[Changshu University of Science and Technology] Amplifier Linear Research

  Design a transistor amplifier circuit. The designed analog circuit can produce no obvious distortion, top distortion and bottom distortion. This project adjusts the position of the static operating point by adjusting the sliding rheostat to study the distortion waveform.

  Saturation distortion design: When the Q point is too high, although the base dynamic current is an undistorted sine wave, the transistor enters the saturation zone during a certain period of time when the positive half cycle of the input signal approaches the peak, causing the collector dynamic current to produce top distortion. , the voltage waveform on the collector resistor will produce the same distortion. Since the output voltage is out of phase with the voltage change across the collector resistor, this causes a bottom distortion in the output waveform.

  Cutoff distortion design: When the Q point is too low, during a certain period of time when the negative half cycle of the input signal approaches the peak value, the total voltage between the transistors be is less than its turn-on voltage. At this time, the transistor is cut off, so the base current will generate a bottom distortion. Designed using the graphical method, when the static operating point of the transistor is set low, due to the superposition of input signals, part of the superimposed waveform may enter the cut-off area, thus causing cut-off distortion. The cut-off distortion of the NPN transistor common-emitter amplifier circuit is manifested as clipping at the top of the output voltage, while the cut-off distortion of the PNP transistor common-emitter amplifier circuit is bottom distortion.

  Contestants Zhao Guangting and Feng Jialu, instructor Xu Jian.