Current series negative feedback circuit and its identification method

Current series negative feedback circuit and identification method Negative feedback Amplifier circuit

The circuit is shown in Figure 7.8. The judgment of the feedback polarity and feedback configuration of this circuit is the same as the above method. The following only introduces the characteristics of this type of circuit:

① The output current tends to remain constant.

1. Voltage feedback and current feedback
According to the sampling method, feedback can be divided into voltage feedback and current feedback.
(1) Voltage feedback: For alternating signals, if the basic amplifier, feedback network, and load are connected in parallel at the sampling end, it is called parallel sampling, also known as voltage feedback.
(2) Current feedback: For alternating signals, if the basic amplifier, feedback network, and load are connected in series at the sampling end, it is called series sampling, also known as current feedback.
(3) Determination of current feedback and voltage feedback: If it is determined that there is feedback, it is not voltage feedback, but current feedback. Therefore, it is only necessary to determine whether it is voltage feedback or current feedback. It is usually easier to determine voltage feedback.
Determination method one - output short circuit method.
Determination method two - determination according to the drop structure.
2. Series feedback and parallel feedback
According to the comparison method, it can be divided into series feedback and parallel feedback.
(1) Series feedback: For AC signals, the signal source, basic amplifier, and feedback network are connected in series at the comparison end, which is called series feedback.
(2) Parallel feedback: For AC signals, the signal source, basic amplifier, and feedback network are connected in parallel at the comparison end, which is called parallel feedback.
(3) Determination method of series feedback and parallel feedback: For alternating components, if the output end of the signal source and the comparison end of the feedback network are connected to the same electrode of the same amplifier device, it is parallel feedback; otherwise it is series feedback.
2. DC feedback and AC feedback
3. According to the frequency of the feedback signal, it can be divided into DC feedback and AC feedback.
(1) Branch feedback: If the DC component can flow in the feedback loop, the feedback loop can generate DC feedback. DC feedback mainly acts on the static operating point.
(2) AC feedback: If the AC component can flow in the feedback loop, the feedback loop can generate AC feedback. AC feedback is mainly used to improve the performance of the amplifier; AC positive feedback is mainly used to generate oscillation.
If both the DC component and the AC component can flow in the feedback loop, the feedback loop can generate both DC feedback and AC feedback.
4. Negative feedback and positive feedback
According to the feedback polarity, it can be divided into negative feedback and positive feedback.
If the feedback signal weakens the net input signal, it is negative feedback; if the feedback signal strengthens the net input signal, it is positive feedback. Negative feedback is mostly used to improve the function of the amplification period; positive feedback is mostly used in oscillation circuits.