The impedance of the capacitor to the AC signal is small, which can be regarded as a channel, and the impedance to the DC signal is large, which can be regarded as an open circuit.

Since the capacitor has the function of blocking DC, the amplified output signal can be sent to the load RL through the output coupling capacitor C 2 , and the DC signal will not be added to the load RL. That is, only an AC signal can be obtained from the load RL.

1 The input signal is added to the base of the transistor V through the input coupling capacitor C 1 .

2 After the transistor V amplifies the signal, the signal output by the collector is added to the load resistor RL through the output coupling capacitor C 2 .