Patent ID: 7797646

Claim:
A computer implemented method for optimizing the use of high and low threshold voltage devices in a speed critical circuit, the method comprising: forming a preliminary physical layout of a circuit using at least one low threshold voltage (low-Vt) cell, the low-Vt cell comprising a plurality of low-Vt devices; and replacing at least one of the plurality of low-Vt devices in the low-Vt cell with at least one high threshold voltage (high-Vt) device without failing to meet a speed constraint of the circuit; wherein the low-Vt cell is in a critical path of the circuit, and the at least one high-Vt devices is in a non-critical path within the low-Vt cell; and wherein the speed critical circuit comprises a plurality of critical and non-critical paths, and replacement of devices is carried on sequentially with a priority from a least critical path of the circuit to a most critical path of the circuit.