Phase plane compensation of the NIST sampling comparator system

This paper describes a compensation method to improve the static and dynamic linearity of the response of an equivalent-time digitizer. The nonlinearity of the digitizer response is represented in a multidimensional lookup table as a function of digitizer state and appropriate parameters, such as the instantaneous signal value and slope. In operation, the lookup table is used to compensate for the nonlinearity of the digitizer response by subtracting the appropriate table value from each new sample taken of the input signal. A second lookup table can be added to compensate digitizer timebase nonlinearity. The digitizer being compensated is a sampling comparator system that produces noticeable distortion in signals such as high frequency sine waves. The performance of the compensated sampling comparator system is presented, for a range of input test signals having a variety of trajectories in the phase plane