A third-order ΣΔ modulator in 0.18-μm CMOS with calibrated mixed-mode integrators

This paper describes a third-order sigma-delta (ΣΔ) modulator that is designed and implemented in 0.18-μm CMOS process. In order to increase the dynamic range, this modulator takes advantage of mixed-mode integrators that consist of analog and digital integrators. A calibration technique is applied to the digital integrator to mitigate mismatch between analog and digital paths. It is shown that the presented modulator architecture can achieve a 12-dB better dynamic range than conventional structures with the same oversampling ratio (OSR). The experimental prototype chip achieves a 76-dB dynamic range for a 200-kHz signal bandwidth and a 55-dB dynamic range for a 5-MHz signal bandwidth. It dissipates 4 mW from 1.8-V supply voltages and occupies 0.7-mm² silicon area.