New concept to control the gain of GaN-cascodes in broadband power amplifiers

This paper presents a new technique to control the gain of cascodes in broadband power amplifiers. The concept replaces the constant stabilization capacitance Cst in the gate path of the common-gate stage by a variable adjustable capacitance. The influence of the stabilization capacitance is shown since the classical cascode cell is modified nowadays for power optimization and/or stability purposes. Two cascode broadband feedback power amplifiers were designed to verify the new idea using an AlGaN/GaN technology. Maintaining an input and output matching better than −10 dB, the conventional cascode design and the new cascode design achieve 13 dB gain with a bandwidth of 17 GHz. Both designs reach an output power of 30 dBm. The small-signal gain of the new concept can be varied between 13 dB and 17 dB by an external control-voltage without changing the operation class of the power amplifier. The concept allows an electronic compensation of process variations as well as a frequency-response calibration of broadband power amplifier systems.