Design of Two-Stage Fully-Differential Operational Transconductance Amplifier Using a Standard 0.35µm CMOS Process

Abstract

The paper presents a design of a two-stage fully-differential operational transconductance amplifier (OTA) for a 10-bit 40-Msamples/s Nyquist rate analog-to-digital converter (ADC) using  a standard 0.35µm complementary metal-oxide semiconductor (CMOS) process.  A telescopic cascode topology is implemented as main stage, with common source amplifiers as output stage for the differential outputs. The open loop amplifier achieved a gain of 108dB, while the closed loop gain is at 12dB with settling time of less than 11ns for an accuracy of 0.5%.  Total output noise achieved is 63.4uVrms.  Loop unity gain bandwidth is 205MHz with phase margin of 77.6°. The design has a dynamic range of 88.3dB, and power consumption of 26.6mW from a 3V supply.