Optimal Choice of Waveform for Library Characterization for Accurate Delay Calculation

Accuracy of waveform aware delay calculation approaches in STA tools require selection of an appropriate driver waveform during library characterization. The optimal waveform shape is dependent on process corner, voltage, temperature, parasitics and also the properties of the transistors involved. Traditionally used ramp waveform is not suitable for accuracy particularly at lower voltages and temperatures. Identification of waveform shape across a wide range of operating corners and for different transistor types can involve significant cost in terms of resources and time. This paper discusses an efficient approach for finding the driver waveform for library characterization. It also enlists the factors that influence the waveform shape and the related careabouts during the waveform identification process. Lastly, it proposes an approach to reduce the run-time and resources used to get the optimal characterization waveform at all operating corners.