A HIGH-FREQUENCY FULLY DIFFERENTIAL BICMOS OPERATIONAL-AMPLIFIER

This paper presents a high-frequency fully differential BiCMOS operational amplifier designed for use in switched-capacitor circuits. The op amp is integrated in a 3.0-GHz, 2-mu-m BiCMOS process with an active die area of 1.0 mm x 1.2 mm. This BiCMOS op amp offers an infinite input resistance, a dc gain of 100 dB, a unity-gain frequency of 90 MHz with 45-degrees phase margin, and a slew rate of 150 V/mu-s. The differential output range is 12 V. The circuit is operated from a +/- 5V power supply and dissipates 125 mW. The op amp is unity-gain stable with 7 pF of capacitive loading at each output. The op amp is a two-stage, pole-split frequency compensated design that employs a PMOS input stage for infinite input resistance and an n-p-n bipolar second stage for high gain and high bandwidth. The frequency compensation network serves both the differential- and common-mode amplifiers so the differential- and common-mode amplifier dynamics are similar. A dynamic switched-capacitor common-mode feedback scheme is used to set the output common-mode level of the first and second stages.