Pure-capacitance-load source-follower comparators for low-power winner-take-all circuitry

DC-current-free pure-capacitance-load source-follower comparators have been developed for low-power winner-take-all circuits. The concept of charge-transfer amplifier was implemented in the CMOS source-follower configuration as well as in NMOS and PMOS source-followers. In the former, the separate gate biases to NMOS and PMOS and the positive feedback scheme have enabled a nearly full logic swing operation. In the latter, the trigger type comparator was formed by cascaded PMOS and NMOS source-followers. Two types of WTA circuits, namely the binary-search type WTA and the ramp-voltage-scan type WTA, were developed using the feedback type and the trigger type comparators, respectively. The test circuits were fabricated in a 0.6-μm double-polysilicon triple-metal CMOS technology, and their operation was experimentally verified