1. 77GHz Phased-Array Transceiver in Silicon
Natarajan, A. Babakhani, A. Komijani,
X. Guan, and, A. Hajimiri
California Institute of Technology

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

3. Wireless Communications
Motivation
24GHz
60GHz
77GHz
Wireless Communications
Vehicular Radar
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.

4. Challenges 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.

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

6. Antenna on Silicon Top-Side Air, ε=1 <5 % >95% Silicon, εr=11.7
Silicon’s high dielectric constant (er~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

7. On-Chip Ground Shield Air, ε=1 SiO2, ε=4 h Silicon, ε=11.7
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%)

8. Dielectric Lens Air, ε=1 Top-Side SiO2, ε=4 Silicon, ε=11.7 Air, ε=1
Silicon Lens
Back-Side
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))
["Integrated-Circuit Antennas," by D.B. Rutledge, et al., Infrared and Millimeter Waves, 1983.]

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

10. Earlier Implementations
24GHz 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 0.18mm CMOS,” ISSCC 2005.

11. Local 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. .

12. Local 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. .

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

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

15. 52GHz Phase Rotator Quadrature signal generated locally using a delay.
Phase-shifter resolution limited by DAC resolution.

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

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

18. LNA Gain and NF Measured LNA peak gain @ 77GHz = 23dB
BW = 6GHz, NF = 6dB

19. Receiver 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

20. System 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

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

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

23. PA Measurements 3dB bandwidth larger than 15GHz (20% fractional BW).
Small-signal Gain
77GHz
3dB bandwidth larger than 15GHz (20% fractional BW).
Output-referred 1dB compression point: 14.5dBm.
Simulated peak power and PAE: 16dBm, 14%.

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

25. Loopback Testing
In loopback mode, output of upconversion mixer connected
to input of downconversion mixer.
Pattern measurement possible with baseband input and
baseband output.
A. Babakhani et al., “A 77GHz 4-Element Phased Array Receiver with On-Chip Dipole Antennas,” ISSCC 2006.

26. 2-element Loopback Array Pattern
Array pattern measured with two elements active in the
receiver and the transmitter.

27. His visionary prophecy is fulfilled in silicon 40 years later.
What 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

28. Acknowledgements 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.