[Keysight Technologies Thanksgiving Month Essay Contest] How to use an oscilloscope to perform EMC spectrum analysis on waveforms

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[Keysight Technologies Thanksgiving Month Essay Contest] How to use an oscilloscope to perform EMC spectrum analysis on waveforms [Copy link]

Keysight Technologies (NYSE: KEYS) is a leading global electronic measurement company that provides you with a new measurement experience through continuous innovation in the fields of wireless, modular and software solutions. Keysight Technologies is a direct descendant of HP and Agilent, so it has world-class measurement platforms, software and consistent measurement technology to provide the most advanced measurement solutions for markets such as wireless communications, aerospace and defense, and semiconductors. The company has 9,500 employees in more than 100 countries around the world to provide customers with excellent services. Keysight Technologies' business originated from HP in the United States. It is a high-tech multinational company established by the reorganization of HP's Electronic Measurement Group into Agilent Technologies in 1999 and then spun off and listed again in 2014. Keysight Technologies (China) Co., Ltd. is a branch of Keysight Technologies in China, headquartered in Beijing, with several branches in Shanghai, Shenzhen, Guangzhou, Chengdu and other places. It currently has more than 800 employees, and its business involves electronic measurement instruments, systems and related software, software design tools and services. I first came into contact with Keysight instruments when I was in college. It was an old-fashioned HP5180A. At that time, I was doing various circuit experiments such as analog electronics, digital electronics, and high-frequency circuits. It accompanied me throughout my undergraduate studies. DSOX3024A Oscilloscope: 200 MHz, 4 channels Main features and technical indicators Observe longer and deeper signal details: Largest display in its class: 8.5-inch WVGA display Fastest update rate up to 1,000,000 waveforms/second Deepest memory: 4 Mpts (optional, 2 Mpts crossover standard) Four-in-one instrument offers more capabilities: Best-in-class oscilloscope Integrated logic timing analyzer (MSO, upgradeable via DSOX3MSO) Unique built-in 20 MHz function generator: WaveGen Unique hardware-based protocol analyzer Upgradeability: Add bandwidth, digital channels, or WaveGen after purchase Optional serial protocol analysis applications include: I2C, SPI, RS232, UART, CAN, LIN and I2S Segmented memory Mask testing When we design switching power supplies, we need to perform RF testing. So how about using the oscilloscope in your hand to conduct a preliminary assessment within the company to see if the radiation exceeds the standard? I am taking advantage of Keysight's Thanksgiving Month event to discuss some of my own experiences. First: Use an oscilloscope to view waveforms. For example, at the S pin of the MOS tube, or the reverse end of the diode, use an oscilloscope to directly measure the waveform, as shown in the figure below Analyze whether the waveform is likely to be interfered with from the waveform captured by the oscilloscope, as shown in the figure below, The rise of the waveform is very jittery and there are very narrow jumps at the top of the waveform. Then your radiation test is likely to exceed the standard at the multiple frequency of the switching frequency. At this time, the measures to be taken are to modify the absorption circuit parameters of the waveform and slow down the drive signal of the drive switch tube end. However, it should be noted that a long rise time will lead to excessive switching losses, which will cause the switch tube to heat up and the efficiency to be too low. 2. If your oscilloscope has FFT function, it will be more convenient to locate. Analyze the spectrum from the captured waveform. See the figure below. The 1Khz square wave generated inside the oscilloscope is used for FFT transformation. It can be seen that the spectrum power is the largest at 1Khz, and there is also power distribution at other multiple frequency points. The following is the waveform and FFT transformation I tested at the freewheeling diode end of a switching power supply. It can be seen that the switching frequency is around 25K, so we focus on the spectrum power at each multiple frequency point of 25K to evaluate whether there are any spectrum points with particularly large power. We set the frequency to 500Khz and the center frequency to 200K (normally it is /2 of the frequency. I set it to 200k to observe the power of the 200Khz frequency point). You can directly observe the power of this frequency point from the oscilloscope. In addition to the first 25Khz with the largest power, the third and fifth waveforms also have large amplitudes, and the third to last amplitude is also not small, so these frequencies need to be controlled when designing. Below is the waveform of the measured switch pin output and the FFT transformation result. The last figure is the power distribution of the switch waveform within the range of 5Mhz. . This content is created by EEWORLD forum user 飞扬自己. If you need to reprint or use it for commercial purposes, you must obtain the author's consent and indicate the source In 2018 Keysight Thanksgiving Month, oscilloscopes are given away for free! Scan the QR code, register once, and win prizes every day during the entire working day of March!

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If you are rectifying after testing the RF radiation exceeding the standard and getting the frequency point of exceeding the standard, then it will be more targeted. How to operate it? How to use the FFT in the oscilloscope to replace the expensive spectrum analyzer or even the EMC-specific receiver plus near-field probe? 1. If it is exceeding the standard at 350Mhz, take the switching power supply as an example. The main interference points of the switching power supply are the switching tube, the freewheeling diode, etc., which are the most serious. Of course, there are other radiation hotspots. So how to use the waveform combined with the FFT function of the oscilloscope to locate it? A. First, you can measure the switch tube S or D. Under normal working conditions, capture the waveform, perform FFT transformation, and locate the waveform near 350Mhz, that is, set the center frequency to 350Mhz and the bandwidth to about 700M, so that you can see the power distribution of the spectrum points near +/-350M. B. The second step is that since you know the frequency point of the interference point, then determine which transmission hotspot position has the frequency component of the exceeding point in the waveform, and after finding the location, take corresponding suppression measures, such as absorption, or delay, or transfer the path through which the energy flows,,,

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Feiyang self-published on 2018-2-5 16:42 If you test the RF radiation and get the frequency point that exceeds the standard, then the rectification will be more targeted. How to operate? How...

It can replace the spectrum analyzer. To use the oscilloscope to this extent, you must be an expert,,, Not bad

飞扬自我

Thank you for letting me in. Thank you for letting me in.

szy123

Learned!!! Thanks for sharing!!

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BtronXu posted on 2018-3-8 13:49 Free EMC testing and rectification plan! 13554890865

You can reply, but don't advertise, hehe

cyzz7212

I learned a lot! Thanks for sharing!