The simplest kind of electronics, known as analogue
electronics, works with continuous signals – a smoothly rising and
falling sound wave goes through an analogue circuit as a smoothly rising and
falling voltage. Digital electronics works differently. Using SAMPLING, it converts signals into strings of numbers that can be
processed mathematically by electronic circuits.
ANALOGUE – SIMPLE BUT RISKY
The wiggly grooves of a record mimic the shape of the original sound wave. The
pick-up produces an electrical wave the same shape as the wiggles.
Unfortunately, it copies faithfully everything it finds on the disc – so
scratches come out as noisy clicks.
Before a signal can be handled by digital electronics, it
has to be converted into digital form. In sampling, circuits called
analogue-to-digital converters make thousands of measurements of the signal
each second. The measurements are then converted into binary form, which is a
way of writing numbers with just two digits – ideal for on–off
electronic switches.
The numbers from the sampled sound wave are handled in binary
code, which uses only two digits – 1 and 0. In electronics, the
corresponding code is “on” and “off”. Samples in
this form can be sent as pulses. On a CD, samples use a complex
error-correcting code to make the CD more resistant to scratches.
Sampling is not limited to sound. It is used to convert the
picture in a camera phone into digital form. The picture is sliced into
thousands of tiny square samples, called pixels. A small computer inside the
phone works on the samples to produce a simplified picture, which can be sent
to someone else more quickly than the original picture. Their phone changes the
samples back into a picture again.
Pocket calculators would not be possible without digital
electronics. They handle numbers as electrical signals that are either on or
off. This is because they do their maths with transistors – electronic
switches that, like other switches, can only turn on or off. Numbers in this
form can easily be processed by the calculator’s LOGIC CIRCUITS to produce the right result.
Computers function by breaking big problems down into
thousands of smaller ones. They then solve these little problems one by one
until the job is done. All the actual work is done by logic gates –
circuits that obey the rules of logic. Each logic gate obeys a single, simple
rule, such as saying that C is true only if A and B are true. With enough
gates, computers can solve any problem that is strictly logical. Most of the
millions of transistors at the heart of a computer are in logic gates.
The large, complex chips in digital circuits are often supported
by smaller logic chips. Each of these devices contains only a few logic gates.
The gates are made from transistors and resistors formed on the surface of
silicon.
Logic signals turn on (1) and off (0) to signal true and false.
Gates have any number of inputs, but only one output. An inverter always has
one input. Here are two examples of logic gates.
The output turns on only if all of the inputs are on. It turns
off if any of them are off.
The output turns on if any of the inputs are on. It turns off
only if all of them are off.
The output turns on only if the input is off. It turns off only
if the input is on.
BIOGRAPHY: GOTTFRIED LEIBNIZ German, 1646-1716
A binary system was known in ancient China, but mathematician
Gottfried Leibniz wrote about it in 1703. He was, however, mainly interested in
its philosophical meaning because, before computers, it was not of much
practical use. Leibniz was also one of the inventors of calculus, a branch of
mathematics that is very important in science.
