Ultra-broadband, efficient, microwave power amplifiers in gallium nitride HEMT technology.

摘要

Wide bandwidth power amplifiers are key components in phased-array radars and instrumentation. Obtaining a combination of high power, decade (10:1) bandwidth and high power-added-efficiency (PAE) requires both advanced semiconductor devices and improved microwave circuit design techniques. AlGaN/GaN HEMTs have high ftauVbr products, and can provide high output power at microwave frequencies. Efficient broadband circuits that operate over high percentage of transistor's f tau are required. Simple lumped broad-band amplifiers have gain-bandwidth products limited by the transistor current-gain cut-off frequency, ftau Distributed amplifiers are limited by the power-gain cut-off frequency, fmax, but have poor efficiency due to the drain-line reverse wave.; To obtain efficient wideband amplification over bandwidths of ∼40% of the transistor's ftau two competing topologies have been developed. The cascode-delay-matched traveling wave amplifier is a distributed amplifier topology capable of obtaining gain-bandwidths limited by fmax, with efficiencies up to the class-A theoretical limit of 50%. The ftau -doubler feedback power amplifier is a lumped amplifier topology which in addition to obtaining similar bandwidths and efficiencies, has a much lower output reflection coefficient, and uses a smaller die area. To further improve bandwidth and efficiency high ftau - high Vbr cascode cells (or dual gate devices) and broad-band class-AB push-pull stages are proposed which could be incorporated into either circuits.; Scale-models were fabricated in a GaAs MESFET technology to verify the circuit concepts. ftau-doubler feedback power amplifiers using AlGaN/GaN HEMTs achieved ∼10 dB gain, 1--8.0 GHz bandwidth amplifiers with ∼5.12 W output power and up to 23% PAE. GaAs MESFET - GaN HEMT cascode-delay-matched distributed power amplifiers achieved 1--10 GHz bandwidth with 10 dB small signal gain and >1 W output power. With device scaling and improved thermal performance these circuits are capable of providing 10's of Watts over 2--20GHz with up to 40% PAE.