Study of Q factor and loop delay effects of a continuous-time Δ Σ AD modulator

Abstract

This paper describes the design and analysis of a continuous-time bandpass ΔΣ AD modulator for RF sampling. We determined the SNDR degradation due to finite Q value of the loop resonator, and due to excess loop delay (ELD). SNDR was improved by 20 dB by adding a digital filter which compensates for the effect of finite Q value, and SNDR was further improved by 20 dB by feedforward with parameters optimized to compensate for ELD. We have confirmed the effectiveness of the digital filter and feedforward proposals using Matlab and SPICE simulations.