[ibis-macro] Re: AMI Touchstone Analog Model BIRD
- From: "Muranyi, Arpad" <Arpad_Muranyi@xxxxxxxxxx>
- To: IBIS-ATM <ibis-macro@xxxxxxxxxxxxx>
- Date: Tue, 19 Feb 2013 16:36:10 +0000
Walter,
I just want to double check (or clarify).
Is the BIRD you distributed with this email the
so called "Press release BIRD" we talked about
at the IBIS Summit?
Thanks,
Arpad
================================================
From: ibis-macro-bounce@xxxxxxxxxxxxx [mailto:ibis-macro-bounce@xxxxxxxxxxxxx]
On Behalf Of Walter Katz
Sent: Friday, February 15, 2013 3:10 PM
To: IBIS-ATM
Subject: [ibis-macro] AMI Touchstone Analog Model BIRD
All,
I am enclosing the BIRD that defines AMI Parameters to support Touchstone
Analog Buffer Models.
I reviewed last week's meeting minutes. There was a request that I indicate
whether the specification should define how the impulse response should be
generated for a channel. The generation of the impulse response of a channel is
well defined when the Tx and Rx buffers specify a Touchstone file in accordance
with the enclosed BIRDs. Since the channel is LTI and these analog buffers are
LTI there are many methods that can be used to generate the impulse response,
and one can prove these methods should give identical results within numerical
accuracy. The first method is to do a step response SPICE simulation using the
differential voltage range specigied by Tx_R. The impulse response is the first
derivative of the differential signal at the Rx Touchstone nodes specified on
this BIRD. A second way is to convert the channel into an s4p Touchstone field.
Using the S Parameter arithmetic James presented recently, all one needs to do
is cascade the Tx s4p, channel s4p and Rx s4p into a single s4p, inverse
Fourier transform this s4p, and voila, one has the impulse response of the
channel.
On can similarly describe various methods to generate the impulse response of a
channel when the Tx and Rx are legacy models with linear IV curves. This is
true because one can generate an s4p analog model for these Tx and Rx legacy
model.
Defining a method to generate the impulse response of a channel when the Tx
and/or Rx have non-linear IV curves is problematic since the premise of AMI
modeling implies Linear Time Invariant (LTI). Which is another way of saying a
"Small Signal Interface". Since most implementations of the IBIS B element
require a digital stimulus, and according to the common understanding that IBIS
B elements (and external model) have digital stimulus, then an impulse response
generate with a SPICE simulator using the IBIS B element can only generate a
step response across the full swing of the Tx.
Walter
Walter Katz
wkatz@xxxxxxxxxx<mailto:wkatz@xxxxxxxxxx>
Phone 303.449-2308
Mobile 303.335-6156
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