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gmittal
Joined: 28 Dec 2007
Posts: 24
Helped: 6
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 29 Jul 2008 14:24 Layer Stack up and routing issues |
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Hi All
In my design I have 7 power supplies (1.2, 1.5, 1.8, 2.5, 3.3, 5, -5). I am using the following layer stack up.
top
gnd
power 1 (split plane for 1.5, 5)
signal 1
signal 2
power 2 (3.3 V)
power 3 (split plane for 2.5,-5)
signal 3
signal 4
power 4 (split plane for 1.8, 1.2)
gnd
bottom
Most of the signals with frequency 500 MHz pass through these split planes. will there be a lot of interference, or any other problem with this type of routing?
Having a separate layer for each power supply will increase the number of layers and cost, (that's why I went for split planes).
Is there a way I can reduce this interference and reflection.
Any help will be greatly appreciated
Thanks
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Anonymous_Ricky
Joined: 26 Dec 2006
Posts: 146
Helped: 7
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| 30 Jul 2008 5:47 Layer Stack up and routing issues |
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Hi,
Routing over split planes is definitely going to create the issues for return path.
Also the layer stackup you have mentioned is not balanced try to have a gnd plane for every power plane for better decoupling effect one thing you could do is you could increase splits in some outer power planes and have inner planes with single power so that you can route your critical signals in electrical layers adjacent to it and non critical signal on outer electrical layer which are adjacent to outer power planes with splitting in them.
I would say that you change power 3 layer with gnd and put 2.5 and -5 in outer planes put signal 2 and signal 3 i b/w them i would prefer a layer stackup as below
top
gnd
power 1 (split plane for 1.5, 5,2.5)
signal 1
signal 2
power 2 (3.3 V)
signal 2
signal 3
gnd
signal 4
power 4 (split plane for 1.8, 1.2,-5)
gnd
bottom
in this layer stackup you can route your high frequency signals in signal 2 and signal 3(signal1 and signal4 can be used).
Hope that it will help you and would appreciate if any member who finds something wrong to kindly correct it.
Regards
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egemini
Joined: 02 Apr 2002
Posts: 157
Helped: 2
Location: GOC
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| 30 Jul 2008 18:32 Re: Layer Stack up and routing issues |
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Do you have any learning material to assist in the layer stack designing and PCB routing of mixed signal PCB, which contains both RF and DSP which handles high speed signals.
For example, PCB design for a mobile phone.
I have been facing very high interference from digital parts in my designs
thank you in advance:D
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DavidReina
Joined: 28 Jan 2008
Posts: 19
Helped: 3
Location: Mexico
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| 26 Sep 2008 3:26 Re: Layer Stack up and routing issues |
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Do you really need that amount of copper for your pwr supply?
You can exchange some pwr planes segments for gnd and give some gnd reference for your critical signals, also, use some signal layers for pwr o gnd. miscellaneous signals such as enables and low speed doesn't matter that much. hope this helps.
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