Coherent switching power for an analog circuit tester
AssigneeCredence Systems Corporation
InventorsMichael R. Ferland, Jeffrey D. Currin
Life of this patent
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Abstract
A circuit tester stimulates an analog circuit device under test (DUT) with a test signal and periodically digitizes a resulting DUT output signal to produce an output data sequence that may be analyzed to ascertain DUT operating characteristics. The tester is powered by a switching power supply that induces periodic noise spikes in the DUT output signal. To eliminate the influence of the noise spikes on test results, the period of the switching power supply noise is made coherent with the digitization period. The phase of digitization is then adjusted so that the tester avoids digitizing the noise spikes in the DUT output signal.
Claims13
A circuit tester comprising:
- first means for stimulating an analog circuit device under test (DUT) with an electrical test signal such that said analog circuit device produces a DUT output signal in response to said test signal;
- second means for periodically digitizing said DUT output signal to produce an output sequence of digital data values that may be analyzed to ascertain DUT operating characteristics, wherein each of said data values represents an instantaneous magnitude of said DUT output signal;
- and
- third means for supplying direct current power to at least one of said first and second means, wherein said direct current power induces periodic noise in the DUT output signal, and wherein a period of a substantial portion of said noise is coherent with a period of said digitizing.
An apparatus for testing an analog circuit device under test (DUT) by transmitting an electrical test signal to the DUT and sampling an output signal produced by said DUT in response to said electrical test signal, the apparatus comprising:
- first means for generating a periodic reference clock signal at a fixed frequency;
- second means for generating a direct current power signal in response to said periodic reference clock signal, said direct current power signal containing periodic noise spikes occurring at a noise frequency that is coherent with said fixed frequency;
- third means powered by said direct current power signal for generating and transmitting said electrical test signal to said DUT in response to said periodic reference clock signal;
- and
- fourth means for sampling said DUT output signal in response to said periodic reference clock signal at a sampling frequency that is coherent with said fixed frequency.
An apparatus for testing an analog circuit device under test (DUT), the apparatus comprising:
- means for generating a periodic reference clock signal;
- a switching power supply responsive to said periodic reference clock signal for producing an output direct current power signal having noise spikes occurring therein with a period that is coherent with said periodic reference clock signal;
- a waveform synthesizer powered by said direct current power signal for generating an electrical test signal and for transmitting said electrical test signal to said DUT, wherein said DUT produces an output signal in response to said electrical test signal, wherein said noise spikes occurring in said direct current power signal induce periodic noise in the DUT output signal that is coherent with said periodic reference clock signal;
- and
- a digitizer responsive to said periodic reference clock signal for digitizing said DUT output signal at a frequency that is coherent with said periodic reference clock signal, thereby to produce an output digital data sequence representing amplitudes of said DUT output signal at a succession of discrete times.
A method of operating an analog circuit tester of the type which tests an analog circuit device under test (DUT) by stimulating a DUT input terminal with an electrical test signal, digitizing a DUT output signal produced in response to said electrical test signal at a digitizing frequency and digitizing phase to produce a digital data sequence representing a time varying behavior of said DUT output signal, and then analyzing the output digital data sequence to ascertain operating characteristics of the DUT, wherein the tester includes a direct current power supply that induces periodic noise spikes in the DUT output signal, comprising the step of controlling a frequency of said noise spikes so that it is coherent with said digitizing frequency.
Dependencies are inferred from the claim text.