TABLE OF CONTENTS Outside the restricted world of digital computation, the majority of industrial, commercial and scientific microelectronic applications involve some analogue signals at input(s) and/or output(s). The analogue input signals may be converted into digital signals entirely within specific transducers (sensors), and therefore from the OEM point of view may not be regarded as mixed-signal designs, the OEM designer accepting such items as self-contained off-the-shelf components with digital outputs. Similarly, it may be possible to have self-contained output components to translate appropriate digital output signals directly into some analogue output display or other facility.
We will not, therefore, be concerned here with systems which use separate self-contained analogue to digital sensors and digital to analogue output devices; such systems have full accessibility of the digital interfaces, and testing can therefore be a digital-only test of the circuit design, plus an overall functional system test as appropriate. Instead we will here consider the more complex situation where there may be some analogue signal processing, some A-to-D and D-to-A conversion and/or some signal processing, the whole representing some fairly large design of VLSI complexity.
Figure 8.1 illustrates the possible complexity that may be encountered. In many situations the analogue processing may not be as complex as indicated here, all the required processing being done in the digital domain. However, any filtering may involve operational amplifiers, and hence there may not be a simple A-to-D conversion from the analogue input(s) directly to the digital logic core in all cases.
