Linear Amplification of Transistor Signal

In this case, the C pole current is β times that of the B pole current. Take the triode amplifier circuit as an example:
(1) The problem of DC operating point, why is there a DC operating point? What causes the working point to be unstable? What measures are taken to stabilize the DC operating point?
Taking the NPN tube as an example, the DC of the three circuits of common emitter, common base and common collector are all in the same direction. Regardless of the connection method of the triode circuit, their DC current direction is the same. After adding a weak AC small signal to the input (emitter junction), it can only disturb the output loop current, and generally cannot change the direction of these currents. However, there is a disturbance signal in the output loop current that is affected by the input AC signal. What we want is this disturbance signal (output AC signal). This disturbance signal is larger than the input signal. This is amplification. It can also be said that amplification is actually is the output loop current controlled by the input signal.
If the DC operating point is set properly, the disturbance signal is proportional to the input AC small signal, and is larger than the input signal. This is what we want.
(2) For AC signal amplification, what are the functions, advantages and disadvantages of common emitter, common collector and common base circuits? How to overcome the nonlinearity of the circuit? Why common emitter – common base circuit can expand the frequency band? Why should the common collector amplifier circuit be placed in the last stage of the multi-stage amplifier circuit? What are the requirements for the input stage of a multi-stage amplifier circuit? What is the purpose of people designing current sources in integrated circuits? What does it do? How to overcome the zero drift caused by direct coupling? Why should it be designed as deep negative feedback? What are its advantages and problems? What is the reason for deep negative feedback self-excitation? What is the structural phase shift of a circuit? What is the additive phase shift of the circuit? Under what circumstances does an additional phase shift appear between the output signal of the circuit and the input signal? etc.
(3) Integrated operational amplifier, in order to overcome the non-linear problem of semiconductor devices (the amplification factor of different amplitude signals is different), people deliberately made a high-gain integrated operational amplifier, and two external resistors constitute the in-phase or Reverse proportional amplification circuit, at this time, the voltage magnification of the whole circuit is approximately irrelevant to the semiconductor characteristics (under the condition of deep negative feedback), the magnification is only related to the two external resistors, and the temperature characteristics of the resistance material are better than that of the semiconductor material , and the linearity is also improved. Pay attention to the use of “virtual short” and “virtual break” when calculating. It is too simple to learn analog electronics here. Therefore, if you do not consider the cost, who would use an amplifier circuit composed of triode discrete components? DC operating point. There are many other applications of integrated operational amplifiers, such as active filters, signal generation circuits, etc.

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