Explain the different classes of the power amplifiers (Class-A, Class-B, Class-AB and Class-C) and mention where the Q-point is for each one. Also mention about their applications.

· In your own words, explain the different classes of the power amplifiers (Class-A, Class-B, Class-AB and Class-C) and mention where the Q-point is for each one. Also mention about their applications.

class A – Class A amplifiers operate in the linear region for the entire input cycle and consist of both large and small signal amplifiers as long as they operate within this region. Since this class operates with linear conduction this means that the output is proportion to the variation of the input. The maximum Q point for a Class A amplifier is at the center of the ac load line. Class A amplifiers can be used in audio circuits, displays, and tv receivers. 

Class B – A Class B amplifier operates for half of the input cycle and is in cut off for the other half, in other words the amplifier operates in the positive swing of the sine wave of cycle. The Q-point for a class B amplifier is at cut off. Some applications for Class B amplifiers are PA systems and audio power amplifiers.

Class AB- The class AB amplifier operates very similar to the class B. The difference between the two is that the class AB amplifier's biasing is adjusted to overcome distortion which is when the transistors aren't conducting. This process allows small conduction even when no input signal is present. Applications include instrumentation and automotive audio.

Class C – This class of amplifier is the most efficient due to the amount of output that can be obtained. This class of amplifier is nonlinear because the output is not a replica of the input. These amplifiers are used in oscillators and modulators.

 

· What is the difference between a 200W stereo amplifier and a 100 W stereo amplifier in dB?

A doubling of power requires it to be 3db different.

· What is dBm? Where is it commonly used?

dBm is decibels per milliwatt. A common application would be in fiber optical communication. 

· A utility company is interested in purchasing a Public Address system (audio frequencies). Because the company works near high-voltage power lines, where 60Hz interference is common, they have requested that the PA system be designed to minimize pickup from the power lines. What would be the best way to minimize this interference?

I would recommend incorporating a high pass filter. I would set the cut off frequency to be above 60Hz.

References:

Understanding Amplifier Operating “Classes” | Electronic Design

Links to an external site.

Don Tuite March 21, 2012

Floyd, T. L. (2017).  Electronic Devices (Conventional Current Version) (10th ed.). Pearson Education (US).  https://ecpi.vitalsource.com/books/9780134414553