How to determine the type of negative feedback in a circuit

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How to determine the type of negative feedback in a circuit [Copy link]

Adding negative feedback to the amplifier circuit can improve many performance indicators of the amplifier, such as increasing the input impedance of the amplifier, reducing the output resistance, expanding the frequency response of the amplifier, and improving the stability of the closed-loop gain. Therefore, the current amplifier circuit generally adds various negative feedbacks according to actual needs. Since many beginners cannot judge which type of negative feedback the circuit belongs to, here we will introduce in detail how to judge the type of negative feedback. 1. Judgment of voltage negative feedback and current negative feedback When judging whether an amplifier circuit is voltage negative feedback or current negative feedback, you can see that if the feedback signal is directly drawn from the output end of the amplifier circuit, it is voltage feedback; if it is drawn from the side of the load resistor close to the ground end, it is current feedback. 2. Judgment of series negative feedback and parallel negative feedback. To determine whether an amplifier circuit is series negative feedback or parallel negative feedback, we can see that if the input signal and feedback signal are added to the amplifier's non-inverting input and inverting input respectively, it is series negative feedback; if both signals are added to the amplifier's inverting input, it is parallel negative feedback. After knowing the basic judgment method, we can take a look at what kind of negative feedback the following two circuits are. Voltage parallel negative feedback circuit. In the figure above, the resistor Rf is the feedback resistor. The output voltage Vout signal can be fed back to a part of the input terminal through this resistor. Since the feedback signal is directly drawn from the output terminal of the amplifier, this circuit is voltage negative feedback; since the input signal Vin and the feedback signal are simultaneously added to the inverting input terminal a of the amplifier, the circuit is parallel negative feedback. From the above judgment, it can be seen that this circuit is a voltage parallel negative feedback circuit. Current series negative feedback circuit. In the circuit above, Rf is the feedback resistor, and the feedback signal is drawn from the lower end of the load RL and added to the inverting input of the amplifier through Rf, so the circuit is current negative feedback; since the feedback signal is added to the inverting input of the amplifier, and the input signal Vin is added to the non-inverting input of the amplifier, it is series negative feedback. In summary, this amplifier circuit is a current series negative feedback circuit.