Measuring skew between digitizer channels using fourier transform

An apparatus for reducing timing skew from time measurements made between digitizer channels in an automatic test system, comprising:

• means for sampling a waveform with each digitizer channel to produce a respective data record;
• means for calculating a phase value of the waveform from each data record;
• means for converting the phase values to time values;
• and
• means for applying the time values to time measurements made between digitizer channels to correct for the effects of timing skew.

An apparatus for capturing waveforms in an automatic test system, comprising:

• first and second digitizer channels each including sampling hardware for sampling a waveform and having access to a memory for storing respective data records;
• a computer processor for calculating phase values from waveform data stored in the memory for each of the first and second digitizer channels and converting the phase values to time values;
• and
• software for applying the time values to measurements made between the first and second digitizer channels to correct for the effects of timing skew.

A method of manufacturing an integrated circuit, comprising:

• fabricating a circuit on a semiconductor wafer;
• and
• testing the circuit, including measuring at least one time interval between a first electrical event, using a first digitizer channel, and a second electrical event, using a second digitizer channel,
• wherein the first and second digitizer channels are deskewed by a process that includes
• sampling a waveform having a known frequency with the first and second digitizer channels to produce respective data records;
• calculating a phase value of the waveform from each data record;
• converting the phase values to time values;
• and
• applying the time values to time measurements to correct the time measurements for the effects of timing skew.

An automatic test system, comprising:

• a waveform source;
• a plurality of digitizer channels;
• an interconnect for conveying an output of the waveform source and an input of each of the plurality of digitizer channels to nodes of a device under test;
• and
• software for reducing timing skew between different ones of the plurality of digitizer channels, said software performing the steps of
• causing the waveform source to generate a calibration signal;
• configuring the interconnect to couple the output of the waveform source to the input of at least one of the plurality of digitizer channels;
• causing said at least one of the plurality of digitizer channels to sample the calibration signal to produce a respective data record;
• calculating a phase value of the calibration signal from each data record;
• converting the phase values to time values;
• and
• storing the time values so that they can be later applied to measurements between digitizer channels to correct for timing skew.

A method of making measurements between digitizer channels in an automatic test system, comprising:

• sampling a waveform with first and second digitizer channels to produce first and second data records;
• calculating a skew correction from the first and second data records;
• capturing a first signal with the first digitizer channel and a second signal with the second digitizer channel;
• making a time measurement between the first and second captured signals;
• and
• applying the skew correction to the time measurement to enhance its accuracy.