[SI-LIST] Re: adjacent power plane spacing with sensitive power nodes
- From: Ignas Mikulevicius <mikulevi@xxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Fri, 9 Oct 2009 14:56:19 -0700
Hello,
First, some background:
I have a PCB design that is experiencing some jitter issues that we are
trying to get to the bottom of. It is a PCI Express design utilizing a
Xilinx FPGA. The PCI Express transceivers are powered by 1.0V core
circuitry, and 1.2V circuitry for the actual transmitter and the PLL. The
core and the PLL circuitry are extremely sensitive to noise.
One theory brought up was that we might be getting noise coupled into these
sensitive nodes from adjacent power planes. The nodes are implemented as
mini-planes on various layers of a 12 layer PCB.
For example, one of the PLL mini islands is on layer 8, with a +12V plane on
layer 7, with only a 3.4 mil spacing between the planes. There is no
adjacent ground plane, only a signal plane on layer 9, which is 12 mils
away. Similarly, layer 12 contains the 1.0V core mini-island as well as the
1.2V transmitter power supply mini-plane. Layer 11 is flooded with +3.3V,
with a 2.9 mil separation from layer 12.
*My question: Is it possible that noise on the +12V and +3.3V planes is
coupling into the sensitive transceiver nodes and causing jitter?*
My initial opinion was that any ripple on the voltage planes would be too
small to actually couple into an adjacent plane, but maybe I am wrong? I
have read some of the archived posts considering similar topics, but did not
seem to find a definitive response.
Thank you very much in advance,
Ignas M.
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
