Subelement G: Transmitters— Topic 51: Amplifiers-1
Question 3-51G5
Element 3 (GROL)What class of amplifier is distinguished by the bias being set well beyond cutoff?
Explanation
Class C amplifiers are biased well beyond cutoff, meaning the active device conducts for significantly less than 180 degrees of the input signal cycle (typically 90-120 degrees). This highly nonlinear operation results in very high efficiency, making Class C ideal for RF power amplifiers in applications like FM or CW, where the output tank circuit can reconstruct the full sine wave from the short pulses of current.
In contrast:
* **Class A** amplifiers are biased to conduct for the entire 360-degree input cycle, offering high linearity but low efficiency.
* **Class B** amplifiers are biased exactly at cutoff, conducting for 180 degrees of the input cycle.
* **Class AB** amplifiers are biased slightly above cutoff, conducting for slightly more than 180 degrees to reduce crossover distortion while maintaining good efficiency.
Related Questions
3-51G3 Which class of amplifier has the highest linearity and least distortion?3-51G4 Which class of amplifier provides the highest efficiency?3-51G6 Which class of amplifier has an operating angle of more than 180 degrees but less than 360 degrees when driven by a sine wave signal?3-52G1 The class B amplifier output is present for what portion of the input cycle?3-52G2 What input-amplitude parameter is most valuable in evaluating the signal-handling capability of a Class A amplifier?