My approach as well. This requires that each PDS voltage be designed for low
ripple as it will couple onto signals with no attenuation.
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On ;
Behalf Of Jeff Loyer
Sent: Wednesday, July 27, 2016 7:21 AM
To: pratapasimha@xxxxxxxxx; Si-list <si-list@xxxxxxxxxxxxx>
Subject: [SI-LIST] Re: Return path on an unrelated power plane
When I looked at this for server designs, including building boards which used
power reference instead of GND, I concluded that for server designs with lots
of layers (>6) and inter-plane capacitance, copper is copper, the signals don't
care what voltage potential they're at. The caveat was that if you reference
to a relatively high voltage (12V in our unfortunate case), the noise from that
voltage can get induced on the signals (not an issue with differential
signals). I don't have any data for designs with fewer planes that are spaced
far apart (e.g., a typical 4-layer design).
Jeff Loyer
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Pratap Simha
Sent: Tuesday, July 26, 2016 5:07 PM
To: Si-list
Subject: [SI-LIST] Return path on an unrelated power plane
Hi experts,
I have couple of (3GHz Nyquist) SERDES stripline traces that have GND as
reference plane.
Instead of GND if I use an unrelated power (say 3.7V Main board power) plane,
will there be any impact on return path (huge loop?) in this situation, if
there is no bypass capacitors located close to either Driver or Receiver?
(there will be bypass capacitors on the board however for this unrelated power,
but not close to Driver or Receiver)
If I want to use an unrelated power plane as reference can I use bypass
capacitors locating one at the driver and one at the receiver so the return
path (with smaller loop) can easily be established ?
Is there a way to simulate this ? because the simulation tools only have option
to include a reference plane that is either GND or the VDD plane of the traces
that we are simulating.
Thank you,
Pratap
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