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Class A, Class C, Class D, Class B, Class AB, Class F, Class E, Class G,…
Class A
- Amplifier device remains active for the entire time & use the complete input signal
- Better high frequency and feedback loop stability
- High power loss: emit heat and requires higher heat sink space
- High distortion and noise: power supply and the bias construction need the careful component selection to avoid unwanted noise and minimize the distortion
- Efficiency only 25%~30% (very poor), not more than 45%~50%
- Only suitable for low signal or low power level amplification purpose
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Class C
- Differently from other amplifier classes, it works in 2 different operating modes
- The efficiency of class C is much more than A, B, AB, typically 60~70%
(Maximum 80% efficiency can be achieved in radio frequency related operation)
- It uses less than 180 degree conduction angle
- Untuned mode: amplifier also gives huge distortion across the output
- Tuned mode (Clamper): the circuit clamps the output bias level with the average output voltage equal to the supply voltage
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Class D
- A switching amplifier which uses PWM
- It is the highest power efficient amplifier class in the A, B, C and D segment
- It has smaller dissipation
- It is a widely used topology in digital audio players or controlling the motors as well.
- It is not a perfect choice as it has bandwidth limitations in few cases depending on the low pass filter and converter module capabilities
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Class B
- Two active devices which get biased one by one during the positive and negative half cycle of sinusoidal wave
- It provides more than 60% efficiency theoretically, not more than 78%
- The heat dissipation is minimized in this class providing a low heat sink space
- Limitation: the cross over distortion
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Class AB
- It has the same configuration with 2 active devices, but each device does not leave the conduction immediately after completing the half of the sinusoidal waveform
- Diode need to be chosen with the exact same rating and placed as close as possible to the output device
- Sometimes, designers tens to add small value resistor to provide stable quiescent current across the device to minimize the distortion across the output
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Class F
- It is a high impedance amplifier in respect of the harmonics.
- It can be driven using square wave or sine wave
- For the sinusoidal wave input, this amplifier can be tuned using an inductor and can be used to increase the gain
Class E
- Highly efficiency power amplifier which uses switching topologies and works in radio frequencies
- A single pole switching element and the tunes reactive network is the main component to use with the class E amplifier
Class G
- use rail switching to decrease the power consumption and to improve efficiency performance
- Class H is the further improved version of class G
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