Classifications of Amplifiers
October 28, 2007
A device using small amount of energy to control large amount of energy is known as electronic amplifier and it is often used for audio applications. A transfer function of an amplifier is a relationship of input to the output of an amplifier expressed as input frequency. Its magnitude is termed as gain.
There are different classes of amplifiers. For example, A Class D audio amplifier is fundamentally a switching amplifier or PWM amplifier.
Various classes of amplifiers
"A" class amplifier always has bias current flowing in the output device. It is linear and has the least distortion in topology, but has the least efficient at about 20%. It is not a complementary with high or low side output devices.
"B" class amplifiers are totally different from A class amplifiers and for this the output device conducts for half the sinusoidal cycle. It is 50% more efficient than A class, but has some issue with linearity at the crossover point due to time it takes to turn one device on and the other off.
”AB” class amplifiers are a combination of the A and B classes which is at present one of the common types of power amplifiers in subsistence. Both devices are allowed to conduct at the same time with a little amount of modification near the crossover point. The device conducts more than half a cycle which the inherent non-linearity of B class overcomes with the inefficiencies of an A class. It has 50% efficiency.
"D" class amplifiers is a PWM amplifier which has switches either fully on or off, it significantly reduces the power losses in the output devices with the possible efficiencies of 90 to 95%. To modulate a PWM carrier signal, it uses audio signal to drive the output devices.
All these classified amplifiers are termed as linear amplifiers, in linear amplifiers signals always remain in the analogue domain. The output transistors act as linear regulators to modulate the output voltage. The efficiency is reduced when a voltage drops across the output devices. D class amplifiers have many forms, some with digital inputs and some with analogue inputs. So try to have amplifiers with analogue inputs.
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