Sense Amplifier Half-Buffer (SAHB) A Low-Power High-Performance Asynchronous Logic QDI Cell Template

摘要

We propose a novel asynchronous logic (async) quasi-delay-insensitive (QDI) sense-amplifier half-buffer (SAHB) cell design approach, with emphases on high operational robustness, high speed, and low power dissipation. There are five key features of our proposed SAHB. First, the SAHB cell embodies the async QDI 4-phase (4φ) signaling protocol to accommodate process-voltage-temperature variations. Second, the sense amplifier (SA) block in SAHB cells embodies a cross-coupled latch with a positive feedback mechanism to speed up the output evaluation. Third, the evaluation block in the SAHB comprises both nMOS pull-up and pull-down networks with minimum transistor sizing to reduce the parasitic capacitance. Fourth, both the evaluation block and SA block are tightly coupled to reduce redundant internal switching nodes. Fifth, the SAHB cell is designed in CMOS static logic and hence appropriate for full-range dynamic voltage scaling operation for VDD ranging from nominal voltage (1 V) to subthreshold voltage (~0.3 V). When six library cells embodying our proposed SAHB are compared with those embodying the conventional async QDI precharged half-buffer (PCHB) approach, the proposed SAHB cells collectively feature simultaneous -.64% lower power, -.21% faster, and ~6% smaller IC area; the PCHB cell is inappropriate for subthreshold operation. A prototype 64-bit Kogge-Stone pipeline adder based on the SAHB approach (at 65 nm CMOS) is designed. For a 1-GHz throughput and at nominal VDD, the design based on the SAHB approach simultaneously features -.56% lower energy and -.24% lower transistor count advantages than its PCHB counterpart. When benchmarked against the ubiquitous synchronous logic counterpart, our SAHB dissipates -.39% lower energy at the 1-GHz throughput.