Design and implementation of quadrature bandpass sigma-delta modulator used in low-IF RF receiver

This paper presents the design and implementation of quadrature bandpass sigma–delta modulator.A pole movement method for transforming real sigma–delta modulator to a quadrature one is proposed by detailed study of the relationship of noise-shaping center frequency and integrator pole position in sigma–delta modulator.The proposed modulator uses sampling capacitor sharing switched capacitor integrator,and achieves a very small feedback coefficient by a series capacitor network,and those two techniques can dramatically reduce capacitor area.Quantizer output-dependent dummy capacitor load for reference voltage buffer can compensate signal-dependent noise that is caused by load variation.This paper designs a quadrature bandpass Sigma-Delta modulator for 2.4 GHz low IF receivers that achieve 69 d B SNDR at 1 MHz BW and-1 MHz IF with 48 MHz clock.The chip is fabricated with SMIC 0.18μm CMOS technology,it achieves a total power current of 2.1 m A,and the chip area is 0.48 mm;.

This paper presents the design and implementation of quadrature bandpass sigma–delta modulator.A pole movement method for transforming real sigma–delta modulator to a quadrature one is proposed by detailed study of the relationship of noise-shaping center frequency and integrator pole position in sigma–delta modulator.The proposed modulator uses sampling capacitor sharing switched capacitor integrator,and achieves a very small feedback coefficient by a series capacitor network,and those two techniques can dramatically reduce capacitor area.Quantizer output-dependent dummy capacitor load for reference voltage buffer can compensate signal-dependent noise that is caused by load variation.This paper designs a quadrature bandpass Sigma-Delta modulator for 2.4 GHz low IF receivers that achieve 69 d B SNDR at 1 MHz BW and-1 MHz IF with 48 MHz clock.The chip is fabricated with SMIC 0.18μm CMOS technology,it achieves a total power current of 2.1 m A,and the chip area is 0.48 mm^2.