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key strategies to minimize interference and ensure that the PCB operates reliably?
I can get information on what to reduce and what not to maybe some AI thing ?
I can get information on what to reduce and what not to maybe some AI thing ?
How do you design for EMI/EMC compliance?
- Thread starter LerryFLyer
- Start date
sure books are better! AI is easy. thanks for the book btw!
The first key strategy is to have a single GND plane.
The second key strategy is to have two complete GND planes.
Two GND planes would be very good, on a dual sided PCB, and as it does not leave any room to route signals or even power to IC’s. you will not have any EMC problems. A minor inconvenience is that your circuit also will not work at all. Two GND planes on a dual sided PCB is not practical.
For 4 or more layers, two GND planes are both practical and advisable. The reason is that prepreg is much thinner then the PCB core, and the closer the GND plane is to the (high speed) signals, the better the coupling is for the return current, and better coupling is less stray EMC (both receive and emit).
Rick Hartley (from altium) has posted an excellent 2 hour and 19 minute video about creating a proper ground plane. The video is both interesting and important enough to watch at least twice (with a few months in between). Have pen and paper or a text editor ready to make some notes.
All off-board connections are also of primary concern. Every wire or cable connected to the PCB is an antenna and filtering components are common. From inductors in power lines to ferrite beads and feed through capacitors.
Another common practice is the configurable output drive of some microcontrollers and other programmable stuff such as FPGA’s. The faster the flanks of uC pins, the more EMC they will create. Series resistors can be used to decouple an output pin from the track capacitance. Thinner PCB tracks result in less capacitance, and thus less peak current and less EMC problems. I once built a uC circuit on Matrix (vero) board. It was continuously scanning a keyboard matrix, and I also wanted to use the built in ADC. That was a big mess, but also an educational moment. If you can build your uC circuit (first prototype) on a matrix board in such a way that it behaves reasonably nice, then it probably behaves excellently once a real PCB with a decent GND plane is made.
Look into near field probes. These are often very expensive from the “west” side of this mudball we live on, but there is not much in them and a cheap set probably works (almost) as well. You can also DIY it, but you probably need a pre-amplifier as they do not deliver much output signal.
With simulators you can identify locations of quick current changes (which are a mayor EMI source), but a SPICE like emulator is not of much use for EMC. You can characterize cable filters with it, but PCB layout is an extremely important part of EMC performance, and to do that you will need an electromagnetic field simulator, and that is a completely different beast. This tends to be more specialized (expensive, little Open Source available), but even watching some youtube video’s help to build insight in how electromagnetic fields around wires behave. And you can use that insight to improve your PCB’s even without having used such an emulator yourself.
Ground rule is that electrons move through conductors, but nearly all the electromagnetic field (and thus energy) is outside of the conductor. Shaping the form of that field (with GND planes, shielding) and it’s rate of change (fast output pins, chokes, inductors, resistors, etc) are the mayor ingredients of the game.
The second key strategy is to have two complete GND planes.
Two GND planes would be very good, on a dual sided PCB, and as it does not leave any room to route signals or even power to IC’s. you will not have any EMC problems. A minor inconvenience is that your circuit also will not work at all. Two GND planes on a dual sided PCB is not practical.
For 4 or more layers, two GND planes are both practical and advisable. The reason is that prepreg is much thinner then the PCB core, and the closer the GND plane is to the (high speed) signals, the better the coupling is for the return current, and better coupling is less stray EMC (both receive and emit).
Rick Hartley (from altium) has posted an excellent 2 hour and 19 minute video about creating a proper ground plane. The video is both interesting and important enough to watch at least twice (with a few months in between). Have pen and paper or a text editor ready to make some notes.
All off-board connections are also of primary concern. Every wire or cable connected to the PCB is an antenna and filtering components are common. From inductors in power lines to ferrite beads and feed through capacitors.
Another common practice is the configurable output drive of some microcontrollers and other programmable stuff such as FPGA’s. The faster the flanks of uC pins, the more EMC they will create. Series resistors can be used to decouple an output pin from the track capacitance. Thinner PCB tracks result in less capacitance, and thus less peak current and less EMC problems. I once built a uC circuit on Matrix (vero) board. It was continuously scanning a keyboard matrix, and I also wanted to use the built in ADC. That was a big mess, but also an educational moment. If you can build your uC circuit (first prototype) on a matrix board in such a way that it behaves reasonably nice, then it probably behaves excellently once a real PCB with a decent GND plane is made.
Look into near field probes. These are often very expensive from the “west” side of this mudball we live on, but there is not much in them and a cheap set probably works (almost) as well. You can also DIY it, but you probably need a pre-amplifier as they do not deliver much output signal.
With simulators you can identify locations of quick current changes (which are a mayor EMI source), but a SPICE like emulator is not of much use for EMC. You can characterize cable filters with it, but PCB layout is an extremely important part of EMC performance, and to do that you will need an electromagnetic field simulator, and that is a completely different beast. This tends to be more specialized (expensive, little Open Source available), but even watching some youtube video’s help to build insight in how electromagnetic fields around wires behave. And you can use that insight to improve your PCB’s even without having used such an emulator yourself.
Ground rule is that electrons move through conductors, but nearly all the electromagnetic field (and thus energy) is outside of the conductor. Shaping the form of that field (with GND planes, shielding) and it’s rate of change (fast output pins, chokes, inductors, resistors, etc) are the mayor ingredients of the game.
