A circuit-level implementation of fast, energy-efficient CMOS comparators for high-performance microprocessors

Datapath components in modern high performance superscalar processors employ a significant amount of associative addressing logic based on the use of comparators that dissipate energy on a mismatch. These comparators are used to detect a full match, but as mismatches are much more common than full matches in some components of the CPU, considerable energy-inefficiencies occur within the associative logic. We propose the design of two new comparator circuits that predominantly dissipate energy on a match, thus resulting in very significant savings in comparator power dissipation. The proposed designs are evaluated using SPICE simulations of actual VLSI layouts of the comparators in 0.18 micron 6-metal layer process and micro-architectural level statistics.