---
tags: [circuits]
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# Digital circuits

Ultimately every process in a computer is the product of a digital
[circuit](Circuits.md) that is
working on binary values. In contrast to electrical circuits, digital circuits
are not represented in an
[analogue](Analogue_and_digital.md) fashion.

Analogue circuits work on the basis of real continuous phenomena in the world:
charges and currents. As a result, the key properties of a circuit - voltage,
current and resistance - can vary over a wide range of values. This is the
reason that we require components like batteries and resistors: to control the
natural flow of current and ensure that it only runs within desired parameters.

In a standard electrical circuit, voltage, current and resistance can vary over
a wide range of values however in the binary context we want to deal with
discrete values (zeros and ones) which can be fed into the various
[logic gates](Logic_gates.md).

We therefore need a way to represent 'on' and 'off' as single quantities. We do
this by stipulating that a given voltage corresponds to 'on' (high) and another
corresponds to 'off' (low). Of course these are not really discrete values since
voltage is inherently analogue but we basically binary-encode them. Formally
'on' has a voltage of 1 and 'off' has a voltage of 0. In reality 'on' tends to
be within 2-5V depending on the circuit design and anything between 0 - 0.8V is
considered off.

The [transistor](Transistors.md) is
the electrical component that enables us to represent given voltage ranges as
being 'on' or 'off'.