[PCB_FORUM] Re: Power plane -vs- gnd path signal return path
- From: William Gerner - Sun Microsystems <William.Gerner@xxxxxxx>
- To: icu-pcb-forum@xxxxxxxxxxxxx
- Date: Thu, 13 Mar 2008 08:54:03 -0500
From my limited understanding, your assumption is correct and the key
is achieving the correct (capacitive) coupling between the planes.
Jim Wages wrote:
Ok, folks. Let me know if my thinking is wrong here.
I have a 14 layer stack up. External etch layers are adjacent to power
planes, which are adjacent to ground planes. Lyr 2 is a split power
plane. Lyr13 is a solid 3.3V plane.
Do you see any signal "return path" or integrity issues with routing a
critical signal trace on the bottom layer as long as the driver of the
signal was powered by 3.3V. What about a differential pair?
I'm assuming that the power and gnd planes would be perceived as a short
to hi-frequency signals, so that the return path would not have to get
to a ground plane, but would just stay on the 3.3V plane directly
beneath the trace until it returned to the driver.
Thoughts?
*//**/Jim S. Wages/*
*SR. PCB Layout Designer*
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