High-speed precision equivalent time sampling a/d converter and method

Abstract

A circuit for precisely measuring very high-speed recurring waveforms includes a comparator coupled between an analog input terminal and a successive approximation register. A digital-to-analog converter is also coupled between the digital output circuit of the successive approximation register and the second input terminal of the comparator, and a high-speed digital latch is coupled between the output of the comparator and the input of the successive approximation register for freezing the output states of the comparator upon the application of hold signals from a hold signal generator means, so that a first sequential series of hold signals are applied to the latch, coincident in time with the occurrence of a first portion of the recurring analog waveforms being measured, until the successive approximation register completes its measurement of the voltage amplitude of such first portion. A counter in the hold signal generator means is thereafter stepped, to enable the measurement of a second portion of the recurring waveform, adjacent the first portion, to be carried out by the application of a second series of hold signals, each coincident in time with the occurrence of the second portion of the waveform, until the voltage amplitude at the second portion is evaluated by the iterative operation of the successive approximation register. The counter is again stepped, and the process is repeated until numerous points upon the recurring waveform under examination are measured.