Microwave Circuits using Fieldplated GaN HEMT

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Microwave Circuits using Field-plated GaN HEMT
Hongtao Xu, Christopher Sanabria, Steven Gao,
Alessandro Chini, Sten Heikman, Stacia Keller,
Umesh K. Mishra, Robert A. York University of
California, Santa Barbara, CA
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Outline

• Study of Field-plated GaN HEMT Oscillators
• High Power and high efficiency GaN HEMT
  Oscillator GaN VCO
• High Efficiency GaN HEMT Class-E PAs
• GaN HEMT ft Doubler
• Conclusion
• Future Works

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1. Study of Field-plated GaN HEMT Oscillators
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Circuit Schematic

• Same circuit topology.
• Used improved large signal model for power and
  non-linearity simulation.
• Applied field-plated HEMT structures.
• Optimized passive components for best power
  performance and compact layout.

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Circuit photograph
New
Previous

• Die area
• (0.72mm x 0.7mm)

• Die area
• (1.4 mm x 1.6 mm)

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Power and efficiency of oscillators
Lg0.7um Wg4x125um Vgs-4.5 V Vds40V

• Circuits with different field-plate length are
  identical.
• Both output power and efficiency increase as LF
  increases.
• Larger distortion was observed with higher output
  power.

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Carrier frequency and power density
Lg0.7um Wg4x125um Vgs-4.5 V Vds40V

• Carrier frequency decreases as LF increases, due
  to larger Cgd.
• Field-plate can dramatically improve power
  performance.

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Power and efficiency of oscillator
FP length1.1 um
Lg0.7um Wg4x125um Vgs-4.5 V Vds40V

• Output power reaches 33 dBm (4 W/mm) with a peak
  dc-to-RF efficiency of 24 .

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Phase noise of oscillators
FP length1.1 um

• HEMT oscillators with field-plate are better than
  the one without field-plate.

-103 and -132 dBc/Hz at offset frequencies of 100
kHz and 1 MHz.
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Pushing and pulling

• The pulling figure measures the frequency shift
  as a function of the output reflection
  coefficient phase for a constant return lass of
  -12 dB.

The pushing figure measures the frequency shift
as a function of bias voltages for gate and drain.
lt 0.1 variation
lt 3 variation
Vgs-4.5 V Vds40V
FP length1.1 um
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Summary

• GaN HEMT oscillators with different field-plated
  lengths were designed and fabricated.
• Measured results show that oscillators with
  field-plated HEMTs have better power capacity,
  efficiency and phase noise performance, compare
  to circuits with non-FP HEMTs.
• An oscillator of 4 W/mm output power, over 20
  efficiency and -132 dBc/Hz phase noise was
  implemented at 45 V drain bias, using GaN HEMT
  with 1.1µm field-plate length.
• Further investigation is required to understand
  the impact of field-plate on phase noise.

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2. High Power and high efficiency GaN HEMT
Oscillator GaN VCO
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Issures of Common Gate Oscillator
The sum of impact of Rds, Rgd and unloaded Q
Power, efficiency and loaded Q is limited by rs,
esp. for high power oscillators.
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Propose Common Source Oscillators
Zin
Vo
V1
Z is the high gate input impedance.

• If ZingtgtRL, load-line, output power, efficiency,
  loaded Q and phase-noise is limited by RL.
• RL is an external circuit component. Z0 can be
  easily transformed to a high resistance using
  appropriate impedance transformer circuitries.

If choose
high impedance
180o phase shift
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Common Source Oscillator (5 GHz)
Size 0.6mm x 1.3mm
Schematic and layout
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Power, efficiency and linearity
Field-plated HEMT Lg0.7um Wg2x125um FP
length0.7 um
Measured carrier frequency 4.6 GHz
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Phase noise
Drain bias voltage 20V
Phase noise at 100kHz -99.99 dBc/Hz 1MHz
-130.5 dBc/Hz
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Common Gate Oscillator (5 GHz)
Schematic and layout
Size 0.65mm x 0.7mm
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Power, efficiency and linearity
Field-plated HEMT Lg0.7um Wg2x125um FP
length0.7 um
Phase noise at 1MHz -128.54 dBc/Hz
Measured carrier frequency 5 GHz
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GaN VCO (6 GHz)
Size 0.8mm x 0.8mm
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Power, efficiency and linearity
Field-plated HEMT Lg0.7um Wg2x125um FP
length0.7 um
Measured carrier frequency 6 GHz
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Tuning range and phase noise
Field-plated HEMT Lg0.7um Wg2x125um FP
length0.7 um
Drain bias voltage 20V
Phase noise at 1MHz -97.62dBc/Hz (0V turning
Bias)
5 tuning range
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Summary

• To further improve the power capacity, a common
  source feedback oscillator was proposed and
  analysis.
• Both CS and CG GaN HEMT oscillators were designed
  and fabricated for comparison.
• Measured results show that CS oscillators with
  field-plated HEMTs have further improved power
  capacity, efficiency and phase noise performance,
  compare to CG oscillators, for high power
  application.
• An oscillator of 4 W/mm output power, 30
  efficiency and -130.5 dBc/Hz phase noise was
  measured at 25 V drain bias using GaN HEMT with
  0.7 µm field-plate length.
• A 6 GHz GaN HEMT VCO using GaN varactor was
  designed and tested. 5 tuning range was achieved.

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3. High Efficiency GaN HEMT Class-E PAs
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Introduce Class-E PA
Vdd
excessive reactance
ideal resonator _at_ f0
0.0
Is
Io
output capacitance
ideal switch
Fundermantal frequency fo

• A 50 duty cycle is used.
• The switch has 0 on-resistance and 8
  off-resistance.
• An ideal RFC, a high Q-factor resonator, lossless
  and linear componets in load networks are used.

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Class-E PA Design Rules
Output power Equivalent dc resistance Shunt
susceptance Load angle (inductive) Load
network impedance Excessive reactance Peak
switch voltage Peak switch current Maximum
frequency
Limited by the Vbr and Idss.
Limited by intrinsic Cds and operation condition.
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2 GHz GaN HEMT Class E PA(1 stage)
Size 2.4mm x 2.2mm
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Power and efficiency I
field-plated HEMT Lg0.7um Wg8x125um FP
length0.7 um
Vds 30V Maximum power level 5.4W/mm
Vds 40V Maximum power level 7.7W/mm
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Power and efficiency II
field-plated HEMT Lg0.7um Wg8x125um FP
length0.7 um
Vds 30V
Freq1.9 GHz
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2 GHz GaN HEMT Class E PA(2 stages)
Size 3.5mm x 2.2mm
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Power and efficiency I
Vds 30V Maximum power level 5.5W/mm
Vds 35V Maximum power level 6.4W/mm
field-plated HEMT FP length0.7 um 1st stage
Lg0.7um Wg2x125um 2nd stage Lg0.7um
Wg8x125um
Vds 40V Maximum power level 7.2W/mm
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Power and efficiency II
Vds 35V
field-plated HEMT 1st stage Lg0.7um
Wg2x125um 2nd stage Lg0.7um Wg8x125um
Freq2 GHz
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Compare different technologies
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Reference

• 1 T. Sowlati, C. A. T. Salama, J. Sitch, G.
  Rabjohn, D. Smith, Low voltage, high efficiency
  GaAs Class E power amplifiers for wireless
  transmitters, IEEE J. Solid-State Circuits, vol.
  30, pp. 1074-1080, Oct. 1995.
• 2 T. Sowlati, Y. Greshishchev, C. Andre and T.
  Salama, 1.8 GHz class E power amplifier for
  wireless communications, IEE Electronics
  Letters, vol. 32, pp. 1846-1848, Sept. 1996.
• 3 T. K. Quach, P. M. Watson, W. Okamura, E. N.
  Kaneshiro, A. Gutierrez-Aitken, T. R. Block, J.
  W. Eldredge, T. J. Jenkins, L. T. Kehias, A. K.
  Oki, D. Sawdai, R. J. Welch and R.D. Worley,
  Ultrahigh-efficiency power amplifier for space
  radar applications, IEEE J. Solid-State
  Circuits, vol. 37, pp. 1126-1134, Sep. 2002.
• 4Y. Tan, M. Kuma, J. K. O. Sin and J. Lau, A
  900-MHz fully integrated SOI power amplifier for
  single-chip wireless transceiver applications,
  IEEE J. Solid-State Circuits, vol. 35, pp.
  1481-1486, Oct. 2000.
• 5 K. L. R. Mertens and M. S. J. Steyaert, A
  700-MHz 1-W Fully Differential CMOS Class-E Power
  Amplifier, IEEE J. Solid-State Circuits, vol.
  37, pp. 137-141, Feb. 2002.
• 6 C. Yoo, Q. Huang, A Common-Gate Switched
  0.9-W Class-E Power Amplifier with 41 PAE in
  0.25-µm CMOS, IEEE J. Solid-State Circuits, vol.
  36, pp. 823-830, May 2001.
• 7 K. C.Tsai and P. R. Gray, A 1.9-GHz, 1-W
  CMOS Class-E PowerAmplifier for Wireless
  Communications, IEEE J. Solid-State Circuits,
  vol. 34, pp. 962-970, July 1999.
• 8 C. C. Ho, C. W. K, C. C. Hsiao and Y. J.
  Chan, A fully integrated class-E CMOS amplifier
  with a class-F driver stage, IEEE Radio
  Frequency Integrated Circuits (RFIC) symposium,
  pp. 211-214, June, 2003.

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Summary

• First demonstration of single-stage and two-stage
  class-E MMIC PAs in GaN HEMT Technology
• Use field-plated GaN HEMT devices for high-power
  performance
• Single-stage MMIC PA at 1.9 GHz achieves a PAE of
  57 and 37.2 dBm output power
• Two-stage MMIC PA at 2 GHz achieves a PAE of 50
  and 37.5 dBm output power
• State-of-the-art power/efficiency performances
  achieved.

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4. GaN HEMT Ft Doubler
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Introduce ft doubler
Circuit gain-bandwidth is limited by ft. Low ft
makes analog circuit design harder.
ft doubler is made of a pair of transistors and a
source resistor.
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The concept
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GaN HEMT ft doubler (2x75um)
Size 0.3mm x 0.42mm
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ft of single device and ft doubler
non-plate HEMT Lg0.7um Wg2x75um
Vds 20V Ids200mA/mm
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Summary

• A GaN HEMT ft doubler was design and fabricated.
• Using ft doubler, ft was increased to 43 GHz from
  a ft25.5 GHz GaN HEMT device. (69 improvement)

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Conclusion

• Field-plated GaN HEMTs can improve both power and
  noise performance.
• GaN oscillators can be a candidate for compact
  high power and high efficiency microwave sources.
• Use GaN HEMTs to simultaneously achieve both high
  power and low phase noise performance in a single
  oscillator circuit.
• GaN HEMT class E power amplifiers exhibit 50-100
  times better power density than other
  technologies, with comparable efficiency.

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Our current progress
Material
Models
HEMT Devices
Passive Devices
Precise Design

• MMIC

High Power
Low Noise
High Eff.
High Freq.
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Future Works

• Fabricate designed circuits on different material
  or device structures.
• Design and fabricate low noise and high frequency
  circuits.
• Use circuit results to verify material and device
  improvement.