[ibis-macro] Re: BIRD 158.3 - 2
- From: "Muranyi, Arpad" <Arpad_Muranyi@xxxxxxxxxx>
- To: "ibis-macro@xxxxxxxxxxxxx" <ibis-macro@xxxxxxxxxxxxx>
- Date: Sun, 26 May 2013 04:10:54 +0000
Radek,
While you are correct that the text book definition of
"the step response of a circuit is the output signal ... when a unit step
signal ... is applied to the input",
but I was not commenting on that. I wanted to point out
a contradiction in the draft I was commenting on in one
of the sentences: "This BIRD defines what that unit excitation is...".
Knowing that the BIRD defined Tx_V (now Tx_Voh and Tx_Vol),
the excitation voltage source may have any magnitude, which
is in direct contradiction with the word "unit" which was
used in the first part of this sentence.
Now, regarding IBIS-AMI, according to pg. 122 in the v5.1
specification, "The "analog" portion of the channel is characterized by means
of an impulse response leveraging the IBIS constructs for device models defined
in Sections 6, 6A and 6B.".
Also, on pg. 161 we read: "Step 1. The EDA tool obtains the impulse response
for the analog channel. This represents the combined impulse response of the
transmitter's analog output, the channel and the receiver's analog front end.
The transmitter's output or receiver's input characteristics must not include
any filtering effects, for example equalization, in this impulse response,
although it may include any parasitics which are included in the Tx or Rx
analog model."
Since [Model]-s are not restricted to have a unit step
and the only restriction is that when generating the
impulse response for the channel the Tx buffer should
not have its EQ turned on, the impulse response of a
channel characterization simulation will also include
the information on what the unequalized signal swing
of the Tx buffer is.
The executable AMI models will apply their EQ algorithms
to this non-unit excitation based impulse response, and
the results will come out with the correct amplitude based
on that. This is why Walter proposes the Tx_V... parameters
in this BIRD, because the S-parameter model does not add
gain to a unit excitation input to represent the Tx
buffer's unequalized signal swing.
So as far as I can tell, the stimulus to the Touchstone
data (Tx model) is not a unit step. We might be using the
wrong terminology in the spec when we are talking about
step responses and impulse responses. That could be
discussed in the editorial committee.
Thanks,
Arpad
=============================================================
From: radek_biernacki@xxxxxxxxxxx [mailto:radek_biernacki@xxxxxxxxxxx]
Sent: Friday, May 24, 2013 1:31 PM
To: bob@xxxxxxxxxxxxx; wkatz@xxxxxxxxxx; Muranyi, Arpad;
ibis-macro@xxxxxxxxxxxxx
Subject: RE: [ibis-macro] Re: BIRD 158.3 - 2
Hi All,
In my opinion the latest changes made the proposal somewhat more confusing. The
common-mode input is introduced quite unnecessarily. All that is needed is the
difference of Tx_Vol and Tx_Voh and the proposal asks for two numbers where
just one number is needed. The one number needed could be either half of the
differential voltage swing or the full differential voltage swing. (That would
correspond to either Tx_Vol = -Tx_V and Tx_Voh = Tx_V, or Tx_Vol = -Tx_V/2 and
Tx_Voh = Tx_V/2, and specifying just Tx_V as before.)
Furthermore, the use of inherent common-mode concept associated with specifying
two (could be arbitrary) numbers will be more confusing to the users of the AMI
technology, and model developers in particular.
Arpad: your comment about the unit excitation was quite incorrect. By
definition, the step response of a circuit is the output signal (here the
output differential voltage) when a unit step signal (the input differential
voltage) is applied to the input. The circuit inside must not have independent
sources in it. The framework in which this BIRD is written does not follow this
convention, and suggests independent sources being part of the circuit. In fact
these sources should properly be described as voltage-controlled voltage
sources that are controlled by an input signal that is not shown. A unit
excitation (Dirac delta, or unit step function) must be applied to that input
to determine the impulse response needed for AMI simulation. In the context of
the picture in the BIRD that unit excitation will result in the voltages of the
sources as described. Those voltages are poorly termed in the BIRD as "step
response stimulus". In fact the picture does not reflect an input-output model
of the actual circuit, but shows a schematic for impulse response calculation -
that should be explicitly stated.
Radek
From: ibis-macro-bounce@xxxxxxxxxxxxx<mailto:ibis-macro-bounce@xxxxxxxxxxxxx>
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Bob Ross
Sent: Friday, May 24, 2013 8:44 AM
To: wkatz@xxxxxxxxxx<mailto:wkatz@xxxxxxxxxx>;
Arpad_Muranyi@xxxxxxxxxx<mailto:Arpad_Muranyi@xxxxxxxxxx>; 'IBIS-ATM'
Subject: [ibis-macro] Re: BIRD 158.3 - 2
All:
Looks good enough to me for submission.
Bob
From: ibis-macro-bounce@xxxxxxxxxxxxx<mailto:ibis-macro-bounce@xxxxxxxxxxxxx>
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Walter Katz
Sent: Friday, May 24, 2013 7:43 AM
To: Arpad_Muranyi@xxxxxxxxxx<mailto:Arpad_Muranyi@xxxxxxxxxx>; 'IBIS-ATM'
Subject: [ibis-macro] Re: BIRD 158.3 - 2
All,
I have made the changes requested by Bob and Arpad (enclosed). Any additional
comments before I send the formal version to Michael this afternoon would be
appreciated.
Walter
From: ibis-macro-bounce@xxxxxxxxxxxxx<mailto:ibis-macro-bounce@xxxxxxxxxxxxx>
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Muranyi, Arpad
Sent: Friday, May 24, 2013 10:03 AM
To: IBIS-ATM
Subject: [ibis-macro] Re: BIRD 158.3
Walter,
Here are my comments on this BIRD draft.
What does "differential transmission" mean in this sentence:
"This Impulse Response characterizes the differential transmission of the Tx
analog buffer model,"?
Could you make this clearer with better wording?
In the following sentence you are talking about the "die side
of the package":
"For a Tx buffer, the Transmitter Circuit defines the analog buffer model
between the zero impedance stimulus input voltage source and the die side of
the package model. For an Rx buffer, the Receiver Circuit defines the analog
buffer model between the die side of the package model and a high impedance
probe at the input to the Rx Algorithmic model."
However, it is not clear whether this means that the buffer model
described by the data in the Touchstone file can/should also
include the on-die interconnect or not. I think this should
be clearly stated otherwise different people will make different
assumptions to model on-die interconnects.
This sentence:
"Note that this Touchstone analog model only represent the on-die model between
the die pad and buffer interface to the algorithmic model"
is somewhat misleading, because it can be interpreted as if the
Touchstone model is **the** on-die interconnect model between the
pad and the buffer's terminals ("buffer interface").
You use the words "unit excitation". This sentence:
"This BIRD defines what that unit excitation is when the Tsonefile parameter is
present."
really doesn't make sense, because by definition a unit = 1,
i.e. the "unit excitation" would have to have a fixed and
predefined magnitude of 1 volt, yet in this BIRD you define
Tx_Voh and Tx_Vol, which is not "unit" anymore. Also, please
correct the spelling of "Tsonefile" in this sentence (missing
"t").
You mention in the discussion of the Impulse Response generation
that the Tstonefile parameter is a Reserved Parameter, but you
don't say anywhere in the document whether the rest of the parameters
in this BIRD are Reserved or Model_Specific. Please specify what
you want them to be.
I would also like to request to put a "0" before and after each
decimal point for properness. For example, instead of "(Range 1. .5 1.)"
please write "(Range 1.0 0.5 1.0)", it is much more readable that way...
Thanks,
Arpad
======================================================================
From: ibis-macro-bounce@xxxxxxxxxxxxx<mailto:ibis-macro-bounce@xxxxxxxxxxxxx>
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Walter Katz
Sent: Thursday, May 23, 2013 9:04 PM
To: IBIS-ATM
Subject: [ibis-macro] BIRD 158.3
All,
Please review version 158.3 (Tstonefile AMI models) before I send the final
version to Michael tomorrow afternoon.
The major change is that there are now two Tx voltage levels (Tx_Vol and
Tx_Voh) that determine the differential step response stimulus that is assumed
for generating the Impulse Response of the channel. This make BIRD158
Tstonefile models directly convertible to BIRD 160 external models, and gives
the model maker the ability to determine the common mode voltage when
generating the Impulse Response of a channel.
Walter
Walter Katz
wkatz@xxxxxxxxxx<mailto:wkatz@xxxxxxxxxx>
Phone 303.449-2308
Mobile 303.335-6156
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