Design and Analysis of Broadband Darlington Amplifiers With Bandwidth Enhancement in GaAs pHEMT Technology

This paper presents a bandwidth enhancement technique for broadband Darlington amplifiers. A detailed analysis of the high-frequency performance of the Darlington amplifier and the effect of bandwidth enhancement is provided. A design procedure is also given for broadband feedback Darlington amplifiers with bandwidth enhancement and gain flattening. A single- and a three-stage feedback amplifier with the proposed improvements are designed and implemented in a 0.25- μm AlGaAs-InGaAs pHEMT technology. The single-stage amplifier provides 6±0.4 dB of small-signal gain in the frequency band of 1-30 GHz. The three-stage amplifier features 17.8±0.8 dB of small-signal gain in the frequency band of 2-29 GHz. It provides a gain-bandwidth product of 217 GHz, which is 3.3 times larger than the unity gain frequency (f
_T
) of the process.