"One week's work on Analog Electronics" - Basic amplification circuit

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One 、 Triode amplifier circuit

The following figure shows the common emitter amplifier circuit ：

R8 The voltage value at both ends is inversely related to the input signal , The simulation diagram is as follows ：

1. Saturation distortion and cutoff distortion

The ratio of the output voltage signal to the input voltage signal is about 250, By amplifying the waveform, it can be seen that the second half period of the output signal waveform is truncated .
Why is the output signal truncated ？ Because the input signal is too large Saturation distortion .
This problem can be solved by increasing the input resistance .

The input resistance is too high , If set to 2M, The first half of the output signal will be distorted , Cut off distortion , As shown below ：

2. Static working point

Q The value is the static work point , The corresponding resistance value can be obtained , The relationship between static work points and variables .

Two 、 Improvement of amplifying circuit

Partial voltage bias circuit

A rise in temperature ,Q Value moves towards saturation , The output signal may have saturation distortion ; The temperature drops ,Q The value moves to the end area , The output signal may be distorted .
Therefore, the above circuit is improved ,

Adding resistance to the circuit R9 and R10, At this time, the static operating point has nothing to do with the triode , Not affected by temperature .（ In essence, there is a negative current feedback relationship between input and output ）.

1、 change R10 Parameters can change the magnification of the circuit .
2、 The emitter stage capacitor has the function of increasing the amplification factor of the output stage , There will be power consumption when the resistance is introduced into the emitter circuit , At this time, adding capacitors will reduce power consumption for AC power .

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