high band width circuit techniques for cmos-rf

UNIV TEL AVIV M. Moyal1

High Band Width Circuit Techniques for CMOS-RFHigh Band Width Circuit Techniques for CMOS-RF


Agenda

1) Applications for High Speed Design

2)Feed Backs

3) Inductors as BW boosters

4) CMOS “ Synthesized Inductors”

5) High Speed Buffers- Cherry Hopper and CTLE

6) “RF” ADCs for 10GS/s


2)Feed Backs



5) High Speed Buffers- Cherry Hopper and CTLE



APPLICATIONS

Serial Transmission Receivers Getting in and out the NIC/Servers/backplaes..

Wireless systems.. 60GHz-HDMI..

On chip communications…


Increased speed by going to smaller L is an expensive option ~1.4 mill$/maskset@65nm

Can we squeeze more speed (BW) with CMOS circuits techniques ?

At 45nm it’s a battle to deal with CMOS/RF and transistor variations and leaks--->.~2ua/um..65nm

This lecture is. about..trying to avoid this with ckt. techniques..

Increased speed by going to smaller L is an expensive option ~1.4 mill$/maskset@65nm

Can we squeeze more speed (BW) with CMOS circuits techniques ?

At 45nm it’s a battle to deal with CMOS/RF and transistor variations and leaks--->.~2ua/um..65nm

This lecture is. about..trying to avoid this with ckt. techniques..


2) Feed backs to boost BW


Basic Feed back to boost BW

t/RCe-Vin[1 Vout(t) −

=

CR∗=τ )1/()( +∗= ACRnew τ

VinVout

A

VoutAVy ∗=

R

C

R

C

1)/RCt(A-e-1 [ Vin Vout(t)

+=

1+A

1)}RSC/(A1/{1 Vout/Vin ++=


Simulation: a=2 and a=10

Ac response Time domain

)(/ fViVo

Frequency

ac TF RC/fdback )(/ fViVo

Time

Step response

)(/ fViVo


CSA

R1=n*R2

C1

C2=n*C1

R2

R3

IoutIin

Gain dB

Freqω

Closed loop op-ampMain pole @ R1C1

Zero of PZ cancelation net @ R2C2

Total BW of CSA stage pole @ R3C2

IinIo/

The Math: Transfer function with ideal opamp.H1(s)=R1/(1+R1C1S). One pole at -1/R1C1

The zero part is H(s)=(1+R2C2S)/(R2+R3+R2R3C2S)a zero at -1/R2C2=-1/R1C1 and a pole at –(R2+R3)/(R2R3C2)Combination of these two cancels the pole leaving R1/(R2+R3+R2R3C2S) one pole. When R3<<R2 this reduces to a pole at -1/R3C2. with gain of R1/R2=n

Basic Feed back to boost BWIn X ray detection…

Frequency

)(1 SH


Problem remain: We need “open loop” structure or very fast feedback to go beyond GHz speed

A Solution: lets look at Transistors and passives elements since they are the fastest basic block we got.


In frequency domain: Idea: set L to increase the gain as f. ( not at low frequency). BW can be boosted to ~1.8x – with peaking !

In frequency domain: Idea: set L to increase the gain as f. ( not at low frequency). BW can be boosted to ~1.8x – with peaking !

Bad: L takes lot of area~ 1pHn/micronPeaking and control (Q)

Bad: L takes lot of area~ 1pHn/micronPeaking and control (Q)

Good: Simple passive.L has no Noise !

Good: Simple passive.L has no Noise !

R

C

R

CVinp Vinn

Itail

Voutdiff

R

C

R

CVinp

Itail

Voutdiff

Vinn

Evolution data comm: make 10GHz in CMOS 0.15u

UNIV TEL AVIV M. Moyal13Source: Prof. green lecture

VCC

R R

IssVbias

inp innoutnoutp

M1

M2 M3


Bad: Need to know CIn ~GHz not less..L may need to be wide

Bad: Need to know CIn ~GHz not less..L may need to be wide

Step outputWith & W/0 Inductor

Step outputWith & W/0 Inductor

Frequency

Data out

Source: Prof. green lecture


What’s inductor looks like and behave in IC plan

L weakly depend on W (long L)

L weakly depend on W (long L)

Z descends at high frequency Z descends at high frequency


Problem may still be there..

Inductors are: “area takers”


BW INCREASE BY ~1.7

R

C

)(driverI

Vdd

Vout

Zin

""__ inductorMOS

uu 1.0/20

Zin

f

gm/1

R

SRC)SC/(1V(gm I ++=

C is already made C is already made

RCπ2/1 Cgm π2/

Bad: Vth: Takes more voltageBe aware of noise of R

Bad: Vth: Takes more voltageBe aware of noise of R

Key: Play with R to get best BW ( peaking)

Key: Play with R to get best BW ( peaking)

Good: Simple area is smallGain is process independent

Good: Simple area is smallGain is process independent


Vinn

Itail

Voutdiff

R

C

Vdd

""__ inductorMOSuu 1.0/20

R

C

Vdd

uu 1.0/20

Example: - Synthesized L


Example: DFF- With Synthesized L

CML Flip Flop


5) High speed Buffers- Cherry hopper & CTLE

High speed TIA’s VGA’s :

Can we do it without Inductors ?Can we take circuits from bipolar designs

UNIV TEL AVIV M. Moyal22Source: C.H. Holdenried + U.of. Calgary

Used in SiGe, LA op


BW INCREASE- C. Hooper buffer

Frequency

AC domain

Circuit

Comparison CML Vs. Hooper buffer


CTLE- BW INCREASE

R R

1CVinp

Itail

Voutdiff

Cl

1R

Frequency

AC response

~R/R1 DC gain and R1C1 set the zero RCl the pole


At last: Even the faster known digital element the inverter can have

higher BW with some thoughts..


High BW INVERTER High BW INVERTER

different feed backdifferent feed back

Frequency

time response

AC domain

Frequency

f/bf/b


BW INCREASE“forget the BW do it another way?”

Digital-Half rates and..

DATA CONVERTERInterleaved with slow elements



Even f/2Even f/2

Q

CKo

Q

CK

D

Odd f/2Odd f/2

CK

CKe

CKe CKe

D

muxmux

Cut rate by 2 – parallel data…parallel CPUs..


““SlowSlow”” ADCs can be put in parallelADCs can be put in parallel

ADC1

ADC1

ADC1

ADC1

ADC1

ADC1

Vin(t)

fck1

delta=1.25ns

Vo(NT)

Analog S/H & Analog S/H & DemuxDemux Dig Dig MuxMux

fck2

Time interleavedTime interleaved


..Recent advances in ADCs..Recent advances in ADCs

But we need lots of ADCs But we need lots of ADCs ––Power could kill the idea..Power could kill the idea..

So lets look at old ADC type....So lets look at old ADC type....


SAR ADCs FOM HISTORY

0

0.05

0.1

0.15

0.2

2005 2006 2007 2008 2009Year

FOM

(pJ/

conv

)Is the SAR Is the SAR ““coming backcoming back”” ??

NbitteSamplingRaPower

2cision Energy/De

⋅=


100ff100ff

1V1V00 00

50ff50ff00

00

25ff25ff

00

25ff25ff

VOUT(DAC)VOUT(DAC)

25)2550100/(100Vout(dac) +++∗= V1 VdacVout 2/1)( =

100ff100ff

1V1V00

50ff50ff00

00

25ff25ff

00

25ff25ff

VOUT(DAC)VOUT(DAC)

1V1V

25)255050/(100Vout(dac) +++∗= V1

operation..operation..


Vin(t)

CompSAMPLE HOLD DIGITAL

Vo(nT)

offset DACoffset DAC

Lin DACLin DAC 10b DAC10b DAC

Gain DACGain DAC

ADC slice – lots of calibrations…


תודה על ההקשבהתודה על ההקשבהThank youThank you

high band width circuit techniques for cmos-rf

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