A 40 Gbps GaAs-HBT distributed amplifier with an over-f/sub T/ cut-off frequency: analytical and experimental study

The bandwidth potential of HBT distributed amplifiers following the traveling-wave concept (TWA) is studied. Basic parameters are the transistor characteristics as well as the losses of the artificial transmission lines. As a result, a relation between f/sub T/ and f/sub max/ of the HBTs and the -3dB cut-off frequency of the amplifier is derived. Based on this, an over-f/sub T/ cut-off-frequency TWA is realized with 6 dB broadband gain and 42 GHz f/sub c/ using GaAs HBTs with 36 GHz f/sub T/ and 170 f/sub max/.