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

In mixed-signal integrated circuits (IC's), substrate noise produced by high-speed digital circuits passes to the on-chip analog circuits through the substrate and seriously degrades their performance. We have developed a method for measuring the substrate noise by using noise-selective chopper-type voltage comparators as noise detectors. This method can detect the wideband substrate noise so we can analyze and further reduce its effect. A switched capacitance is selectively loaded on the output of the inverter amplifier of the comparator during the comparison period in order to reduce the noise detected at the transition from compare to auto-zero. In contrast, the noise at the transition from auto-zero to compare can be selectively detected. Waveforms of high-frequency substrate noise were reconstructed by using this on-chip noise detector incorporating the noise-selective comparators implemented using a 0.5-mu m CMOS bulk process.