[ibis-macro] Re: An AMI Overview
- From: "C. Kumar" <kumarchi@xxxxxxxxx>
- To: wkatz@xxxxxxxxxx, ibis-macro@xxxxxxxxxxxxx, fangyi_rao@xxxxxxxxxxx
- Date: Mon, 12 Oct 2009 04:39:34 -0700 (PDT)
point 2:
it need not be convolution in the strict sense. it can be a "filtered"
response.
bottom line is you get a modified impulse response; the technique to get that
response is not relevant
--- On Sun, 10/11/09, fangyi_rao@xxxxxxxxxxx <fangyi_rao@xxxxxxxxxxx> wrote:
From: fangyi_rao@xxxxxxxxxxx <fangyi_rao@xxxxxxxxxxx>
Subject: [ibis-macro] Re: An AMI Overview
To: wkatz@xxxxxxxxxx, ibis-macro@xxxxxxxxxxxxx
Date: Sunday, October 11, 2009, 8:22 PM
Hi, Walter;
Thanks for your clarification of AMI methodology. I’d like
to see the overview or the spec also states clearly about following two topics.
1.
For non-LTI models that have GetWave, how does AMI_Init enable
model developers to also support statistical simulation using LTI
approximation?
2.
Do we explicitly assume the modified impulse returned by AMI_Init
is the CONVOLUTION between input impulse and the equalizer? I know at least one
model vendor would not be happy about this assumption because their modified
impulse is not from convolution.
Regards,
Fangyi
From:
ibis-macro-bounce@xxxxxxxxxxxxx [mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On
Behalf Of Walter Katz
Sent: Saturday, October 10, 2009 2:20 PM
To: IBIS-ATM
Subject: [ibis-macro] An AMI Overview
All,
We
have all been getting into the nuts and bolts of AMI. I think we need to step
back and understand what AMI is all about. The following has been said in many
ways in many places, but I think it is appropriate to review it at this time. I
do not know if this belongs in the IBIS AMI specification, but it sure would be
nice.
Walter
AMI
Overview
The
analysis of high speed (>4 Gbps) offers some simplifications and some
challenges. The simplifications arise from the fact the driver (Tx) final stage
output, and the receiver (Rx) input along with the interconnect between them
can be treated as Linear and Time Invariant (LTI) “Analog-Channel”.
This allows various mathematical techniques to be applied improving simulation
performance by orders of magnitude. The complication that has led to the
development of the AMI standard arises from the need for complex signal
processing in both the Tx before the final stage driver and particularly the Rx
after the Rx receiver. The good news is that the signal processing does not
interact with the Tx/Interconnect/Rx Analog-Channel. The signal processing that
is going on is considered important Intellectual Property (IP) of the IC
vendors, and this along with the need for simulating millions of bits and the
IP considerations led to the AMI standard.
A
SerDes-Channel consists of Tx signal processing, Analog-Channel and Rx signal
processing. The Tx AMI model represents the Tx signal processing, an impulse
response represents the Analog-Channel, and the Rx AMI model represents the Rx
signal processing.
The
Analog-Channel is represented as an impulse response hAC(t). It is the
differential mode impulse response of the interconnects between the Tx and the
Rx and includes the reactive load (impedance) of the Tx final stage driver and
the Rx receiver. This impulse response can be created using many mathematical
techniques, including, but not limited to simulation and TDR measurement.
Traditional IBIS does not model differential LTI buffers, this will be addressed
when I introduce new AMI reserved parameters. This is also related to the topic
of Vladimir’s presentation this Tuesday.
The
Tx AMI model and Rx AMI model may themselves be either LTI or non-LTI. If they
are LTI they can be represented accurately by an impulse response. If they are
not LTI, they can be approximated by an impulse response. AMI models are
delivered as executable code in the form of a Shared Object (SO) or a
Dynamically Linked Library (DLL), and an .ami ASCII file. All AMI DLL’s
have an AMI_Init entry, and an AMI_Close entry. This is all that is required if
the model is LTI. If a model is non-LTI then is must also have an AMI_GetWave.
If a model does have an AMI_GetWave then the model make is telling the EDA tool
that the model is non-LTI and that using the just impulse response from the
AMI_Init is not deemed sufficient to accurately model the channel.
The
.ami file tells the EDA tool if the model has an AMI_GetWave entry, and
sufficient information to configure the model, and to analyze the results that
the model generates.
When
a model is LTI it does not need a GetWave entry. When LTI, the only information
that need be abstracted from the model is the impulse response of the models
equalization. The input to the Tx AMI_Init function is the impulse response of
the channel. The input to the Rx AMI_Init function is the impulse response of
the channel combined with the impulse response of the Tx equalization obtained
from the call to Tx AMI_Init.
When
a model is non-LTI (or more importantly, the IC Vendor believes that the
non-LTI behavior is important) then it does require an AMI_GetWave entry. The
AMI_Init entry is used to return to the EDA tool an approximate impulse
response of the models equalization, and to pass on initialization information
to be used by the AMI_GetWave entry. The AMI_GetWave entry is then called
repeatedly with sequential blocks of waveforms. The waveforms are that are
input to Tx AMI_GetWave indicate the transition times of the digital stimulus
input to the Tx equalization circuitry. The waveforms that are output of Tx
AMI_GetWave are the waveforms that drive the Analog-Channel. The waveform that
is input to Rx AMI_GetWave is the waveform that is the input to the Rx buffer.
The output of the Rx AMI_GetWave is the waveform at the Rx decision point, and
optionally clock ticks indicating the location of each recovered clock. The EDA
tool processes the waveform at the Rx decision point, and either uses the clock
ticks or the Clock Recovery Mean and Rj to generate bathtub curves, BER and
other channel data.
A
fundamental principle of AMI modeling is that every EDA platform (both software
and hardware) will give the same results when presented with the same
Analog-Channel impulse response, the same AMI model conditions, and the same
input stimulus pattern. Each EDA platform may differ on how its sets the Tx and
Rx AMI model conditions, the stimulus pattern, how it creates the
Analog-Channel impulse response, and how it processes the resulting outputs.
Walter Katz
303.449-2308
Mobile
720.333-1107
wkatz@xxxxxxxxxx
www.sisoft.com
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