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Chairman Mao warned us that the enemy of learning is self-satisfaction. To learn something seriously, one must never start complacent!
The last time the authors said that Shandong Haohan Wujiro is not right. It is the study of laser ranging on APD reverse high voltage. In fact, as long as we are serious, we will take a lot of detours.
You imagine this scenario. Generate a high voltage (approximately 5 seconds) with a voltage of about 110V in a 3.3V single-chip microcomputer system. Measure this high voltage with an oscilloscope. The vertical axis will reach 10V. Then mix the peak-to-peak voltage at about 3V in this high voltage. Sine, can you observe it for the first time? Anyway, I didn't see it for the first time in the sixth time. At the time, there was a bit of clutter on the oscilloscope at high pressure. At that time, it was only believed to be interference. It was not a serious matter. It was not serious, and it cost more than two weeks.
1 Capacitance can do a lot of things
The nature of the capacitor is the result of the charge interaction between the two sides. We usually use a capacitor, or put it near the power supply side to play a filtering role, this time it is like a reservoir, drought and flood protection; there are more widely used op amps, use its capacitive reactance (Xc = 1 / (2πfC )) Zoom in and filter. The capacitive reactance is different from the impedance, it will show the capacitive reactance of different magnitudes with the input of different frequency, this is the essence of low-pass, band-pass or high-pass filtering too. Before the production encountered a technical problem, in the circuit that has already been completed, I hope that the emitter output of the transistor can have a delay of several tens of milliseconds compared to the input of the primary level. I will say that as long as the capacitor is connected to the ground in the base level, Yes, different values ​​of the capacitance result in different lengths of delay, which is also an application of the capacitor. But now I have to say another role of the capacitor: coupling.
Let's take a look at the circuit below. APD is connected to reverse high voltage VA. As long as there is photon input, APD anode will have a certain output. The copy board saw the capacitor C at the time, but it didn't analyze its role seriously. Up to the point of study of the O point waveform, it was found that a sine wave was mixed on the high pressure side, and the frequency was also consistent with the parameters required for the mixing. It was just like Tao Yuanming's arrival at Peach Blossoms. VB as a low voltage, can not be directly mixed to the APD cathode, need to rely on this capacitor to "straight" and "coupled." Blocking is due to the infinite capacitance of the capacitor to DC (Why infinity refers to capacitive reactance formula), capacitive infinity is equivalent to a "breakpoint"; coupling is because the capacitor can pass a certain frequency signal. In this way, the photons act on the APD output and the VB signals form a mix on the APD. Understand this mixing, the basic implementation of laser ranging has slowly been demonstrated, but also let us find a key breakthrough in laser ranging; and the key to this mixing is the understanding of the role of capacitance .
Capacitor coupling circuit for APD high voltage
2 Einstein's Greatness: Wave and Particle Duality
Einstein's greatest place was that he proposed many theories or ideas. At that time, few people could understand or think of it. But many years later, with the development of science and technology, it proved its correctness. Iconicity and gravitational waves that have only recently been captured are all examples. In order to meet the requirements of the "thousand-letter words" of the published article, let me look at the duality of wave-particles.
Simply put, light has a particle nature, and you can think of it as consisting of many individual "photons"; it also has all the properties of "waves". These many single photons collectively represent waves. The application of APD is the best explanation of wave-particle duality. Under the condition of adding reverse high voltage, APD will receive a “photon†with certain signal output; after receiving a lot of photons, it will have a certain waveform output. There is a strong correlation between the output waveform and “lightâ€. In short, it is to input a certain wavelength of light waves. The result is to output a sine wave of this frequency to complete the conversion of photons to electrons. This is also “optoelectronicsâ€. The origin of the diode.
Finally, it is emphasized that the reason why laser ranging is difficult is because it contains many basic physical properties, as well as the use of principles, algorithms, and operational amplifiers above these properties, as long as one of them is not known. It is impossible to understand the entire process of laser ranging. So we hope that everyone will listen carefully to the video course and don’t care less about the efforts made from doing development to doing the courseware; of course, it’s not your tuition fees.
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