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B. E. Boser 1
Advanced Analog Integrated Circuits
MOS Switches
Bernhard E. BoserUniversity of California, Berkeley
Copyright © 2016 by Bernhard Boser
EE240B – MOS Switches
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MOS Switches
EE240B – MOS Switches
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Ideal Track and Hold
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Sampling versus Charge Processing
Sampling
• Input varies (often rapidly)
Charge Processing (SC)
• Input ~constant
EE240B – MOS Switches
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Signal Nomenclature
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MOS Sample & Hold (Track & Hold)
EE240B – MOS Switches
(simplest realization)
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Advanced Analog Integrated Circuits
Switch Nonidealities
Bernhard E. BoserUniversity of California, Berkeley
Copyright © 2016 by Bernhard Boser
EE240B – MOS Switches
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Nonidealities
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Switch on-resistance
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Ron
0 VDD
NMOS PMOS CMOS
VTHVi
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Signal Dependent on-resistance
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Hold-Mode Feedthrough
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Hold-Mode Leakage
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Gate Leakage
• 65nm CMOS: ~ 1V/ms droop– Addressed in sub-65nm technologies with high-k dielectrics
Ref: A. Annema et al, “Analog circuits in ultra-deep-submicron CMOS,” IEEE JSSC, Jan. 2005, pp. 132-43.
EE240B – MOS Switches
Min
imum
f s
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Thermal Noise
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Clock Jitter
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Advanced Analog Integrated Circuits
Charge Injection and Clock Feedthrough
Bernhard E. BoserUniversity of California, Berkeley
Copyright © 2016 by Bernhard Boser
EE240B – MOS Switches
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Charge Injection and Clock Feedthrough
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Slow Gating
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Slow Gating Model
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Fast Gating
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Charge Split Ratio a
Ref: G. Wegemann et al, “Charge injection in analog MOS switches,” IEEE JSSC, June 1987, pp. 1091-7.
EE240B – MOS Switches
𝑅#$𝐶&𝑇(
�
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Slow Switching or Fast Switching?
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Fast Gating Model
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Fast à Slow Gating Errors
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Technology Scaling
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Advanced Analog Integrated Circuits
Mitigating Charge Injection Error
Bernhard E. BoserUniversity of California, Berkeley
Copyright © 2016 by Bernhard Boser
EE240B – MOS Switches
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Mitigating Charge Injection Error
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Charge Cancellation
Ref: Ch. Eigenberger et al, “Dummy Transistor compensation of analog MOS switches,” JSSC Aug 1989, pp. 1140-6.
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Charge Cancellation Example
• ~ 6-Bit accuracy
Ref: M. Choi et al, “A 6-b 1.3-Gsample/s A/D converter in 0.35mm CMOS.” JSSC Dec 2001, pp. 1847-58.
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CMOS Switch
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Differential Sampling
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Advanced Analog Integrated Circuits
Clock Bootstrapping
Bernhard E. BoserUniversity of California, Berkeley
Copyright © 2016 by Bernhard Boser
EE240B – MOS Switches
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Clock Bootstrapping
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Input and Clock Waveforms
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Booster Circuit
EE240B – MOS Switches
𝑅*$ ≅1
𝜇$𝐶*.𝑊𝐿
𝐶1𝐶1 + 𝐶345
𝑉77 −𝐶345
𝐶1 + 𝐶345𝑉#$ − 𝑉9: 𝑉#$
(square law model)
Cpar
Vin
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Booster Performance Example
• Good to ~ 10 Bits
Ref: S. Louwsma et al, “A 1.35 GS/s, 10 b, 175 mW time-interleaved AD converter in 0.13 um CMOS”, JSSC April 2008, pp. 778-86.
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Advanced Analog Integrated Circuits
Bottom Plate Sampling
Bernhard E. BoserUniversity of California, Berkeley
Copyright © 2016 by Bernhard Boser
EE240B – MOS Switches
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Bottom Plate Sampling
• References– D. G. Haigh and B. Singh, “A switching scheme for SC filters which reduces the
effect of parasitic capacitances associated with switch control terminals,” ISCAS 1983, pp. 586-9.
– K.-L. Lee and R. G. Meyer, “Low-distortion switched-capacitor filter design techniques,” IEEE JSSC, Dec 1985, pp. 1103-13.
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1) Sample
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2) Disconnect CH
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Charge at Node X
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DQ1
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Open-Loop Charge Processing
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Closed-Loop Charge Processing
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Charge Conservation Analysis
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Cancelling the Offset: Fully Differential
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Advanced Analog Integrated Circuits
Sampling Network
Bernhard E. BoserUniversity of California, Berkeley
Copyright © 2016 by Bernhard Boser
EE240B – MOS Switches
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SC Gain with Common-Mode Cancellation
Ref: S. H. Lewis and P. R. Gray, “A pipelined 5 MSample/s 9-bit analog-to-digital converter,” IEEE JSSC Dec 1987, pp. 954-61.
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Flip-Around T/H
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Ref: W. Yang et al, “A 3-V 340-mW 14-b 75-MSample/s CMOS ADC with 85-dB SFDR at Nyquist input,” IEEE JSSC Dec 2001, pp. 1931-36.
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Sampling Network Design
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Ref: Y.-M. Lin et al., “A 13-b 2.5-MHz self-calibrated pipelined A/D converter in 3-um CMOS,” IEEE JSSC April 1991, pp. 628-36.
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Realization of Shorting Switch
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Advanced Analog Integrated Circuits
Capacitors
Bernhard E. BoserUniversity of California, Berkeley
Copyright © 2016 by Bernhard Boser
EE240B – MOS Switches
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Capacitors
EE240B – MOS Switches
Ref: C. H. Ng et al, “MIM capacitor integration for mixed-signal/RF applications,” IEEE Trans ED, July 2005, pp. 1399-1409.
Ref: R. Aparicio et al, “Capacity Limits and Matching Properties of Integrated Capacitors,” IEEE JSSC, March 2002, pp. 384-93.
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Capacitor Top and Bottom Parasitics
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Connection of Capacitors
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