Digital Interface Design and Application

4 Analogue Interface Subsystems

4.1 Analogue Interfaces

A quick review will reveal that many embedded system designs require some form of analogue interface because of the analogue nature of the real world in which such systems have to operate. This chapter will focus on analogue to digital and digital to analogue interface techniques because they will be required whenever an analogue signal has to be created or monitored in a digital computer algorithm.

Taking temperature measurement as just one analogue example, it is evident that the basic analogue measurement must be converted to digital form so that the computer can manipulate its digital representation in a control algorithm. Similarly, the drive for a DC servo will be calculated as a digital value in the control algorithm but will have to take analogue form to activate the motor control voltage. This chapter will present, in particular, the Analogue to Digital converter (ADC) and the Digital to Analogue converter (DAC) through a discussion of the conversion techniques employed in some popular designs. The ADC converter actually presents a considerable design challenge so there are a wide range of different solutions to be found in commercial practice. Also, as the rate of conversion is a key factor in many applications, the key aspects of performance for these subsystems will be summarised. The chapter will include a description of simple sampling applications, for signal acquisition, in a variety of practical situations. ...