A Digital CMOS Parallel Counter Architecture Based on State Look-Ahead Logic

摘要

We present a high-speed wide-range parallel counter that achieves high operating frequencies through a novel pipeline partitioning methodology (a counting path and state look-ahead path), using only three simple repeated CMOS-logic module types: an initial module generates anticipated counting states for higher significant bit modules through the state look-ahead path, simple D-type flip-flops, and 2-bit counters. The state look-ahead path prepares the counting path's next counter state prior to the clock edge such that the clock edge triggers all modules simultaneously, thus concurrently updating the count state with a uniform delay at all counting path modules/stages with respect to the clock edge. The structure is scalable to arbitrary $N$-bit counter widths (2-to-$2N$ range) using only the three module types and no fan-in or fan-out increase. The counter's delay is comprised of the initial module access time (a simple 2-bit counting stage), one three-input and-gate delay, and a D-type flip-flop setup-hold time. We implemented our proposed counter using a 0.15-$mu$ m TSMC digital cell library and verified maximum operating speeds of 2 and 1.8 GHz for 8- and 17-bit counters, respectively. Finally, the area of a sample 8-bit counter was 78 125 $mu$ m$^2$ (510 transistors) and consumed 13.89 mW at 2 GHz.