Design of active phase shifters based on multichannel heterojunction field effect transistors (MCHFET's)

Abstract

Design criteria of active phase shifters based on GaAs/AlGaAs multichannel (MC) HFET in the frequency range 4-60 GHz are presented. The phase characteristics of MCHFET devices were studied using the computer aided design program TOUCHSTONE. The dependence of transmission phase on various intrinsic elements in the equivalent circuit model as a function of control gate bias was also studied. There are limited gate bias ranges which correspond to the active regions of the two conducting wells for which a quasi-linear continuous phase shift for analog applications was achieved. Continuously varying the gate bias from V/sub gs/=-1.9 V to V/sub gs/=-0.6 V results in a quasilinear phase shift of 10/spl deg/, 15/spl deg/, 21/spl deg/, and 29/spl deg/ at f=12, 20, 30, and 60 GHz, respectively. Similarly, varying the gate bias from V/sub gs/=-0.4 V to V/sub gs/=0.7 V a quasi-linear phase shift of 21/spl deg/, 26/spl deg/, 27/spl deg/, and 23/spl deg/ at f=12, 20, 30, and 60 GHz, respectively, was achieved. The gain variation was less than 3 dB in these bias regions. With digital applications in mind, a maximum differential phase shift of around 50/spl deg/ was obtained by switching the gate bias discretely. The transmission phase of single gate MCHFET mostly depends on variation of gate source capacitance with gate bias rather than on other intrinsic elements. The dependence of phase shift on various geometrical and structural parameters is also presented. To test the practicality of the device, other scattering parameters (e.g., S/sub 11/, S/sub 22/, S/sub 12/) and the noise figure (NF) were finally studied.