Timing simulator by waveform relaxation considering the feedback effect

Timing simulators are widely used nowadays for analysing large scale MOS digital circuits. However, they have several limitations such as nonconvergence and/or inaccuracy for circuits containing tightly coupled feedback elements or loops. The authors describe a new timing simulator that aims at solving these problems. The algorithm employed is based on the waveform relaxation method and exploits the signal flow along the feedback loops. Each of the feedback loops is treated as one circuit block, and then local iterations are performed to enhance the timing simulation. An approach to partitioning bidirectional subcircuits is also presented.