“We will use many transistor amplifier circuits in our studies and life, but maybe many people are stupid and confused about the type of amplifier. For example, the author is such a person. Today, I will make a brief summary of them.
We will use many transistor amplifier circuits in our studies and life, but maybe many people are stupid and confused about the type of amplifier. For example, the author is such a person. Today, I will make a brief summary of them.
(1) Among the three types of amplifiers, the common emitter amplifier is the most widely used. It is used in various frequency amplification systems and is the preferred circuit for signal amplification.
(2) The common collector amplifier is mainly used for isolation in the amplifier system due to its large input impedance and low output impedance. The mutual influence between the pre-stage circuit and the post-stage circuit of the amplifier is minimized.
(3) The common base amplifier has excellent high frequency characteristics, so it is mainly used in circuits with relatively high operating frequencies.
By judging by the transistor connection, you can know its amplification type and characteristics
(1) The principle of judging what type of amplifier the transistor is connected to is: the amplifier has an input loop and an output loop, each loop needs to have two pins, while the transistor has only three pins, one pin must be shared by input and output For example, a common emitter is a common emitter amplifier.
(2) The judgment method is: the ground wire of the amplifier is the common reference point in the circuit. Therefore, this pin of the triode should be AC grounded. As long as you see which pin of the triode is AC grounded, you can know what type of amplifier it is.
1. The method of judging the common emitter amplifier
The circuit is shown in the figure:
In the circuit shown in the figure, the emitter of Q1 is directly grounded, and the emitter of Q2 is grounded through a capacitor C3. Because the capacity of C3 is large, the capacitive reactance for AC signals is small and it is a path, so it is equivalent to the emitter for AC signals. It is grounded, so this is a common emitter amplifier.
It can be seen from the circuit that the base and collector of the triode are not grounded, and the input signal is input from the base to the ground to the triode. The output of the input signal from the collector of the triode to the ground is simply said to be from the collector. Electrode output.
2. The method of judging the common collector amplifier
The circuit is shown in the figure
Basic judgment methods for 3 types of amplifiers based on analog technology
The collector is connected to the DC power supply +V. For AC, the +V terminal is equivalently grounded (C1 connects the +V terminal to AC ground), so the collector of the triode is grounded, which is a common collector amplifier. The AC signal is input from the base (input between the base and ground), and the signal is output from the emitter (output between the emitter and the ground). No bypass capacitor can be connected between the emitter and the ground, otherwise the amplifier will be AC short-circuited and no signal will be output.
Judging the common base amplifier method
The base is AC grounded through the bypass capacitor C2, so that the base is shared, so this is a common base amplifier. The AC signal is input from the emitter (input between the emitter and the ground), and output from the collector (output between the collector and the ground).