A high-frequency fully differential BiCMOS operational amplifier

A high-frequency fully differential BiCMOS operational amplifier design for use in switched-capacitor circuits is presented. The operational amplifier is integrated in a 3.0-GHz, 2- mu m BiCMOS process with an active die area of 1.0 mm*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 +or-5-V 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 uses 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.<
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