Abstract: A method for reducing drift in a step stimulus from a sampling system, such as an oscilloscope, is described having an initial step of setting a calibration repetition rate. A step stimulus stabilization calibration is performed to acquire a reference mid-crossing time and the current mid-crossing time. Acquisition cycles of TDR/TDT waveform samples are acquired equal to the repetition rate with the initial strobe delay interval in the sampling system being adjusted by the difference between the reference mid-crossing time and the current mid-crossing time. The step stimulus stabilization calibration is performed again to acquire a new current mid-crossing time and initial strobe delay interval and more acquisition cycles of TDR waveform samples are acquired equal to the repetition rate. The process continues until a stop command is activated for the sampling system.

Abstract: A method of calibrating a timebase in a digitizing instrument estimates the frequency of the clock signal from the clock generator that clocks a coarse delay counter in a strobe generator. The dynamic range of the interpolator in the strobe generator is defined in digital-to-analog converter code values as a function of the clock signal period. A linear horizontal look-up table of equally spaced digital-to-analog converter code values is generated over the defined dynamic range of the interpolator. Residual nonlinearities of the interpolator over the defined dynamic range of the interpolator are characterized and scaled to digital-to-analog converter code values. The digital-to-analog converter code values of the characterized residual anomalies are combined with the digital-to-analog converter code values of the linear horizontal look-up table to generate a horizontal look-up table having DAC code value compensating for the nonlinearities of the interpolator.