A Switched-Capacitor Filter With Reduced Sensitivity to Reference Noise for Audio-Band Sigma–Delta D/A Converters

摘要

A switched-capacitor analog reconstruction filter with a new reference switching scheme is presented for reducing sensitivity to reference noise in audio-band sigma–delta ( ) digital-to-analog converters. By sampling a single reference voltage with its polarity depending on the filter digital input, the ac component of the reference voltage is attenuated by a first-order difference to appear at the filter output. Considering that the oversampling ratio in many audio-band modulators is equal to or higher than 128, the integrated reference noise power in the signal band is reduced by more than 40 dB at the filter output. To verify the effectiveness of the proposed switching scheme, two experimental prototypes have been implemented using 0.25- devices in a 28-nm CMOS technology: one with a conventional reference switching scheme and the other with the proposed one. The measured results show that, in the proposed filter, the noise floor in the signal band is significantly reduced, which results in an improved converter dynamic range.