Amplifier
An electronic amplifier, amplifier,
or amp is an electronic device that increases the power of
asignal.
It does this by taking energy from a power
supply and controlling
the output to match the input signal shape but with a
larger amplitude.
In this sense, an amplifier modulates the output of the power supply.
Numerous types of electronic amplifiers are
specialized to various applications. An amplifier can refer to
anything from an electrical
circuit that uses a
single active
component, to a complete
system such as a packaged audio hi-fi amplifier.
Amplifiers are described according to their
input and output properties. They have some kind of gain,
or multiplication factor that relates the magnitude of the output
signal to the input signal. The gain may be specified as the ratio of
output voltage to
input voltage (voltage
gain), output power to input
power (power
gain), or some combination
of current, voltage, and power. In many cases, with input and output
in the same unit, gain is unitless (though often expressed
in decibels).
For others this is not necessarily so. For example,
a transconductance
amplifier has a gain
with units of conductance .The
power gain of an amplifier depends on the source and
load impedances used
as well as its voltage gain; while an RF amplifier
may have its impedances optimized for power transfer, audio and
instrumentation amplifiers are normally employed with amplifier input
and output impedances optimized for least loading and highest
quality. So an amplifier that is said to have a gain of 20 dB
might have a voltage gain of ten times and an available power gain of
much more than 20 dB (100 times power ratio), yet be delivering
a much lower power gain if, for example, the input is a 600 ohm
microphone and the output is a 47 kilohm power amplifier's input
socket.
In most cases an amplifier should be linear;
that is, the gain should be constant for any combination of input and
output signal. If the gain is not constant, e.g., by clipping the
output signal at the limits of its capabilities, the output signal is
distorted. There are however cases where variable
gain is useful.
There are many types of electronic amplifiers,
commonly used
in radio and television transmitters and receivers, high-fidelity ("hi-fi")
stereo equipment, microcomputers and other electronic digital
equipment, and guitar and
other instrument
amplifiers. Critical
components include active
devices, such as vacuum
tubes or transistors.
A brief introduction to the many types of electronic amplifier
follows.
Computer
A computer is a general purpose
device that can be programmed to
carry out a finite set of arithmetic or logical operations. Since a
sequence of operations can be readily changed, the computer can solve
more than one kind of problem.
Conventionally, a computer consists of at
least one processing element, typically a central
processing unit (CPU)
and some form ofmemory.
The processing element carries out arithmetic and logic operations,
and a sequencing and control unit that can change the order of
operations based on stored information. Peripheral devices allow
information to be retrieved from an external source, and the result
of operations saved and retrieved.
The first electronic digital computers
were developed between 1940 and 1945 in the United Kingdom and United
States. Originally they were the size of a large room, consuming as
much power as several hundred modern personal
computers (PCs). In
this mechanical analog
computers were used for
military applications.
