GaAs HBT power amplifier with smooth gain control characteristics

A gain control scheme giving simultaneously an effective power switch-off operation and smooth gain control characteristics is presented. The concept was applied to a 3-stage power amplifier which was a part of a 900-MHz transmitter chip. The chip was realised by using GaAs MMIC technology and was mounted on a ceramic substrate. The power amplifier was tested separately by mounting it directly on a conventional FR4 board. In this lossy environment the power amplifier delivered an output power of 33.2 dBm with a supply voltage of 3.5 V. The maximum value of the gain control slope was 22 V/V showing a good agreement to the simulations.