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Unformatted text preview: IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 46, NO. 12, DECEMBER 1998 2553 112-GHz, 157-GHz, and 180-GHz InP HEMT Traveling-Wave Amplifiers Bipul Agarwal, Adele E. Schmitz, J. J. Brown, Mehran Matloubian, Michael G. Case, Senior Member, IEEE , M. Le, M. Lui, and Mark J. W. Rodwell Abstract We report traveling-wave amplifiers having 1112 GHz bandwidth with 7 dB gain, and 1157 GHz bandwidth with 5 dB gain. A third amplifier exhibited 5 dB gain and a 180- GHz high-frequency cutoff. The amplifiers were fabricated in a 0.1- " m gate length InGaAs/InAlAs HEMT MIMIC technology. The use of gate-line capacitive-division, cascode gain cells and low-loss elevated coplanar waveguide lines have yielded record bandwidth broad-band amplifiers. Index Terms Distributed amplifier, MMIC, traveling-wave amplifier, TWA. I. INTRODUCTION B ROAD-BAND amplifiers find applications as gain blocks in multigigabit fiber-optic receivers and as preamplifiers in broad-band instrumentation. Future 100- and 160-Gbit/s optical transmission systems will require amplifiers with very high bandwidths. High-electron mobility transfer (HEMT) traveling-wave amplifiers (TWAs) with 100 GHz band- widths have been demonstrated . Pusl et al.  used capacitive voltage division  on the gate synthetic line to obtain 11 dB gain over a 196-GHz bandwidth. Capacitive division decreases the frequency-dependent losses on the gate synthetic transmission line. With these losses reduced, the number of TWA cells can be increased to increase TWA gain. In this manner, the feasible gain for a given design bandwidth is increased. With very small capacitive division ratios, losses associated with the HEMT input resistance are reduced to the point where other loss mechanisms are significant. If the dominant loss mechanisms are the HEMT series input resistance and shunt output conductance, the capacitive-division TWA can obtain gainbandwidth products limited by the transistor power gain cutoff frequency . If a cascode cell is used as the transconductance element with the TWA, the gainbandwidth product can be increased well beyond the transistor . For design bandwidths above 100 GHz, TWA design is strongly impacted by both the losses and physical dimen- sions of the synthetic transmission lines. With small capac- itive division ratios and design bandwidths above 100 GHz, Manuscript received March 20, 1998; revised August 15, 1998. This work was supported by DARPA under the Thunder and Lightning program and a California/Hughes MICRO no. 8960808. B. Agarwal and M. J. W. Rodwell are with the Department of Electrical and Computer Engineering, University of California, Santa Barbara, CA 93106 USA (e-mail: firstname.lastname@example.org)....
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This note was uploaded on 08/06/2008 for the course ECE 145 taught by Professor Rodwell during the Fall '07 term at UCSB.
- Fall '07