MMIC power amplifiers in gallium nitride HEMT and indium phosphide HBT technologies.

摘要

Key components in any wireless communication system are the high frequency power amplifiers that must meet strict performance specifications regarding power gain, output power, linearity and power added efficiency (PAE). Class A power amplifiers have high linearity, but exhibit PAE well below 50%. Improved efficiency is obtained with switched-mode circuits. These, unfortunately, show high distortion. Push-pull class B amplifiers offer the potential for improved efficiency, at a theoretical limit of 78.6%, combined with distortion as low as class A. For operation in sub-octave bandwidths, a classical push-pull class B can be replaced by a single-ended class B amplifier with an output bandpass or lowpass filter. The high breakdown voltage (>50 V) and 50 GHz current gain cutoff frequency ftau of an AlGaN/GaN high electron mobility transistors (HEMT) result in record power densities (>12.1 W/mm) in the 7--10-GHz frequency band. A common-source class B circuit fabricated in this technology demonstrated 4 W maximum saturated output power at 8 GHz with 13-dB power gain. High linearity, >35-dBc intermodulation suppression under two-tone operation and high PAE of 34% has been achieved under class B operation.; The second phase of research involved developing 75--220-GHz power amplifiers which have applications in wide-band communication systems, atmospheric sensing and automotive radar. Modern InP double heterojunction bipolar transistors (DHBTs) simultaneously exhibit 6 V Vbr, 400 GHz fmax, 3.5 mA/mum2 collector current density and high thermal conductivity, resulting in high power density in the 75--220-GHz frequency band. The common-base topology exhibits higher maximum stable gain in this band when compared to common-emitter and common-collector topologies. Layout parasitics including base inductance, Lb and collector to emitter overlap capacitance, Cce can cause instability. A single-sided collector contact has been employed to reduce Cce. A single-stage common-base tuned amplifier exhibited 7-dB small-signal gain at 176 GHz. This amplifier demonstrated 8.77 dBm output power with 5-dB associated power gain at 172 GHz. A two-stage common-base amplifier exhibited 8.1 dBm output power with 6.35-dB associated power gain at 176 GHz and demonstrated 9.13 dBm of saturated output power. This two-stage common-base amplifier exhibited 10.3 dBm output power at 150.2 GHz.