Feedback circuit of transistor amplifier 1

The so-called feedback refers to taking a portion of the output signal from the amplifier and sending it back to the input terminal through a certain method, as shown in Figure 5-51 (a). diode There are two types of feedback: positive feedback and negative feedback. If the signal returned from the output of the amplifier has the same phase as the input signal, that is to say, when the original input signal is a positive half cycle, the signal returned is also a positive half cycle, further enhancing the input signal,diode as shown in Figure 5-51 (b.). This feedback is called positive feedback. If the signal sent back is in phase opposite to the original input signal, that is to say, when the original input signal is positive for half a cycle, the signal sent back is negative for half a cycle, weakening the input signal, as shown in Figure 5-51 (...). This type of feedback is called negative feedback.diode
The positive feedback circuit can enhance the input signal of the amplifier, so the output signal will also increase, so the positive feedback device can increase the gain of the amplifier. Regenerative radio is a type of radio that incorporates positive feedback into high or medium amplifier circuits, resulting in improved sensitivity and selectivity of the radio. However, positive feedback can increase the distortion and noise of the amplifier,diode  narrow the passband, and deteriorate stability. If the feedback amount is too large, it can also cause self-excited oscillation and howling, affecting the normal operation of the amplifier. In short, although positive feedback can improve amplifier gain, it reduces the quality of the amplifier.diode