Let us discuss. Report errors. Categorize the power efficiency of each class of amplifier, from worst to best. Which operation class is generally used in radio or communications? In a class AB amplifier, if the V BE drops are not matched to the diode drops or if the diodes are not in thermal equilibrium with the transistors, this can result in A.
Answer: Option D Explanation: No answer description available for this question. Also, due to high linearity, Class A amplifier provides distortion and noises.
The power supply and the bias construction need careful component selection to avoid unwanted noise and to minimize the distortion. Because of high power loss in Class A amplifier, it emits heat and requires higher heat sink space. The Class B amplifier is a bit different from the Class A. It is created using two active devices which conduct half of the actual cycle , ie degrees of the cycle.
Two devices provide combined current drive for the load. In the above image, an Ideal Class B amplifier configuration has been shown. It consists two active devices which get biased one by one during the positive and negative half cycle of sinusoidal wave and thus the signal gets pushed or pulled to the amplified level from both positive and negative side and combine the result we get complete cycle across the output.
We can see each device input and output signal graph in the below image. The heat dissipation is minimized in this class providing a low heat sink space. But, this class also have limitation. A very profound limitation of this class is the crossover distortion.
As two devices provides each half of the sinusoidal waves which are combined and joined across the output, there is a mismatch cross over in the region, where two halves are combined. This is because when one device complete the half cycle, the other one needs to provide the same power almost at the same time when other one finish the job. It is difficult to fix this error in class A amplifier as during the active device the other device remains completely inactive. The error provides a distortion in the output signal.
Due to this limitation, it is a major fail for precision audio amplifier application. An alternate approach to overcome the cross-over distortion, is to use the AB amplifier. Same as class B, it has the same configuration with two active devices which conducts during half of the cycles individually but each device biased differently so they do not get completely OFF during the unusable moment crossover moment. Each device does not leave the conduction immediately after completing the half of the sinusoidal waveform, instead they conduct a small amount of input on another half cycle.
Using this biasing technique, the crossover mismatch during the dead zone is dramatically reduced. But in this configuration, efficiency is reduced as the linearity of the devices is compromised. The efficiency remains more than the efficiency of typical Class A amplifier but it is less than the Class B amplifier system. Also, the diodes need to be carefully chosen with the exact same rating and need to be placed as close as possible to the output device.
In some circuit construction, designers tend to add small value resistor to provide stable quiescent current across the device to minimize the distortion across the output. Class C amplifier is tuned amplifier which works in two different operating modes, tuned or untuned. Class C amplifiers are more efficient than class A, class B or class AB, which means that more output power can be obtained from class C operation. The output amplitude is a nonlinear function of the input, so class C amplifiers are not used for linear amplification.
They are generally used in radio frequency RF applications, such as oscillators that have a constant output amplitude, and modulators, where a high-frequency signal is controlled by a low-frequency signal.
0コメント