Circuits & schematics

Electronics guide

Electronics guide

If you take a close look at an electronic process — any electronic process — you will always find some part of it which is automatic. By this, I mean that some mechanism is established which controls the process to some extent without human involvement.

Electronic control can be based on either of the two electronics principles we’ve already mentioned: analogue circuits, or digital circuits. In the last chapter we saw how analogue circuits can be built into integrated circuits. This chapter concentrates on the use of integrated circuits which contain digital circuits — which we call digital integrated circuits.

As we’ve already seen, integrated circuits (whether analogue or digital) are comprised of transistors — lots of ’em. So it’s to the transistor that we first turn to in this chapter’s look at digital integrated circuits.

When we first considered transistors, we saw that they can operate in only one of two modes: analogue (sometimes, mistakenly called linear) where the transistor operates over a restricted portion of its characteristic curve, and digital (where the transistor merely acts as a electronic switch — which can be either on or off).

It should be no surprise to learn that analogue ICs contain transistors operating in analogue mode, while digital ICs contain transistors operating in switching mode. Just occasionally, ICs contain both analogue and digital circuits, but these are usually labelled digital anyway.

Figure 10.1 shows a transistor switch which shows the general operating principles. It’s a single device, with an input at point A, and a resultant output at point B. How does it work? Well, we need to mull over a few terms first, before we can show this.

Figure 10.1 A simple transistor used as a switch, to form a simple digital circuit

• Logically speaking
• Every picture tells a story
• Other logic circuits
• Boolean algebra
• Other logic gates
• Simple, eh?
• That ol’ black magic!
• The Boolean Way — It’s Logical!