trn ta c: = k.U . Nh vy, ta thy rng khi U = const th = const, nhng khi thay i th mf cng thay i. Khi iu ch n tn, ph ca tn hiu iu tn cha thnh phn o v nhiu thnh phn tn s bin ( o n ) vi n = 1, 2, 3... . Bin ca cc thnh phn tn s bin bin i khng ng u. Mt cch gn ng, rng ph ca tn hiu iu tn sau iu ch c th tnh nh sau: D = 2(m + m +1)F M f f

DFM: rng ca ph sau iu ch tn s. Khi tn hiu iu ch l mt bng tn th ph ca tn hiu iu tn DFM s l:D FM = 2( m f + m f +1) ax m

( max: tn s ln nht trong tn hiu iu ch).

Khi mf > 1 th ph ca tn hiu iu tn c th tnh gn ng: DFM 2.mf. max = 2 Trang 51

Khi mf 1 th ph ca tn hiu iu tn c th tnh gn ng: DFM 2 max *. Gii iu ch tn s tng t: Hnh 1.53 m t mch in gii iu ch tn s theo kiu tch sng t l c s dng rng ri trong k thut gii iu ch tn s v quan h pha ca cc in p trong mch. Mch gm c: Bin p cng hng T1 ghp tn hiu FM vo mch. Cun th cp ca bin p T1 c im gia c u chung. Cun cm RFC to in p lch pha 90o. D1, C7, R1 v D2, C5, R2: to thnh hai mch tch sng bin , trong : D1 ging D2, C7 = C5 v R1 = R2. Cc t C7, C5 v cc in tr R1, R2 to thnh mt mch cu. in p trn C7 v C5 l in p vo ca cu, in p gia C v D l in D p ra ca cu. y chnh l im ly tn 1hiu ra ca mch gii iu ch. C7 C6: t c tr s ln, c nhim v hn ch bin , trnh hin tng iu R1 U1 Tn hiu FM U3 ch tn s. bin k sinh xy ra trong qu trnh C iu gii 2 C D C6 U1: in p na trn ca cun th cp RFC C1 U2: in p na di ca cun thC cp U2 5 R2 (a) U3: in p trn cun cm RFC U1-3 = U1 + U3 U2-3 T1 U2 + U3 D = 2 Khi tn hiu FM u vo l sng Tn hiu iniu U 1 cp vo D1 mang th gii p ch ng bng in p U2 cp vo D2 U nn ccU C7 v C5 c np vi in p t U1 U1-3 1 -3 U1 U1-3 1 bng nhau, du ca in p nh m t trn hnh 1.53 (a). U3 U2-3(b)

U3 U2 U2-3 U2 (d)

U3

(c)

HNH 1.53: Gii iu ch tn s (a) Mch in gii iu ch tn s ,(b) Quan h pha ca cc in p khi tn s trong mch bng tn s sng mang, (c) Quan h pha ca cc in p khi tn s trong mch ln hn tn s sng mang, Trang 52 (d) Quan h pha ca cc in p khi tn s trong mch nh hn tn s sng mang

V: C6 u song song vi C7 v C5 nn in p np cho C6 bng tng in p trn C7 v C5. V C6 c gi tr rt ln (thng dng t ha) nn khi c np y n lun duy tr mt in p n nh. Do R1 = R2 v C1 = C2 nn U R = U R v U C = U C . Nh vy mch cu t trng thi cn bng. Lc ny, in p gia hai im C v D bng 0.1 2 1 2

Gi s rng khi c tn hiu iu ch a vo, in p trn cc t C7 v C5 l U C = U C = 2V c ngha l U C = 4V , khi in p trn cc in tr R1 v4 56

R2 l: U R = U R = 2V .1 2

Nu tn s ca tn hiu FM tng th quan h pha trong mch s thay i nh m t hnh 1.53(b) lm cho U1 > U2 v nh vy in p trn t C7 (Uc7) s ln hn in p trn t C5 (UC5). Gi s in p trn t C7 l 3V th in p trn t C5 l 1V, in p trn R1 v R2 vn bng nhau v bng 2V (v in p np cho C 6 khng i). Lc ny cu khng cn bng, in p gia C v D s khc 0. D dng nhn thy rng in p U CD by gi l -1V. Khi tn s ca tn hiu FM gim th quan h pha trong mch s thay i nh m t hnh 1.53c lm cho U1 < U2 v nh vy in p np cho t C7 nh hn in p np cho C5. Nh phn tch trn, gi s in p trn C7 l 1V th in p trn C5 l 3V, UR1 vn bng UR2 v bng 2V. Lc ny cu khng cn bng nhng theo hng ngc li vi trng hp tn s FM tng. D dng nhn thy UCD by gi bng 1V. Nh vy, khi tn s ca tn hiu FM thay i th in p ra ca cu UCD cng thay i theo. y chnh l tn hiu tin tc gii iu ch. V U CD ph thuc vo t l in p trn C7 v C5 nn mch c gi l mch tch sng t l.Trang 53

+iu ch tn s vi tn hiu s (iu ch FSK) Nh cp phn trc, khi tn hiu iu ch l tn hiu s th iu ch tn s c gi l FSK (Frequency Shift Keying: kha dch tn s). Hin nay c nhiu kiu iu ch FSK: 2 FSK, 4 FSK, 8 FSK .... iu ch 2 FSK l iu ch tn s m sau khi iu ch sng mang ch c hai tn s. Tng t vi 4FSK th sau khi iu ch sng mang c 4 tn s ... . n gin trc ht ta xt iu ch 2FSK S khi ca mch iu ch 2FSK c m t hnh 1.54

M0 LO0 Tn hiu iu ch M1 Tn hiu iu ch

LO1

HNH 1.54: S khi mch iu ch 2FSK

LO1 v LO0: hai b dao ng c lp: LO1 to ra sng mang c tn s f1, LOo to ra sng mang c tn s fo. Mo v M1: cc cng truyn dn c iu khin bi tn hiu iu ch. : b cng c nhim v kt hp cc sng mang fo v f1 to thnh tn hiu 2 FSK. Nguyn l hot ng ca mch hnh 1.55 nh sau: Mch dao ng LO0 to ra tn hiu sng mang c tn s fo a n ng vo ca cng truyn dn Mo. Mch dao ng LO1 to ra sng mang c tn s f1 a n ng vo ca cng truyn dn M1. Tn hiu iu ch c a n iu khin cc cng truyn dn Mo v M1. Khi tn hiu iu ch l bit 0 th cng truyn dnTrang 54

M1 khng c iu khin nn khng cho tn hiu sng mang f1 i qua, cng truyn dn Mo c iu khin nn cho tn hiu sng mang fo i qua. Khi tn hiu iu ch l bit 1 th cng truyn dn Mo khng c iu khin nn khng cho sng mang fo i qua, cng truyn dn M1 c iu khin cho sng mang f1 i qua. Mch cng kt hp cc tn hiu ng ra ca cc cng truyn dn Mo v M1. Kt qu l ng ra ca mch cng ta thu c sng mang iu ch 2 FSK gm hai tn s fo v f 1 ng vi cc bit s liu a vo iu ch. Hnh 1.55 m t dng sng ca iu ch 2 FSK.

U (a ) U (b)

t t

U (c )b)

t

U (d)b )

t

HNH 1.55: Dng sng iu ch 2FSK a) Tn hiu iu ch, b) Sng mang f0 , c) Sng mang f1, d) Sng iu ch 2FSK + Gii iu ch FSK C hai phng php thc hin gii iu ch FSK: Phng php gii iu ch nht qun v phng php gii iu ch khng nht qun. + Phng php gii iu ch khng nht qun:Trang 55

Hnh 1.56 m t s khi ca mch gii iu ch 2 FSK khng nht qun. Mch gm hai b lc thng gii BPF, hai mch tch sng v mt mch khuch i so snh. B lc thng gii BPFo c tn s trung tm l fo, b lc thng gii BPF1 c tn s trung tm l f1. Cc mch tch sng c nhim v bin tn hiu vo thnh in p ra ln hn 0. Mch so snh thc hin so snh in p ng ra ca hai mch tch sng. C th m t hot ng ca mch hnh 1.56 nh sau: BPF0 Tn hiu 2FSK BPF1 Tch sng vng 0+

S liu gii iu ch

Tch sng vng 1

HNH 1.56: S khi gii iu ch 2FSK khng nht qun Tn hiu 2 FSK gm 2 tn s fo v f 1 c a n ng vo ca cc mch lc thng gii BPFo v BPF1. Khi tn hiu 2 FSK c tn s l fo th mch lc thng gii BPF1 khng cho tn hiu qua, ng vo ca mch tch sng f1 khng c tn hiu do ng ra ca n c in p l 0V. Cn mch lc BPFo cho tn hiu c tn s fo i qua, c tn hiu sng mang fo a vo mch tch sng fo nn ng ra ca n c in p l +U. Lc ny chn (-) ca mch khuch i so snh c in p dng hn in p chn (+) ca n nn ng ra c in p l 0V. Khi tn hiu 2 FSK c tn s l f 1 th mch lc BPFo khng cho tn hiu sng mang f1 i qua, mch tch sng fo khng c tn hiu vo a ra in p 0V t vo chn (-) ca mch khuch i so snh, cn mch lc thng gii BPF1 cho sng mang f1 i qua, mch tch sng f1 c tn hiu vo nn a ra in p +U. Lc ny in p chn (+) ca mch khuch i so snh dng hn in p chn (-) ca n nn ng ra c mc cao. Nh vy, ty theo tn hiu 2 FSK u vo m ng ra ca mch khuch i thut ton c mc 0 hoc 1. chnh l cc bit s liu c gii iu ch. Phng php gii iu ch FSK khng nht qun c u im l mch in n gin, khng cn phi khi phc sng mang. Tuy nhin do c tnh ca mch nn yu cu tn hiu FSK c bin tng i ln. khc phc nhc im ny, ngi ta s dng gii iu ch FSK nht qun.Trang 56

* Phng php gii iu ch FSK nht qun: S khi n gin ca mt mch gii iu ch 2 FSK nht qun c m t hnh 1.57. Lc thng M0 S liu gii thp iu ch _ LO0 Tn hiu + LO1 2FSK Lc thng M1 thp HNH 1.57: S khi ca mch gii iu ch2 FSK nht qun Mch gm c: + 2 b dao ng LO1 v LOo khi phc li hai sng mang c tn s f 1 v fo sao cho sng mang khi phc phi ng pha vi sng mang iu ch 2 FSK mt cch tng ng. + 2 b nhn Mo v M1 nhn hai sng mang khi phc vi tn hiu 2 FSK. + 2 mch lc thng thp loi b cc thnh phn tn s cao sau khi nhn v mt mch khuch i so snh. Nguyn l gii iu ch 2 FSK nht qun nh sau: Tn hiu 2 FSK c a n u vo th nht ca cc b nhn Mo v M1. u vo th hai ca Mo l tn hiu sng mang fo c to ra t b dao ng ni LOo. u vo th hai ca b nhn M1 l sng mang c tn s f1 c to ra t b dao ng ni LO1. LO1 v LO2 u c khng ch bi tn hiu 2 FSK nhm m bo fo do LOo to ra ng pha vi fo trong tn hiu 2 FSK v f 1 do LO1 to ra ng pha vi f1 trong tn hiu 2 FSK. Cc b nhn Mo v M1 thc hin nhn sng mang 2 FSK vi cc sng mang khi phc fo v f1 tng ng. Nu sng mang 2 ng vo ca b nhn ng pha v cng tn s th ng ra ca b nhn s c in p l +U. Nu sng mang 2 ng vo ca b nhn cng tn s th b nhn s to ra in p 0V. in p sau cc b nhn c a qua mch lc thng thp loi b cc thnh phn tn s cao to ra sau khi nhn. in p sau khi lc c a vo mch so snh. ng ra ca mch khuch i so snh ta thu c tn hiu s gii iu ch. T phn tch trn, ta thy rng nu tn hiu 2 FSK u vo c tn s l fo th ng ra ca Mo c in p l +U, ng ra ca M 1 c in p bng 0V vTrang 57

tn hiu ra sau gii iu ch l 0. Nu tn hiu 2 FSK c tn s l f1 th ng ra ca Mo bng 0V, ng ra ca M1 l +U v tn hiu ra sau gii iu ch l 1. Mch gii iu ch FSK nht qun khc phc c nhc im ca mch iu ch FSK khng nht qun. Tuy nhin phng php ny c nhc im ln l mch rt phc tp, vic khi phc cc sng mang fo v f1 cng rt kh khn nn t c ng dng trong cc h thng FSK thng thng. *. iu ch pha - gii iu ch pha V iu ch pha tng t t c s dng trong thc t nn trong phn ny ch xt iu ch v gii iu ch pha vi tn hiu s. - iu ch - Gii iu ch pha hai trng thi (2 PSK) + iu ch pha hai trng thi (2 PSK) iu ch pha hai trng thi l iu ch m sau khi iu ch sng mang iu ch c hai trng thi pha so vi pha ca sng mang cha iu ch. Hnh 1.58 m t s khi v dng sng ca mch iu ch pha hai trng thi. M Tn hiu iu ch (a) i m To sng mangmang

LBF Sng

Tn hiu iu ch

Tn hiu U iu ch Sng mang cha iu ch Sng mang iu ch

0

1

0

1

t t t

(b) Sin 1 (c)Trang ch Hnh 1.58: iu58 2 PSK a) S khi ca mch iu ch 2 PSK. b) Dng sng ca iu ch 2 PSK. c) Biu pha ca iu ch pha 2 PSK

0 Cos

Tn hiu nh phn cn iu ch trc ht c a vo mch chuyn m bin i t m NRZ n cc sang NRZ lung cc. Sau , s liu c a n b nhn M nhn vi sng mang 2 . A cos( t +o ) to ra t mch to dao ng sng mang. ng ra ca b nhn ta thu c mt tn t hiu m thnh phn chnh l d(t) 2 . A cos( +o +t ) v mt s thnh phn pht sinh khng mong mun. Cc tn hiu ny c a qua mch lc bng loi b cc thnh phn khng cn thit. Kt qu, ng ra ta thu c mt tn hiu iu ch 2 PSK:U (t ) = d (t ) 2 . A cos( +o + ) . t t

Trong : d(t) l s liu s cn iu ch,2

o: pha ban u ca sng mang, A

: bin ca sng mang.2 . A cos t

V b nhn M nhn tn hiu iu ch d(t) vi sng mang min pha nn c th vit li U(t) nh sau: U (t ) = A 2 . cos( t +t ch

theo

+o )

Trong t l gc lch pha do s liu iu ch gy ra ti thi im iu ( t = 0 hoc t = ). Ta nhn thy rng khi tn hiu iu ch l bit 0 tng ng vi d(t) = -1 v sng mang sau iu ch l: U ( t ) = A 2 .cos( t + o + 0) . Khi tn hiu iu ch l bit 1 th d(t) = +1 v sng mang sau iu ch l:U ( t ) = A 2 .cos( t + o + )

Nh vy sng mang sau iu ch pha c hai trng thi l ng pha vi sng mang cha iu ch (khi iu ch bit 0) v ngc pha vi sng mang cha iu ch (khi iu ch bit 1). Pha thu s da Tn hiu vo s chuyn pha ca sng mang thc hin gii iu ch. gii iu ch M1 +Gii iu ch pha hai trng thi: Lc thng thp Hnh 1.59 m t s khi ca + ) gii iu ch 2 PSK bng vng mch cos( t o Tn hiu kha pha COSTAS. M3 Lc vng VCO 2PSK Phn nhnh 90o sin( t + o) Lc thng Trang 59 thp M2 HNH 1.59: Mch gii iu ch 2 PSK bng vng COSTAS

Chc nng ca cc khi hnh 1.60 trn nh sau : B phn nhnh c nhim v chia tn hiu 2 PSK u vo thnh hai ng c bin bng nhau. M1 v M2 l cc b nhn thc hin gii iu ch. 90o: mch dch pha 90o bin sng mang t mang A 2 . sin( +o ) .A 2 . cos( +o ) t

thnh sng

VCO: b dao ng c iu khin bng in p. Lc thng thp: lc b cc thnh phn tn s cao pht sinh sau khi nhn tn hiu 2 PSK vi sng mang khi phc. M3: b nhn tm kim sai pha gia sng mang 2 PSK v sng mang khi phc. Kt qu sai pha s th hin bng in p li. Lc vng: lc in p t ng ra ca b nhn a vo iu chnh tn s v pha ca b dao ng VCO. C th phn tch nguyn l hot ng ca mch da trn s khi hnh 1.59 nh sau: Sng mang 2 PSK c chia thnh hai ng a n cc b nhn M1 v M2. M1 thc hin nhn sng mang 2 PSK c biu thc: U ( t ) = A 2 .cos( t + o + t ) vi sng mang khi phc c to ra t b dao ng VCO: cos( t + o ) . B nhn M2 nhn sng mang 2 PSK: A 2.cos( t + o + t ) vi sng mang khi phc to ra t b dao ng VCO v qua dch pha 90o: sin(t + o ) . ng ra ca M1 ta thu c tn hiu l: A=2.cos( t + o + t ) . cos( t + o ) =

1 .2 A[sin( 2t + 2o + 2t ) + sin t ] = A. sin( 2t + 2o + t ) + A. sin t 2

ng ra ca b nhn M2 ta thu c tn hiu l:Trang 60

A 2.cos( t + o + t ) . cos( t + o ) =

=

1 .2 A[sin( 2t + 2o + t ) + sin t ] = A. sin( 2t + 2o + t ) + A. sin t 2

Nh vy sau hai b nhn ta u thu c 2 thnh phn: 1 thnh phn tn s cao c tn s v gc pha l: (2t + 2o + 2t ) , 1 thnh phn tn s thp c gc pha l t. Cc thnh phn ny u mang tin, tuy nhin thnh phn tn s cao l khng cn thit. Cc b lc thng thp sau M1 v M2 s lc b cc thnh phn tn s cao, thnh phn tn s thp thu c sau cc b lc u l s liu gii iu ch. Tuy nhin ch cn ly s liu u ra ca mt b lc thng thp l . Tn hiu sau 2 mch lc thng thp c nhn vi nhau ti b nhn M3 pht hin s sai pha ca sng mang 2 PSK vi sng mang to ra t b dao ng VCO. Nu c sai pha hoc sai tn th M3 s to ra mt in p li. in p ny c lc qua mch lc vng a v iu chnh tn s v pha ca b dao ng VCO. Phng php iu ch, gii iu ch pha 2 trng thi c u im l mch in tng i n gin, khong cch gia cc trng thi pha ln nn c kh nng chng nhiu cao. Tuy nhin, do mi trng thi pha ch th hin c mt bit thng tin nn hiu qu truyn tin khng cao. tng hiu qu truyn tin, ngi ta thc hin iu ch pha nhiu trng thi hn. *. iu ch pha 4 trng thi - Gii iu ch pha 4 trng thi + iu ch pha 4 trng thi (QPSK) iu ch pha 4 trng thi cn c gi l iu ch 4 PSK hay iu ch cu phng pha hay iu ch QPSK, l phng thc iu ch pha m sng mang sau iu ch c 4 trng thi pha, mi trng thi pha mang hai bit thng tin. Hnh 1.60 m t s khi ca iu ch pha 4 trng thi: Mch hnh 1.60 gm c cc khi: M1 + S/P: (mch chuyn i lung s t ni tip sang song song) c nhim v chia lung s iu ch thnh hai lung c tc bng nhau v bng 1/2 Z1 S (t) 1 lung s vo. Tn Tn hiu hiu QPSK VCO iu ch 90o S/P Z2 S2(t)2

Trang 61 M

Hnh 1.60 S khi ca iu ch pha 4 trng thi:

+ Z1 v Z2: cc mch chuyn i m c nhim v bin cc lung s S 1 v S2 t m NRZ n cc thnh m NRZ lng cc. + VCO: b to dao ng iu khin bng in p. + 90o: mch dch pha 90o bin sng mang A.cos ( t + ) thnh A.sin ( t + ). + M1 v M2: hai b nhn thc hin nhn cc tn hiu s S1(t) v S2(t) vi cc sng mang A.cos( t + ) v A.sin ( t + ) tng ng. + : mch cng c nhim v cng cc tn hiu sau cc b nhn M1 v M2 c tn hiu QPSK. Nguyn l hot ng ca mch iu ch pha nh sau: S liu iu ch a n mch bin i t ni tip sang song song c bin thnh hai lung s c tc bng nhau v bng 1/2 lung s vo. Cc lung s S 1 v S2 sau U c chuyn m t NRZ n cc sang NRZ lng cc nh cc mch S liu 0 0 0 1 1 1 1 0 1 1 iu Sau chuyn m Z1 v Z2.ch khi chuyn m ta thu c cc lung t tng ng s 0 0 1 1 l S1(t) v S2(t). B nhn M1 nhn tn hiu S1(t)1vi sng mang A.cos( t + t Lung s VCO to ra, b nhn M nhn tn hiu S (t) vi sng S1 ) do b dao ng 2 2 0 1 1 0 1 Lung ) S2 mang A.sin( t + s do b dao ng VCO to ra v qua dcht pha 90 o. Sau cc b nhn M1, mang thu c cc tn hiu 2 PSK l S1(t).Acos( t + ) v Sng M2 ta t cha ). ch S2(t).Asin( t + iu Hai tn hiu ny c cng vi nhau qua mch cng v ng ra caSng mang ta thu c tn hiu 4 PSK (QPSK) c biu thc ton mch cng t iu ch hc l: S1(t).Acos( t + ) +(a)2(t).Asin( t + ) = A.cos ( t + + t) S Sin 01 (135o) 00 (45o) Cos 11 (225o) 10 (315o)

Trang 62 (b) HNH 1.61: Dng sng (a) v biu pha ca iu ch QPSK (b)

t: gc dch pha do iu ch pha sinh ra Hnh 1.61 m t dng sng v biu pha ca iu ch pha 4 trng thi: + Gii iu ch pha 4 trng thi (gii iu ch QPSK) C nhiu phng php thc hin gii iu ch pha 4 trng thi, trong c mt s phng php nh: vng nhn pha, iu ch li, vng kha pha COSTAS. Ti liu ny cp n phng php gii iu ch QPSK bng vng COSTAS. Hnh 1.62 m t s khi ca mch gii iu ch ny. Nhim v ca cc khi trong s hnh 1.62 nh sau: M1 Tn hiu QPSK90o

Lc thng thp VCO Lc thng thp

Lung s S1

M3LPF

M5 M4

M2

Lung s S2

Hnh 1.62 S khi ca mch gii iu ch Trang 63 QPSK s dng vng kho pha COSTAS

M1, M2: cc b nhn c nhim v nhn sng mang iu ch QPSK vi sng mang khi phc. Mch lc thng thp c nhim v lc b cc thnh phn tn s cao sau khi nhn. M3, M4: cc b nhn cho pht hin sai pha ca cc tn hiu sau gii iu ch. M5: b tr xc nh sai pha gia sng mang iu ch QPSK v sng mang khi phc. LPF (Low Pass Filter): mch lc thng thp cn gi l mch lc vng. VCO: b dao ng c tn s v pha iu khin bng in p. 90o: mch dch pha 90o bin sng mang cos( t + ) thnh sin( t + ). M3, M4, M5 v LPF to thnh mt mch vng gi l vng COSTAS S1, S2: 2 lung s thu c sau gii iu ch C th phn tch nguyn l hot ng ca mch nh sau: Tn hiu sng mang iu ch QPSK l: A.cos( t + + t) c ng thi a n hai b nhn M1 v M2. b nhn M1: tn hiu ny c nhn vi sng mang cos( t + o). b nhn M2 tn hiu ny c nhn vi sng mang khi phc sin ( t + o) trong o l pha ca sng mang khi phc. Sau M1 ta c:A. cos( t + + t ). cos( t + o ) = 1 A[cos( 2t + t + + o ) + cos( t + o )] = 2

A A . cos( 2t + + t + o ) + . cos( t + o ) 2 2

Sau M2 ta c:A. cos( t + + t ). sin( t + o ) = 1 A[cos( 2t + t + + o ) + sin( t + o )] = 2

A A . cos( 2t + o + + o ) + . sin( t + o ) 2 2

Sau cc mch lc thng thp ta thu c cc thnh phn l:S1 = A A . cos( t + o ), S 2 = . sin( t + o ) 2 2

Trang 64

Cc tn hiu ny c ti sinh, khi phc xung nhp v bin i t song song sang ni tip to li lung s nguyn thy nh tn hiu iu ch bn pht. Sau lc thng thp tn hiu c nhn cho vi nhau ti M 3 v M4. Sau M3 v M4 ta thu c:U S = S1 . S 2 = A A .cos( t + o ). .sin( t + o ) = 2 2 2 2 A 1 A . sin 2( t + o ) = sin( 2 t + 2 2 o ) 2 2 4

Tn hiu US sau hai b nhn M3 v M4 c tr cho nhau ti M5 xc nh s sai pha ca tn hiu gii iu ch S1 v S2. sai pha ca hai tn hiu ny c th hin bng in p li v c lc vng qua mch lc thng thp LPF a v hiu chnh pha ca sng mang VCO sao cho hai tn hiu US ng pha nhau, c ngha l cc tn hiu S1 v S2 ng pha nhau. 2. S KHI H THNG CORDLESS PHONE V NGUYN L HOT NG a. Cc k thut bo v cho my cordless phone trong vic chng nghe trm v dng trm ng dy V bng tn v tuyn dnh cho in thoi b gii hn, do s c nhiu in thoi ng thi dng cng knh, iu ny cng gy mt s kh khn nht nh. Tuy nhin vi tm lin lc thch hp v s dng nhng k thut chnh xc, vic gim ti a giao thoa, reo chung sai v vn an ton c thc hin vic s dng in thoi corless phone t hiu qu tt. Chng ta i vo kho st nhng k thut ny. - Tn s rung chung ring bit Vic reo chung sai c gim thiu bng cch dng nhng tn s rung chung ring bit cho lin kt gia my m & my con. Bng cch ny hai in thoi dng cng knh hoc vng ph sng chng ln nhau khng gy rung chung ca my ny sang my khc. - Tn hiu iu khin hoc Tone bo v ring bit. S dng nhiu tn hiu iu khin ( pilot signal ) hoc Tone bo v ( guardtone) cho lin kt gia my m & my con chng li vic s dng trm ng dy in thoi. My m p ng vi my con khi tn hiu thoi iu khin chnh xc c gi t my con nu my con dng cng knh v tuyn vi my m. - M ho s.Trang 65

Vi my in thoi cordless phone i c ch dng tn hiu iu khin v tn s rung chung bo v chng dng trm ng dy in thoi v rung chung sai. i vi nhng my i mi c s dng k thut m s gia my m v my con. Vi k thut ny khng cn dng nhng tn hiu iu khin, tn s rung chung ring bit, v vy tt c cc my in thoi corless phone c s dng k thut m ho s u c s dng chung 1 tn hiu iu khin v tn hiu rung chung. Tuy nhin i vi mi hng sn xut khc nhau h s dng mi phng php m ho s khc nhau. b. S khi h thng *. S khi BASE UNIT (my m) : Hnh 1.63 - Chc nng cc khi Hybrid: Cu sai ng phn chia hng pht & hng thu Mic Amplier: B khuch i mic nhm nng cao mc in dng pht thoi. Ring Detector: B tch sng chung: thu tn hiu chung h tn t tng i a ti & tch sng ly thnh phn mt chiu cp cho b to dao ng. Ring OSC: B to dao ng sng chung m tn. Audio Amplier: B khuch i m tn.( b tin khuch i dng pht thoi) FM Modulator: B iu ch tn s (b iu tn). RF Amplier: B khuch i cao tn. RF Output: B khuch i cng sut ra cao tn. Mixer: B gii iu ch. IF Filter: B lc trung tn. .

Trang 66

Call detecter RF AmpIF Mixer IF Mixer Filter Filter1 2 1 2IF Amp Limiter

Chime Audio Amp Audio Ouput

Detector

LPF

OSC1

OSC2

Pilot Detector

SRY Relay Tel/INT Switch ngLine

dy

Hybrid

SRY

RF Output

RF Amp

FM Modulator

Audio Amplifier

Audio Amp

Mic

Call Pilot Switching Ring Ring OSC Detecter Hnh 1.64. S khi BASE UNIT (my m) Call D2

IF Ampli Limitter: B khuch i trung tn hn ch bin . Detector: B tch sng. Low Pass Filter: B lc thng thp (LPF) Call Filter: B lc tn hiu gi. Audio Output: B khuch i cng sut ra. Pilot Detector: B tch sng iu khin. SRY Relay: Rle ng m mch m thoi. Chime: B to tn hiu chung m tn. *. S khi Handset (my con) hnh1.64 - Chc nng cc khi RF Amplier: B khuch i cao tn. Mixer: B gii iu ch. IF Filter: B lc trung tn. IF Ampli Limitter: B khuch i trung tn hn ch bin .Trang 67

Detector: B tch sng. Audio Amplifier: B khuch i m tn. Call Detector: B tch sng tn hiu gi. Audio Output: B khuch i cng sut ra. Speaker Ring: Loa chung. (a pht m) Speaker switching: iu khin tn hiu ra loa. RF Power Amplifier: B khuch i cng sut cao tn. RF Trippler Amplifier: B khuch i nhn tn. TX OSC Amplifier: B khuch i dao ng pht. FM Modulator: B iu tn ( b iu ch theo tn s). Key Board: Bn phm.

Pilot OSC / Call: B to tn hiu iu khin dao ng hoc to tn hiu gi. Call Pilot Switching: Chuyn mch tn hiu iu khin gi.RF Amp Mixer IF Filter IF Amp LimiterDetector

LPF

Audio Amp

Speaker Ring OSCCall Detector

Audio Ouput speaker Swiching Speaker

Thu 3,6 Volt 2 1 0 2 1 0

Pht t Mic RF Power Amp RF Trippler Amp Tx OSC Amp FM Modulator Audio Amp Call Pilot Switching Key Board Call Pilot OSC/CALL

Hnh 1.64 : S khi Handset (my con)Trang 68

c - Phn tch hot ng ca h thng *. Mch thu chung - Mch thu chung t tng i ti Ngun chung h tn t tng i ng dy Ring detector. B Ring Detector tch sng tn hiu chung h tn ly ngun mt chiu cp cho Ring OSC. B Ring OSC to dao ng chung m tn a ti b Audio Amplifier khuch i nng cao mc in p a ti FM Modulator iu ch theo tn s. Bin tn hiu chung m tn thnh tn hiu chung cao tn a ti b RF Amplifier khuch i cao tn nng cao mc in p a ti RF Output khuch i cng sut - a ln anten pht - a ln khng gian ti anten thu ca my con. Tn hiu chung cao tn ti anten thu ca my con c RF Amplifier khuch i cao tn nng cao mc in b p li phn tiu hao trong khng gian - a ti Mixer gii iu ch vi dao ng ti tn OSC bin i tn hiu chung cao tn thnh tn hiu chung trung tn - a qua b lc IF Filter lc ly tn hiu trung tn a ti b IF Amplifier Limitter khuch i hn ch bin trung tn nng cao mc in v gt b thnh phn nhiu v bin - tn hiu chung a ti b Detector tch sng ly thnh phn tn hiu chung m tn a ti b lc thng thp (LPF) lc ly thnh phn tn hiu chung m tn, a ti b Audio Amplifier khuch i m tn nng cao mc in p a qua b call Detector tch sng tn hiu chung m tn, a qua b khuch i cng sut ra Audio Output ti a pht m. a pht m pht ra ting chung m tn bo cho ch thu bao bit c cuc gi ti. - Mch thu chung t my m gi ti my con: Khi my m (Base Unit) mun gi my con (Handset) th my m n Tel/ In tch ng dy ra khi mch m thoi, n Call cp mass cho Ring OSC. Ring OSC c cp mass c ngun lm vic to ra dao ng chung m tn a ti b Audio Amplifier khuch i m tn nng cao mc in p a ti FM Modulator iu ch theo tn s. Bin tn hiu chung m tn thnh tn hiu chung cao tn a ti b RF Amplifier khuch i cao tn nng cao mc in p a ti b khuch i cng sut cao tn RF Output - a ln anten pht - a ln khng gian ti anten thu ca my con. Tn hiu chung cao tn ti anten thu ca my con c RF Amplifier khuch i cao tn nng cao mc in p b p li phn tiu hao trongTrang 69

khng gian - a ti Mixer gii iu ch vi dao ng ti tn OSC bin i tn hiu chung cao tn thnh tn hiu chung trung tn - a qua b lc IF Filter lc ly tn hiu trung tn a ti b IF Amplifier Limitter khuch i hn ch bin trung tn nng cao mc in v gt b thnh phn nhiu v bin - tn hiu chung a ti b Detector tch sng ly thnh phn tn hiu chung m tn a ti b lc thng thp (LPF) ti b Audio Amplifier khuch i m tn p a qua b call Detector tch sng ly tn hiu chung, a qua b khuch i cng sut ra Audio Output ti a pht m. a pht m pht ra ting chung m tn bo cho ch thu bao bit c cuc gi t my m ti. - Mch thu chung t my con gi my m: Khi my con (Handset) cn gi my m (Base Unit) th my con n talk cp ngun cho cc b phn trong my con lm vic v n Call Pilot Switching th b Pilot OSC / Call to ra dao ng chung m tn a ti b FM Modulator iu ch tn s bin i tn hiu chung m tn thnh tn hiu chung cao tn, a qua b TX OSC Amplifier khuch i dao ng pht cao tn & b RF Trippler Amplifier khuch i nhn tn v b RF Power Amplifier khuch i cng sut tn hiu cao tn, nng cao mc in tn hiu chung cao tn a ln anten pht my con - a ln khng gian ti anten thu ca my m. Tn hiu chung cao tn t anten thu my m c a ti b RF Amplifier khuch i cao tn nng cao mc in p b p phn tn hiu b tiu hao trong khng gian - a qua b Mixer1 Amplifier gii iu ch ln 1 vi dao ng ti tn OSC1. Tn hiu sau khi c gii iu ch ln 1 c a qua b lc trung tn 1 (IF Filter1) lc ly di tn s 10,7 MHz - tn hiu ny c a qua b gii iu ch ln 2 (Mixer 2) & a qua b lc trung tn 2 (Filter2) lc ly tn hiu trung tn c di tn s 455KHz. Tn hiu trung tn c b khuch i hn ch ( If Amplifier Limitter) khuch i nng cao mc in trung tn v gt b thnh phn nhiu v bin - a qua b tch sng (Detector) tch ly thnh phn tn hiu chung m tn a qua b tch sng chung (Call Detector) tch ly thnh phn tn hiu chung m tn, a ti b to dao ng chung m tn (chime), ti b khuch i cng sut ra (Audio Output) nng cao mc in a ra loa - pht ra ting chung bo cho ngi my m bit c my con gi ti. *. Mch thu - pht thoi (m thoi)Trang 70

- Mch thu - pht thoi vi i phng Khi nghe chung gi, n nt Talk my con. B Pilot OSC / Call lm vic iu khin cp ngun mt chiu cho cc b phn my con lm vic, ng thi pht i mt xung dng (tn hiu iu khin Pilot). Xung dng ny i qua b FM Modulator - iu ch theo tn s bin i tn hiu Pilot thnh tn hiu cao tn, a ti TX OSC Amplifier khuch i dao ng pht cao tn ti b RF Trippler khuch i nhn tn, ti RF Power Amplifier khuch i cng sut cao tn, nng cao mc in pht a ra anten pht my con a ln khng gian ti anten thu my m a vo RF Amplifier khuch i nng cao mc in p cao tn b p li phn tiu hao trong khng gian, a ti b gii iu ch 1(Mixer1) vi dao ng ti tn OSC1. Tn hiu sau khi gii iu ch ln 1 c a qua b lc trung tn 1( Filter1) lc ly di tn s 10,7 MHz - tn hiu ny c a qua b gii iu ch trung tn 2 (Mixer2) vi dao ng ti tn OSC2 sau a qua b lc trung tn 2 (Filter 2) lc ly tn hiu trung tn c di tn s 455KHz a qua b khuch i hn ch Amplifier Limitter khuch i nng cao mc in trung tn v gt b thnh phn nhiu v bin , ti b tch sng (Detector) tch ly phn tn hiu m tn a qua b tch sng iu khin (Pilot Detector) tch ly thnh phn mt chiu cp cho Rle (SRY Relay). Rle ng tc ng tip im SRY ni kn mch vng thu bao. + Mch thu thoi: Tn hiu thoi t i phng ng dy Tel/INT.Switch SRY Hybrit (Audio Amplifier) khuch i m tn nng cao mc in p FM Modulator iu ch theo tn s, bin i tn hiu m tn thnh tn hiu cao tn RF Amplifier khuch i in p cao tn b khuch i cng sut ra cao tn RF Output anten pht khng gian anten thu ca my con (Handset) b khuch i cao tn RF Amplifier nng cao mc in p b p li phn tiu hao trong khng gian b gii iu ch tn s vi ti tn osc (Mixer) bin i tn hiu cao tn thnh tn hiu trung tn b lc trung tn (IF Filter) b khuch i trung tn hn ch bin trung tn (IF Amplifier Limitter) khuch i nng cao mc in v gt b thnh phn nhiu v bin b tch sng (Detector) tch ly tn hiu m tn b lc thng thp (LPF) lc ly thnh phn tn hiu m tn b khuch i m tn (Audio Amplifier) nng cao mc in p b khuch i cng sut raTrang 71

(Audio Output) b iu khin tn hiu ra loa (Speaker Switching) tai nghe. + Mch pht thoi: Dng pht thoi i t Mic ca my con b khuch i m tn (Audio Amplifier) khuch i nng cao mc in p FM Modulator iu ch tn s, bin tn hiu ting ni m tn thnh tn hiu cao tn b khuch i dao ng pht, khuch i nhn tn & b khuch i cng sut cao tn nng cao mc cng sut pht anten pht ca my con khng gian anten thu ca my m b khuch i cao tn (RF Amplifier) nng cao mc in p b p li phn tiu hao trong khng gian Mixer1 gii iu ch ln 1 vi ti tn osc1, thc hin bin i tn hiu cao tn thnh tn hiu trung tn b lc trung tn 1 ( IF Filter 1) lc ly di tn 10,7 MHz Mixer2 gii iu ch ln 2 vi ti tn osc2 b lc trung tn 2 ( IF Filter2) lc ly di tn 455KHz b khuch i hn ch trung tn (IF Amplifier Limitter) khuch i nng cao mc in & gt b thnh phn nhiu v bin b tch sng (Detector) tch ly tn hiu m tn Low pass Filter lc ly tn hiu m tn bng thoi b khuch i m tn (Audio Amplifier) nng cao mc in cu sai ng (Hybrid) SRY IN/ TEL Switch ng dy i phng. - Mch m thoi gia my m vi my con + My m ni - my con nghe: Khi my m mun m thoi vi my con th my m n nt Tel/IN Switch ct mch m thoi vi i phng & my con n Talk cp ngun cho cc b phn my con lm vic. Khi ni p lc m thanh tc ng vo ng ni (Mic). Mic bin dao ng m thanh thnh dao ng in a ti Mic Amplifier khuch i in p m tn, nng cao mc in Audio Amplifier khuch i m tn FM Modulator iu ch tn s, bin i tn hiu m tn thnh tn hiu cao tn RF Amp khuch i in p cao tnRF Output khuch i cng sut ra anten pht khng gian anten thu ca my con RF Amplifier khuch i in p cao tn b p li s tiu hao ca tn hiu qua khng gian Mixer thc hin gii iu ch tn s vi ti tn osc bin i tn hiu cao tn thnh tn hiu trung tn b lc trung tn IF Filter lc ly bng trung tn tn tn hiu thoi IF AmplifierTrang 72

Limitter khuch i trung tn hn ch nng cao mc in gt b thnh phn nhiu v bin b tch sng Detector tch ly tn hiu m tn b lc thng thp LPF lc ly bng tn m thoi Audio Amplifier khuch i nng cao mc in p m tn Audio Output khuch i cng sut ra Speaker Switching iu khin tn hiu thoi ra tai nghe a ra ng nghe my con. + My con ni - my m nghe: Khi ni trc ng ni, p lc m thanh tc ng vo ng ni, ng ni bin dao ng m thanh thnh dao ng in Audio Amplifier khuch i m tn nng cao mc in p FM Modulator iu ch tn s bin tn hiu m tn thnh tn hiu cao tn TX OSC Amplifier khuch i dao ng pht cao tn RF Tripple Amplifier khuch i nhn tn nng cao mc in p RF Power Amplifier khuch i cng sut tn hiu cao tn anten pht khng gian anten thu ca my m RF Amplifier khuch i in p cao tn b p li s tiu hao ca tn hiu qua khng gian Mixer1 gii iu ch ln 1 bin i tn hiu cao tn thnh tn hiu trung tn b lc trung tn 1 ( IF Filter 1) lc ly bng tn 10,7MHz Mixer 2 thc hin gii iu ch ln 2 b lc trung tn 2 ( IF Filter 2) lc ly bng tn 455KHz IF Amplifier Limitter khuch i trung tn hn ch bin nng cao mc in & gt b thnh phn mhiu v bin b tch sng Detector tch ly tn hiu m tn b lc thng thp Low pass Filter lc ly bng tn m thoi Audio Amplifier khuch i nng cao mc in p Audio Output khuch i cng sut ra a ra loa my m. *. Mch pht s - Pht s ch pulse . Chuyn kho P/T sang v tr Pulse (P) . Khi mun gi ti i phng, thu bao n nt Talk cp ngun cho my con lm vic, nghe m mi n s mi tin hnh n s thu bao b gi. . Khi n phm, bn phm tc ng ti IC pht s, cn c cc s c n IC pht s a dng xung thp phn c s chu k xung tng ng vi phm c n Pilot OSC chuyn mch iu khin gi theo dng xung thp phn FM Modulator iu ch tn s, bin tn hiu iu khin thnh tn hiu cao tn TX OSC Amplifier khuch i dao ng pht cao tn RF TripplerTrang 73

Amplifier khuch i nhn tn nng cao mc in p cao tn RF Power Amplifier khuch i cng sut tn hiu cao tn anten pht khng gian anten thu my m RF Amplifier khuch i in p cao tn b p s tiu hao ca tn hiu trong khng gian Mixer1 gii iu ch tn s ln 1 bin i tn hiu cao tn thnh tn hiu trung tn b lc trung tn 1 ( IF Filter1 ) lc ly di tn 10,7 MHz Mixer2 gii iu ch tn s ln 2 b lc trung tn 2 ( IF Filter2 ) lc ly di tn 455KHz IF Amplifier Limitter khuch i hn ch trung tn nng cao mc in v gt b thnh phn nhiu v bin Detector tch sng ly thnh phn m tn Pilot detector tch sng iu khin rle (SRY Relay) nh, ht ng m mch vng thu bao to dng xung thp phn a ln ng dy n tng i, tng i s nhn c s in thoi t my con pht n - Pht s Ch tone. . Chuyn kho P/T sang v tr tone (T) . Khi n phm, bn phm tc ng ti IC pht s, IC pht s s a dng DTMF l 1 t hp 2 sng hnh sin c tn s tng ng vi hng v ct ca phm c n FM Modulator iu ch tn s, bin i tn hiu DTMF thnh tn hiu cao tn TX Osc Amplifier nng cao mc in RF Amplifier khuch i in p cao tn RF Power Amlifier khuch i cng sut cao tn anten pht khng gian anten thu my m RF Amlifier khuch i in p cao tn b p li phn tiu hao trong khng gian Mixer 1 gii iu ch ln 1 vi ti tn Osc1 bin i tn hiu cao tn thnh tn hiu trung tn b lc trung tn 1 ( IF Filter1) lc ly di tn 10,7MHz Mixer 2 gii iu ch ln 2 vi ti tn Osc 2 b lc trung tn 2 ( IF Filter2) lc ly di tn 455KHz IF Amplifier Limiter khuch i trung tn hn ch bin nng cao mc in v gt b thnh phn nhiu v bin Detector tch sng ly thnh phn tn hiu m tn Low Pass Filter lc ly tn hiu m tn Audio Amplifiter khuch i nng cao mc in p Hybrid phn chia hng pht hng thu qua tip im Rle, SRY Tel/Int Switch ng dy tng i, tng i nhn c dng DTMF t my con gi n. BI TP CHNG I BI TP 1: MY IN THOI N PHMTrang 74

Mc ch: Gip hc vin lm quen v c k nng phn tch mch, khoanh vng pan, lp t, sa cha c my in thoi n phm thng dng. Ni dung: I. MY IN THOI SIEMENS 802 MODEL 3 1. MCH IN NGUYN L: Hnh bt1.1 2. TC DNG CC LINH KIN R301: bo v qu p, bo v an ton cho ton my R300: bo v qu p, bo v an ton cho cc mch in trong my U8: bo v qu p, bo v an ton cho IC: TEA1062A U5: bo v qu p, bo v an ton cho IC: W91314A U1 U4: cu chng o cc, gi cho cc tnh ngun 1 chiu cp cho

cc c kin trong my c nh. U31: (kho in t) n ng m mch vng thu bao v tham gia vo

mch iu khin pht s ch pulse. U34: tham gia cng vi R4, R11, R13 lm mch nh thin phn p cho

U31 v tham gia vo mch iu khin pht s ch pulse c