Chapter 3 - A to D conversion

Abstract

This chapter discusses A to D signal conversion. An analogue to digital converter (ADC) is a device that converts an analogue signal at its input into an equivalent multibit digital output signal. Various methods of performing analogue to digital conversion exist. Binary counter ADC is also known as a ramp type of converter, and this type of ADC consists of a binary counter. Tracking converter follows or tracks the analogue input. Its operation is similar to the ramp type of ADC except that it uses an up-down counter and a window comparator. The counter types of ADC suffer from the fact that they are relatively slow in operation and that the conversion time varies according to the analogue input voltage. The conversion time may be greatly reduced and made more consistent by using a conversion method known as successive approximation. This method involves setting each bit of the input to the DAC, in turn, starting with the most significant bit. In parallel (flash) converter, a resistor network is used to generate a number of different reference potentials, one for each bit of the converter. A large number of monolithic ADCs are available from various manufacturers. When selecting an ADC for a particular application, reference should be made to the manufacturer's data sheets to determine its suitability.