VLSI- A to D and D to A converters with multi-stage noise shaping modulators

Abstract

High resolution oversampling analog-to-digital and digital-to-analog converters are proposed. These converters utilize novel multi-stage noise shaping modulation techniques which can be implemented with fine pattern MOS technology. The modulators consist of multi-connected delta sigma modulation loops with single integration. The quantization noise in the first loop is re-quantized by the second loop. That is, the noise is canceled by adding the second loop output signals to the first loop output. The resolution of the modulators increases in proportion to the number of stages and there are no feedback-loop stability problems. An experimental prototype chip is fabricated using 1.5µm CMOS technology. This chip achieves a wide dynamic range of 88dB at a baseband of 3.4KHz and sampling rate of 2.048MHz. This dynamic range corresponds to a 14-bit equivalent resolution.