A full W-band, MMIC amplifier has been tested on-wafer. The chip delivers 25-43 mW with 6.2±1.2 dB associated large-signal gain across 75-110 GHz when input power is held constant at 8 mW. This is the widest bandwidth MMIC amplifier ever published that delivers at least 25 mW over the entire W-band

Leong, Y. C.

Weinreb, S.

Caltech Authors - Main

WE4A-3 A 
FULL W-BAND MMIC MEDIUM POWER AMPLIFIER 
Y.C. Leong’ and S. Weinreb2 
‘U. of Massachusetts, 619 Lederle GRC, Amherst, MA 01003 
Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109-8099 2 
ABSTRACT 
A full W-band, MMIC amplifier has been 
tested on-wafer. The chip delivers 25-43 mW 
with 6.2k1.2 dB associated large-signal gain 
across 75-110 GHz when input power is held 
constant at 8 mW. This is the widest 
bandwidth MMIC amplifier ever published 
that delivers at least 25 mW over the entire 
W-band. 
INTRODUCTION 
GaAs HEMTs have been demonstrated to 
possess good power capability in W-band. A 
MMIC power amplifier with a device periphery 
of 1.28 mm has been reported [l] to yield 300 
mW of RF power at 94 GHz. Using the same 
device structure and process, similar performance 
has been repeated in the frequency range of 100- 
110 GHz [2]. 
All the results reported were relatively narrow- 
band and the amplifiers are targeted for very 
specific applications. On the other hand, a 
broadband, medium power W-band amplifier 
would have many applications. It can be used for 
general instrumentation purposes or it can be 
used in the development of new mm-wave sub- 
systems to test out new concepts or ideas. 
However, a search in the published literatures did 
not find any such amplifier. This paper describes 
the construction of a full W-band medium power 
MMIC amplifier that will deliver 25 to 43 mW of 
output power across the entire W-band. 
The amplifier can be used with frequency 
multipliers to construct a compact, full W-band, 
electronically tunable source. Compared to 
the traditional Gunn diode oscillators in the same 
frequency range, the new signal source has the 
capability to set the output fiequency quickly and 
electronically over a wide range of frequencies. 
This can be used as local oscillator for designing 
new wide-band transceivers, or it can be used as 
a general instrumentation source to develop new 
mm-wave subsystems. An application example 
will be described in the later section. 
DEVICE CHARACTERTZATION AND 
MODELING 
w 
mi The circuit uses the proven 0.1 p.m AlGaAsLnGaAdGaAs power HEMT [ 11 device 
and MMIC process developed by TRW. A 160 
pm wide device on 50 pm thick GaAs substrate 
has been used as the basic cell for device 
modeling and characterization. DC and pulsed 
IV, diode IV and multi-bias S-parameter 
measurements from 1-40 GHz were performed 
on the basic device. The small-signal equivalent 
circuit model parameters were extracted using 
cold/hot FET method [3] for each biasing point. 
Angelov’s [4] model was used to fit the pulsed 
IV characteristics and gate-source, gate-drain 
capacitances’ variations across different bias. 
Calvo’s formulation [5] was then used to resolve 
0-7803-5687-W00/$10.00 0 2000 IEEE 
95 1 
2000 IEEE MlT-S Digest 
discrepancies between the large-signal and small- 
signal models at the biasing point. 
CIRCUIT DESCRIPTION 
The amplifier consists of four stages of 
amplification. Each of the first three stages 
utilizes a 160 pm wide devices while the last 
stage consists of two 160 pm devices connected 
in parallel via a Y-junction. The size of the chip 
is 2300 pm by 1200 pm. Figure 1 shows the 
photograph of the fabricated chip. 
Figure 1. Photograph of the broadband 
amplifier. Chip size is 2300 pm x 1200 pm x 50 
Clm. 
The extracted large-signal model for the FETs 
was entered into HP MDS by defining custom 
equations for the current and charge sources. 
Load-pull contours were simulated across the 
entire W-band to determine the optimized 
loading impedances for the device. For the last 
two stages, the length of the RF-shorted shunt 
stubs and the length of series transmission lines 
between stages were adjusted for good output 
power across the entire band, by trading off with 
power efficiency. The matching networks for the 
front two stages were optimized for flat overall 
small-signal gain. Clamping resistors were used 
at the last stage to suppress any possible odd- 
mode oscillation. Grounded coplanar waveguide 
transmission lines were used to reduce parasitic 
elements that will limit high frequency 
performance. All the discontinuities were 
simulated using a full 3-D electromagnetic 
simulator. 
RESULTS 
The amplifier was attached to a copper plate with 
off-chip R-C networks to prevent bias 
oscillations. The small-signal gain, input and 
output return loss were measured via on-wafer 
GGB WR-10 probes using an HP 8510 VNA 
with 80-120 GHz frequency extender. The plot 
for the small-signal gain and input return loss 
from 75-110 GHz is shown in Figure 2. At 75 
GHz, the gain and power were measured using 
a scalar setup, which used a HP 8350B source 
driving a DBS Microwave active doubler driving 
a Pacific Millimeter tripler. An Hp 8486A power 
sensor and HP 437B power meter were used to 
measure the output power and gain. 
25 
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75 80 85 90 95 100 105 110 
Freq(GW 
Figure 2. Measured small-signal gain and input 
return loss over entire W-band. 
From 80-1 10 GHz, a wide-band mechanically 
tunable (Carlstrom) Gunn oscillator was used to 
supply the input power to the chip for output 
power measurements. A Hitachi WR-10 
precision variable attenuator was used to control 
the input power and a Tektronix harmonic mixer 
is attached to a frequency counter to monitor the 
actual frequency via a 15-dB Millitech coupler. 
HP 8486A power sensor and HP 437B power 
952 
meter were used to measure the output power 
from the chip. All measurements were referred 
to the pads of the chip and Figure 3 shows the 
output power, associated large-signal gain and 
P.A.E across the W-band frequencies with the 
input available power being kept constant at 8 
mW. 
The small-signal gain rolls off quickly from 23 
dB at 75 GHz to 15 dB at 85 GHz. From 85- 
110 GHz, the gain is generally flat with a typical 
value of about 10 dB. When the input power is 
held constant at 8 mW, the chip delivers 43 mW 
at 80 GHz, and generates more than 25 mW 
across the rest of the band. Under these 
conditions, the associated large-signal gain is flat 
with 6.2k1.2 dB across 75-110 GHz. 
I + ! ! ! ! ! ! ! ! ! ! ! !  ! I  
75 80 85 90 95 loo 105 110 
Freq ( G W  
Figure 3. Measured Pout, associated large-signal 
gain and PAE across W-band. Pin is held 
constant at 9 a m .  
The originally simulated results predicted a flat 
small-signal gain of about 12 dB and a higher 
output power of 50-100 mW across 75-110 
GHz. The discrepancy seems to be caused by 
inaccuracies in the EM-simulation results of the 
discontinuities and process variation. Re- 
simulation of the circuit was performed without 
including effects of the discontinuities and with a 
new extracted model from the same wafer run. 
It predicted a small-signal gain of similar roll-off 
trend as seen from the measured data and it also 
predicted a flat gain of about 9 dB from 85-110 
GHz. The large-signal re-simulation gave an 
output power of 25-40 mW across W-band, 
which is also close to the actual result. 
The P.A.E. for the entire chip is between 2.3- 
4.7%. With better models for the discontinuities 
and by using smaller gate-width devices for the 
front two stages, it is believed that a P.A.E. of 5- 
10% can be achieved across the entire W-band. 
A second iteration of the design has been planned 
and higher output power, P.A.E and small-signal 
gain are expected. 
APPLICATION 
Figure 4. 240-320 GHz single-sweep scalar 
setup using the amplifier to drive a high 
frequency tripler. 
Two of the amplifiers were mounted in WR-10 
waveguide blocks with alumina waveguide- 
microstrip transitions 161 wire-bonded to the 
input and output pads. The amplifier module 
amplifies x6 (Avantek active doubler + in-house 
built tripler) signals derived from the hndamental 
HP 8350 source to drive a high efficiency 
frequency tripler [7] to produce signals in the 
range of 240-320 GHZ. Together with a WR-3 
waveguide coupler and Pacific Millimeter WR-3 
power detector, transmissiodreflection scalar 
953 
measurement can be made with a single sweep. 
The photograph of the arrangement is shown in 
Figure 4. The setup is used to develop frequency 
multipliers for application in sub-millimeter 
receiver systems to study radio astronomy 
phenomena such as the early universe formation. 
ACKNOWLEDGEMENT 
We appreciate the excellent work of the TRW 
GaAs MMIC processing group, especially Y.C. 
Chen and M. Nishimoto, for fabricating the 
devices described in this paper. The fabrication 
work was support by the FIRST program of 
JPL/Caltech under contract to NASA. 
REFERENCES 
[l]Pin-Pin Huang et al., “A 94-GHz 0.35-W Power 
Amplifier Module,” IEEE Trans. Microwave Theory 
Tech., vol. 45, no. 12, pp. 2418-2423, Dec. 1997. 
[2] L. Samoska et al., “MMIC Power Amplifier Chip Set 
Developed for 70-1 15 GHz,” Technical Digest of the 
IEEE Topical Workshop on Power Amplifiers for 
Wireless Communications, Sep. 13-14 1999, San Diego, 
CA, Paper No. 5.3. 
[3 J Gilles Dambrine et al., “A New Method for 
Determining the FET Small-Signal Ekpivalent Circuit,” 
IEEE Trans. Microwave Theory Tech., vol. 36, no. 7, pp. 
1151-1159, Jul. 1988. 
[4] Iltcho Angelov et al., “A New Empirical Nonlinear 
Model for HEMT and MESFET Devices,” IEEE Trans. 
Microwave Theory Tech., vol. 40, no. 12, pp. 2258-2266, 
Dec. 1992. 
[5] M.V. Calvo et al., “Resolving Capacitor Discrepancies 
Between Large and Small Signal FET Models,” 1995 
IEEE MlT-S Int. Microwave Symp. Dig., pp. 1251-1254. 
[6]Y. C. Leong, S. Weinreb, ‘‘Full Band Waveguide-to- 
microstrip Probe Transitions,” 1999 IEEE MlT-S 
International Microwave Symposium Digest, vol. 4, pp. 
1435-1438, Anaheim, CA, June, 1999. 
[7]N.R. Erickson, R.P.Smith, S.C. Martin, B. Nakamura 
and I. Mehdi, “High Efficiency MMIC Frequency 
Triplers for Millimeter and Submillimeter Wavelengths,” 
accepted at the IEEE M3T-S International Microwave 
Symposium to be held in Boston, MA, June, 2000. 
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Full W-band MMIC medium power amplifier

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Full W-band MMIC medium power amplifier

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