[ibis-macro] AMI Touchstone Analog Model BIRD

  • From: "Walter Katz" <wkatz@xxxxxxxxxx>
  • To: "IBIS-ATM" <ibis-macro@xxxxxxxxxxxxx>
  • Date: Fri, 15 Feb 2013 16:09:43 -0500 (EST)



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


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 Katz

 <mailto:wkatz@xxxxxxxxxx> wkatz@xxxxxxxxxx

Phone 303.449-2308

Mobile 303.335-6156


Attachment: BIRD_AMI_Tstonefile.docx
Description: MS-Word 2007 document

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