Peak current reduction by simultaneous state replication and re-encoding

Abstract

Peak current is one of the important considerations for circuit design and testing in the deep sub-micron technology. In a synchronous finite state machine (FSM), it is observed that the peak current happens at the moment of state transitions and it has a strong correlation with the maximum number of state registers switching in the same direction simultaneously [2], which we refer to as the peak switching value (PSV). We propose a FSM synthesis method to reduce P SV by seamlessly combining state replication and state re-encoding techniques.Our experiments show that out of 52 FSM benchmarks encoded by a state-of-the-art power-driven encoding algorithm POW3 [1], 36 of them are not optimal in terms of PSV. Our approach can improve on 34 of them with an average 39.2% PSV reduction, while the only comparable PSV-driven FSM synthesis technique [2] can improve on 27 benchmarks with an average 24.5% reduction. Furthermore, we compare our approach with [2] after the FSMs are implemented using an industry EDA tool. The results show that our approach reduces the peak current in the circuits by 13% on average and the total power by 3% with a mere 2% overhead in area.

Design Methodologies for Reliable Clock Networks

“…Then, they iteratively updated the PB expression to extract a state transition which results in the highest switching, and running PB-Solver with the additional conjunctive normal form (CNF) constraints. On the other hand, Gu et al [37], similar to the work in [33], started from an encoded FSM with minimal total switching, but they identified a set of transitions (called working set S) that cause peak current and applied both state-replication and state-encoding to S. State-replication replicates a state to assign another code to each replicated state with the proper generation of state transitions while stateencoding re-encodes the given code of a state to another unused code. With an input FSM with minimum total switching, by applying state-replication and state-encoding in a combined manner iteratively, they reduced the peak switching.…”