Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

Questions tagged [emc]

Electromagnetic compatibility (EMC) is a branch of electronics related to identifying and solving problems caused by electromagnetic interference (EMI) between devices. It encompasses both attempting to prevent unwanted emissions from a device and also ensuring that emissions from another device will not cause spurious operation. EMC depends upon many system-level details; when asking questions, please provide as much information as possible.

936 questions
73
votes
3 answers

What does the Y capacitor in a SMPS do?

It seems that a well-designed SMPS has a capacitor connecting the ground planes of the primary and secondary sides of the transformer, such as the C13 capacitor here. What is the purpose of this capacitor? I've let myself understand that it's for…
Dolda2000
  • 895
  • 1
  • 8
  • 9
43
votes
3 answers

What's radiating on my PCB?

I recently did a proper EMC test on a PCB of mine. It failed the test, and seems to be radiating in the 300MHz - 1GHz region, with peaks every 50MHz, and little peaks on the 25MHz. Looking at the near field, you can clearly see lots of 25MHz…
Rocketmagnet
  • 26,933
  • 17
  • 92
  • 177
38
votes
4 answers

Identifying Source of Periodic Artifact at Op-Amp Output

My MAX44251 dual op-amp has a very small unwanted 131KHz periodic artifact at the output, seemingly regardless of how it's configured. My assumption was EMI, but I can't see this 131KHz signal on any other part of the circuit. I've also tested this…
Keegan Jay
  • 1,280
  • 1
  • 11
  • 28
33
votes
2 answers

Ground ring -- good or bad?

Here are two routings: Which is better? On one hand, the first is bad because ground ring is one-turn coil, hence induction current will be appear. On other hand, the second is bad because potential in the opposite points of ground plane will…
user54579
31
votes
6 answers

Why do some EMI/RF shields have holes on the top and some don't?

I am not talking about cutouts for tall components. I don't think they are for ventilation as they are often covered with manufacturer labels.
Dojo
  • 919
  • 10
  • 19
30
votes
4 answers

Why is it good to slow down digital lines with resistors?

I've heard that sometimes it is recommended to "slow down" a digital line by putting a resistor on it, let's say a 100 ohm resistor between the output of one chip and the input of another chip (assume standard CMOS logic; assume the signalling rate…
Alex I
  • 3,341
  • 2
  • 36
  • 59
25
votes
3 answers

Is twisting a single ended signal with its own GND really useful?

I know that the most robust way of transferring an analog signal over long distances is via differential pairs which are twisted together and then shielded (shield grounded at one end only). But sometimes, we have to make do with single ended…
user42875
  • 1
  • 2
  • 22
  • 35
24
votes
2 answers

Via fences for noise reduction of a chip antenna?

I'm working on a 4-layer PCB that has a wifi module and a chip antenna, the antenna is placed at the corner of the PCB and the copper beneath it is removed, I see that via fences are used on the breakout board of the same module, but the reference…
mux
  • 1,866
  • 5
  • 23
  • 27
24
votes
2 answers

Alternatives to SPI because of EMI

I currently make a system consisting of a plastic enclosure which contains an MCU talking to 7 ADCs using 2MHz SPI over wires about 5cm long. The problem is that I'm concerned about EMI. Everything I have read suggests that any kind of digital…
Rocketmagnet
  • 26,933
  • 17
  • 92
  • 177
19
votes
2 answers

PCB routing: EMI and signal integrity, return current questions

If there's any EMI/SI lesson I've taken in, it's to minimize return loops as much as possible. You can work lots of EMI/SI guidelines from that one simple statement. However, not having or ever even seen Hyperlynx or any sort of full RF simulation…
darron
  • 3,491
  • 2
  • 29
  • 42
18
votes
3 answers

Why do some PCBs have exposed plated perimeters?

I've seen a number of PCBs, largely high speed and RF boards, that have exposed copper, either at the perimeter of the entire board, or in various sections, often with stitching vias. I've never fully understood the purpose of these. Some…
Kirill Safin
  • 293
  • 2
  • 6
18
votes
3 answers

What problems could occur when chaining 40 shift registers?

I'm planning on chaining together 40 x 74HC595 shift registers. The whole chain of 74HC595s will be controlled by a 5 V microcontroller, which will generate the SDI, CLOCK & LATCH signals. Each shift register and the microcontroller will have its…
m.Alin
  • 10,638
  • 19
  • 62
  • 89
17
votes
5 answers

Why does a simple conductor start to emit EM waves when carrying a signal?

I understand that on circuit board traces with a clock, if the higher harmonics have sufficient power, it results in electromagnetic waves being emitted from the traces which creates EMI. What I don't understand is why this happens in the first…
quantum231
  • 11,218
  • 24
  • 99
  • 192
17
votes
6 answers

Failed radiated emissions test on USB cable - USB module hardware and firmware improvements

I posted a few days about ago how our product failed ESD testing. Well, it also failed radiated emissions testing so I thought I'd make a separate post. The product is a 5V USB powered, non-radio, 3v3 LDO regulated, 2 layer PCB inside a plastic…
Geo
  • 744
  • 8
  • 21
17
votes
2 answers

To "ground fill"or not to "ground fill"?

I have been reading up on the EMI issues in Electromagnetic Compatibility Engineering by Henry Ott. (wonderful book btw). One of the topics "PCB Layout and Stackup" (aka Ch 16) there is section about ground fill (16.3.6). Basically what it states,…
Wally4u
  • 323
  • 2
  • 7
1
2 3
…
62 63