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What is an Amplifier?

  Think of a public address (PA) system, where a person speaks into a microphone and whose speech is amplified by the PA system and heard by the audience, Figure 1.

  

Figure 1: PA system.

Ideally, distortion should be minimized, so the amplifier's outputs should be a magnified copy of the the speaker's voice.

The amount of amplification is determined by the gain, A. Mathematically, this means

 

v_out = A v_in . (1)

This relationship between amplifier input and output can be described by a block diagram, Figure 2.  

  

Figure 2: Amplifier block diagram.

Example. Suppose the gain A=10, and we input a pure tone $v_{in}=2 \sin (1,000 t) \ V$ of amplitude 2V and frequency $\omega = 1,000$ rad/sec.

Then the output is $v_{out}=20 \sin (1,000 t) \ V$, with amplitude 2V and frequency $\omega = 1,000$ rad/sec, Figure 3.

  

Figure 3: Amplifier input and output waveforms.

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