Distributed Amplifier with Narrowband Amplifier Efficiency

A fully integrated tapered output line distributed cascode SiGe HBT amplifier is presented which presents an identical load to each transistor. A nodal analysis of currents in the output transmission line gives insight into the often assumed efficiency/bandwidth trade-off of a distributed amplifier. The four section one half watt amplifier with 50 Ω input and output exhibits a gain of 21 dB from 100 to 800 MHz with a saturated collector efficiency of 79% at 100 MHz.