A CMOS class-AB transconductance amplifier for switched-capacitor applications

A CMOS operational transconductance amplifier (OTA) using a fully differential single-stage core OTA as the input stage and a differential to single current converter as the output stage, each biased at a separate current level, is presented. A large gain-bandwidth product (2.7 MHz) and a high slew-rate (5 V/μs) can be obtained by applying a large bias current to the core OTA. Due to the class-AB operation of the output stage, a high output impedance can be obtained by applying a small bias current to the output stage, resulting in a high DC-gain (61.6 dB). When the performance of this class-AB OTA is compared with that of basic single-stage OTAs it is found that the output impedance of the class-AB OTA is increased without limiting the bandwidth or slew-rate