A tunable SC bandpass delta-sigma modulator for multi-standard applications

This paper presents a double-sampling switched-capacitor (SC) tunable resonator for bandpass (BP) DeltaSigma modulators. The resonator is implemented with a single opamp to reduce the power consumption. In addition, the resonant frequency can be easily tuned by controlling the number of shunting capacitors. Based on the resonator, a fourth-order BP DeltaSigma modulator is proposed. With the tuning ability, the resonant frequencies of the two resonators in the modulator not only can be varied to the same center frequency for narrow-band applications, but also to the frequencies symmetric to the center frequency, one quarter of the sampling frequency, for wide-band applications. The BP DeltaSigma modulator is implemented in a 0.18 mum CMOS technology, and Matlab and HSPICE simulation results are presented to demonstrate the design concept.