Exact Design of All-MOS Log Filters X.Redondo and F.Serra-Graells - - PowerPoint PPT Presentation

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Exact Design of All-MOS Log Filters X.Redondo and F.Serra-Graells - - PowerPoint PPT Presentation

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Exact Design of All-MOS Log Filters Intro MOS-C Generalization All-MOS Examples Conclusions Exact Design of All-MOS Log Filters X.Redondo and F.Serra-Graells Design Department Institut de Microelectrnica de Barcelona Centre Nacional de

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Exact Design of All-MOS Log Filters Intro MOS-C Generalization All-MOS Examples Conclusions

Exact Design of All-MOS Log Filters

X.Redondo and F.Serra-Graells

Design Department Institut de Microelectrònica de Barcelona Centre Nacional de Microelectrònica Spain

24th May 2004

X.Redondo and F.Serra-Graells IEEE ISCAS’04

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SLIDE 2

Exact Design of All-MOS Log Filters Intro MOS-C Generalization All-MOS Examples Conclusions

Introduction Low-voltage MOS-C log circuits Generalization to non-linear capacitors Exact all-MOS proposal Design examples Conclusions

X.Redondo and F.Serra-Graells IEEE ISCAS’04

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Exact Design of All-MOS Log Filters Intro MOS-C Generalization All-MOS Examples Conclusions

Instantaneous companding filters

d¯ Iss dt = ¯

A¯ Iss + ¯ B ¯ Iin ¯ Iout = ¯ C ¯ Iss + ¯ D¯ Iin

F

  • 1

1 s G 1 s G 1 s G Vss1 Vss2 VssN Vin1 Vin2 VinM G G G

F F F compression non-linearintegration expansion externallylinear F

  • 1

F

  • 1

Iin1 Iin2 IinM Iss1 Iss2 IssN

High-frequency (bipolar) Low-voltage ? Non-linear capacitors

MOS log-mapping

VGB VSB VDB ID

D S B G

weak inversion:

VSB,DB ≫ VGB−VT O

n

forward saturation:

VDB − VSB ≫ Ut

ID = ISe

VGB−VT O nUt

e− VSB

Ut

IS = 2nβU 2

t

IC = ID IS

X.Redondo and F.Serra-Graells IEEE ISCAS’04

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SLIDE 4

Exact Design of All-MOS Log Filters Intro MOS-C Generalization All-MOS Examples Conclusions

Introduction Low-voltage MOS-C log circuits Generalization to non-linear capacitors Exact all-MOS proposal Design examples Conclusions

X.Redondo and F.Serra-Graells IEEE ISCAS’04

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SLIDE 5

Exact Design of All-MOS Log Filters Intro MOS-C Generalization All-MOS Examples Conclusions

Compressors and expanders

Ccomp Cin 1× K× Iref

Iref K

Vref Vin Iin Iref Iref Vout Vref Iout

◮ Companding function: I = F(V ) = Irefe

V −Vref nUt

I > 0

◮ Class-A operation: Imax ≡ Iref

2

◮ Frequency compensation of input parasitics: ζ = 1

2

  • KCcomp

Cin

X.Redondo and F.Serra-Graells IEEE ISCAS’04

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SLIDE 6

Exact Design of All-MOS Log Filters Intro MOS-C Generalization All-MOS Examples Conclusions

Integrators

¯ A =   · · · + 1

τ21

− 1

τ22

+ 1

τ23

· · ·   single-coefficient linear ODE: dIout dt = ±1 τ Iin non-linear ODE in the compressed domain: dVout dt = ±nUt τ e

Vin−Vout nUt

circuit realization in the Q-domain: dQout dt = Co dVout dt

  • Icap

= ±Itunoe

Vin−Vout nUt

Icap = G(Vin, Vout) τ = nUtCo Ituno

Co Ituno Vin Vout Icap

◮ Single phase (+ 1

τ case)

◮ Operating point ensured

by the ¯ A matrix

◮ Half of G can be shared

by the same row of ¯ A

◮ Valid only for grounded

linear capacitors

X.Redondo and F.Serra-Graells IEEE ISCAS’04

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SLIDE 7

Exact Design of All-MOS Log Filters Intro MOS-C Generalization All-MOS Examples Conclusions

Introduction Low-voltage MOS-C log circuits Generalization to non-linear capacitors Exact all-MOS proposal Design examples Conclusions

X.Redondo and F.Serra-Graells IEEE ISCAS’04

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SLIDE 8

Exact Design of All-MOS Log Filters Intro MOS-C Generalization All-MOS Examples Conclusions

Voltage-dependent capacitors

dQout dt = C dVout dt + dC dt Vout dQout dt =

  • C +

dC dVout Vout dVout dt distortion due to:

◮ Signal swing (Vout) ◮ Non-constant capacitance (

dC dVout )

Tuning compensation strategy

Itun Ituno = C Co + dC dVout Vout Co . = f(Vout)

C Itun Vin Vout f

◮ Valid for non-abrupt C-V ◮ Linear case reduction:

dC dVout = 0 Itun ≡ Ituno

X.Redondo and F.Serra-Graells IEEE ISCAS’04

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SLIDE 9

Exact Design of All-MOS Log Filters Intro MOS-C Generalization All-MOS Examples Conclusions

Introduction Low-voltage MOS-C log circuits Generalization to non-linear capacitors Exact all-MOS proposal Design examples Conclusions

X.Redondo and F.Serra-Graells IEEE ISCAS’04

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SLIDE 10

Exact Design of All-MOS Log Filters Intro MOS-C Generalization All-MOS Examples Conclusions

Grounded NMOS device

◮ Single poly-Si

structure

◮ Digital process

compatible

◮ High-density [F/m2]

Cgate ≫ Cpoly−poly

◮ Strong non-linearity

around VT O ×

◮ Low-voltage versus

distortion ? (i.e. Vref vs VT O)

(

  • )/

Vout V Ut

TO

weakinversion

  • 20
  • 15
  • 10
  • 5

5 10 15 20 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 C Co /

stronginversion

Vout C

moderate inversion

X.Redondo and F.Serra-Graells IEEE ISCAS’04

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SLIDE 11

Exact Design of All-MOS Log Filters Intro MOS-C Generalization All-MOS Examples Conclusions

Analytical compensation

all-regions quasi-static CGG: C = Co

n−1 n

+ 2 √ IC

  • 1 − e−

√ IC

1 + 2 √ IC

  • 1 − e−

√ IC

  • IC = ln 2

1 + e

Vout−VT O 2nUt

  • for Vout,ref ≥ VT O (i.e. IC ≫ 1):

C Co = 1 − Ut Vout − VT O Itun Ituno = 1 + VT OUt (Vout − VT O)2

Ituno Ituno

VT OUt (Vout−VT O)2

Vin Vout C

equivalent to add a positive signal-dependent tuning current. . .

X.Redondo and F.Serra-Graells IEEE ISCAS’04

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Exact Design of All-MOS Log Filters Intro MOS-C Generalization All-MOS Examples Conclusions

Circuit realization

Itun Ituno = 1 + VT OUt (Vout − VT O)2 matched device in strong inversion: Icomp = β2 2n (Vout − VT O)2 Itun = Ituno + Ituno Icomp IS2VT O (2n)2Ut tuning compensation synthesis: Itun = Ituno + ItunoImult Icomp Imult = IS2 VT O (2n)2Ut

M2 Ituno Ituno Imult Vin Vout M1 C Itun Icomp

×

Ituno Icomp Vref Itun − Ituno Imult

X.Redondo and F.Serra-Graells IEEE ISCAS’04

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SLIDE 13

Exact Design of All-MOS Log Filters Intro MOS-C Generalization All-MOS Examples Conclusions

Introduction Low-voltage MOS-C log circuits Generalization to non-linear capacitors Exact all-MOS proposal Design examples Conclusions

X.Redondo and F.Serra-Graells IEEE ISCAS’04

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SLIDE 14

Exact Design of All-MOS Log Filters Intro MOS-C Generalization All-MOS Examples Conclusions

Third-order low-pass filter

200 m ¹

◮ 0.35µm technology ◮ Poly-Si(dashed) versus

NMOS(solid) results

Input-Amplitude/Full-Scale[dB] THD [%] 0.5 1 1.5 2

  • 30
  • 20
  • 10

◮ f−3dB = 8KHz

fin = 2KHz

◮ VDD =1.2V

Vref =0.6V

X.Redondo and F.Serra-Graells IEEE ISCAS’04

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Exact Design of All-MOS Log Filters Intro MOS-C Generalization All-MOS Examples Conclusions

Second-order band-pass filter

1× K× Iref

Iref K

Vref Vin Iin Iref Iref Vout Vref Iout Ituno Ituno Imult Itun C1 Itun − Ituno

×

Ituno Ituno Imult C2

×

X.Redondo and F.Serra-Graells IEEE ISCAS’04

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Exact Design of All-MOS Log Filters Intro MOS-C Generalization All-MOS Examples Conclusions

Second-order band-pass filter

IMD [%] Vref [V] 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.5 1 1.5 2 2.5 3 VTO proximityeffect multiplier saturation topology limitation

◮ fo = 50KHz and Q = 1 ◮ fin1 = 46KHz

fin2 = 54KHz

◮ Half full-scale input ◮ VDD =1.2V ◮ 0.35µm technology

  • Ideal poly-Si (dotted)
  • Simple NMOS (dashed)
  • NMOS with tuning

compensation (solid)

X.Redondo and F.Serra-Graells IEEE ISCAS’04

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SLIDE 17

Exact Design of All-MOS Log Filters Intro MOS-C Generalization All-MOS Examples Conclusions

Second-order band-pass filter

200 m ¹

X.Redondo and F.Serra-Graells IEEE ISCAS’04

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SLIDE 18

Exact Design of All-MOS Log Filters Intro MOS-C Generalization All-MOS Examples Conclusions

Second-order band-pass filter

200 m ¹ translinear-loops currentsources andmirrors telescopicdevices MOScapacitors

X.Redondo and F.Serra-Graells IEEE ISCAS’04

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Exact Design of All-MOS Log Filters Intro MOS-C Generalization All-MOS Examples Conclusions

Second-order band-pass filter

200 m ¹ tuning-compensation band-passfilter Overhead:

◮ Si area (no-routing) ∼0.04mm2 (12% of 0.33mm2) ◮ Static power ∼50µW (33% of 150µW)

X.Redondo and F.Serra-Graells IEEE ISCAS’04

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SLIDE 20

Exact Design of All-MOS Log Filters Intro MOS-C Generalization All-MOS Examples Conclusions

Introduction Low-voltage MOS-C log circuits Generalization to non-linear capacitors Exact all-MOS proposal Design examples Conclusions

X.Redondo and F.Serra-Graells IEEE ISCAS’04

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SLIDE 21

Exact Design of All-MOS Log Filters Intro MOS-C Generalization All-MOS Examples Conclusions

◮ Analytical design of all-MOS log filters based on

compensation of tuning currents

◮ Suitable for very low-voltage applications ◮ Compatible with digital technologies ◮ Area & power overhead proportional to filter order ◮ Technology dependence not critical ◮ Sub-micron low-voltage examples ◮ Extension to Class-AB operation?. . .

X.Redondo and F.Serra-Graells IEEE ISCAS’04