US Patent 7511652 Comparison device and analog-to-digital converter

The comparison device includes a first through second comparators, a chop switching unit, a delta-sigma modulation unit, and a first through second compensation units. The chop switching unit transmits a first and a second signals to two input terminals of the first comparator during a first period, and inverses the first and second signals during a second period. The delta-sigma modulation unit compares the comparison results of two parallel comparators and generates the digital control codes for the comparators with the awareness of the chop switching unit. The first and the second compensation units adjust the threshold voltages of the comparators according to the digital control codes and a step size for calibrating the offset voltages of two comparators. The calibration scheme requiring no assumption on the input signal statistics is background thus the comparison device will not interrupt normal operation and is immune to PVT variations.