Feedback circuit of transistor amplifier 3

In some specific circuits, it is often difficult to distinguish between voltage negative feedback and current negative feedback. In this case, as long as the load resistance RfZ is short circuited, even if uo=0, then check the reverse of u. If the reverse of u is also equal to zero, then this feedback is voltage feedback; diode If u is not equal to zero when uo=0, then this feedback is called current feedback. This can be clearly seen from Figure 5-53. According to the relationship between feedback signals and input signals, feedback can be divided into two types: series feedback and parallel feedback. Series feedback: If the input voltage u of the amplifier is formed by the reverse series connection of the voltage us of the signal source and the feedback voltage u, diode then this feedback is called series feedback. If the phase of u is opposite to that of us, it is called series negative feedback. Figure 5-54 shows the connection of series negative feedback. Series negative feedback reduces the current injected by the signal source, thus increasing the input impedance of the amplifier. Series negative feedback reduces the voltage amplification factor of the amplifier. Parallel feedback:diode  If the input signal of the amplifier is composed of the signal from the signal source and the feedback signal in parallel, then this feedback is called parallel feedback. Figure 5-55 shows the connection of parallel feedback. Parallel negative feedback increases the current i5 of the signal source, diode resulting in a decrease in the input impedance of the amplifier. The current amplification factor of the parallel negative feedback amplifier decreases.