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A/D I D/A KONVERZIJA
ANALOG-DIGITAL & DIGITAL-ANALOGCONVERSION
DIGITALNA ELEKTRONIKAZimski semestar 2005/6. Godine
Elektronski fakultet - Niš
analog-to-digital converter
ADC
digital-to-analog
converterDAC
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UZORKOVANJE
KVANTOVANJE
KODOVANJE
A/D
REGENERISANJE
DEKODOVANJED/A
Uianalog
Uoanalog
Veličina napona u digitalnom obliku
OBRADA U DIGITALNOM
DOMENU
Operacije pri A/D i D/A konverziji
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Uzorkovanje( Semplovanje )
UZORKOVANJE( Ideal Sampling )
NYQUIST’S THEOREM: fs > 2f1
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UZORKOVANJE( Real Sampling )
SAMPLE-AND-HOLD CIRCUIT
A2A1
Ch
AnalogInput
To ADCinput
Ts = 1/fs
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KVANTOVANJE
Uamin
Uamax
~~
000000000100010
11111
∆V∆V=Ups/(2n-1)
For an n - bit converter
1 LSB = ∆V
The Ideal Transfer Function (DAC)
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OFFSET ERROR
BIPOLAR OFFSET ERROR
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Calibrating bipolar offset error. (Note: The stair-step transferfunction has been replaced by a straight line, because this
graph shows all codes andthe step size is so small that the line appears to be linear.)
Unipolar offset error
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GAIN ERROR
Offset, gain, and full-scale errors
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Gain error reduces dynamic range
Differential Nonlinearity(DNL) Error
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DNL error: no missing codes
DNL error: Code 10 is missing.DNL error: At AIN* the digital code can be one of three
possible values. When the input voltage is swept, Code 10 will be missing.
DNL error: no missing codes
Integral Nonlinearity (INL) Error
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Absolute Accuracy(Total) Error
Voltage-reference-drift requirements relate to ADC resolution
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APERTURE ERROR
D/A KONVERTOR SA TEŽINSKOM OTPORNOM MREŽOM
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Četvorobitni D/A konvertor sa lestvičastom otpornom mrežom
D/A konvertor sa kratkim vremenom postavljanja
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A/D KONVERTORI
1. SA DIREKTNOM KONVERZIJOM• Podatak po podatak - simultani (flach)• Bit po bit - sa sukcesivnom aproksimacijom• Kvant po kvant - brojački
2. SA POSREDNOM KONVERZIJOM•V/F konvertori•V/T konvertori
A/D konvertor sa paralelnim komparatorima
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A/D konvertor sa sukcesivnim aproksimacijama
Promena napona DAK tokom A/D konverzije
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Logička šema A/D konvertora sa sukcesivnim aproksimacijama
Jedna realizacija A/D konvertora sa sukcesivnim aproksimacijama
CLR
1C
LK9
1D3
1Q2
2D4
2Q5
3D6
3Q7
4D11
4Q10
5D13
5Q12
6D14
6Q15
U?MC74HC174
34U?B
HC05
56U?C
HC05
1 2
U?A
HC05
1312U?F
HC05
1110U?E
HC05
98U?D
HC05
R?RES2
GND GND
+5V
123
U?A
SN74
HC
0012
3U
?ASN
74H
C00
123
U?A
SN74
HC
001213
12U
?ASN
74H
C10
U?
KO
NV
ERZI
JA U
TO
KU
U?
KRAJ KONVERZIJE
1 2U?A
HC04
123
U?A
SN74
HC
0012
3U
?ASN
74H
C00
123
U?A
SN74
HC
001213
12U
?ASN
74H
C10
123
U?A
SN74
HC
0012
3U
?ASN
74H
C00
123
U?A
SN74
HC
001213
12U
?ASN
74H
C10
123
U?A
SN74
HC
0012
3U
?ASN
74H
C00
123
U?A
SN74
HC
001213
12U
?ASN
74H
C10
R?
R
R?
R
R?
R
R?
2R
R?2R
R?2R
R?2R
R?2R
R?
2R
R?
OPAMP
R?
R
R?
R
R?
R
R?
R
GND
R?2R
R?
OPAMP
Vx
91011
8
U?C
SN74HC10
12
1312
U?A
SN74HC10
12U?A
HC04
C?
CAPACITOR
R?RES2
R?RES2
R?
RES2
S?
SW SPDT
GND
+5V
GND+5V
C?
1nF
R?
RES2
GND
12 U?AHC04
R?
LD+5V
12 U?AHC04
R?
LD+5V
12 U?AHC04
R?
LD+5V
12 U?AHC04
R?
LD+5V
R?RES2
R?RES2
U?
START KONVERZIJE
R?RES2
+5V
R?
RES2
+5V
+5V
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Prateći A/D konvertor
Vremenski dijagram pratećeg A/D konvertora
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Serijski A/D konvertor sa referentnim D/A konvertorom
Vremenski dijagrami kod serijskog ADC-a
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A/D konvertor sa dvojnim nagibom
Vremenski dijagrami A/D konvertora sa dvojnim nagibom
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Sigma - Delta A/D konvertor
R
R
P
+
_
R
R
+
_
C
+
_
DIGITALNI
D Q
Q FILTAR
Qn-1
Q1Q0 D
igita
lna
vred
nost
A
K
-Vr
+Vr
Takt
Va
Uul
Vi
Uul = t1 - t2t1+t2 Vr