Subject: [IBIS] BIRD 75 comments - True Differential Buffers
From: Muranyi, Arpad (arpad.muranyi@intel.com)
Date: Thu Sep 19 2002 - 14:37:34 PDT
Bob,
I have another question, this is regarding the True Differential Buffers.
I either don't understand what is in the BIRD, or the BIRD does not
completely
define how these animals are connected. Here is what I mean:
We have a pin list, on which there are two pins listed which have a
differential
pair behind them. The BIRD requires that they use the same [Model] name.
[Pin]
1 data_pos True_diff_buf
2 data_neg True_diff_buf
Now, I have the diff pin keyword:
[Diff Pin] inv_pin vdiff tdelay_typ tdelay_min tdelay_max
1 2 200mV -1ns 0ns -2ns
Then we have the model itself which now references an [External Model].
This
buffer being a true differential buffer will have two I/O nodes that connect
tot he die pad. Let's call these nodes A_signal_pos and A_signal_neg.
Here are my questions:
How does the tool know that this [External Model] doesn't need to be
instantiated
twice because it is a true differential model and has two I/O nodes? The
pin list
calls it twice, and the [Diff Pin] keyword doesn't say anything about this
being
a true differential buffer model. For that matter, it could be a
differential
model that is formed from two single ended models.
Once we figured out the answer to the above question, and the tool knows
that it
should only instantiate it once, how does the tool know which node goes to
with
pin (i.e. A_signal_pos to pin 1, and A_signal_neg to pin 2)? I don't see
anything
that would provide that connectivity information.
Can you explain this to me?
Thanks,
Arpad
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