Optimising a GaAs HBT amplifier for maximum gain efficiency

The authors report a GaAs HBT amplifier which achieves a gain efficiency of 2.14 dB/mW at 17 GHz which is believed to be among the highest reported for a self-biased MMIC in this frequency range. The amplifier's optimum gain bias was determined by finding the maxima of a simple bipolar gain-bias function which involves the graphical solution of a transcendental equation. This design calculation was experimentally verified for a four-stage Ku-band HBT amplifier which achieves 11.94 dB gain at 17 GHz while consuming only 5.64 mW of DC power through a 1.88 V supply. This method for optimising the gain efficiency can be applied to the design of ultra-low DC power HBT gain blocks for communication and radio-astronomy applications.