This paper presents an improved architecture of the multistage multibit sigma-delta modulators (ΣΔMs) for wide-band applications. 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). Because of in-band zeros introduced by internal loop filters, the proposed architecture enhances the suppression of the in-band quantization noise at a low OSR. The HQCRFF-based modulator with single-bit quantizer has two modes of operation, modulation and oscillation. When the HQCRFF-based modulator is operating in oscillation mode, the feedback path from the quantizer output to the input summing node is disabled and hence the modulator output is free of the quantization noise terms. Although operating in oscillation mode is not allowed for single-stage ΣΔM, the oscillation of HQCRFF-based modulator can improve dynamic range (DR) of the multistage (MASH) ΣΔM. The key to improving DR is to use HQCRFF-based modulator in the first stage and have the first stage oscillated. 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 problem. According to theoretical and numerical analysis, the proposed MASH architecture can inherently have wide DR without using additional calibration techniques.

This work presents a new sigma-delta modulator (SDM) architecture for a wide bandwidth receiver. This architecture contains dual-bandwidth for W-CDMA and GSM system applications. Low-distortion swing-suppressing SDM and interpolative SDM cascaded units are used together. Using the low-distortion swing-suppressing technique, the resolution can be improved even under non-linearity effects. The interpolative SDM extends the signal bandwidth and represses the high-band noise. The SDM used in the W-CDMA and GSM applications was designed and simulated using 0.25-µm 1P5M CMOS technology. The simulated peak SNDR of W-CDMA and GSM are 72/70 dB and 82/84 dB in Low-IF/Zero-IF standards.