EMC Concept (1)

EMC Concept (1)

Because the SoC is growing fast and SOP is constructed well, the system hardware engineer learns less things than before. Base on the above reason, do you want to learn more? Please come in and leave your comments. The article includes a lot of sections, so we separate the article into more chapters.

EMC stands for Electromagnetic Compatibility. It involves two parts, one is EMI and the other is EMS. It means that do not interfere to and do not be interfered from other devices. 

The commercial and industrial products are focusing on different compliance. For example it requires EMI class B in commercial products whereas class A in industrial devices and the industrial devices need more EMS protection level...etc. Whatever commercial, industrial, medical, military, car...etc, the most important thing is to pass the EMC test to fulfill each country requirements.

I won't introduce the certification test items and grades. Just write down the experience. 
  
First, there is a EMI figure shown below. From the x-axis, we know that it is in the frequecncy domain. So we should understand the Fourier Series and Transform equations. 

A periodic function can be represented as linear combination of more basic signals, like following figures (1)、(2)。

(1)

(2)

After Fourier Series, we could get the waveform in frequency domain and magnitude of Cn.

If the duty cycle is 50%:

From the result we know that:

1. If the duty cycle is not 50%, the even part of Cn will not be zero
2. Square waveform within the 50% duty cycle is equal to system clock
3. We ofter heard the hamonics are from odd parts of Cn, because even parts are zero
4. In the spectrum, we will see regular spikes

This is because when we see the regular spikes in the lab, we should find out the clock source then give a solution to solve the problems.

Appedix

EMI有
Conduction(傳導干擾)
Radiation (輻射干擾)
Harmonic (電源諧波干擾測試)
Voltage Fluctuation & Flicker (電壓變動與閃爍干擾測試)
Disturbance Power (干擾功率)
Click（喀嚦率）

EMS有
ESD (靜電放電耐受測試)
RS (輻射耐受測試)
EFT (電性快速突波耐受測試)
Surge (雷擊耐受測試)
CS (傳導耐受測試)
PMF (電源頻率磁場耐受測試)
Dip (電壓下降瞬斷測試)
Harmonics and Interharmonics (諧波與諧間波耐受測試)