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Asynchronous design of systolic array architectures in cmos

İsmailoğlu, Ayşe Neslin
In this study, delay-insensitive asynchronous circuit design style has been adopted to systolic array architectures to exploit the benefits of both techniques for improved throughput. A delay-insensitivity verification analysis method employing symbolic delays is proposed for bit-level pipelined asynchronous circuits. The proposed verification method allows datadependent early output evaluation to co-exist with robust delay-insensitive circuit behavior in pipelined architectures such as systolic arrays. Regardless of the length of the pipeline, delay-insensitivity verification of a systolic array with early output evaluation paths in onedimension is reduced to analysis of three adjacent systoles for eight possible early/late output evaluation scenarios. Analyzing both combinational and sequential parts concurrently, delay-insensitivity violations are located and corrected at structural level, without diminishing the early output evaluation benefits. Since symbolic delays are used without imposing any timing constraints on the environment; the method is technology independent and robust against all physical and environmental variations. To demonstrate the verification method, adders are selected for being at the core of data processing systems. Two asynchronous adder topologies in the delay-insensitive dual-rail threshold logic style, having data-dependent early carry evaluation paths, are converted into bit-level pipelined systolic arrays. On these adders, data-dependent delay-insensitivity violations are detected and resolved using the proposed verification technique. The modified adders achieved the targeted O(log2n) average completion time and -as a result of bit-level pipelining- nearly constant throughput against increased bit-length. The delay-insensitivity verification method could further be extended to handle more early output evaluation paths in multi-dimension.