Discreate-Time Second-Order Delta-Sigma A/D Modulator Improving SQNR and Suppressing Harmonic Distortions by Correlated Level Shifting Technique

Abstract

Signal-to-quantization-noise ratio (SQNR) of discrete-time delta-sigma modulators (DTΔΣMs) are degraded when low-gain operational amplifiers (Op-Amps) are used. Correlated level shifting (CLS) technique has been proposed to compensate gain of Op-Amp in pipeline analog-to-digital converters. In this paper, we show that gain of the Op-Amps are improved by applying CLS technique to Op-Amps in the integrators of DTΔΣM, and SQNR is improved even if low-gain Op-Amps are used. The simulation results show that SQNR is improved by 6 dB and SQNR using 374x gain Op-Amp is equivalent to that using 30x gain with CLS technique, and considering nonlinearity of Op-Amps, harmonic distortions are suppressed by over 15 dB.