The basic amplifier circuit of the common emission configuration is that the input signal is added between the base and the emitter, and the coupling capacitors C1 and Ce are regarded as short circuits to the AC signal. The output signal is taken out from the collector to the ground, and the DC amount is separated by the coupling capacitor C2, and only the AC signal is added to the load resistance RL. The common emission configuration of the amplifying circuit actually means that the transistors in the amplifying circuit are in a common emission configuration.
When the input signal is zero, the DC power supply provides DC base current and DC collector current for the triode through each bias resistor, and a certain DC voltage is formed between the three poles of the triode. Due to the DC blocking effect of the coupling capacitor, the DC voltage cannot reach the input and output terminals of the amplifier circuit.
When the input AC signal is applied to the emitter junction of the triode through the coupling capacitors C1 and Ce, the voltage on the emitter junction becomes the superposition of AC and DC. The signal situation in the amplifying circuit is more complicated. The symbols of each signal are specified as follows: due to the current amplification effect of the triode, ic is several times larger than ib. Generally speaking, as long as the circuit parameters are set properly, the output voltage can be much higher than the input voltage. times. A part of the AC quantity in the uCE reaches the load resistance through the coupling capacitor to form the output voltage. Complete the amplification of the circuit.
It can be seen that the DC signal of the collector of the triode in the amplifier circuit does not change with the input signal, but the AC signal changes with the input signal. During the amplification process, the collector AC signal is superimposed on the DC signal, and through the coupling capacitor, only the AC signal is extracted from the output. Therefore, when analyzing the amplifier circuit, the method of separating the AC and DC signals can be used, which can be divided into DC paths and AC paths for analysis.