Author Topic: EEVblog #1117 - PCB Power Plane Capacitance  (Read 1055 times)

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Offline EEVblog

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EEVblog #1117 - PCB Power Plane Capacitance
« on: August 31, 2018, 01:13:39 pm »
Are power planes in a 4 layer PCB any good as a capacitor?
Can it work as one big bypass capacitor?
A look at an discussion on PCB layer stackups, and some measurements on 4 and 8 layer PCB power planes with different prepreg thicknesses and how well they work as a capacitor.

https://www.xilinx.com/support/documentation/application_notes/xapp623.pdf
https://www.researchgate.net/publication/242415439_High_Performance_FPGA_Bypass_Networks


 
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Offline Bud

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Re: EEVblog #1117 - PCB Power Plane Capacitance
« Reply #1 on: August 31, 2018, 01:45:49 pm »
Thanks, but I am unconvinced about the connection wires from the calibration plane to the board. Seemed good 20 cm of loop wire to me, which resonated with the inter-plane capacitance and that created a dip in the chart. Proper calibration has to be done at the connection points on the board.
 

Offline dardosordi

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Re: EEVblog #1117 - PCB Power Plane Capacitance
« Reply #2 on: September 01, 2018, 02:34:22 am »
Yeah, can we see the capacitors hooked up to the leads to compare ?

BTW, great video!
 

Offline PA0PBZ

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Re: EEVblog #1117 - PCB Power Plane Capacitance
« Reply #3 on: September 01, 2018, 03:56:27 am »
So it looks like the board is a low Q capacitor. Would be interesting to see what a similar board will look like when populated with the bypass capacitors or even fully populated.
Keyboard error: Press F1 to continue.
 

Offline schratterulrich

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Re: EEVblog #1117 - PCB Power Plane Capacitance
« Reply #4 on: September 06, 2018, 04:50:48 am »
 I have written a tool to simulate the impedance of plane / cap combinations with irregular shapes. You can find it at leiterplatte.jimdo.com/pdn-sim/. Maybe it can be useful for someone.
You can see the effect of combining caps with interplane capacitance with this tool.
 


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