A digitally-controlled seven-state X-band SiGe variable gain low noise amplifier

This work describes the design of a digitally-controlled seven-state variable gain low noise amplifier. The amplifier utilizes separately biased transistor cores to activate additional transistor area and change the amplifier gain. Variable gain low noise amplifiers enable greater dynamic range in RF receivers and provide amplitude control for phased-array systems. The amplifier was fabricated in a 180 nm SiGe BiCMOS technology platform featuring SiGe HBTs with an f_T/f_max of 240/260 GHz. When all transistor cores are activated, the amplifier achieves 16.5 dB of gain and a noise figure of 1.6 dB at 10 GHz. A gain variation of 7 dB from the maximum to the minimum state is demonstrated. In addition, the noise figure, linearity, and gain all improve with increasing transistor area and power dissipation, indicating an optimum state can be selected to meet receiver requirements while minimizing power dissipation.