Chapter 4 - Analog/Digital Conversions

Abstract

This chapter focuses on the data conversion of data acquisition systems. Data conversion lies at the heart of data acquisition systems. Data must be in a digital form. Digital waveforms have discrete values and have a specified time interval between values. The process of converting an analog signal to a digital one is called analog-to-digital conversion and the device that does this is an analog-to-digital converter (ADC). The reverse process of converting digital data to an analog signal is called digital-to-analog conversion and the device that does this is called a digital-to-analog converter (DAC). DACs use either current or voltage switching techniques to produce an output analog value equal to the sum of several discrete analog values. It is easier to sum currents using analog circuitry, most commonly available DACs are current-mode devices. On the other hand, one of the simplest approaches in implementing an ADC is the ramp converter. It consists of a digital counter, a DAC, an analog comparator, and control logic with timing generation. Basically, when an analog conversion is requested, the digital counter starts counting up from zero.