Microwave Performance of Dual-Gate Cascode MESFET and HEMT Devices with High Gain at Low Noise Levels

Abstract

Quarter micron dual-gate MESFETs and pseudomorphic HEMTs connected as a cascode circuit have been fabricated and investigated. The devices exhibit a high output impedance and a very low feedback capacitance resulting in high voltage gain factors gm/gd up to 125 and a Cgs/Cgd ratio up to 45. The maximum stable gain obtained with dual-gate HEMTs is 23.5 dB 10 GHz and 19 dB at 20 GHz, the current gain cutoff frequency is 45 GHz. The cascode PHEMTs show a low noise figure of 1.1 dB with an associated gain of 22 dB at 10 GHz. These results represent the highest gain values and the best noise performance yet reported for dual-gate HEMT devices. With dual-gate MESFETs a dynamic range of more than 35 dB can be obtained for the insertion gain/loss up to 40 GHz by applying a DC voltage swing of 4 V at the second gate electrode. Thus these elements are very promising for gain controllable amplifiers for both low noise and high gain as well as for switching applications.