A fast settling, high DC gain, low power OPAMP design for high resolution, high speed A/D converters

A fast settling, low power, high dynamic range OPAMP with a DC gain of 96 dB has been designed. Simulations have been performed in 0.35 μm CMOS technology for slow, nominal and fast models. High DC gain has been achieved by adding gain boosting active blocks to the main OPAMP. In this design, a telescopic OTA has been chosen as the main opamp due to its fast settling and low power advantages, as well as the gain boosting OPAMPs. Transient simulation indicates a settling time of 17ns for a global feedback with β= 1/2 . Although telescopic OPAMPs suffer from inherent low output voltage swing, a dynamic range of 83 dB has been achieved in this design. A power consumption of 4.1 mW is obtained for the total circuit including the main OPAMP, gain boosters and the bias circuitry.