Assignment 2 – Amplifier types and functions
Task 1
In this task I will successfully explain the operation of the Class A amplifier and the Class B amplifier.
Class A
3086100488950Firstly the Class A amplifier is the most common and simplest form of power amplifier that uses a transistor in the standard common emitter circuit configuration. The transistor is always biased ON so that it conducts during one complete cycle of the input signal waveform. This means then that the Class A Amplifier arrangement is ideal because there can be no crossover or switch-off distortion to the output waveform even during the negative half of the cycle.
It uses a single transistor for its output stage with the resistive load connected directly to the collector terminal. When the transistor switches ON (around 0.6v – 0.7v) it pulls the output current through the collector resulting in a voltage drop across the emitter resistance which will limit the negative output. The efficiency of this type of circuit is very low and delivers small power outputs for a large drain on the DC power supply.
Class B
2990850690880Also called the push pull amplifier, this arrangement is usually considered as an upgraded version of the Class A amplifier. The class B amplifier reduces the wasted power (heat) which in turn increases the power efficiency of the earlier Class A amp. The reason they are called “push – pull” amplifiers is because instead of having just one transistor there are two, one being the NPN type and the other being the PNP type. In this situation both transistors are receiving the same signal in, but in opposite phase to each other, which amplifies differently. For the first transistor this inverts the signal and only amplifies the positive half cycle. For the second transistor the inverts the signal and will only amplify the negative half cycle. Both transistors meet again at the output putting the output signal back together forming a fully amplified 360 degree sine wave.
One of the disadvantages of the Class B amplifier is that it can be quite expensive to construct from design because of the transformers which are centre tapped and balanced. Getting around this is quite easy by building a transformerless circuit which uses pairs of power transistors instead.
Task 2
For this task I will explain the different effects of feedback on the function of an amplifier with respects to its gain, impedance, noise and distortion
Feedback can be itemised into two separate headings, either positive or negative. Positive feedback is mainly used