RETIMING SEQUENTIAL CIRCUITS FOR LOW POWER

Abstract

Switching activity is a primary cause of power dissipation in combinational and sequential circuits. In this paper, we present a retiming method that targets the power dissipation of a sequential circuit by reducing the switching activity of nodes driving large capacitive loads. We explore the implications of the observation that the switching activity at flip-flop outputs in a synchronous sequential circuit can be significantly less than the activity at the flip-flop inputs. The method automatically determines positions of flip-flops in the circuit so as to heuristically minimize weighted switching activities summed over all the gates and flip-flops in the circuit. We extend this method to minimize power dissipation with a specified clock period. For this work we need to obtain efficiently an estimation of the switching activity of every node in the circuit. We give an exact method of estimating power in pipelined sequential circuits that accurately models the correlation between the vectors applied to the combinational logic of the circuit. This method is significantly more efficient than methods based on solving Chapman–Kolmogorov equations. Experimental results are presented on a variety of circuits.