An efficient ΔΣ ADC architecture for low oversampling ratios

As the demand for ΔΣ (delta-sigma) analog-to-digital converters (ADCs) with higher bandwidth and higher signal-to-noise ratio (SNR) increases, designers have to look for efficient structures with low oversampling ratio (OSR). The Leslie-Singh or M-0 MASH architecture is often used in such applications. Based on this architecture, a reduced-sample-rate structure was introduced, which needs less chip area and power, but increases the noise floor. This paper describes a modification of the reduced-sample-rate structure which realizes an optimized transfer function, and avoids an SNR loss. In fact, it increases the SNR for high-order modulators. The method can also be applied to one-stage modulators. Simulation results for different MASH ADCs and sensitivity analysis verify the usefulness of the proposed technique.