Programmable analog to digital converter

Abstract

A programmable analog to digital (A/D) converter useful for example, in ultrasonic medical diagnosis systems, for providing transfer functions that in some arrangements may be manually selected and in other arrangements may be automatically selected as a function of time. A ladder network providing the comparator reference voltages in the converter is driven at a plurality of control nodes or points by programmed control voltage sets received from, for example, a resistive network or from a digital source through a digital to analog converter. In the arrangement in which the transfer function changes as a function of time, different transfer curves are selected having a predetermined relationship to the amplitude levels of the input signal which, for example, may be an ultrasonic return signal in a medical diagnosis system. The analog to digital converter of the invention has the advantage in a system providing imaging data, that gray levels of interest may be emphasized without increasing the finite number of overall system gray levels.