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Science and Technology^189

FIND OUT MORE. Computers 190 • Electronics 188

A microchip is an electronic device built as a single unit

from many miniature components, mainly transistors.

It is plugged into a socket on a printed circuit board to

connect it to other components.

WHAT IS BINARY CODE?

Digital microchips send and receive digital electronic

signals in binary code. All information is represented

by on/off signals. These signals are processed by the

transistors on microchips. When a switch is on, it is

the digit 1; when it is off, it is the digit 0. The binary

code for the letter “a” on a keyboard is 01100001.

WHAT DO MICROCHIPS DO?

Each kind of microchip performs a different task, and

is identified by a code number. Some microchips work

with analogue signals (A microchip with code 741 is

an analogue amplifier). Others work with digital

signals – to act as. LOGIC GATES, or to get

digital sound from a CD.

A logic gate is a digital circuit that makes a simple decision.

Logic gates include AND, OR, NOT, NOR, and NAND gates. Logic

gate circuits can be made with individual transistors, or formed

on microchips.

HOW ARE MICROCHIPS MADE?

Microchips are made by building up electronic circuits

in a tiny wafer (slice) of pure silicon in a complicated

layer-by-layer process. The different circuit

components are producing by doping (treating) areas

of the silicon with different chemicals.

HOW ARE LOGIC GATES USED?

You can link logic gates to make complex decisions,

or perform difficult calculations. For example, a

washing machine will only start when a programme

has been selected AND the door is closed AND the

water supply is on.

Microchips

4 SILICON WAFER

Hundreds of identical copies of a microchip

are made on a slice of pure silicon. The

circuits are tested and faulty units rejected.

Those that work are linked by gold wires to

pins and sealed in their capsules (cases).

LOGIC GATES

INPUT A INPUT B OUTPUT

0 0 0

1 0 0

0 1 0

1 1 1

INPUT A INPUT B OUTPUT

0 0 0

1 0 1

0 1 1

1 1 1

LOGIC GATES 3

A logic gate may have one or two

inputs, and an output. Whether

the output is on (1) or off (0)

depends on the state of the

inputs according to the logic

set out in the tables.

CIRCUIT BOARDS 1

These technicians are checking

the quality of circuit boards

before final assembly. Individual

microchips are linked on circuit

boards to form electronic devices,

such as computers.

4 CERAMIC CAPSULE

A microchip is encased in an

insulating capsule. This capsule

has a transparent cover – the

chip is inside. It is a charged-

coupled device (CCD) used to take

images in digital cameras.

1 THE “AND” GATE

This has two inputs, A and B. If both inputs are

on, then the output is on.

1 THE “OR” GATE

The output of this gate is on when either input A,

or input B, or both, are on.

1 THE “NOT” GATE

This gate has only one input. The

output is on when the input is not on.

INPUT OUTPUT

0 1

1 0

Metal pins

plug into a

socket on a

circuit board

A single CCD

is a grid of a

million or more

transistors

A B

INPUT

A B

INPUT

OUTPUT OUTPUT OUTPUT

INPUT

microchips