Low Voltage Low Power Current Mirror OTA for Sigma-Delta Modulator

Abstract-A low voltage low power class-AB operational transconductance amplifier (OTA) used in Sigma-Delta modulator is presented in this paper. To reduce the power consumption under low voltage, a current mirror topology with near rail-to-rail output swing is proposed. Its DC gain is enhanced by gain enhancement architecture without extra power consumption. Moreover, to achieve very low errors and smaller settle time, a novel switched-capacitor common-mode feedback (SC CMFB) circuit is introduced. Using 0.35 mum TSMC CMOS standard process, the OTA is designed to operate at 1.5 V supply voltage. For a 2.5 pF load capacitor the OTA achieves a DC gain of 60.58 dB, a GBW of 6.30 MHz and a slew rate of 3.24 V/ mus. The static power consumption is about 22 muW exclusive of that of CMFB circuit. It shows that the proposed OTA topology could be applied to low voltage low power switched- capacitor application.