A 4-MHz Bandwidth Continuous-Time Sigma-Delta Modulator With Stochastic Quantizer and Digital Accumulator

A 4-MHz bandwidth continuous-time (CT) sigma-delta modulator (SDM) is described. The CT-SDM employs a stochastic quantizer consisting of 63 comparators whose random input offset provides linear multi-bit quantization. The output of the stochastic quantizer is accumulated by a digital accumulator before feeding it back to the input of the loop filter of the CT-SDM, which greatly improves the linearity of the stochastic quantization. The CT-SDM implemented in a 65-nm CMOS technology shows the peak signal-to-noise+distortion ratio of 72.5-dB while consuming 3.6-mW from a 0.9-V supply.