Waveform aware delay calculation approaches in STA tools require selection of driver waveform during library characterization for accuracy. 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 transistors can involve significant optimization effort. This paper discusses an efficient approach for finding the characterization waveform for library characterization.