Design of a 10GHz bandwidth variable gain amplifier using a GaAs HBT technology

Abstract

This paper reports a fully differential variable gain amplifier (VGA) using GaAs heterojunction bipolar transistors (HBTs). Gilbert cells with transimpedance loads are applied to achieve wide bandwidth. According to the single-ended measurements, the 3-dB bandwidth is 10.5GHz at a maximum gain of 22dB. A gain-bandwidth product of 132GHz is achieved. The circuit consists of two cascaded variable gain stages to offer a high dynamic range. The experiment results show the dynamic range is larger than 28dB. The chip consumes 368mV at a supply voltage of -5.2V. Design considerations and experimental results are presented in this paper.