Amplifier Classification

Just as an amplifier is a device that provides amplification , the process is defined as an increase in AMPLITUDE. Amplitude is a term that describes the size of a signal.

In terms of a.c., amplitude usually refers to the amount of voltage or current. A 5-volt peak-to-peak a.c.signal would be larger in amplitude than a 4-volt peak-to-peak a.c. signal.

The second class is by their frequency response. In other words what frequencies are they designed to amplify?

If you describe an amplifier by these two classifications (function and frequency response) you will have a good working description of the amplifier.

You may not know what the exact circuitry is, but you will know what the amplifier does and the frequencies that it is designed to handle.

We will start out by going over Voltage and Power amplifiers.

A POWER AMPLIFIER is an amplifier in which the output signal power is greater than the input signal power. In other words, a power amplifier amplifies the power of the input signal.

Most power amplifiers are used as the final amplifier (stage of amplification) and control (or drive) the output device.

The output device could be a speaker, an indicating device, an antenna, or the heads on a tape recorder. Whatever the device, the power to make it work (or drive it) comes from the final stage of amplification which is a power amplifier.

Voltage amplifier block diagram.

The first illustration shown above is a simple block diagram of a voltage amplifier with its input and output signals and a power amplifier with its input and output signals.

Notice that in the illustration the output signal voltage islarger than the input signal voltage. Since the current values for the input and output signals are not shown, you cannot tell if there is a power gain in addition to the voltage gain.

Power amplifier block diagram.

In the second illustration the output signal voltage is less than the input signal voltage. As a voltage amplifier, this circuit has a gain of less than 1. The output power, however, is greater than the input power. Therefore, this circuit is a power amplifier.

The amplifier classification as a voltage or power amplifier is made by comparing the characteristics of the input and output signals. If the output signal is larger in voltage amplitude than the input signal, the amplifier is a voltage amplifier. If there is no voltage gain, but the output power is greater than the input power, the amplifier is a power amplifier.

(back) (top) (next) (return to amplification page)