Dynamic error correction of a digitizer for time-domain metrology

A method for numerical correction of distortion in a digitizer used for metrology applications is described. Investigation of the digitizer´s error behavior in the phase plane leads to the development of an analytic error model that describes the digitizer´s distortion behavior. Of particular significance is the model´s ability to describe nonlinear error in the fundamental spectral component manifested as amplitude and frequency-dependent gain and phase error. When fitted only to the harmonic distortion content of the digitizer´s output data, the model generates an amount of fundamental that correctly accounts for the error in the digitizer´s gain that is not due to linear system response. The model is therefore able to improve not just the total harmonic distortion (THD) performance of the digitizer but its ac root mean square measurement accuracy as well. At 1 MHz, the model linearizes the digitizer to 70 μV/V over a range of 1 to 8 V and reduces harmonic distortion by >20 dB. It is believed that this is the first time that results of this nature have been reported in the literature.