There are 4 different amplifier classes.
Class A is used in applications where the output is an amplified replica of the input signal. Class A consists of both small-signal and large signal amplifiers if operated in the linear region at all times. Class A also consists of Power Amplifiers which are a large signal type amplifier that’s objective is to distribute power to a load. These amplifiers are rated for more than 1W and needs a form of heat dissipation when used in an application. Class A
Amplifiers achieve maximum signal when q-point is center of the ac load line.
Class B is biased at cutoff, operating in the linear region for 180o of the input cycle and is in cutoff for 180o . This class of amplifiers are more efficient than class A in terms of output power to input power ratio. The class B amplifier however only conducts for the positive have of a sinusoidal waveform. An operation referred to as a push-pull consists of two Class B amplifiers working together to achieve conduction on the negative portion of the cycle.
Class AB is similar to Class B in the sense that it is more efficient than a class A amplifier. A class AB amplifier in the push-pull stage can be used to overcome crossover distortion which occurs when the dc base voltage in a class B amplifier reaches zero. When this happens neither transistor is conducting so the biasing is adjusted to overcome the VBE of the transistors.
Class C is a nonlinear amplifier, meaning that the output is not a replica of the output. The transistor is biased below cutoff with a negative VBB supply putting the Q-point outside the load line. The transistor is turned on for a short interval when the base voltage exceeds the barrier potential of the base-emitter junction while the AC source peak voltage is slightly greater than
.
- Explain what is meant by ‘TFT’ that you always find in the specs for laptop displays.
TFT stands for Thin Film Transistor and is used to enhance the operation of the LCD displays.”The thin film transistor (TFT) is a type of semiconductor device used in display technology to enhance efficiency, compactness, and cost of the product. In conjunction with its semiconductor properties, the TFT LCD is an active matrix display, controlling pixels individually and actively rather than passively, furthering the benefits of this semiconductor device.”(Orient Display, 2022).
- Discuss an application of Darlington Pair transistors.
A Darlington Pair transistor consists of two bipolar junction transistors combined to yield a high current gain. The first transistor amplifies then the second further amplifies. can consist of either two PNP transistors or two NPN transistors connected back-to-back sharing a common collector.
References:
How does TFT LCD Display Work | Orient Display
Darlington Transistor: What is it? (Darlington Pair) | Electrical4U
October 11, 2020 by Electrical4U