Design method of high performance and low power functional units considering delay variations

As VLSI technology advances, delay variations will become more serious. Delay-insensitive asynchronous dual-rail circuits tolerate any delay variation, but their energy consumption is more than double that of the single-rail circuits because signal transitions occur every cycle in all bits regardless of the input bit pattern. However, in functional units, a significant number of input bits may not change from the previous input in many cases. In such a situation, calculation of these bits is not required. Thus, we propose a method, called unflip-bits control, makes use of the above situation, to reduce energy consumption. We evaluate the energy consumption and performance penalty for the method using HSPICE and the verilog-XL simulator, and compare the method with the conventional dual-rail circuit and a synchronous circuit. Our evaluation results reveal that the proposed asynchronous dual-rail circuit has a 12-60 lower energy consumption compared with a conventional asynchronous dual-rail circuit.