Optimization of NULL Convention Self-timed Circuits


Self-timed logic design methods are developed using Threshold Combinational Reduction (TCR) within the NULL Convention Logic (NCL) paradigm. NCL logic functions are realized using 27 distinct transistor networks implementing the set of all functions of four or fewer variables, thus facilitating a variety of gate-level optimizations. TCR optimizations are formalized for NCL and then assessed by comparing levels of gate delays, gate counts, transistor counts, and power utilization of the resulting designs. The methods are illustrated to produce (1) fundamental logic functions that are 2.2-2.3 times faster and require 40-45% fewer transistors than conventional canonical designs, (2) a Full Adder with reduced critical path delay and transistor count over various alternative gate-level synthesis approaches, resulting in a circuit with at least 48% fewer transistors, half as many gate delays to generate the carry output, and the same number of gate delays to generate the sum output, as its nearest competitors, and (3) time, space, and power optimized increment circuits for a 4-bit up-counter, resulting in a throughput-optimized design that is 14% and 82% faster than area- and power-optimized designs, respectively, an area-optimized design that requires 22% and 42% fewer transistors than the speed- and power-optimized designs, respectively, and a power-optimized design that dissipates 63% and 42% less power than the speed- and area-optimized designs, respectively. Results demonstrate support for a variety of optimizations utilizing conventional Boolean minimization followed by table-driven gate substitutions, providing for an NCL design method that is readily automatable.


Electrical and Computer Engineering

Keywords and Phrases

NULL Convention Logic (NCL); Asynchronous Logic Design; Dual-Rail Encoding; Full Adder; Quad-Rail Encoding; Self-Timed Circuits; Threshold Gates; Up-Counter

Document Type

Article - Journal

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© 2004 Elsevier, All rights reserved.

Publication Date

01 Jan 2004