Amplifier nonlinear distortion research device

topic:

1.  Design a transistor amplifier circuit. The designed analog circuit can generate one or all of the above three waveforms ;

2  The designed circuit can be produced by adjusting no more than 2 components; 

3  Improvement: Other functions will explain themselves

Award information: Second Prize

Team member information: Liu Zhanzhi and Hu Bo

Instructor: Li Xin

Circuit principle description

The picture above is the experimental circuit diagram of a resistor-divided working point stable single-tube amplifier. Its bias circuit uses a voltage divider circuit composed of R _W and R _B2 and R _{B1 , and a} resistor RE is connected to the emitter to stabilize the static operating point of the amplifier. When the input signal U _i is added to the input end of the amplifier , an output signal U ₀ with an opposite phase to U _i and an amplified amplitude can be obtained at the output end of the amplifier , thus realizing voltage amplification.

Measurement of static operating points

To measure the static operating point of the amplifier, it should be carried out when the input signal U _i =0 , that is, the input terminal of the amplifier is short-circuited to the ground terminal, and then a digital multimeter with a suitable range is selected to measure the collector current I _C of the transistor and each electrode. The potentials U _B , U _C and U _E with respect to the ground . In general experiments, in order to avoid disconnecting the collector, the method of measuring the voltage and then calculating I _C is used. For example, as long as UE _is measured , I _C. can be calculated _.

Debugging at static operating points

The debugging of the amplifier's static operating point refers to the adjustment and testing of the triode collector current I _C (or U _{CE ).}

Whether the static operating point is appropriate has a great impact on the amplifier's performance and output waveform. If the operating point is too high, the amplifier will easily produce saturation distortion after adding an AC signal. At this time, the negative half-cycle _of uO will be cut off. If the operating point is low, it will easily produce cut-off distortion, that is, the positive half-cycle _of uO will be cut off. None of these situations meet the requirements for distortion-free amplification. Therefore, after selecting the operating point, dynamic debugging must be performed, that is, adding a certain u _i to the input end of the amplifier to check whether the size and waveform of the output voltage u _O meet the requirements. If it is not satisfied, the position of the static working point should be adjusted.

Changing circuit parameters will cause changes in the static operating point, but the method of adjusting the bias resistor is usually used to change the static operating point.

Finally, it should be noted that the "high" or "low" operating point mentioned above is not absolute. It should be relative to the amplitude of the signal. If the signal amplitude is very small, even if the operating point is higher or lower, it will not be absolute. Distortion does not necessarily occur. So to be precise, waveform distortion is caused by improper coordination between signal amplitude and static operating point settings. If larger signal requirements must be met, the static operating point should be as close to the midpoint of the AC load line as possible.