Base bootstrap circuit analysis (b)

In order to reduce the shunt effect of the bias resistor Rh on the base. use.
    1. The circuit shown in Figure 8-10 is completed.
Qiu and capacitor c are added to this circuit . This circuit is called "base bootstrap circuit ". For the convenience of analysis, its AC equivalent
circuit is drawn as shown in Figure 10(a) as shown in Figure (b). In the figure, Rb = ruler bl∥Rt;e, «=RL∥Re. It can be seen from the figure that the capacitor C feeds back all the output voltage Vo to
R (RH, rolling). When C is large enough, the common point Ao of Biao is "=K. According to the following characteristics of the emitter follower , vo=
V. Therefore Vi= VA. This conclusion is the key to this circuit. It shows that the two ends of the resistor (i.e., between
points ) are approximately at the same potential for the AC signal, so the input signal current flows through Nao≈00 We know that for the signal
source, only when the AC equivalent impedance of ‰ is close to infinity, there will be fⅪ≈o. It can be seen that
after adding Biao and C, the shunting effect of the bias circuit becomes It is greatly reduced, that is, the input impedance R of the circuit is increased.