MULTISTAGE BANDPASS DELTA-SIGMA MODULATORS

A new architecture for oversampled delta sigma A/D conversion of high-frequency narrow band signals using cascaded low-order stages to obtain high overall order of noise shaping is described. The architecture involves using resonators in individual stages to suppress quantization noise at the resonant frequency. Many of the problems of previous single stage high-order architectures including poor stability, large component spread and design complexity are overcome by this new approach. Switched capacitor resonator circuit implementations and simulation results for a sixth-order modulator example are included. Estimates of the potential for 16-bit A/D conversion of 2.5 MHz signals exceed the 80 kHz capability of existing monolithic oversampled CMOS A/Ds.