[ibis-macro] Re: Init_Returns_Impulse
- From: "Walter Katz" <wkatz@xxxxxxxxxx>
- To: <ambrishv@xxxxxxxxxxx>, <gedlund@xxxxxxxxxx>, <ibis-macro@xxxxxxxxxxxxx>
- Date: Tue, 30 Apr 2013 14:48:58 -0400 (EDT)
Greg,
On Page 158, the introduction to application scenarios makes it quite
clear. I highlighted in red the core point that the output of Init and the
output of GetWave are "independent representations of the device's
equalization". There are two fundamental ways of analyzing SerDes channels
- statistical and time domain. Statistical (e.g. StatEye) makes an LTI
approximation of the equalization, and allows for simulating large numbers
of UI and therefore predicting BER ~1e-12 to 1e-18. Most Tx and Rx can
accurately be modeled with the LTI approximation. Time domain simulations
are limited to 1e6 to 1e8 UI, and therefore are unable to predict BER
<1e-8 without extrapolation of bathtub curves, something that can easily
be shown to be unreliable.
Bottom line is that Statistical allows accurate prediction of small BER,
time-domain can be more accurate, but cannot predict small BER accurately.
"Dual models" allow the user to choose the appropriate method of
simulation, depending on the problem he is trying to solve.
10.2 Application Scenarios
The next two sections provide an overview of the two simulation types
supported for algorithmic models by the IBIS specification. Statistical
simulations require that the algorithm in the executable model file is
linear and time-invariant (LTI). Time domain simulations do not have this
requirement. Therefore executable model files used in time domain
simulations may also contain non-linear and/or time-variant (non-LTI)
algorithms.
System simulations will commonly involve a transmitter (Tx) and a receiver
(Rx) executable model file, each of which may perform filtering in the
AMI_Init function, the AMI_GetWave function, or both (i.e., a "dual"
algorithmic model). In the case of a "dual" algorithmic model, the
filtering functionality in the AMI_Init and AMI_GetWave functions are each
intended to be independent representations of the device's equalization.
Users of a dual model can elect to use either the AMI_Init or AMI_GetWave
filtering functionality, but not combine both simultaneously.
While the primary purpose of the AMI_Init function is to perform the
required initialization steps, it may also include LTI signal processing
algorithms. Therefore, statistical simulations may be performed using the
AMI_Init function alone.
Even though time domain simulations may also be performed with the LTI
AMI_Init and/or LTI AMI_GetWave functions, AMI_GetWave functions
containing non-LTI algorithms may only be simulated in the time domain.
Walter
From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Ambrish Varma
Sent: Tuesday, April 30, 2013 2:35 PM
To: gedlund@xxxxxxxxxx; ibis-macro@xxxxxxxxxxxxx
Subject: [ibis-macro] Re: Init_Returns_Impulse
Greg,
If GetWave_Exists = TRUE, Getwave is supposed to do any equalization for
the time domain waveform that it will receive. Init will only perform
equalization on the impulse response.
The idea for such models is that they can be used for both statistical
(Init based) AND time domain (Getwave based) processing. If you think that
it is slightly confusing - then I agree with you.
Thanks,
Ambrish.
From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Gregory R Edlund
Sent: Tuesday, April 30, 2013 2:15 PM
To: ibis-macro@xxxxxxxxxxxxx
Subject: [ibis-macro] Init_Returns_Impulse
If Init_Returns_Impulse = TRUE and GetWave_Exists = TRUE, what is GetWave
supposed to do? It can't do any equalization, right? Equalization is
happening in Init if Init_Returns_Impulse = TRUE.
Thanks in advance.
Greg Edlund
Senior Engineer
Signal Integrity and System Timing
IBM Systems & Technology Group
3605 Hwy. 52 N Bldg 050-3
Rochester, MN 55901
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