No, the traces are not imbedded.
The traces of interest are not on layer 1, they are on layer 4.
But that is not even important. Sorry if I was unclear.
The real question is:
What if the traces are interspersed between solid planes, and
although they are part of a +2.6V circuit, they happen to be
closer to a +5V plane.
I think they will use the +5V plane but it doesn't matter.
Does it matter? Is a plane a plane?
"Kowalewski,
Andy"
<AKowalewski@sych
ip.com>
To: "'(Designers Council Forum)'" <[log in to unmask]>
07/14/2003 02:04 "'Jack C. Olson'" <[log in to unmask]>
PM cc:
Subject: RE: [DC] Reference Planes for Impedance Controlled Signals
Caterpillar: Confidential Green Retain Until: 08/13/2003
Retention Category: G90 -
General
Matters/Administration
Need more info.
Is your trace of interest on layer 1 and the planes are in sequence below
that?
I assume you don't mean that the trace is embedded in the +2.6V or +3.3V
layers?
I'm not sure why you mention the 4th signal layer. Is that significant? Is
that where your trace of interest is?
The power and ground planes are equal reference planes if they are tightly
coupled together to AC signals. That happens if the planes are very close
together or there are lots of decoupling capacitors scattered around the
board that tightly couple them.
Of course, changing signal layers can change a microstrip configuration to
a
stripline, balanced or unbalanced, as well as change reference planes.
Andy K.
Sychip Inc
Office (972) 202 8852
-----Original Message-----
From: Jack C. Olson [mailto:[log in to unmask]]
Sent: Monday, July 14, 2003 12:56 PM
To: [log in to unmask]
Subject: [DC] Reference Planes for Impedance Controlled Signals
Reference Planes for Impedance Controlled Signals
I might be showing my ignorance by asking this question.
I thought I knew, but now I'm being challenged on it.
If I have impedance controlled signals that are part of
a circuit that is being run on +2.6V or +3.3V, but there
is a closer plane available, like +5V, the signal returns
will snap to the closer one, right? Does it matter which
TYPE of plane is being used a reference? The text I
received from a colleague implies that if my 2.6V plane
is too far from my 4th signal layer, which is next to the
+5V plane, then they will not be impedance controlled.
Doesn't sound right to me...
Jack (the new guy)
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