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77GHz Phased-Array Transceiver77GHz Phased-Array Transceiverin Siliconin Silicon

A. Natarajan, A. Babakhani, A. Komijani,

X. Guan, and, A. Hajimiri

California Institute of Technology

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OutlineOutline

Motivation On-chip Antennas Local LO-Path Phase-Shifting Architecture A 77GHz Phased-Array Transceiver in SiGe Measurement Results Conclusion

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BLINDSPOTDETECTION

ADAPTIVE CRUISE CONTROL

PARKINGASSISTANCE

MotivationMotivation

24GHz 60GHz 77GHz

Vehicular RadarWireless Communications

Fully-integrated silicon-based multiple-antenna systems enable widespread commercial applications at high frequencies. Complex, novel architectures can be realized on silicon with greater reliability and lower cost.

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Challenges of mm-Waves in SiChallenges of mm-Waves in Si

Substrate high dielectric constant (absorbs the fields). Conductive substrate (substrate losses). Low breakdown voltages (power challenges). Poor metal conductivity. High-frequency interface.

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OutlineOutline

Motivation On-chip Antennas Local LO-Path Phase-Shifting Architecture A 77GHz Phased-Array Tranceiver in SiGe Measurement Results Conclusion

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Antenna on SiliconAntenna on Silicon

Silicon’s high dielectric constant (r~11.7) and conductivity

of silicon substrate are the major design challenges Most of the power gets absorbed into silicon It may appear that ground shields might solve this problem

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100

1 4 7 10 13 16Dielectric Constant

No

rmal

ized

po

wer

(%) Pdielectric

Pair

Air, ε=1

Silicon, εr=11.7

<5 %

>95%

Top-Side

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On-Chip Ground ShieldOn-Chip Ground Shield

Typical distance between the top and bottom metal layers

is very small (less than 15μm) Even for 15μm ground distance, the radiation resistance

is around 0.02Ω (efficiency of 1-2%)

hAir, ε=1

Silicon, ε=11.7

SiO2, ε=4Ground

Distance from Ground(µm), h

Half-Wavelength Dipole Antenna with Ground Layer

Eff

icie

ncy

(%)

Res

ista

nce

(Ω)

10-2

10-1

100

101

102

10-2

10-1

100

101

102

0 60 120 180 240 300

Radiation Resistance

TotalResistance

Efficiency

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A dielectric lens on the backside combines most of the surface wave power and couples it into air

Reflection from silicon-air boundary can be eliminated by a matching layer

Is a good thermal heat sink (Si thermal conductivity = 149 W/(m.k) better than Brass (120W/(m.k))

Dielectric LensDielectric Lens

Silicon, ε=11.7

SiO2, ε=4Air, ε=1

Air, ε=1Silicon Lens

Back-Side

Top-Side

["Integrated-Circuit Antennas," by D.B. Rutledge, et al., Infrared and Millimeter Waves, 1983.]

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OutlineOutline

Motivation On-chip Antennas Local LO-Path Phase-Shifting Architecture A 77GHz Phased-Array Transceiver in SiGe Measurement Results Conclusion

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Earlier ImplementationsEarlier Implementations24GHz Phased-Array Transmitter 24GHz Phased-Array Receiver

Multiple-phase VCO

Distribution Network

Multiple phases of VCO were generated and distributed to each element, where one phase was selected. Well-suited for low-resolution beam steering with few elements.• H. Hashemi, X. Guan, and A. Hajimiri, “A Fully-Integrated 24GHz 8-Path Phased-Array Receiver in Silicon,” ISSCC 2004.

• A. Natarajan, A. Komijani, and A. Hajimiri, “A 24GHz Phased-Array Transmitter in 0.18m CMOS,” ISSCC 2005.

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Local LO Phase-Shifting ArchitectureLocal LO Phase-Shifting Architecture

The desired phases are generated locally by interpolating between I and Q phases using phase rotator. Phase shift resolution is limited by the interpolator rather than by number of phases generated by the VCO. Scales with larger number of elements as it reduces area and complexity of LO signal distribution network..

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90˚

cos(θ)

sin(θ)

LO signalcos(ωt - θ)

Phase-shiftedLO signal

cos(ωt)

Local LO Phase-Shifting ArchitectureLocal LO Phase-Shifting Architecture

Element 1

Element 1

Element 1

Element 1

The desired phases are generated locally by interpolating between I and Q phases using phase rotator. Phase shift resolution is limited by the interpolator rather than by number of phases generated by the VCO. Scales with larger number of elements as it reduces area and complexity of LO signal distribution network..

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OutlineOutline

Motivation On-chip Antennas Local LO-Path Phase-Shifting Architecture A 77GHz Phased-Array Transceiver in SiGe Measurement Results Conclusion

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Transceiver ArchitectureTransceiver Architecture

A. Babakhani et al., “A 77GHz 4-Element Phased Array Receiver with On-Chip Dipole Antennas,” ISSCC 2006.

Fully-integrated 4-element 77GHz phased-array transceiver. Two-stage frequency translation. (LO1: 52GHz, IF=LO2:26GHz) Local phase shifting in each element enables beam steering.

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52GHz Phase Rotator52GHz Phase Rotator

Quadrature signal generated locally using a delay. Phase-shifter resolution limited by DAC resolution.

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Die MicrographDie Micrograph

0.12m SiGe transistors in BiCMOS process, ft : 200GHz. 7 metal layers: Top two layers are 4m and 1.25m thick.

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OutlineOutline

Motivation On-chip Antennas Local LO-Path Phase-Shifting Architecture A 77GHz Phased-Array Transmitter in SiGe Measurement Results Conclusion

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LNA Gain and NFLNA Gain and NFLNA Gain and NF

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5

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74 75 76 77 78 79 80 81 82

Frequency(GHz)

Gai

n &

NF

(dB

)

LNA Gain

LNA NF

Measured LNA peak gain @ 77GHz = 23dB BW = 6GHz, NF = 6dB

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Receiver Conversion Gain and NFReceiver Conversion Gain and NF

More than 35dB gain between 78.5GHz and 80GHz 3-dB bandwidth is more than 2GHz Minimum NF of 8.0dB measured at 79.2GHz

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76 77 78 79 80 81 82 83Frequency(GHz)

Ga

in &

NF

(dB

) Gain

NF

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System Packaging and SetupSystem Packaging and Setup

Silicon chip is thinned down to 100μm Floorplan issues lead to edge antennas A 500μm silicon wafer for mechanical stability Low frequency signals using wire-bond and board traces

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Antenna GainAntenna Gain

Peak Gain of +2dBi has been achieved in the E-plane Lens improves the gain by more than 10dB

E-Plane Pattern

-35

-25

-15

-5

5

-30 -15 0 15 30Angle(degree)

An

ten

na

Gai

n(d

B)

With Lens

Without Lens10dB

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Transmitter Test SetupTransmitter Test Setup

Combination of waveguide probe testing and internal self- test mechanisms. Stand-alone PA testing and mixer output tested through internal test pads.

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PA MeasurementsPA MeasurementsSmall-signal Gain Large-signal @ 77GHz

3dB bandwidth larger than 15GHz (20% fractional BW). Output-referred 1dB compression point: 14.5dBm. Simulated peak power and PAE: 16dBm, 14%.

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Transmitter PerformanceTransmitter Performance

Output-referred 1dB compression point is +10.6dBm. 40dB conversion gain from baseband to RF.

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Loopback Loopback TestingTesting

In loopback mode, output of upconversion mixer connected to input of downconversion mixer. Pattern measurement possible with baseband input and baseband output.

LO2_I LO2_Q

DivBy 2

52GHz

77GHz PA

Φ

Φ

Φ

Φ

IBB

QBB

LO2_I

LO2_Q

IF Amplifiers@ 26GHz

RF Mixer

PhaseRotator

Φ

Φ

Φ

Φ

IBB

QBB

LO2_I

LO2_Q

CombiningAmplifier@ 26GHz

RF Mixer

77GHz LNA

A. Babakhani et al., “A 77GHz 4-Element Phased Array Receiver with On-Chip Dipole Antennas,” ISSCC 2006.

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00.20.40.60.8

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7080

2-element 2-element LoopbackLoopback Array Pattern Array Pattern

Array pattern measured with two elements active in the receiver and the transmitter.

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What the Future HoldsWhat the Future Holds Silicon systems at yet higher frequencies (mm-wave and

beyond).

Systems that leverage the benefits of integration to realize complex architectures that include mm-wave, analog, and digital circuits,

Elimination of all high frequency interfaces to the outside world

The last paragraph of Gordon Moore’s seminal paper published in 1965: “Even in the microwave area, structures included in the definition of integrated

electronics will become increasingly important. … The successful realization of such items as phased-array antennas, for example, using a multiplicity of integrated microwave power sources, could completely revolutionize radar.”

His visionary prophecy is fulfilled in silicon 40 years later.

G. E. Moore, “Cramming more components onto integrated circuits,” Electronics, vol. 38, no. 8, pp. 114–117, Apr. 1965.

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AcknowledgementsAcknowledgements Lee Center for Advanced Networking, Caltech,

Prof. Rutledge (Caltech), Dr. Analui (Caltech/Luxtera) and Theodore Yu (Caltech/UCSD), Dr. Weinreb of JPL, Prof. Hashemi of USC,

The DARPA Trusted Foundry program and IBM T. J.

Watson for chip fabrication

Software Assistance: Cadence, Agilent Technologies, and Zeland Software, Inc.