In the previous unit we examined analog signals and the use of transducers to encode
This unit will cover digital signals, most often used by computers
and other integrated circuits to encode information.
Since most instruments today
manipulate information via digital processes, it is important to learn what it means to be
digital, and the basics regarding digital logic.
What is digital?
Say the word digit, and you think of numbers and counting.
digital world we deal with discrete integers, whole number values.
To sum up digital,
think of signals as specific values; on/off, true/false, 1/0.
A light switch is digital in
The switch is up, and the light is on.
When the switch is down, the light is off.
There isn’t a middle value with a conventional light switch.
It’s the same way with
This is completely different from analog, which could be looked at as a
The light level is not encoded as on or off, but as many variable values
between the two extremes of on and off.
You might think that you can get more detail
with an analog signal, since there are many possible values. In some sense this is correct.
Theoretically, the dimmer switch can supply many more values than the on/off switch,
but there is good reason why computers are digital in nature.
The transistor, first produced by Bell Labs in 1949, is the light switch of the electronics
world. Transistors are solid state components that can turn on or off depending on input
Each transistor acts as an on/off, or 1/0 switch, and if you put a lot of
them together, you get many more possibilities.
All of a sudden you have similar detail
from a digital device as you do from an analog equivalent, only smaller, more consistent
and much more versatile.
One of the most obvious uses of transistor technology is in
Today it’s not uncommon to find tens of millions of transistors on a
single silicon wafer 0.5 inches square.
But the beauty of a microprocessor is its ability to
You can get a computer to do just about anything, because software can
be used to reconfigure the transistors in many ways.
Most analog technology is
hardwired – it cannot learn new tricks.
In the last unit we discussed electrical quantities: voltage, current, charge, and power.
Digital signals are often electrical in nature.