In one embodiment, a method for determining the voltage current phase relationship of a piezoelectric phacoemulsification handpiece generally includes the steps of obtaining an analog AC voltage signal corresponding to the operating AC voltage of a piezoelectric handpiece along with an analog AC current signal corresponding to the operating AC current of the piezoelectric handpiece. Using reference detection circuits, a digital voltage signal and a digital current signal is produced. A synchronous sample clock is taken that has a frequency that is 2N times faster than the frequency of the operating ultrasonic handpiece (i.e., driving frequency), where N is the number of digital bits allocated to the sample clock.. This clock measures the time between onsets of a voltage and current cycle. This time value equates to the phase time delta between the two signals. Dividing the synchronous sample clock to obtain the driving frequency ensures the signals are synchronous. Further dividing the end count value into 360° results in the phase shift between the two signals in degrees that is independent of the operating frequency.
