Page 40 - Basics of Electrical, Electronic and Communication

Chapter 12

Amplifiers and Oscillators

12.1 Principle of electronic amplifiers

Amplification means making things bigger. In the context of electron-
ics, it is the process of increasing the amplitude of signals. The func-
tional block that accomplishes the task of signal amplification is called
amplifier. Here, the term amplifier usually describes an electronic am-
plifier, in which the input signal is usually a voltage or a current.
There are both passive and active amplifiers. Example for passive
amplifier is a step-up transformer. If an alternating voltage signal is
applied at the input, a larger voltage signal will be available at the
output. The power delivered to a load will be always less than the
power absorbed at the input. Thus a transformer may provide voltage
amplification but it cannot provide power amplification. Even though
several passive amplifiers exist there, the most important and useful
electronic amplifiers are active amplifiers.
A widely used symbol for an amplifier is shown in figure 12.1.
Here V i is the input voltage, V o is the output voltage and A v represents
voltage gain which is the ratio of the output voltage to input voltage.
The active amplifiers take power from an external energy source
and use it to boost the input signal. Thus it delivers an output signal
whose waveform corresponds to the input signal but its power level is
higher.

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