A Digitally Controlled Op-Amp with Level-Crossing-Based Approximation and its Application to a 10-bit Pipeline ADC

Abstract

A digitally controlled operational amplifier (op-amp) with level-crossing-based approximation is proposed. A high gain is effectively obtained by means of a damping control without a stability problem occurring in the multiple gain stages. Compared to the previous version of the zero-crossing-based algorithmic approximation, the proposed scheme further improves the settling time with the class AB operation obtained by switching of multiple driving paths. For verification, the designed op-amp is applied to a 10-bit pipeline ADC and implemented in a 0.18[Formula: see text][Formula: see text]m CMOS technology. Measured results show that the designed op-amp successfully operates at 10-bit resolution, 10[Formula: see text]MSample/s pipeline ADC and achieves an effective gain of more than 60[Formula: see text]dB.