Design of a 0.5–30 GHz Darlington amplifier for microwave broadband applications

Design of a 0.5-30 GHz Darlington amplifier using a 2 μm InGaP/GaAs HBT process for microwave broadband applications is presented in this paper. A device size ratio of the Darlington pair and a series inductor in the input are investigated to enhance the bandwidth of the Darlington pair. The proposed method is applied to the circuit design, and the bandwidth of Darlington amplifier is higher than one-thirds maximum oscillation frequency (f_max) of the device. The Darlington amplifier features a 3-dB bandwidth of from 0.5 to 29.7 GHz with an average small signal gain of 10.5 dB. This work demonstrates the highest figure of merit (FOM) among all the HBT Darlington amplifiers so far.