On reducing leakage quantization noise of multistage /spl Sigma//spl Delta/ modulator using nonlinear oscillation
The paper presents an improved architecture of multistage (MASH) multibit sigma-delta modulators (/spl Sigma//spl Delta/Ms). The architecture can be immune to circuit nonidealities over a large portion of input range when the oversampling ratio (OSR) is low, and hence the dynamic range (DR) can be improved. Our approach is based on two resonator topologies, high-Q cascade-of-resonator-with-feedforward (HQCRFF) and low-Q cascade-of-integrator-with-feedforward (LQCIFF). The key to improving DR is to use an HQCRFF-based single-bit structure in the first stage and have the first stage oscillate. When the first stage oscillates, the coarse quantization noise vanishes and hence circuit nonidealities, such as finite op-amp gain and capacitor mismatching, do not cause leakage quantization noise problems. In addition, because of the in-band zeros introduced by the resonators, the proposed architecture enhances the suppression of the in-band quantization noise for wideband applications. As the results of simulation, the proposed MASH architecture can inherently have wide DR without using additional calibration techniques.