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Small Signal Amplifiers
Small Signal Amplifiers are also known as Voltage Amplifiers.
Voltage Amplifiers have 3 main properties, Input Resistance, Output Resistance and Gain.
The Gain of a small signal amplifier is the amount by which the amplifier “Amplifies” the input signal.
Gain is a ratio of output divided by input, therefore it has no units but is given the symbol (A) with the most common types of transistor gain being, Voltage Gain (Av), Current Gain (Ai) and Power Gain (Ap)
The power Gain of the amplifier can also be expressed in Decibels or simply dB.
In order to amplify all of the input signal distortion free in a Class A type amplifier, DC Base Biasing is required.
DC Bias sets the Q-point of the amplifier half way along the load line.
This DC Base biasing means that the amplifier consumes power even if there is no input signal present.
The transistor amplifier is non-linear and an incorrect bias setting will produce large amounts of distortion to the output waveform.
Too large an input signal will produce large amounts of distortion due to clipping, which is also a form of amplitude distortion.
Incorrect positioning of the Q-point on the load line will produce either Saturation Clipping or Cut-off Clipping.
The Common Emitter Amplifier configuration is the most common form of all the general purpose voltage amplifier circuit using a Bipolar Junction Transistor.
The Common Source Amplifier configuration is the most common form of all the general purpose voltage amplifier circuit using a Junction Field Effect Transistor.
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