[SI-LIST] Re: Split gnd planes - for/against? - Thanks!
- From: <simsonl@xxxxxxxxxxxxxx>
- To: steve weir <weirsi@xxxxxxxxxx>, Tony Luan <luant@xxxxxxxxxxx>
- Date: Thu, 9 Apr 2009 23:26:11 -0400
Steve,
The book you mentioned in an earlier post, "Noise Coupling in Integrated
Circuits", is on amazon.com bundled with a simulation software. Did you get
yours with that software and can it simulate multiple (split) power/ground
planes?
Thanks
Larry
---- steve weir <weirsi@xxxxxxxxxx> wrote:
> Tony usually that is the right decision. However, there are cases when
> a package will not fit and still provide adequate isolation between
> circuits without implementing a split. These don't happen in digital
> designs running one signaling level.
>
> But suppose that you have a big digital bus switching 5A / ns that is
> 0.25" away from some analog circuit that is sensitive to 10uV noise. Do
> you think the 0.25" separation will be enough? If you cannot change the
> placement to put the analog circuitry further away, what will you do?
>
> Steve.
>
> Tony Luan wrote:
> > Hi Sol,
> >
> > I think to split GND plane is not a good idea.
> > For any high frequency noise, GND and power plane are playing completely
> > equivalent role. How can a high frequency noise tell which plane is GND?
> > Which plane is power? Why not split power plane instead and keep a solid
> > complete GND plane, because in package or PCB, we have tons of power
> > rails and power islands already.
> > The biggest disadvantage to split GND plane I saw is that it increases
> > routing difficulty when try to avoid high speed signal, clock, parallel
> > bus across those gaps on GND plane.
> >
> > Thanks
> > Tony
> > -----Original Message-----
> > From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
> > On Behalf Of Sol Tatlow
> > Sent: Thursday, April 09, 2009 4:58 AM
> > To: si-list@xxxxxxxxxxxxx
> > Subject: [SI-LIST] Re: Split gnd planes - for/against? - Thanks!
> >
> > One last mail to put this thread 'to bed'...
> >
> > Thanks to everyone who took the time to reply, particularly to
> > those who actually gave me what I asked for, those reluctant beasts,
> > the real-life examples - it's great that you're willing to so fully
> > participate in such a discussion. After all, theory is great;
> > coupled with real-life examples it's even better.
> >
> > Of course, the specific examples can't be applied 1:1 to any other
> > design, as has been said 'x' times, but I, for one, am nevertheless
> > wiser for the experiences that have been shared... I believe I'm a
> > good engineer, but won't stop learning 'till the day I die.
> >
> > It was also good to see that I am not the only one suffering at the
> > hands of less-than-perfect datasheets and the implementation of
> > often contradictoray 'hints' :) - regardless of simulation results
> > and past experiences, it's not always easy when it comes to
> > persuading a customer, who is still convinced that app notes are
> > written by all-knowing beings, to 'do the right thing'.
> >
> > Sol
> >
> >
>
>
> --
> Steve Weir
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