Introduction to Amplifiers
An amplifier is a circuit which increases the strength of a
weak signal. The amplifier of the input signal is generally very small of some
micro volts to several volts. Amplifiers that are dealing with input voltage of
very small magnitudes will operate only in the linear portion of the transistor
characteristics. Such a type of amplifiers are called signal amplifiers. Small
signal amplifiers may operate in the range of audio frequencies, radio
frequencies, video frequencies or at ultra-high frequencies.
The gain obtained from a single transistor amplifier stage is
usually inadequate for most of the applications, hence several stages are
connected in cascade. The resulting system that a practical amplifier is always
a multistage amplifier. A practical amplifier always consists of a number of
stages that amplify a weak signal until sufficient power is available to
operate a loudspeaker or other output devices. The first few stages in the
multistage amplifier have the function only voltage amplification. However the
last stage is designed to provide maximum power. Therefor the final stage is
power amplifier.
In some applications, feedback technique is used to alter
some of the properties like gain, bandwidth, input and output impedances of the
amplifier. The amplifier which employs the feedback technique is known as feedback
amplifiers. An operational amplifier is basically a direct coupled high
gain amplifier with feedback, available in form of integrated circuit.
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