Measurement of the Absolute Phase Error of Digitizers

This paper proposes a method for the measurement of digitizer absolute phase errors, defined as the phase displacement between the digitized output and the input analog waveform. The measurement procedure is based on the use of a phase reference signal (PRS), which is theoretically synchronous with the input analog waveform and that triggers the digitizer sampling clock. From the characterization of the waveform generator phase response and the measurement of the time delay of the digitizer sampling clock with respect to the PRS, an accurate evaluation of the digitizer absolute phase error is obtained. The method has been applied to a high-performance digitizer, measuring the absolute phase errors of two different channels. The expanded uncertainty of the method has been quantified as a few microradians at 50 Hz and 150 μrad at 20 kHz.