Science & Technology in Action

4th Edition

Digital Electronics


The principles of digital electronics are summarised in this lesson. The approach is intended to encourage students to build some of the basic circuits in order to understand the operation of logic gates in IC format.
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Contains the full lesson along with a supporting toolkit, including teachers’ notes.

Lesson excerpt

Intel was founded in 1968 and initially its main product was memory ‘chips’. In 1971 the company launched the first commercialmicroprocessor chip while retaining its core business. From the mid 1970s home computers became more widely available – often in kit form and from the early 1980s Intel’s focus moved to microprocessors. In the 1990s Intel became the most profitable supplier to the computer industry.

What is a ‘chip’?
Chips or integrated circuits (ICs) are ‘components’ that contain electronic circuits composed of many components such as diodes, resistors and transistors. ICs are more economical to produce and are much more compact than circuits made of discrete components; they have standardised inputs and outputs and so can be linked together very flexibly. The introduction of integrated circuits in the 1960s revolutionised not only electronics but the electronic design process.

Many of the earliest ICs contained logic gates such as those described in this lesson. But first we’ll have a look at the basics. We will examine the principles behind digital electronic circuits.

A key concept is the voltage divider, an understanding of which will clarify the operation of basic digital electronic circuits such as logic gates. A voltage divider is very easy to set up; all you need is two resistors and a battery. In Fig.2 a battery is connected to two resistors in series. If the two resistors are equal then the voltage of the battery (6 V) will be divided equally; the voltage across each of the resistors will be 3 V. The same circuit is shown more schematically in Fig. 3. The voltage across R2 could be measured by attaching a voltmeter to the terminals marked V2; this is the voltage we are generally most interested in.

True or False?

  1. Integrated circuits were independently invented in 1950 by ack Kilby and Robert Noyce
  2. The introduction of integrated circuits made electronic design more difficult
  3. Logic gates are digital electronic circuits whose outputs are related in a logical way to the inputs
  4. The output of a voltage divider is either high or low
  5. A NAND gate has four possible output states
  6. Logic gates are the basic building block of digital electronic circuits
  7. If two equal resistors are used to construct a voltage divider the output voltage will be twice the input voltage
  8. Standard logic gates can be linked together to form more complex circuits
  9. Modern microprocessor chips can have over a million transistors per square millimetre
  10. Diodes, resistors and transistors are discrete electronic components