IBIS Macromodel Task Group

Meeting date: 20 June 2023

Members (asterisk for those attending):
Achronix Semiconductor:       Hansel Dsilva
Amazon:                       John Yan
ANSYS:                      * Curtis Clark
                            * Wei-hsing Huang
Aurora Systems:               Dian Yang
Cadence Design Systems:       Ambrish Varma
                              Jared James
Google:                       Hanfeng Wang
                              GaWon Kim
Intel:                      * Michael Mirmak
                            * Kinger Cai
                              Chi-te Chen
                            * Liwei Zhao
Keysight Technologies:      * Fangyi Rao
                              Majid Ahadi Dolatsara
                              Stephen Slater
                            * Ming Yan
                              Rui Yang
Marvell:                      Steve Parker
Mathworks (SiSoft):          Walter Katz
                              Graham Kus
Micron Technology:          * Justin Butterfield
Missouri S&T:                 Chulsoon Hwang
                              Yifan Ding
                              Zhiping Yang
Rivos:                        Yansheng Wang
SAE ITC:                      Michael McNair
Siemens EDA (Mentor):       * Arpad Muranyi
                            * Randy Wolff
Teraspeed Labs:             * Bob Ross
Zuken USA:                  * Lance Wang

The meeting was led by Arpad Muranyi.  Curtis Clark took the minutes.

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Opens:

- None.

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Review of ARs:

Bob: Send information about the recent IEEE SPI IBIS Summit presentation on PSIJ
     to the ATM list.
     - Done.

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Call for patent disclosure:

- None.

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Review of Meeting Minutes:

Arpad asked for any comments or corrections to the minutes of the June 13th
meeting.  Michael moved to approve the minutes.  Lance seconded the motion.
There were no objections.

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New Discussion:

PSIJ Sensitivity Discussion:
Kinger shared draft11 of the proposal, in particular figure 4 and equation 8, in
order to discuss issues raised by Fangyi in an email reply to draft11.  Arpad
asked whether the 3 VCC_m names shown in figure 4 represented 3 independent
supplies.  Kinger said they represent the same supply rail applied to 3 distinct
blocks.  Fangyi asked where PSIJ_VCC_m_CKTi was measured in figure 4.

Fangyi asked whether the intent was to measure the jitter at the output of each
of the cascaded blocks, and then the total jitter at the final output is some
combination of them?  In that case, Fangyi said he understood the intent.  He
said the measurement location(s) should be described in the BIRD.  Kinger
agreed.

Fangyi said he thought "multiplication" was probably not the right term to use
with regard to combining PSIJ_VCC_m_CKTi terms.  He noted that equation 8 would
have issues with the final units for PSIJ_VCC_m, given that it specified a
possible mix of multiplication and addition of the individual terms.  Referring
to figure 5, he said the curves combined via "multiplication" looked more like
typical filter behavior in which each of the cascaded stages had a unitless
jitter transfer function applied to its input.

Fangyi asked how we would use this information in a transient simulation.
Kinger said the goal was to enable an evolution of high-level SI/PI
cosimulation.  Traditionally we totally separate SI and PI simulations and then
use a simple peak to peak noise design target.  More recently people had been
attempting to do SI/PI cosimulation by simulating everything together, but this
can be nearly impossible to do if we consider full SPICE models of each of the
circuit blocks.  He said that with this proposal we are thinking of a pure SI
simulation with ideal voltage sources and then an independent simulation to
determine the noise on each power rail considering all the circuit blocks.  We
convert each power rail's noise to a power spectral density, multiply with the
PSIJ Sensitivity curve for that rail and a particular signal to get the jitter
spectrum, and can then use IFFT to compute the peak-to-peak jitter distribution.
This can then be applied to the results from the ideal SI simulation.  This
provides a holistic approach that can cover all supply rails and all circuit
blocks.

Kinger said he would set up an offline meeting with Fangyi to review his
suggestions.

Kinger briefly discussed the recent IBIS Summit presentation on PSIJ from the
Indian Institute of Technology Jodhpur.  He said he thought it was focused on
a simulation algorithm for computing the jitter contribution of an individual
circuit block, where Kinger's proposal is more of a high-level system approach.
He said he did not think his proposal conflicted with the summit presentation or
BIRD220.  The group discussed Fangyi's questions about the presentation, which
he had sent to the ATM list.  Bob agreed to forward Fangyi's questions to the
authors.

AMI Support for [Test Data]/[Test Load]:
Michael reported that, based on feedback from the previous week's discussion,
he was planning on altering the draft to move any test load interconnect details
over to the traditional [Test Load] keyword, and then he would create a new
[AMI Test Data] keyword for AMI.  Per the suggestions, [AMI Test Data] would
only provide the channel impulse response to be passed to the AMI executable
model by the tool.  The impulse response waveform itself will be provided in
a separate file, which is referred to by the [AMI Test Data] keyword.

Arpad recalled that during the previous week's discussion Ambrish has suggested
that if we provide the impulse response, then we can extend the use of the
original [Test Load] to cover AMI.  Michael said that if we want to make the
existing [Test Load] more useful, we need to support IBIS Interconnect Model
syntax to properly model modern high-speed lossy channels.  He said that would
decouple the issues of channel modeling and channel characterization from AMI.
However, he noted that this would enable people to compare channel
characterization results from different tools.  So, it would not get us around
the contentious issue from the previous meeting about comparing different
tools' channel characterizations.  It would only decouple the issue from AMI.

Michael said one of the reasons that his proposal originally provided a more
detailed channel model, and not the impulse response itself, was a concern for
the model maker's ability to provide the impulse response itself.  He said he
was concerned that tools might not make their computed channel impulse response
readily available to the user (the model maker in this case).  So, a model
maker might not have an easy way to capture an impulse response waveform if
they had to provide one in the [AMI Test Data].

Arpad recalled that he had previously suggested that instead of inventing a new
new syntax to provide the AMI parameter settings, we could instead specify the
exact parameter string itself.  Michael said his concern here was similar to the
concern about the impulse response.  He was worried about expecting the model
maker to create the fully formed parameter string from scratch.  He said the
BIRD would have to encourage tools to make their generated parameters strings
readily accessible to the user.  This would allow model makers to capture the
generated string and include it in their model.  Wei-hsing asked whether model
makers should take that up with their chosen tool vendors if they needed easier
access to impulse responses, parameter strings, etc., that had been generated by
the tool.  Michael said this was a good point, but he said he generally
considered IBIS to have three main audiences: the end user doing system
simulation, the model creators, and the EDA tool vendors.  He said discussions
in ATM were often biased toward the EDA tool vendor audience.  To facilitate the
adoption of this feature by model makers, we would need to help ensure that the
parameter strings and impulse response waveforms generated by the tools were
more accessible to users.

- Curtis: Motion to adjourn.
- Michael: Second.
- Arpad: Thank you all for joining.

New ARs:

Kinger: Work offline with Fangyi to address Fangyi's suggestions on the PSIJ
        Sensitivity draft11.

Bob: Forward Fangyi's questions to the authors of the IEEE SPI IBIS Summit
     presentation on PSIJ.

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Next meeting: 27 Jun 2023 12:00pm PT
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IBIS Interconnect SPICE Wish List:

1) Simulator directives
