Laser voltage probe methods and apparatus

摘要

A laser voltage probe system in which a repetitive stimulus signal is applied to an integrated circuit (705). A train of laser pulses is generated, and a laser pulse is picked from the train at a selected time during each repetition of the stimulus signal. The picked laser pulses are applied to a semiconductor active region of the integrated circuit which is influenced by voltage on a conductor. Photons reflected from the semiconductor active region are detected to produce a detector signal. The detector signal is sampled in synchrony with application of the laser pulses to the semiconductor active region so as to obtain samples during first gating intervals which depend upon reflected photons and noise and so as to obtain samples during second gating intervals which depend upon noise. Samples obtained during the first gating intervals are integrated with the inverse of samples obtained during the second gating intervals to produce an integrator signal representing a noise-compensated signal. The integrator signal can be compensated for pulse-to-pulse laser power variations.