Working principle of oscillator

When the delay element is connected to the input and output of the positive feedback amplifier, the output can change back and forth.

The stability of the oscillation period depends on the stability of the natural oscillation frequency of the delay component.

For example, in the distant past, sinusoidal oscillation could be caused by mercury delay, serial register and spring delay.

At present, the common RC delay link has insufficient delay at low frequency, so it needs three sections in series to produce a large phase delay.

Timing crystal is a stable delay element.

If the input-output transfer function of the amplifier is linear, then the delay element can also transmit sinusoidal signals linearly, and with the perfect control of initial shock and amplitude stability, stable sinusoidal oscillation output can be produced, which is the most difficult; If the control is not good, the same circuit may produce triangular wave oscillation output and square wave oscillation output.

If the voltage comparator and Schmidt voltage comparator are connected in series in the delay link, triangular wave oscillation output and square wave oscillation output will be generated, such as the common LM555 integrated circuit and the oscillation circuit generated by NAND gate.

The square wave oscillation output is the easiest. When the oscillation frequency is fixed, a low-pass filter composed of capacitors turns a square wave into a sine wave. When the oscillation frequency changes, the variable digital filter can be used for dynamic filtering.

Undergraduate evaluation expert, although the above explanation is not rigorous, is it still popular?

Rectification requirements:

First of all, immediately cancel all kinds of non-reusable publicity banners in schools. The superior checks the actual teaching level. Seeing these disposable publicity materials, you will know that you are wasting social resources and have no practical significance for improving your teaching quality. Schools that focus on state investment should pay special attention to correcting these wrong behaviors.

Private schools are too extravagant and wasteful to be condemned by the public.

There is no direct and inevitable connection between the teaching quality and the huge spray-painted banners on the external walls of large buildings, banners hanging on campus roads, large-scale spray-painted publicity columns in colleges and grass-roots teaching departments, and related printed materials in a manual. Doesn't it hurt to see such a large-scale waste of social resources?

The nozzle of this printer is not made in China.

Hundreds of square meters of grass-roots teaching institutions, spent 400 thousand decoration. After repeated revisions, the cost increased by 200,000 yuan. A 5-meter by 3-meter agency introduction plaque was set up, which cost 6,543,800 yuan. In order to meet the evaluation, it cost 6.5438+0 million. Who will cover the cost?

Advocate all kinds of reusable and rewriteable propaganda methods. Electronic newspaper is an innovative display technology, which should be applied and reported to the party and the people with its engineering ability.

Electronic display screen is a mature technology and should not be bought from the market. Schools should compile their own programs and students should complete them themselves. All drawings, procedures, etc. All of them are archived in the school, and students can check them for free, which provides a platform for future maintenance.

Vigorously compress, reduce and replace hard-copy teaching and research files that cannot be rewritten on paper, protect the environment, save expenses, reduce the establishment of management personnel, and effectively use the teaching building area.

Modern digital photographic equipment is cheap and the text recognition software is perfect, so it should be given priority. The use of traditional photocopiers should be reduced, especially the A3 format copy price is too high, which is 10 times higher than the A4 format unit area price ratio, and students and teachers are not allowed to retrieve materials with limited value at will. Is such a high cost worth building for evaluation?

Establish a mass storage hard disk system, and encourage bid evaluation experts to consult all kinds of related materials remotely. Modern visiting methods do not use receptionists, are not discovered by the inspected units, have a large number of visits, can truly reflect the actual level, do not interfere with the normal teaching and scientific research activities of the school, do not need police cars to clear the way, do not need to block roads, and oppose skimming inspection.

Encourage experts to check the classroom teaching situation through Internet video, and ask questions suddenly, so that the inspected units are caught off guard.

For the damaged part of the net bag behind the seat of the vehicle that receives the experts, it should be darned and darned.

Teaching materials and experimental devices for high-frequency power amplifiers are imported from * * * *. The experience of * * is that it is difficult to produce decent output after groping for several experimental classes during undergraduate study. As soon as the output waveform comes out, the power tube in 3DG 12 will burn.

Therefore, during the Cultural Revolution, * * * successfully copied the electron tube radio station according to foreign lines. The experience of * * * is that in the electron tube high-frequency amplifier, even though the electron tube itself consumes a lot of power, the nickel plate on the screen burns red (commonly known as screen red), and it still works normally, and * * * was also very good at it at that time; However, solid-state high-frequency amplifiers-transistors and semiconductor high-frequency power amplifiers-have low efficiency when the power tube has a large excess power, which inexplicably burns out the power tube.

Even domestic military radio stations with foreign lines and imported cermet high-frequency power tubes have similar problems.

The existing textbooks and professional books at home and abroad have no specific solutions, and the relevant contents are the same. Now everything from security walkie-talkies to people's mobile phones, as well as hot-fried wireless tag high-frequency read-write cards, military communication stations and RF power chips are imported, and others will not tell you their theory and technical know-how.

A variety of semiconductor high-frequency power amplifier teaching devices designed and manufactured by myself have been applied to students' practical teaching practice, and the above problems have been completely solved in the devices (the principle, design and debugging methods are not introduced). Since * * * years ago, I made up my mind to use a computer, so I can't make these handwritten materials public in the form of electronic documents (the computer I am using now is personal). The teaching device of high-frequency power amplifier designed and manufactured by ourselves, in order to be intuitive and avoid damaging the magnetic core when students adjust, tries to use ceramic skeleton instead of closed coil. The manufacturers of this ceramic skeleton are: No.999 Factory and No.897 Factory of the former Fourth Machinery Department (Ministry of Radio Industry) in Jingdezhen, Jiangxi. While 1000 to more than 2000, the volume of the packaging container is 40cm×40cm×80cm. These ceramic skeletons were destroyed by * * * *, and the rest were destroyed by * * * *, and their direct economic value exceeded the number of * * *.

The core significance of my above work is that there are various accurate test methods, and the parameters and working conditions of the circuit can be tested and adjusted by common instruments according to the prescribed steps, and the test is orderly, measurable and comparable in graphics. However, the popular saying that the distribution parameters of high-frequency circuits are complex and the performance of high-frequency circuits depends on the structure and shape is not really reflected.

At present, the popular circuit simulation software and integrated circuit design software can not truly reflect the working state of the actual circuit, especially the simulation under the condition of high frequency and high speed. Only with the correct basis of circuit testing and adjustment can we make the best RF integrated circuit by changing the layout of integrated circuits and semiconductor technology.

I hope someone can turn these handwritten materials into electronic documents for free.

In the 2007 National Electronic Design Competition for College Students, I instructed the contestants to adopt wireless transmitting and receiving circuits with discrete components. And nearby players, under the guidance of * * * *, all used imported wireless modules, all of which were eliminated.

I design mechanical and electrical products independently in * * *, and sell them all over the country. At that time, my colleagues all knew that I could explain the basis of a design from many aspects, especially why I did it, specific details, strong language expression ability in engineering technology, rigorous conception, precise manual technology and * * *.

More than 20 years ago, I broke the way teachers taught by the book. Instead, students randomly ask questions and then solve them together. Because I don't usually have working conditions in the laboratory, I will give a comprehensive answer.

* * * students like to answer questions on the spot in experimental classes and when writing graduation thesis. I can solve the problem at once. Most of my unprepared questions can be answered accurately with rapid fire. This is the position in charge of education and a unique ability, which has aroused * * * *. I made this exquisite teaching equipment at my own expense and gave it away for free.

For example, when he was in undergraduate experiments, he always burned triodes, and other * * * made fun of him and humiliated him. When I passed by, I lectured the two students orally and found out the reason on the spot. All the students have started. The circuit of the experiment was selected and downloaded from the Internet by themselves. I didn't know beforehand that their circuit structure was correct. The problem lies in their cognitive ability and debugging skills, and there is no relevant content in books and online.

This is the ability to accurately grasp and inspire students (tí hú guàn dǐng), so that students can understand the classroom content thoroughly and have a high level. Even the explanation of a basic concept will open your eyes and make you suddenly enlightened.

As far as * * * is concerned, no one has the most basic ability to design a diode circuit, and no one did in the past; For laymen, it is mistaken for exaggeration, but for truly capable people, there are no more than 10 small components, which are used in low noise, low power consumption, switching state, low current switch, high current switch, high speed switch, low speed switch, high frequency small signal, high frequency, high efficiency and high power, high power supply voltage, low power supply voltage, AC coupling, DC multistage coupling, etc. In fact, gain and noise level are related to many trade-offs. I'm good at this. As soon as the students asked questions, my answers were endless, eloquent and tired, which was scarce at that time. And in * * *

Starting from the fundamental interests of the country, from * * * to * * *, I went to the student dormitory and wandered around the laboratory for a long time, giving students free counseling. For example, you can do a survey on * * *. His experience is that before graduation, he really realized that he didn't have the ability to solve practical problems. He was looking forward to having relevant books, but he couldn't find them online or in the library. I stipulate that you can't ask political questions except pure math questions. I answered most of his questions on the road and in the dormitory for several months, and made specific explanations in writing on the spot.

For another example, * * *, when he is doing the challenge cup experiment, he will not * * *. When he was ready to give up, I gave guidance three times a day in the morning, middle and evening during the holiday that year, and he achieved the expected goal without specific hands-on operation. When I was given 600 yuan, I also gave a topic, provided hardware, and urged him to complete the application of image processing. Under the background of * * * *, I instructed him to write the patent application documents, and I applied for the relevant invention patents at my own expense, and now I have entered the substantive examination stage. Because of his small writing mistakes, I made corrections according to the examiner's requirements.

From * * * to * * *, I have been working without * * *, overcoming insurmountable man-made obstacles, working silently, being serious and responsible, being the most practical and having the best endurance. My spirit has not been destroyed. I am stubborn, tenacious and persevering. I have bought basic maintenance equipment for a long time, which is the embodiment of loyalty to education.

Let me give you a few examples; I have inspected the use of * * * experimental devices produced by * * in various schools, and the results are generally not good. At the same time of hardware modification, I also instructed the experimenters in the communication laboratory of * * University to demonstrate the correct waveform synchronization method on the spot. In fact, the same is true of the basic experiment of digital circuits. Only by refitting or making oscilloscopes can the effect of waveform synchronization be improved.

For ordinary digital circuit and logic circuit experiments, the level amplitude can basically deflect the cathode ray tube directly without amplification, and a self-made teaching device should be made together with the oscilloscope.

The experience of digital circuit teaching practice, especially the experience of modern communication teaching, is that the synchronous operation of eye diagram observation should be supported by an independently designed hardware synchronous circuit.

For frame synchronization signal, the synchronization of analog modulation and digital modulation of various frames is its concrete embodiment.

In modern communication, the synchronization effect of modulation process and demodulation process directly affects students' perceptual knowledge of modern communication principles; However, the phase, delay and channel conditions between modulation and demodulation are uncertain parameters. In order to accurately show their logical relationship under synchronous conditions, they must be designed and manufactured by themselves. At present, there are no ready-made products that can be used directly, right?

Moreover, all the design data, debugging experience, component data, assembly drawings, waveform diagrams, purchasing and processing locations, methods, processes, prices, etc. should be provided to students in electronic format to provide them with an outstanding platform.

One teaching method is that the values of the main components of the circuit can be changed linearly independently, instead of clicking and pulling with the mouse. For example, in the exam, we should be able to calculate the relevant values according to the predicted direction, and calculate them with formulas, which can change the shape and verification of the eye diagram. The textbooks of Massachusetts Institute of Technology have been published online. Only by passing the exam can they be skilled in system integration, instead of challenging their masters from the bottom.

One way to test the quality of teachers' teaching is to use the existing textbooks outside the classroom and laboratory to give questions. Can you tell me the maximum and minimum range of this component? Is there a calculation basis?

A consensus at home and abroad is that in the world-leading research, there must be unique, top-class and self-made instruments and equipment; Relying on the existing commercial instruments in the market, we can't distance ourselves from our competitors. Behind the scientific and technological level of advanced countries is the support of advanced experimental equipment.

At present, teachers in most colleges and universities in China do not have the ability to manufacture commodity instruments that are superior to the market. As soon as the plan for purchasing instruments came out, suppliers from all walks of life flocked to it, and it was really cool to be worshipped. At the same time, he is overbearing and arrogant, and there is * * *.

No matter what degree teachers come to teach, they buy experimental devices in the market and copy the textbooks provided by suppliers as handouts.

One of the criteria for undergraduate evaluation is the self-made rate of teaching instruments, the design drawings of teaching instruments, the working principle, the integrity and openness of test data, the advanced technology compared with existing commercial instruments, and the intuitive teaching. My homemade instrument is reliable, maintainable, testable and supportable.

An assessment standard for teachers and laboratory personnel is to be able to maintain the comprehensive logistics capabilities of the laboratory such as water supply, drainage, power supply, furniture, doors and windows, lighting and locks. Now teachers call maintenance workers for a little thing, which consumes a lot of social resources. This little thing can't be done, let alone designing and making teaching instruments. Do I need an electrician's license to change the lights? Is it easy to get a certificate? It's easy to specialize in many things.

Education in China should always serve proletarian politics, combine with productive labor, focus on political and economic construction, and attach importance to the fundamental interests of the country.

Here, * * * puts forward several minor rectification tasks:

The bases of various detachable roadblocks on campus have been changed into built-in and all-stainless steel structures. For example, standard parts of stainless steel internal expansion screws can be used. Now that the synthetic diamond drill sleeve has been popularized and standardized, it is not difficult to design and manufacture such a lock. For many years, the base of the detachable barricade on campus is higher than the ground and made of carbon steel, which has insufficient strength. After being crushed and disintegrated by a motor vehicle, it is repaired repeatedly. The appearance is crooked and rusty, and the cost has already exceeded the all-stainless steel structure. The common expansion screws for floor paving have short service life and low strength, and cannot be reused.

Some pedestals are hollow. Don't want children's feet, pets' embroidered legs, and ladies' high heels break as soon as they step in?

* * * can test the loyalty of the Ministry of Education to the motherland.

* * * * Lead paint is often painted, which pollutes the campus environment and needs to be redesigned.

Computers owned by colleges and universities are state property and cannot be specially allocated to contract workers to play games; The interior of the teaching building is a teaching place, so it can't be provided free of charge to contractors to collect the recyclables they collect; Contractors who are not members of the school police force are not allowed to stay in the teaching building, especially when they live together, especially when the room is messy and the curtains are untidy. What's wrong with colleges and universities? The collection and treatment of waste office supplies, paper and other saleable materials in the teaching and research building are contracted by students, and the school police force manages the entry and exit of recyclable materials in each building, and individuals are not allowed to illegally occupy them; The sending and receiving of documents in each teaching department and the cleaning of the office are all handled by the staff in the department, which is their own work. Indeed, because of the shortage of manpower, it should be contracted by students and retirees, and a large number of service contract workers should be recruited. This is a manifestation of corruption.

The contractor who stayed in the building cooked in the power distribution room, called rats into the power distribution cabinet, which caused an explosion and interrupted the power supply of the whole building.

At present, the impact noise from the door closers in the family area and teaching area of the university is loud enough, and those senior scholars who often pay public funds to visit abroad turn a blind eye. Where is the high academic position in the field of control and manufacturing?

Dozens of graduate students have graduated with wireless tags as their graduation thesis topics, and the cumulative number will soon exceed 50. Then, for the management of motor vehicles and bicycles entering and leaving the campus, parking in the campus can be charged automatically. Can you use the corresponding equipment? This can only reflect your application level of the thick film circuit designed by yourself. There is no requirement for volume here. It is really unnecessary to spend 3 million yuan to build an iron fence.

Visiting abroad, receiving domestic leaders, foreign dignitaries and scholars at home and abroad, the method of demonstrating strength should not be papers, certificates and purchased experimental instruments; Instead of giving away all kinds of handicrafts and monographs, we use independent innovation devices with small size, precise structure, design and research, and no precedent in the world to reflect the style of independent innovation through image display.

I often win the first prize in college student competitions at home and abroad, which is an achievement. The following example is a procurement standard market standard parts. One-dimensional bar code printing recognition is used as the system integration of innovative laboratory undergraduate evaluation of outstanding works, which attracts experts from XXX to visit in turn as the promotion of XXX, so the previous results are questionable.

It is easy to introduce visiting professors and hire scholars with international status and influence. However, people's working conditions require you to import large-scale, sophisticated and state-of-the-art instruments and equip them with full-time personnel. We don't lack such masters. What are the value-added benefits of high-tech achievements based on others?

Politicians who spend a lot of money to hire overseas retirees and Nobel Prize winners are introducing diplomatic language. People are arranging global business activities through specialized companies. What they say is the past tense. Can you specifically guide your global innovation?

China needs a master who gropes at the grassroots level like Yuan Longping. As the same person, he can improve the technical index of mass spectrometer, maintain inertial instruments and equipment, personally operate the equipment from traditional machine tools to CNC machining centers, and complete gas shielded welding.

What China needs most is to make international leading devices with domestic metal materials, domestic components and domestic equipment, and openly introduce every detail. The "fast food" of science and technology, engineering, commerce and management, and the pursuit of immediate economic and academic achievements are all timely works, which are the basic daily necessities of the vast majority of China people. Education is the hoop of China's bucket and the basic material of the puzzle. XX, primary and secondary schools, colleges and universities are the only fields that start from the energy base.

In the era of Mao Zedong, it is still progressive to oppose behind closed doors and combine application. While importing equipment, reagents and documents from developed countries, while consuming a lot of national resources to write papers, we must also complete the above minimum requirements in basic education.

The current system in China is correct. In fact, a considerable part of the undercurrent comes from hostile forces abroad. Without firm patriotic belief and rigorous scientific attitude and principles, the result of XXX will inevitably destroy the foundation of China.

While the whole society advocates and publicizes the pursuit of wealth, there should be a substantive, open and free detailed introduction to the details of teaching and engineering in the environment of popular science books and vocational education.

It is a good achievement to hire foreign teachers to teach students who have obtained foreign standard system certificates; Can't we set a new global standard and lead foreign countries to produce goods that adopt this standard?

Combat scientific and technological innovation.

The cheap and fast-growing trees planted on campus in the past can't grow now, because they are fragile and the branches will break from time to time, which is quite scary. In order to safely cut down trees with this diameter around buildings and sidewalks, it costs 2000 yuan a day to rent cranes, and it costs 1 000 yuan a day to rent professionals and chain saws.

This kind of tree has poor variety, poor maintenance and low survival rate, so it can be pushed back; But educators can't do this. When they first received education, they were not ready. For most people, it is impossible to improve after making up lessons. Those who are recruited can't be easily dismissed.

For those commodities made of imported chips, military telemetry vehicles made of low-grade camera monitoring ptz, military coded locks, and laser communicators made of product optical instruments, colleges and universities are not places to make these ordinary commodities, but also recruit a large number of social workers to work in teaching buildings and open companies outside the school. Radio transmission has no viability in the modern battlefield, and even FM stations are living targets. In colleges and universities, it is a place to do spread spectrum transceiver from the foundation and track and lock the laser emission in the mobile state.