AMPLIFICATION TYPES EXPLAINED
What Is Class-D Amplification?
When the signal is instantaneously higher in level than the triangle wave, the output goes positive. When the signal is instantaneously lower in level than the triangle wave, the output goes negative. The result is a chain of pulses where the pulse width is proportional to the instantaneous signal level. Magically simple! We call it 'pulse width modulation', or PWM. And that's all there is to it. You now understand how a Class-D amplifier works, and if anyone tries to pull the wool over your eyes and convince you that the 'D' stands for 'digital', you can tell them how wrong they are, with confidence. Class-D is not digital.
A class A amplifier is a linear power amplifier that uses a single switching transistor to amplify high-frequency signals with minimal distortion. The transistor is always on, even when there's no input signal, which means it's constantly running at full power and generating heat. This results in low efficiency, usually around 25%, as 75% of the amplifier's power is converted to heat.
Class B amplifiers are those in which the output transistors only conduct during half (180 degrees) of the signal waveform. To amplify the entire signal, two transistors are used: one conducting for positive output signals and the other conducting for negative outputs.
A Class AB amplifier is a push-pull amplifier that combines the best features of Class A and Class B amplifiers:
Class A: Good signal reproduction, but less efficient
Class B: More efficient, but more distortion
Class AB amplifiers are considered a good compromise for amplifiers because music signals are often quiet enough to stay in the "class-A" region, where it is amplified with good fidelity. When the signal passes out of this region, it is large enough that the distortion products typical of class B are relatively small.
Class G amplification is a type of amplifier design that's a modification of other amplifier classes, typically Class AB or Class B, to make them more efficient and reduce power dissipation. Class G amplifiers are similar to Class AB amplifiers, but they use multiple supply voltages instead of just one. When the signal level is low, the amplifier uses a lower voltage, but as the signal level increases, it automatically switches to the appropriate voltage. This technique, called "rail switching", allows the amplifier to use the maximum supply voltage only when needed, which increases efficiency and reduces power consumption.
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