[SI-LIST] Re: SSO
- From: "Muranyi, Arpad" <arpad.muranyi@xxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Mon, 12 Aug 2002 12:07:48 -0700
Khalid,
In your equation I wouldn't include L_ground and L_power, because
according to what I wrote before there is no (or only small) di/dt
in the power and ground pin/package for a true differential buffer.
I can only see the di/dt of the signal path developing a voltage
through inductive elements. But you are correct, that this can
couple into the power and ground path if there are mutuals, and
this can depend on SSO.
Arpad
=================================================================
-----Original Message-----
From: Khalid Ansari [mailto:KANSARI@xxxxxxxxxx]
Sent: Monday, August 12, 2002 11:33 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: SSO
One thing that I didn't see mentioned in the responses so far is that
theoretically a true differential pair does not generate any ground
bounce or power droop noise on the die. This is because the total
current flow is constant between power and ground. The current in
the two halves of the differential pair always add up to the same
total current, regardless which leg is on or off.
Arpad,
I agree the current add upto the same but the loops in
each case are different. If we look on the package then
you have ground bounce voltage:
V = (L output + L ground - 2 Lmutual_output_ground)(di/dt)
For the power bounce:
V = (L output + L power - 2 Lmutual_output_power)(di/dt)
The loop inductances add up to be different. If you have
a lot of drivers switching then shouldn't you have SSO noise
issues even if the drivers are differential? I think I have
seen that in the lab before.
Khalid
In theory.
However, since real life is never ideal, you may get some noise,
but that should be much less than the noise single ended buffers
generate.
For that reason SSO noise should be small, or non existent.
Arpad Muranyi
Intel Corporation
=====================================================================
-----Original Message-----
From: Ibrahim Khan [mailto:ikhan@xxxxxxxxxxxxxxxxxxx]
Sent: Sunday, August 11, 2002 9:07 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] SSO
Hello Gurus,
Does the concept of Simultaneous Switching (SSO) apply only to
single-ended signal or the differential pairs as well. In other words,
do we only care (when designing the decoupling strategy) how many
single-ended outputs are switching simultaneously or do we have to
account for diff. pairs as well.
regards
Ibrahim Khan
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