A 5-GHz SiGe HBT return-to-zero comparator for RF A/D conversion

This paper presents a monolithic comparator implemented in a 0.5-μm SiGe heterojunction bipolar transistor (HBT) process. The SiGe HBT process provides HBT npn transistors with maximum f_T over 40 GHz and f_max over 55 GHz. The comparator circuit employs a resettable slave stage, which was designed to produce return-to-zero output data. Operation with sampling rates up to 5 GHz has been demonstrated by both simulation and experiments. The comparator chip attains an input range of 1.5 V, dissipates 89 mW from a 3-V supply, and occupies a die area of 407×143 μm². The comparator is intended for analog-to-digital (A/D) conversion of 900 MHz RF signals