Predictive waveform acquisition

Abstract

A tester exercises a DUT with a repetitive signal pattern, supplying a trigger signal for each repetition. The waveform on a conductor of the DUT is to be acquired by repeatedly measuring voltage at each of a number of sample points following the trigger, using a charged-particle probe system having an integrator-filter loop for analyzing energy of secondary particles. Before measurement at a sample point, integrator is reset and the filter voltage needed to settle the loop for the sample point is set using a predictive scheme. When the measurement is made, the predicted filter voltage is summed with the integrator output voltage to produce the actual filter voltage. The integrator then measures the error between the predicted filter voltage and the actual filter voltage needed to settle the loop. The time needed to settle the loop is thereby minimized. Various predictive schemes can be used. An adaptive predictive scheme uses the error measured by the integrator to update the filter voltage prediction for the next measurement at the same sample point. The predicted filter voltage can be a previous measurement or an average of previous measurements taken at that sample point or an average of previous measurements taken over some time interval or a value determined by any other desired predictive scheme.