A 30-GS/sec Track and Hold Amplifier in 0.13-µm CMOS

Technology

Shahriar ShahramianSorin P. Voinigescu

Anthony Chan Carusone

Department of Electrical & Computer Eng.University of Toronto

Canada

Introduction & Motivation I

Digital EqualizerPhoto

Detector

T/H

ADC

AdaptiveEqualizer

ClockRecovery

EqualizedData

• Equalization required at high bit rates• Analog equalization up to 40 Gb/s• Digital equalization is more robust and flexible

• Require full rate Track & Hold Amplifiers

Introduction & Motivation II• Demonstrated 40-GS/sec THA in SiGe BiCMOS

– fT and fMAX of 160 GHz

• CMOS technologies scaling to nanometre– fT and fMAX exceed 200 GHz for in production CMOS

• CMOS is a serious contender for implementing DSP based equalizers above 10 Gb/s

Introduction & Motivation III

• High speed• Low dynamic range• Requires diodes

• High speed• Lower supply• Isolation in hold mode

Diode Sampling Bridge Switched Emitter Follower

J. C. Jensen, et. al.CICC 02

S. Shahramian, et. al.CSICS 05

Introduction & Motivation IV

• Low supply• Low speed due to

series CMOS RON

• Take advantage of high speed CMOS source follower

Series CMOS Sampler Switched Source Follower

I. H. Wang, et. al.Electronic Letters 06

This workCICC 06

0.13-µm CMOS Technology• Simulated fT and

fMAX of 80 GHz• 8 layer

metallization back end with thick RF top metal layers

• Available triple-well CMOS transistors

• Available low power (high VTH) transistors

THA Block DiagramC

lock TIA CML

INVCMLINV

CM

LIN

VClock Path

CS

CS

TIACS

Diff.Pair

Diff.Pair

Data PathIn

put

Output

T/HCS

DRV

DRV

Input Stage DesignTIA

Active loads

Improve open loop

Gain, T

Eliminating current

source transistor

reduces power

supply voltage

Input Stage DesignTIA

Signal matching

through resistive

feedback

Input Stage DesignTIA

50ΩT1

RZ Fin =

+=

Noise matching

through transistor

sizing

Input Stage DesignTIA

( ) ⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜

⎝

⎛

++⎥⎦

⎤⎢⎣

⎡+

+=

22C

o2oF

OPT

BGRG

RZ1

ω1R1

ω1W

Transistors biased

at J = 0.25 mA/µm,

increased noise

figure for higher

bandwidth

Input Stage DesignTIA

Simulated bandwidth: 30 GHzSimulated input integrated noise over 30 GHz: 0.5 mVrms

Inductors improve

bandwidth, input

matching and filter

high frequency

noise

Input Stage DesignTIA

Input Stage DesignTIA

CS

CS

Transistors Q1 and Q2 are diode-connected at DC and

therefore can bias the next CS stage

Switched source

follower for maximum

bandwidth

THA Stage DesignT/H

THA Stage DesignT/H

During Track, QSF acts

as a source follower

with current IT

THA Stage DesignT/H

During Hold, IT flows

through RL which turns

QSF off and isolates CH

THA Stage DesignT/H

QT and QH operate in

digital mode and

thus are biased at

J = 0.15mA/µm

High VTH devices are

used to drive QT further

into “OFF” region and

reduce leakage

THA Stage DesignT/H

QSF is implemented as a

triple well transistor to

reduce VEFF and lower

power supply voltage

THA Stage DesignT/H

A linear buffer drives the T/H block with 600mVPP

input and output swing

THA Stage DesignT/HDiff.

Pair

Capacitor Cfth is used to match QSF-CGS and thus cancel

input signal feedthrough during hold mode

THA Stage DesignT/HDiff.

Pair

A linear output driver provides signal to external

50Ω resistors and measurement equipment

THA Stage DesignT/HDiff.

Pair

DRV

DRV

Clock Distribution CMLINV

CMLINV

CMLINV

Converts a single-ended 30-GHz clock signal

to a differential signal with 750mVPP swing

Chip Micrograph• Manufactured

using IBM’s 0.13µm CMOS technology

• The circuit operates from a 1.8V supply and consumes 150mA.

1mm

1mm

TIA

CS

CML INV

TIA CS

DR

V

THA

Diff

. Pai

r

Diff

. Pai

r

CML INV

CML INV

Measurement Results: SP

Measurement Results: SP II

Time Domain

Frequency Domain I

Frequency Domain II

Frequency Domain III

Circuit Comparison

CMOS0.18µm

2001.8-24.7 @ 5GHzN/A10I. H. Wang el. al.Electronic Letters 06

Y. Lu et. al.BCTM 05

S. Shahramian et al.CSICS 05

J. Lee et. al.JSSC 03

This Work

12

40

12

30

fsample

[GS/s]

5.5

43

14

7

Track BW[GHz]

-52.4 @ 1.5GHz

-27 @ 20GHz-29 @ 10GHz

-23.3 @ 12GHz

-30 @ 1GHz-29 @ 7GHz

THD[dB @ fin]

3.5

3.6

-5.2

1.8

Supply[V]

700

540

390

270

Power[mW]

SiGe200 GHz

SiGe160 GHz

InP120 GHz

CMOS0.13µm

Process[N / fT]

Conclusion• CMOS emerges as a contender for high speed

DSP based equalizers• Discussed the design methodology for CMOS

switched source follower THA• Demonstrated the first 30-GS/sec THA in CMOS

Acknowledgement• CMC for chip fabrication and providing CAD

tools• NSERC for financial support• OIT and CFI for equipment• ECIT for providing the network analyzer