Patent ID: 6522983
Filing Date: 2003-02-18
Classification: G01R,H03M

Abstract:
In an equivalent time sampling oscilloscope having timebase circuitry that includes a strobe generator having coarse time delay circuitry and fine time delay circuitry with the coarse time delay circuitry receiving a first portion of a strobe delay input for loading a counter with a coarse time delay value and the fine time delay circuitry receiving a second portion of the strobe delay input for generating an analog input signal to an interpolator in the fine time delay circuitry derived from a fine time delay look-up table of digital values with the coarse time delay circuitry responsive to a received clock signal from a clock generator and the interpolator responsive to the analog signal for generating a variable time delay strobe output pulse, a method of a calibrating the time base circuitry comprising the steps of:a)estimating the frequency of the clock signal from the clock generator based on the power spectrum of difference frequencies between the clock generator signal and a reference oscillator signal to generate a coarse estimation of the clock signal frequency, and a fine estimation of the clock signal frequency based on the coarse estimation of the clock signal frequency; b) defining a dynamic range for the interpolator in digital-to-analog converter code values as a function of the clock signal period based on the variance of the difference of a plurality of acquired waveform record pairs of the calibration oscillator signal with each record pair being acquired at selected digital-to-analog converter code values and one record being acquired at a first coarse time delay and the other record being acquired with a second coarse time delay; c) generating a linear horizontal look-up table of digital-to-analog converter code value points taken from the defined dynamic range of the interpolator wherein the code value points are nominally separated by the same number of digital-to-analog converter code values; d) characterizing residual nonlinearities of the interpolator over the defined dynamic range of the interpolator based on a plurality of waveform records acquired at an estimated zero crossing point of the calibration oscillator signal; e) scaling the characterized residual anomalies to digital-to-analog converter code values; and f) combining the digital-to-analog converter code values of the characterized residual anomalies with the digital-to-analog converter code values of the linear horizontal look-up table.