I. What are the types of feedback circuits?
The main functions of feedback circuits include: improving system stability, increasing system dynamic range, improving system static characteristics, and improving system filtering characteristics.
The characteristics of feedback circuits include: improving system stability, increasing the dynamic range of the system, improving the static characteristics of the system, and improving the filtering characteristics of the system.
Feedback circuits can be divided into four basic types: forward series, forward parallel, reverse series, and reverse parallel feedback. A detailed description follows:
Positive series feedback: A portion of the output signal is added to the input terminal through a series circuit, thereby amplifying the input signal and increasing the amplification factor of the circuit. This feedback method is rarely used in amplifiers.
Positive parallel feedback: A portion of the output signal is added to the input terminal through a parallel circuit, reducing the input signal and thus lowering the circuit's amplification factor. This feedback method is often used in circuits that correct the frequency response.
Inverting series feedback: A portion of the output signal is inverted by an inverter and then connected in series to the input, canceling out the input signal and thus reducing the circuit's amplification factor. This feedback method is commonly used in amplifiers to improve their linearity and stability.
Reverse parallel feedback: A portion of the output signal is inverted by an inverter and then connected in parallel to the input terminal to cancel out the input signal, thereby increasing the input impedance of the circuit. This feedback method is commonly used in circuits such as voltage followers and current followers.
II. How to determine the positive and negative terminals of a feedback circuit
The determination of a feedback circuit can be considered from the relationship between the input and output signals. Generally speaking, if the output signal of a circuit has a feedback effect on the input signal, then the circuit is a feedback circuit. The specific determination method is as follows:
There is a connection between the input signal and the output signal: If the input signal and the output signal are connected together through a capacitor, inductor, or the output port of an amplifier, then this is a feedback circuit.
There is control between the input and output signals: If the output signal has a controlling effect on the input signal of the amplifier, then this is a feedback circuit. For example, the output signal can be fed back to the input of the amplifier through a resistor network or transformer, thereby controlling the magnitude or phase of the input signal.
The output signal is fed back to the amplifier's input: If the output signal is fed back to the amplifier's input, then this is a feedback circuit. Depending on the feedback method, feedback circuits can be divided into positive feedback and negative feedback circuits.
