A continuous-time sigma-delta ADC with tunable pass-band for multi-standard applications

In this paper, we present a tunable continuous-time band-pass sigma-delta (ΣΔ) analog-to-digital converter (ADC). Our design is suitable for multi-standard multi-user applications. Additionally, the tunability advantage enhances the obtainable resolution while reducing the power consumption by only operating in the desired bandwidth from the reserved bandwidth required for ADC´s application. Our simulation results demonstrate that a relatively high SNR can be obtained using the designed ΣΔ ADC. We provide an implementation of the designed ADC using Gm-C circuits with 0.18μm IBM CMOS technology. The circuit operates with 8MHz clock frequency and achieves 57.6dB Signal to Noise and Distortion Ratio (SNDR) with 20KHz bandwidth. At the mentioned clock frequency and 1.5V supply level, the circuit consumes less than 1mW power. Our HSPICE simulation results are in very good agreement with our simulated model based on second order modified all-pass transfer functions. The effective number of bits obtained from our implemented ADC was observed to be ENOB=9.28 bits.