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Guess Who?
Post subject: Wire spacing and other PCB stuff Posted: Tue Jan 31, 2006 9:47 am
Greetings!

I understand that the width of a piece of wire (PCB track) depends on how much current is going through it. In dealing with high frequency signals, what is the rule for spacing wires apart?

If I had a DC pin next to a AC (high frequency) pin on an IC, do I need to route the wires away from each other? Also, in this type of setup, would a capacitor from the DC to GND alwasy be recommended?

Also, I've noticed that some high frequency circuits have copper planes on the top and the bottom. Is there a specific reasoning for this? Are these mostly ground planes?

Thanks!


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IR
Post subject: Posted: Sat Feb 18, 2006 3:35 pm

Site Admin


Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
Hello Guess Who,

Quote:
If I had a DC pin next to a AC (high frequency) pin on an IC, do I need to route the wires away from each other? Also, in this type of setup, would a capacitor from the DC to GND alwasy be recommended?



Yes you should route the high-frequency signals away from the DC signals to prevent coupling between them. Capacitors of several values are always needed to bypass voltage supplies. They should be placed as close as possible to the voltage supply pins.

Quote:
Also, I've noticed that some high frequency circuits have copper planes on the top and the bottom. Is there a specific reasoning for this? Are these mostly ground planes?


Yes these copper planes are usually GND planes. In RF PCB layout there is great importance to form a continuous GND plane. Therefore; where no signals are passing the area is covered with GND. I suppose that you have also noticed that GND planes exist on both sides of RF traces (microstrip lines). This type of transmission line is called Coplanar.

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- IR



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