Microwave Traveling Wave Amplifiers

and Distributed Oscillators ICs in

Industry Standard Silicon CMOS

Kalyan Bhattacharyya

Supervisors: Drs. J. Mukherjee and M. Shojaei

EE, IIT, Bombay

E-mail: kalyan@ee.iitb.ac.in

2

Contents

Introduction

Coplanar Waveguide (CPW)

Traveling Wave Amplifier (TWA)

TWA Based Distributed Oscillator (DO)

Conclusion

3

Why CMOS?

Low Cost

50 GHz cut-off frequency for 0.18µm technology

Maturity of process technology

Higher thermal conductivity

Mechanical stability of substrate

Ease of high level integration

4

Introduction Traveling Wave Amplifier (TWA) is for constant gain over a

broad frequency range (applic. in high speed networks)

Designs use the parasitic capacitances of the active devices that typically limit the high-frequency performance

coplanar waveguides (CPW) as on-chip inductors

A Distributed Oscillator operates in the forward gain mode of a TWA, our designs use only n-FETs, CPWs and a loop we called ‘folded CPW’

5

Amplifier with Spiral Inductors

Replace large area inductors with coplanar waveguides

Reduce and use parasitic capacitances in amplifier

6

CMOS on silicon presents some

challenges for RF design:

Lossy substrate and low impedance transmission lines

Low electron mobility in Si

High gate resistance

Low output impedance at the drain

Low transconductance in Si FETs

Design Challenges

7

Distribution of Gain Producing Cells Formation of Gate and Drain Artificial Transmission Lines

RF signal travels down the gate line Each n-FET transfers signal to drain line through its transconductance Signals add in drain line in forward propagating direction

Basic TWA with CPW as InductorsZline, LD

Zo

Zin

Zo

CPW

CPW

CPWCPW

CPWCPW

LD /2

LG /2 LG /2

LD /2LD

LG

IN

OUT

Zline, LG

8

Coplanar Waveguide

L=0.5 mm

TlineTOX

Silicon substrate

W S

9

Layout of Coplanar Waveguide

Measured Loss = 0.32dB at 10GHz

Kalyan Bhattacharyya et al, IEEE Microwave and Wireless Components Letters, Jan, 2004

10

Gain Cells of the ICs and One Element of Artificial Transmission Line

11

Bandwidth of TWA in 0.18micron CMOS

L-H Lu et al; IEEE Microwave and Wireless Components Letters, Nov, 2005

1

12

TWA Based Oscillator Design: OSC-1 Feedback connection from TWA output to input [1][2]

The length of feedback connection is critical

Measured Oscillation Frequency: 12 GHz Output Level: 5.77 dBm, n-FET width: 60 micron Phase Noise: -115.16 dBc/Hz @ 1 MHz offset

Kalyan Bhattacharyya et al; IEEE RAWCON 2004 and WAMICON 2005

L LL LL LL LD

LG LG

DD D

LGLGCc

Zbias

D1

LG1 LG2

D2D3 D

LGLG3

biasZ

ZbiasZbias

V_OUT

L LL LL LL LD

LG LG

DD D

LGLGCc

Zbias

D1

LG1 LG2

D2D3 D

LGLG3

biasZ

ZbiasZbias

V_OUT

D

LG LG

DD D

LGLGCc

ZbiasZbias

D1

LG1 LG2

D2D3 D

LGLG3

biasZbiasZ

ZbiasZbias

V_OUT

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TWA-based Distributed OSC-1 Layout

Size: 1.5x0.642 sq. mm (including the measuring pads)

OUT

Drain Transmission Line

Gate Transmission Line

n-FETn-FET

Fee

db

ack

Drain Transmission Line

Gate Transmission Line

n-FETn-FET

Fee

db

ack

OUT

ZbiasOUT

Drain Transmission Line

Gate Transmission Line

n-FETn-FET

Fee

db

ack

Drain Transmission Line

Gate Transmission Line

n-FETn-FET

-nFE

T

Fee

db

ack

OUT

Zbias

14

Coplanar test structure ‘folded CPW’

15

4 8 12 16 20-2.0

-1.6

-1.2

-0.8

-0.4

Measured loss before pad deembedding

S2

1 (d

B)

Frequency (GHz)

Measured Loss of ‘folded CPW’

Loss: 1.259 dB at 10 GHz before pad deembedding

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9.5 10.5 11.5 12.5-32

-28

-24

-20

Re

flect

ion

s S 1

1(d

B)

an

d S

22(

dB

)

Frequency (GHz)

S11(dB) before pad deembedding

S22(dB) before pad deembedding

Measured Reflections of ‘folded CPW’

S11 = -24.6 dB and S22 = -24 dB at 12GHz

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Measured power spectrum of Osc-1

Fundamental is at 12.00GHz, +5.77dBm

Second harmonic at 23.92GHz, -34 dBm

Bias: 1.8V / 60mA

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Measured phase noise of Osc-1

PN = -115.16dBc/Hz at 1 MHz offset from the 12GHz carrier Figure of Merit [9] = -176.41dBc/Hz

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OperatingFrequency

(GHz)

Power level (dBm)

Bias Voltage,

V

Technology and Reference

16.8 -3.5 1.3 0.18µm CMOS, [1]

12.0 -15.37 2.5 0.35µm BiCMOS, [5]

10 -4.5 2.5 0.35µm BiCMOS, [5]

12 +5.77 1.8 0.18µm CMOS, This work

Comparison of Power Level of Si DO

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VCO-Like Simulation for OSC-1 with Cc

Coupling capacitor allows the independent control of the

dc voltage in the gate and drain lines VCO operation by tuning the parasitic gate and drain capacitances

(‘inherent varactors’ [5]) of the n-FETs

Single n-FET gain cell with n-FET width of 30 micron

VDS= 1.8V, VGS= 1.2V, Freq = 17.921GHz, Power = 5.1dBm

VDS (V) VGS (V) Frequency

Change (MHz)

Power Change (dBm)

2.0V 1.2V 60 MHz +1 dBm

1.8V 1.0 60 MHz -1.3 dBm

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Cascode Cells DO: OSC-2

Simulated Oscillation Frequency: 12.67 GHz,

with 4-stages of cascode gain cells

Kalyan Bhattacharyya et al, IEEE RAWCON’04 and WAMICON’05

A New circuit

for DO Design

Higher Output

Level expected for

OSC-2 than OSC-1,

when both 5 –stages

Zbias

Cc

CS

LD

LG LG

LD

LD

LD

LGLG

+_+_

LD1

LG1 LG2

LD2

LD3

LD

LGLG3

_+

Zbias

Cc

V_OUTZbias

CG

Zbias

Cc

CS

LD

LG LG

LD

LD

LD

LGLG

+_+_

LD1

LG1 LG2

LD2

LD3

LD

LGLG3

_+

Zbias

Cc

V_OUTZbias

CG

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Static Frequency Changing by Varying LChanged Values of Inductive CPWs from:LD1=LG1= LD2= LG2=L/2, LD3= LG3=L

OSC-2 Freq: 12.67 (GHz)

OSC-1 Freq: 17.921 (GHz)

LD1=3L/2 12.05 17.71

LD1=L 12.35 17.76

LG1=3L/2 11.0 15.87

LG1=L 11.75 16.83

LD1=LG1=3L/2 10.55 15.74

LD1 =LG1=L 11.75 16.70

LD2=3L/2 11.0 15.87

LD2=L 11.75 16.83

LG2=3L/2 12.63 17.88

LG2=L 12.42 17.54

LD2=LG2=3L/2 11.0 15.63

LD2=LG2=L 11.75 16.75

LD3=3L/2 12.50 17.69

LD3=2L 12.13 17.51

LG3=3L/2 12.45 16.91

LG3=2L 12.07 16.63

LD3=LG3=3L/2 12.11 17.0

LD3=LG3=2L 11.72 16.28

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Conclusions Coplanar Waveguides and folded CPW used for

Distributed Oscillators in industry-standard CMOS

OSC-1, high Power Level of +5.77dBm at 12 GHz for Silicon DO

Phase noise of –115.16dBc/Hz at 1 MHz

A new distributed oscillator is proposed (RAWCON 2004) where each gain cell uses an n-FET cascode

Frequency variation of DOs by non-uniform transmission lines changing one or two L values

VCO-Like simulation using MOS VARACTORs at IIT, Bombay

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REFERENCES[1] B. Kleveland, “CMOS interconnects beyond 10 GHz,” PhD thesis, Stanford University, August 2000.

[2] Behzad Razavi, “Design of Integrated Circuits for Optical communications,” McGraw Hill, New York, 2003.

[3] Kalyan Bhattacharyya and Ted Szymanski, “Performance of a 12GHz Monolithic Microwave Distributed Oscillator in 1.2V 0.18µm CMOS with a New Simple Design Technique for Frequency Changing,” IEEE Wireless and Microwave Technology Conference, WAMICON’2005, Clearwater, Florida, USA, April 7 and 8, 2005, pp 174-177.

[4] H. Wu and A. Hajimiri, “Silicon-Based Voltage-Controlled Oscillators,” IEEE Journal of Solid-State Circuits, vol. 36, No. 3, pp. 493-502, March 2001.

[5] Kalyan Bhattacharyya’s MASc Thesis, Department of Electrical and Computer Engineering, McMaster University, Hamilton, Ontario, Canada, June 2004.

[6] Yuhua Cheng, M. Jamal Deen and C-H. Chen, “MOSFET Modeling for RF IC Design,” IEEE Transaction on Electron Devices, vol. 52, No. 7, July 2005.

[7] Kalyan Bhattacharyya and M. Jamal Deen, “Microwave CMOS traveling wave amplifiers – performance and temperature effects,” IEEE Microwave and Wireless Components Letters, vol. 14, No. 1, pp. 16-18, January 2004.

[8] Kalyan Bhattacharyya and Ted Szymanski, “1.2V CMOS 1-10GHz Traveling Wave Amplifiers Using Coplanar Waveguides as On-Chip Inductors,” IEEE Radio and Wireless Conference (RAWCON), Atlanta, Georgia, USA, pp. 219-222, September 19-22, 2004.

[9] T. Y. Kim, A. Adams, N. Weste, “High performance SOI and bulk CMOS 5GHz VCOs,” IEEE Radio Frequency Integrated Circuits (RFIC) Symposium, pp. 93 – 96, 8-10 June 2003.

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Thank You