A low power, propagation delay stable, continuous-time comparator

This paper describes a design strategy towards a low power, DC level insensitive comparator with stable propagation time. The comparator is most suitable in applications were a constant propagation delay is critical, such as level crossing detection in ultrasound measurements and time quantization A/D converters. The use of a long absolute propagation delay allows low power consumption while keeping the signal dependent propagation delay variation low. The comparator is able to process signals with all DC level within power rails due to a constant-gm, rail-to-rail, single-ended to differential converter implemented in the input stage. Schematic simulations show that the comparator has less than I ns delay variation at an absolute propagation delay of 12 us. Test signals include frequencies from 0.5 MHz to 10 MHz, amplitudes from 30 mV to 1 V and all DC levels within rails.