Urgently seeking research on the stability of the amplifier's static operating point

jolux

Urgently seeking research on the stability of the amplifier's static operating point [Copy link]

This is the topic of my bachelor's thesis. I am working on it now. I have also looked up relevant information. But I still don't quite understand how to start. The textbooks don't cover this topic very much. It can't meet the 10,000-word thesis requirement. I have a rough outline here: the first part briefly introduces the amplifier's static operating point. The second part explains the importance of static operating point stability. The third part talks about the causes of static operating point instability. The fourth part is how to solve the problem of static operating point instability and introduces several classic circuits.
This is my initial plan, which is not very complete. Can anyone give me some suggestions or supplements? Thank you! !

fighting

Go and read the relevant papers to help you

ldigc

Can you be more specific? What are the requirements?

god

This is too much, right? I am most afraid of writing something like this

fighting

http://www.solw.cn/Index.htmlGo and have a look

duantonglei

Stop writing. I can't write.

weigaole

2. Understanding and adjustment methods of static operating point: 1. Understanding of static operating point Students who have just come into contact with analog circuit experiment class are not very clear about the purpose and function of adjusting the static operating point. Quite a few students even start the small signal amplification experiment without adjusting the static operating point. Therefore, it is necessary to explain to students why the static operating point of the single-stage amplifier should be adjusted? How to adjust the static operating point? So that they can fully understand and understand the reason. The purpose of adjusting the static operating point is to enable the three-stage tube to amplify the signal within a certain AC signal input range under normal working conditions, so that there is no saturation distortion or cutoff distortion at the output end of the amplifier. To achieve this goal, we introduce the concept of static operating point. The four basic elements that constitute the static operating point are: the base current Ib of the transistor, the collector current Ic, the be junction voltage Ube, and the tube voltage drop Uce. These four basic elements are also called the static operating point Q of the amplifier circuit. So how to adjust the static operating point and get the maximum undistorted output voltage Uo? In other words, how to adjust the static operating point Q to the middle of the AC load line? The usual practice is: connect the circuit, turn on the power, use the oscilloscope probe to observe the output waveform UO, gradually increase the amplitude of the input signal Vi, until the positive and negative half cycles of the output waveform are distorted at the same time, otherwise the upper bias potentiometer RW must be repeatedly adjusted to meet this requirement. After determining the static operating point, the corresponding Ib, Vbe, Vrc, Vre, Vce and Ic are also determined. For this reason, it is necessary for students to understand what DC parameters will change due to the change of DC current IB. If IB↑→IC↑(IC=βIB)→VRC↑、VRE↑(IC(RC+RE)→VCE↓(the sum of Vrc, Vce, Vre is equal to VCC). 2. Factors affecting the static operating point: Fluctuations in the power supply voltage will cause changes in the parameters of components in the bias circuit, such as resistance, transistor aging, etc. The temperature change has a relatively large impact on the operating point Q. This is more prominent and obvious for the Vbe and β of silicon tubes. When the temperature rises to a certain level, the output characteristic curve of the transistor will become wider and move upward, and the β value will increase. Under its influence, the static operating point Q moves upward, and saturation distortion is likely to occur, that is, negative half-cycle distortion occurs at the output Uo. The countermeasures and methods adopted are: ⑴. Use a voltage divider bias circuit. ⑵. Use temperature compensation devices, such as diodes and thermistors with negative temperature coefficients. ⑶. Connect a DC negative feedback resistor with appropriate resistance in series with the emitter. For the voltage divider bias circuit, Vb is clamped (voltage remains unchanged), T↑→β↑→Ic↑→Vre↑(Ic≈Ie*Re)→Vbe↓(Vbe=Vb-Vre)→Ic↓, thus controlling the continued increase of Ic. 3. The relationship between the changes of RC and RL and certain circuit parameters: From the output characteristics of the crystal triode, it can be seen that when RC and RL are determined, the DC and AC load lines on its output characteristic curve are also determined. The slope of its DC load line is -1/RC; the slope of the AC load line is -1/(RC//RL); Av=-(Rc//RL)/hie, it is obvious that: ⑴. If β and hie are constants, the change of the resistance value of Rc and RL will inevitably cause the change of the amplification factor AV; ⑵. If the resistance values of RC and RL change, the slope of the DC load line (-1/RC) and the slope of the AC load line (-1/(RC//RL)) will inevitably change. For example, when other parameters remain unchanged, when RC changes from 5.1K to 2K, its magnification decreases; at the same time, its slope becomes steeper, and the original Q point will inevitably produce a horizontal displacement to the right. At this time, IB has not changed, and the Q point will not produce a vertical displacement. ⑶. Due to the change of RC, the slopes of the AC and DC load lines have changed. In summary, the change of RC causes changes in three parameters, namely the magnification, the slopes of the AC and DC load lines. ⑷. The change of RL causes changes in two parameters, namely the magnification and the slope of the AC load line. There is no effect on the DC parameters! When RL=∞, the slope of the AC load line is equal to the slope of the DC load line. 4. Phase relationship between input and output In addition, it was found in the teaching experiment that many students often do not know what kind of distortion is the waveform distortion in the upper half or lower half of the output, and how to adjust the working point. We know that there is a phase difference π between the input and output of the odd-numbered amplifier. If the waveform is found to be distorted in the upper half of the output, it means that the signal appears at the bottom of the amplifier input, and the bottom distortion indicates that the working point Q is low, that is, the base current is small. In order to change this situation, the base current Ib should be increased to move the working point Q upward, so that the negative half-cycle waveform at the output end exits the cutoff area; then increasing IB will reduce the resistance of the upper bias potentiometer RW, so that the negative half-cycle waveform exits the cutoff area and enters the amplification area. When adjusting the resistance of the upper bias potentiometer RW, use an oscilloscope to observe the output UO waveform, and it is easy to know how to adjust the rotation direction of the potentiometer. On the contrary, increase the resistance of the upper bias potentiometer RW. Original URL: http://eelab.gzhu.edu.cn/syzx/bbs/topic.asp?l_id=4&t_id=168 Guangzhou University Electrical and Electronic Experiment Center is a good start.

analogstudy

The above post talks about the setting of the static operating point of the two-stage circuit, which is very good! However, the above description is not applicable to CMOS.