Common emitter amplifier circuit feedback type and function analysis
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Common emitter amplifier circuit feedback type and function analysis

Posted Date: 2024-01-24

1. What is the feedback type of common emitter amplifier circuit?

The feedback type of common emitter amplifier circuit is usually voltage negative feedback (Voltage Negative Feedback).

In a common-emitter amplifier circuit, the output signal is connected to the input signal source or input signal path through a feedback resistor to form a negative feedback loop. Negative feedback can effectively control and adjust the gain, input/output impedance, nonlinear distortion and other performance of the circuit by reversely transmitting part of the output signal back to the input terminal.

The voltage negative feedback of the common-emitter amplifier circuit is beneficial to:

1. Improve gain stability: By introducing feedback, the gain oscillation and changes of the circuit can be reduced and the stability of the system can be improved.

2. Expanded bandwidth: Negative feedback can increase the bandwidth of the common-emitter amplifier circuit, allowing it to operate normally in a higher frequency range.

3. Reduce nonlinear distortion: Voltage negative feedback can reduce the nonlinear distortion of the common emitter amplifier circuit and improve the linearity of the output signal.

4. Control the output impedance: Negative feedback can effectively reduce the output impedance of the common-emitter amplifier circuit and improve the driving capability of the circuit.


common emitter amplifier circuit

2. How to determine the positive and negative poles of common emitter amplifier circuit feedback

In a common-emitter amplifier circuit, the positive and negative poles of feedback can be determined by the following methods:

1. Observe the phase relationship between the output signal and the input signal: In a common-emitter amplifier circuit, the input signal and the output signal are usually in reverse phase (180-degree phase difference). If the output signal is in phase with the input signal, the feedback is negative feedback; if the output signal is in phase with the input signal, the feedback is positive feedback.

2. Observe how the feedback network is connected: Positive feedback and negative feedback are connected differently. In the common emitter amplifier circuit, if the feedback resistor is connected at the output end and returns to the input end, forming a closed loop, then this is negative feedback; if the feedback resistor is connected at the output end but does not return to the input end, or is connected at the input end, So this is positive feedback.

3. Observe the impact of feedback on system characteristics: Positive feedback and negative feedback will have different impacts on the system. Negative feedback can stabilize the system, increase linearity, and improve output characteristics; positive feedback can cause system instability or oscillation and increase nonlinear distortion.

The feedback type of common emitter amplifier circuit is usually voltage negative feedback, that is, the output signal returns to the input terminal through the feedback resistor. Positive feedback is rarely used in common-emitter amplifier circuits because positive feedback can easily lead to system instability and nonlinear characteristics. Therefore, common-emitter amplifier circuits generally use negative feedback to control and adjust system characteristics.

3. Types and calculations of feedback

In common-emitter amplifier circuits, there are three main types of feedback: DC feedback, AC feedback and intermodulation feedback.

1. DC feedback: DC feedback refers to the impact of the DC component generated by the input signal inside the amplifier on the output signal. DC feedback is calculated by multiplying the DC component of the input signal by the transconductance of the amplifier.

2. AC feedback: AC feedback refers to the impact of the AC component generated by the input signal inside the amplifier on the output signal. AC feedback is calculated by dividing the AC component of the input signal by the AC open-loop gain of the amplifier.

3. Intermodulation feedback: Intermodulation feedback refers to the impact of the intermodulation component of the input signal on the output signal. Intermodulation feedback is calculated by multiplying the intermodulation component of the input signal by the amplifier's intermodulation response.


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