a fractional-n sub-sampling pll using pipelined phase ...pipelined phase-interpolator with a fom of...
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Matsuzawa& Okada Lab.
Matsuzawa Lab.Tokyo Institute of Technology
Matsuzawa& Okada Lab.
Matsuzawa Lab.Tokyo Institute of Technology
A Fractional-N Sub-Sampling PLL using Pipelined Phase-Interpolator
with a FoM of -246dB�
A.T. Narayanan, M. Katsuragi, K. Kimura, S. Kondo, K. T. Korkut, K. Nakata, W. Deng,
K. Okada, and A. Matsuzawa �
Tokyo Institute of Technology Japan�

1 ESSCIRC2015 41th European Solid-State Circuits Conference
[C4L-A] A Fractional-N Sub-Sampling PLL using a Pipelined Phase-Interpolator with a FoM of -246dB
Contents
! Motivation ! Conventional Fractional-N PLLs ! Brief Noise Analysis ! Proposed Architecture ! Building Blocks ! Measurement ! Conclusion

2 ESSCIRC2015 41th European Solid-State Circuits Conference
[C4L-A] A Fractional-N Sub-Sampling PLL using a Pipelined Phase-Interpolator with a FoM of -246dB
Motivation ! Wireless carrier generation requires fractional-N PLL.
! Fractional operation introduces additional noise.
! Conventional synthesizer architectures:
! CP Based: Poor close-in phase noise.
! TDC Based: Power-jitter trade-off.
! Injection Locking: Large spurious.
! Sub-sampling: Power-jitter tradeoff.
Aim: Low-power high-purity fractional-N SS-PLL

3 ESSCIRC2015 41th European Solid-State Circuits Conference
[C4L-A] A Fractional-N Sub-Sampling PLL using a Pipelined Phase-Interpolator with a FoM of -246dB
Fractional-N SS-PLL: Prior Art
[1] G. Marucci, ISSCC 2014, [2] Po-Chun Huang, ISSCC 2014, [3] K. Raczkowski, RFIC 2014]
DTC facilitates fractional-N operation
SSPDDTCOutRef
LPF
Dither
Frequency-Locked Loop
CP
Ref
Ref_DTC
Ref_DTC
VCO
D0 D0D1 Dk
TDR,DTC
fout = (N+n)×fref; N- Integer part; n- fractional part

4 ESSCIRC2015 41th European Solid-State Circuits Conference
[C4L-A] A Fractional-N Sub-Sampling PLL using a Pipelined Phase-Interpolator with a FoM of -246dB
DTC only architecture requires large dynamic range
Inpu
t [V]
Out
put [
V]
t
t+Δτdτd
Error in Threshold-crossing
DTC
TVCO
DTC Only
Conventional Frac.-N SSPLL: Challenges
!!",!"# ≥ !!"# !
Inpu
t [V]
Out
put [
V]
t
t+Δτdτd
Error in Threshold-crossing
DTC
TVCO
DTC Only[4] A. Abidi, JSSC 2006
!!!! = 4kTγ!!!!!(!!! − !!")!

5 ESSCIRC2015 41th European Solid-State Circuits Conference
[C4L-A] A Fractional-N Sub-Sampling PLL using a Pipelined Phase-Interpolator with a FoM of -246dB
Highly linear phase-interpolator + DTC results in lower noise
Proposed Technique
Required dynamic range(dr)
!!",!"#!!" = !!"#4
12!
!_!"
!!!+!
!!!"# ∙ 2!_!"# − 1 !
Inpu
t [V]
Out
put [
V]
t
t+Δtdtd
Error in Threshold-crossing
PI
DTCDTC
DTC
DTC
DTC
DTCDTC
DTC
PI
PI
PI
PI
PI
Phase Interpolator+DTC
PI
PI
!!",!"# ≥ !!"# !
Error in threshold-crossing
!!!"! = 4kTγ!!!"!!(!!! − !!")!

6 ESSCIRC2015 41th European Solid-State Circuits Conference
[C4L-A] A Fractional-N Sub-Sampling PLL using a Pipelined Phase-Interpolator with a FoM of -246dB
Dynamic Range Comparison
Dynamic range requirements are relaxed
Dyna
mic
Ran
ge [n
s]
1
0.01
0.1
0.1 1VCO Cycle [ns]
DTC
DTC+Phase-Interpolator
0.25psResolution:
5ps10ps

7 ESSCIRC2015 41th European Solid-State Circuits Conference
[C4L-A] A Fractional-N Sub-Sampling PLL using a Pipelined Phase-Interpolator with a FoM of -246dB
Intrinsic Jitter Comparison
eg: Fvco = 4GHz, required resolution=250fs, DSM: second order RMS Jitter: DTC only = ~150fs DTC+PI = ~50fs
RMS
Jitte
r [fs
]
220
20
60
140
180
100
0.1 1VCO Cycle [ns]
0.25psResolution:
5ps10ps
DTC
DTC+Phase-Interpolator

8 ESSCIRC2015 41th European Solid-State Circuits Conference
[C4L-A] A Fractional-N Sub-Sampling PLL using a Pipelined Phase-Interpolator with a FoM of -246dB
Power and area wastage is minimized
Pipelined Phase-Interpolator
00
900Out
1800
2700
Stage-1
Phase
Interpolator
Φi1Φo1
Φo2
Φo3Φi2
Stage-2
Phase
Interpolator
Φi1Φo1
Φo2
Φo3Φi2
Stage-M
Phase
Interpolator
Φi1Φo1
Φo2
Φo3Φi2
[5] S. Kumaki, APCCAS 2010
! No. of stages: Tournament type: 2N_PI – 1
! No. of stages: Pipelined: N_PI+1

9 ESSCIRC2015 41th European Solid-State Circuits Conference
[C4L-A] A Fractional-N Sub-Sampling PLL using a Pipelined Phase-Interpolator with a FoM of -246dB
Issue of Conventional Phase-Interpolator
Ix Ix
Ix Ix
Φin
1
Φin
2
Φo2
Φi1
Φo1
PI
PIPI
Phase Interpolator(one stage)
PI
C
C
C
Φo2
Φo3
Φi2
Φin1
Φin2
Φo
Φin1
Φin2
Φo
Φin1
Φin2
Φo
00
900
450
00
PI
PI
Phase Interpolator(one stage)
PI
C
C
C
900
Φin1
Φin2
Φo
Φin1
Φin2
Φo
Φin1
Φin2
Φo

10 ESSCIRC2015 41th European Solid-State Circuits Conference
[C4L-A] A Fractional-N Sub-Sampling PLL using a Pipelined Phase-Interpolator with a FoM of -246dB
Conventional Phase-Interpolator
Ix Ix
Ix Ix
Φin
1
Φin
2
Φin1Φin2
Φo1
time
Φo1
Φi1
Φo1PI
PI
PI
Phase Interpolator(one stage)
PI
C
C
C
Φo2
Φo3
Φi2
Φin1
Φin2
Φo
Φin1
Φin2
Φo
Φin1
Φin2
Φo
time
2Ixdvdt
= C

11 ESSCIRC2015 41th European Solid-State Circuits Conference
[C4L-A] A Fractional-N Sub-Sampling PLL using a Pipelined Phase-Interpolator with a FoM of -246dB
Conventional Phase-Interpolator
Ix Ix
Ix Ix
Φin
1
Φin
2
Φin1Φin2
Φo3
time
Φo3
Φi1
Φo3PI
PI
PI
Phase Interpolator(one stage)
C
C
Φo2
Φi2
time
PIC Φo1
Φin1
Φin2
Φo
Φin1
Φin2
Φo
Φin1
Φin2
Φo
2Ixdvdt
= C

12 ESSCIRC2015 41th European Solid-State Circuits Conference
[C4L-A] A Fractional-N Sub-Sampling PLL using a Pipelined Phase-Interpolator with a FoM of -246dB
Conventional Phase-Interpolator
Ix(1-δ)
Ix Ix
Ix Ix
Φin
1
Φin
2
Φin1Φin2
Φo2
IdealActual
dv
dt= C
time
Φo2
timeΦi1
Φo1
PI
PIPI
Phase Interpolator(one stage)
PI
C
C
C
Φo2
Φo3
Φi2
Ixdvdt
=C
Φin1
Φin2
Φo
Φin1
Φin2
Φo
Φin1
Φin2
Φo
δIxsh
ort c
ircui
t cu
rren
t

13 ESSCIRC2015 41th European Solid-State Circuits Conference
[C4L-A] A Fractional-N Sub-Sampling PLL using a Pipelined Phase-Interpolator with a FoM of -246dB
Conventional Phase-Interpolator
Short circuit current results in phase error
Ix Ix
Ix Ix
Φin
1
Φin
2
Φin1Φin2
Φo2
IdealActual
time
Φo2
timeΦi1
Φo1
PI
PIPI
Phase Interpolator(one stage)
PI
C
C
C
Φo2
Φo3
Φi2
2Ixdvdt
= CIxdv
dt=C
Φin1
Φin2
Φo
Φin1
Φin2
Φo
Φin1
Φin2
Φo

14 ESSCIRC2015 41th European Solid-State Circuits Conference
[C4L-A] A Fractional-N Sub-Sampling PLL using a Pipelined Phase-Interpolator with a FoM of -246dB
Proposed Short-Current-Free Topology
Short-circuit current is avoided
Φin1Φin2
time
Φo2
Φo2
timeΦi1
Φo1
PI
PIPI
Phase Interpolator(one stage)
PI
C
C
C
Φo2
Φo3
Φi2
Φin1
Φin2
Φo
Φin1
Φin2
Φo
Φin1
Φin2
Φo
Ixdvdt
=C
Ix Ix
Ix Ix
ΔC
Φin2Φin1
Φin1 Φin2

15 ESSCIRC2015 41th European Solid-State Circuits Conference
[C4L-A] A Fractional-N Sub-Sampling PLL using a Pipelined Phase-Interpolator with a FoM of -246dB
Proposed Short-Current-Free Topology
INL of < 0.5 LSB is achieved
[6] T. Saeki, JSSC 2000
Ixdvdt
=
Φin1Φin2
C2Ixdv
dt= C
time
Φo2
timeΦi1
Φo1
PI
PIPI
Phase Interpolator(one stage)
PI
C
C
C
Φo2
Φo3
Φi2
Φin1
Φin2
Φo
Φin1
Φin2
Φo
Φin1
Φin2
Φo
Ix Ix
Ix Ix
ΔC
Φin2Φin1
Φin1 Φin2
Φo2

16 ESSCIRC2015 41th European Solid-State Circuits Conference
[C4L-A] A Fractional-N Sub-Sampling PLL using a Pipelined Phase-Interpolator with a FoM of -246dB
Proposed FN-SSPLL Architecture
SSPDRef
DTC LPFout
CP
3-Bit Pipelined Phase-Interpolator00
450135022503150
22.5011.250
0.35150
00
900
1800
1800
2700
Quad.Divider
Stag
e 1
Stag
e 2
Stag
e 3 Φi1Φo1
Φo2
Φo3
Φi2
Φi1Φo1
Φo2
Φo3
Φi2
Φi1Φo1
Φo2
Φo3
Φi2
td,s1td,s2td,s3

17 ESSCIRC2015 41th European Solid-State Circuits Conference
[C4L-A] A Fractional-N Sub-Sampling PLL using a Pipelined Phase-Interpolator with a FoM of -246dB
Proposed FN-SSPLL Architecture SSPD
Ref
Ref
DTC LPFout
DSM
PSM
PSM: Power Save ModuleWS:Wave Shaper
PSWL: Phase Switch LogicIFCW: Integer Freq. Control WordFFCW: Fractional Freq. Control Word
WS
CP
FLLIFCW
IFCWR_DTC R_PI Reg
FFCW
Phase Switch Power Down
3-Bit Pipelined Phase-Interpolator
PSWL
RefCW
Register Bank
00
00
900
1800
1800
2700
Quad.Divider
Sta
ge1
Sta
ge2
Sta
ge3 Φi1
Φo1
Φo2
Φo3
Φi2
Φi1
Φo1
Φo2
Φo3
Φi2
Φi1
Φo1
Φo2
Φo3
Φi2

18 ESSCIRC2015 41th European Solid-State Circuits Conference
[C4L-A] A Fractional-N Sub-Sampling PLL using a Pipelined Phase-Interpolator with a FoM of -246dB
Chip Micrograph
LC-VCO SPI
LPF
520 µm
380
µm PI
DTC
PSLSSLFLL&
0.2mm2 core area in Standard 65nm CMOS process

19 ESSCIRC2015 41th European Solid-State Circuits Conference
[C4L-A] A Fractional-N Sub-Sampling PLL using a Pipelined Phase-Interpolator with a FoM of -246dB
Measurement Results
-60
-40
-80
-100
-160
-140
-180
Phas
e No
ise
[dBc
/Hz]
-120
100k 1MFrequency [Hz]
10M10k
4.4716GHz from 40MHz reference [N=111.79]

20 ESSCIRC2015 41th European Solid-State Circuits Conference
[C4L-A] A Fractional-N Sub-Sampling PLL using a Pipelined Phase-Interpolator with a FoM of -246dB
Performance Comparison of Fractional-N PLL This work [1] [2] [7]
Architecture SSPLL SSPLL MDLL TDC Freq. [GHz] 4.1-5.1 2.2-2.4 1.6-1.9 2.412-2.484
4.915-5.825 Power [mW] 3.3 17.3 3 9.5 Area [mm2] 0.2 0.75 0.4 0.3 Phase Noise (in-band)
-112 @400kHz
-112 @50kHz
-112 @100kHz
-106 @100kHz
Integrated Jitter 273fs 266fs 1.4ps 173fs
FoM [dB] -246.1 -239.1 -233.76 -245.5 CMOS Tech. 65nm 180nm 130nm 28nm FDSOI [1] Po-Chun Huang, ISSCC 2014 [2] G. Marucci, ISSCC 2014 [7] X. Gao, ISSCC 2015

21 ESSCIRC2015 41th European Solid-State Circuits Conference
[C4L-A] A Fractional-N Sub-Sampling PLL using a Pipelined Phase-Interpolator with a FoM of -246dB
Performance Comparison of Fractional-N PLL
FoM = 10logJitter
1s
2 Power1mW( ( ( (×
Better
Jitte
r2 (p
s)2
W. Deng, ISSCC 2015
P. Park, ISSCC 2012
M. Gupta, ISSCC 2006
C. H. Lee, VLSI 2014
C. W. Yao, VLSI 2011
M. Talegaonkar, VLSI 2014
G. Marucci, ISSCC 2014
A. Elkholy, VLSI 2014
X. Gao, ISSCC 2015
This Work
10-2
10-1
100
100
101
101
102
102
Power Consumption [mW]
FoM=-220dB
FoM=-230dB
FoM=-240dB
FoM=-250dB

22 ESSCIRC2015 41th European Solid-State Circuits Conference
[C4L-A] A Fractional-N Sub-Sampling PLL using a Pipelined Phase-Interpolator with a FoM of -246dB
Conclusion
! A fractional-N SSPLL architecture is presented. ! Proposed architecture uses a combination of DTC
and phase-interpolator: ! Reduces jitter from the multi-phase generator. ! Power-jitter-resolution tradeoff is mitigated. ! FoM of -246.1dB is achieved.

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