A pulsed-latch is an ideal sequencing element for high-performance application-specific integrated circuit designs due to its simple timing model and reduced sequencing overhead. The possibility of time-borrowing while a latch is transparent is deliberately ignored in pulsed-latch circuits to simplify the timing model. However, using more than one pulse width allows another form of time-borrowing, which preserves the simple timing model. The associated problem of allocating pulse widths is called pulse width allocation (PWA); and we combine it with retiming to achieve a shorter clock period in pulsed-latch circuits than can be obtained by retiming or PWA alone, with less requirement for extra latches than standard retiming. An exact solution can be obtained by an integer linear programming, but this is restricted to small circuits. We therefore introduce a practical heuristic, which performs clock skew scheduling to find the minimum clock period and then brings the clock skew as nearly back to zero as possible by converting it to combined retiming and PWA. Experiments with 45 nm technology circuits suggest that the heuristic algorithm achieves a clock period that is close to minimum in most circuits, with an average 23% reduction compared to initial circuit, at an average cost of a 16% increase in the number of latches. On the same benchmarks, standard retiming achieves a 20% reduction in clock period with a 29% increase in the number of latches. The cost in extra area and energy is reasonable.

Pulsed-latches take advantage of both latches in their high performance and flip-flops in their convenience of timing analysis. To minimize the clock period of pulsed-latch-based circuits for a higher performance, a problem of combined retiming and time borrowing is formulated, where the latter is enabled by using a handful of different pulse widths. The problem is first approached by formulating it as an integer linear programming to lay a theoretical foundation. A heuristic approach is proposed, which solves the problem by performing clock skew scheduling for the minimum clock period and gradually converting skew into a combination of retiming and time borrowing. Experiments with 45-nm technology demonstrate that the clock period close to the minimum can be achieved for all benchmark circuits with an average of 1.03x with less use of extra latches compared to the conventional retiming.