Amplifier

Definition

An electrical or electronic amplifier is a circuit that uses an external power supply to generate an output signal that is a larger replica of its input.

An audio amplifier (an easily recognizable application) is used to increase the volume of a speaker’s voice so they can be heard more easily in large areas. While voltage is the most commonly amplified type of input signal, amplifiers can also be designed to increase current. An amplifier that increases output current drive is called a power amplifier.

Most amplifiers perform linear amplification, but some are logarithmic in nature. In a circuit diagram, an amplifier is usually represented by a triangle.

The formula for a voltage amplifier with Gain A is:

V_out = A * V_in

Amplifiers are classified by linearity and efficiency. A class A amplifier is the most linear (but least efficient) type of amplifier. Other common amplifier classes include B, AB, C, and D in order of decreasing linearity and increasing efficiency.

Apart from high gain an electronic amplifier circuit should have the following characteristics:

• Very high input resistance (ideally infinite)
• Very low output resistance (ideally zero)
• Very little delay (ideally none)

Amplification can be done relative to ground (single-ended) or relative to another terminal (differential). The "operational amplifier," commonly referred to as an op-amp is a special type of differential amplifier which has extremely high (theoretically infinite) gain. This allows it to be used in a negative feedback configuration with other electronic components (resistors, capacitors, inductors) to perform mathematical operations (hence ‘operational’). Apart from amplification, the op-amp can be configured to perform attenuation (lower output voltage), addition, subtraction, differentiation and integration.