a/d converter

The necessity to convert a voltage to a frequency such that the frequency is accurately proportional to the voltage is one which arises in many different electronic systems. Some digital voltmeters use this principle. The voltage to be measured is converted to a proportionate frequency, which is then measured by a conventional counter circuit, and the result displayed digitally. In other caseS,·the requirement is to have a reading of a voltage existing some distance away. In this case the long cables, with their appreciable DC resistance, produce a voltage drop if any current is taken by the measuring instrument, and errors result. If however the information is carried over the cables as a frequency, although the amplitude may fall the frequency will not change. Increasing use of digital computors, digital logic IC`s, digital displays, etc., produces many more applications. A previous design for a convertor circuit gave reasonable performance. However, further work produced several relatively minor changes which improved both linearity and temperature stability, resulting in the circuit described below