Single op-amp second-order loop filter for continuous-time delta-sigma modulators

Abstract

A second-order loop filter (LF) that uses a single op-amp resonator is presented for continuous-time delta-sigma modulators. The proposed technique improves the power and area efficiency of the LF and enhances the controllability of the transfer function and the resonating condition by providing a new RC network. A second-order modulator has been designed to confirm the effectiveness of the proposed scheme. Implemented in a 130 nm CMOS, the prototype modulator occupies an active area of 0.098 mm2 and consumes 5.23mW power from a 1.2 V supply. It achieves a peak SNDR of 60.95 dB over a 15 MHz signal bandwidth with a sampling frequency of 780 MHz.