Applying the IEEE-1057 draft standard to calibration of equivalent-time sampling oscilloscopes

The author presents a methodology for calibrating an equivalent-time sampling oscilloscope using some techniques from the IEEE Standard for Digitizing Waveform Recorders (IEEE-1057). The standard was designed with real-time waveform recorders in mind. Equivalent-time waveform recorders present additional difficulties in time-base calibration. Because each sample is delayed slightly from those before it, careful calibration of the time-base delay generator is necessary. A general algorithm for calibrating vertical, time-base, and trigger subsystems is presented. Special attention is paid to the calibration of the time-base of an equivalent-time sampling oscilloscope. Complications arise when calibrating an equivalent-time sampling oscilloscope with a variable time-base. Nonlinearities in the time-base and its wide operating range can produce a complex calibration curve. Judicious application of sine wave curve fitting, frequency estimation, zero-finding, and local minimum-finding techniques can minimize the need for prior knowledge of the calibration curve