Substrate noise measurement by using noise-selective voltage comparators in analog and digital mixed-signal integrated circuits

In mixed-signal ICs, substrate noise produced by high-speed digital circuits passes to the on-chip analog circuits through the substrate and seriously affects their performance. In this paper, we discuss how the substrate noise can be measured by using noise-selective chopper-type voltage comparators as noise detectors to detect the wide-band substrate noise so as to analyze and further reduce its effect. A switched capacitor is selectively loaded to the inverter amplifier of the comparator during the comparison period to reduce the noise detection at the transition from compare to auto-zero. The noise at the transition from auto-zero to compare can be selectively detected. Waveforms of the high frequency substrate noise were reconstructed by this on-chip noise detector incorporating the noise-selective comparators implemented using a 0.5-μm CMOS bulk process