[ibis-macro] Re: Query on AMI BIRD
- From: Mike Steinberger <msteinb@xxxxxxxxxx>
- To: Huang chunxing <huangchunxing@xxxxxxxxxx>
- Date: Sat, 21 Jul 2007 14:05:33 -0500
Huang-
Your understanding of the problems and challenges is correct. I've added
some more details below.
Mike Steinberger
Huang chunxing wrote:
Mike,
Thanks for your detailed answer. You really help me know some clues to solve
the problems, but I still have some unclear points listed below.
1) What's peaking filter? It is continous time filter composed of zeros and
poles?
You are correct. I apologize for the jargon.
I think the optimal coefficients calculation for non-adaptive equalization
is tough task. In my opinion, the impulse response is most suitable for
determining equalization tap and coefficients range. When we only consider the
transmitter equalization, it may use impulse reponse to calculate optimal
coefficients. In order to dsitinguish receiver equalization, I would like to
call transmitter equalization emphasis. But when receiver have equalization
either, like DFE or CTE, I am not sure the coefficient determined by impulse
response will be best. Because the optimal coefficient is only calculated by
emphasis itself and doesn't consider the equalization case, like type,
coefficients tap and range. I think it will be different from that optimal
coefficient calcuated by the method considering emphasis and equalization
together. Like two cases below, I think optimal coefficients of case a is
different from that of case b.
a)emphasis---link---receiver without equalization
b)emphasis--link---receiver with equalization
You are correct that the equalization solution must jointly optimize
transmit and receive equalization, and that one cannot obtain a good
solution by attempting to optimize the receive equalization without
knowledge of the transmit equalization.
Note, however, that the impulse response output by the transmitter's
Init() function can include the effects of the transmit equalization. If
the impulse response input into the transmitter's Init(0 function is the
impulse response for the passive electrical interconnect, then the
impulse response input into the receiver's Init() function represents
the effects of the transmit equalization and the passive electrical
interconnect. Given this impulse response as its input, the receiver's
Init(0 function can perform a valid optimization.
This same approach also applies to the GetWave() functions.
Obtaining a globally optimal equalization solution is actually quite
difficult, and any such solution may not be unique. The typical approach
is to optimize the transmit equalization and then let the receive
equalization optimize itself. That may not achieve the best solution,
however. It is also possible to choose transmit equalizer settings which
leave more of the equalization to be done by the receive equalization.
Depending on the capabilities of the transmit and receive equalizers,
such a solution may be better. Such solutions can be evaluated by
setting the transmit equalization and then letting the receiver optimize
itself. In this case, however, choosing the transmit equalization
setting requires some insight into the global equalization solution.
IBIS ATM models are sufficient to provide the SerDes characterization
information needed for a global optimization; however, a truly global
optimization must be implemented outside the scope of the IBIS ATM
models themselves.
My knowledge of equalization is very limited , maybe I omitted some optimal
coefficients method which could solve my case, or my talk is just nonsense. : )
2) I know DCD caused by transmitter is different from that caused by receiver and DCD caused by receiver is most contributed by refernece voltage shift. Here I mainly care about DCD caused by transmitter. Only the DCD caused by transmitter do transfer through channel and will be amplified. Whether the method DCD imposed on the data signal or method which DCD imposed internal to the transmitter model you suggested, I think it should be implemented in non-LTI mode in order to modulate the DCD jitter on data signal. In other words, DCD should be implemented in GetWave() function and simulator will do the bit_by_bit simulation. Did I get the right point?
There are actually a number of ways that one can approach the modeling
of transmitter DCD; and running a non-LTI simulation, for example by
using the GetWave() functions, is certainly one valid approach.
I'm aware of several other approaches which can be based on the impulse
response information available from an Init() function; however, the
complete implementation of these approaches is outside the scope of the
Init() functions themselves. In fact, the approach that I think is the
most rigorous, accurate, and efficient needs only the impulse response
information from the Init() functions. This method will be implemented
in an EDA tool, however, and is outside the scope of the modeling standard.
Thanks again. Have a nice day!
Regards,
Huang
Huawei Technologies Co.,Ltd.
Tel: 86 755 28976229
FAX: 86 755 28976758
Email: huangchunxing@xxxxxxxxxx
Web: http://www.huawei.com
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----- Original Message -----
From: "Mike Steinberger" <msteinb@xxxxxxxxxx>
To: <huangchunxing@xxxxxxxxxx>
Cc: "IBIS-ATM" <ibis-macro@xxxxxxxxxxxxx>
Sent: Wednesday, July 18, 2007 10:12 PM
Subject: Re: [ibis-macro] Query on AMI BIRD
Huang-
Thank you for your questions. We very much appreciate your interest in
this standard.
I have inserted some responses below. Please let me know if I have
failed to address your concerns.
Mike Steinberger
SiSoft
Huang chunxing wrote:
Hi Experts,
I have some difficult in understanding the AMI BIRD.
1) Most equalization of RX and TX is non-adaptive. Chip vendors don't have any
adaptation codes to embed into DLL function and the DLL function won't have the
ability to calculate the optimal equalization coefficients. Then who will be in
charge of calculating the optimal equalization coefficients, users or
simulators? Is it possible for simulator to do this kind of work?
You are partially correct in that some of the equalization in the
current designs is not adaptive; however, you're not entirely correct in
that some of the equalization in the current designs is adaptive. In
general, transmit equalization is not adaptive while receive
equalization (either decision feedback equalization (DFE) or peaking
filter) usually is. Thus, a receiver model truly is responsible for
optimizing the receive equalization, and is in fact the only entity in
the simulation which can perform this function, since the receive
optimization algorithms tend to be highly proprietary.
For (non-adaptive) transmit equalization, the situation is more complex.
In most real systems, the transmit equalization settings must be
determined by experiment during system integration; and it is quite true
that the transmitters themselves are not able to perform this
optimization on their own. In simulation, however, there are algorithms
which can determine the optimum transmitter equalization settings given
the impulse response of the channel and the configuration of the
equalizer (e.g., number of taps, tap spacing, available tap weights).
The difference between real world and simulation is that in the real
world, the impulse response of the channel is not available to the
transmitter.
In the simulation, a number of optimization algorithms are possible. All
of them require the impulse response of the channel and the
configuration of the equalizer(s); however, the optimization criterion
can vary quite a bit, and so the algorithm to optimize to the chosen
criterion can vary as well. Thus, while the optimization algorithm for
the transmitter truly is a separate function, it is a function which
offers vendors another opportunity to differentiate their offering.
Since the DLL is some packaging that will already be in place, it is
also a convenient place to put this other function. Please note that
this does not necessarily prevent the EDA platform from also
implementing some form of optimization, although to do so, the EDA
platform must somehow get a description of the equalizer configuration.
2)If the channel is LTS, all simulation will be done by impulse response mode.
How to consider the jitter effects, especially DCD. According to PNA(Phase
Noise Amplifier) and experiment, DCD will be amplified by the low-pass channel.
Direct statistical processing without DCD amplification won't be accurate.
After discussing this point at some length, we concluded that the LTI
assumption is not sufficient for all modeling needs. Thus, while the
Init() function and its associated processing depends on the LTI
assumption, the GetWave() function implements a time domain simulation
which only assumes that the passive electrical interconnect is LTI.
Thus, the GetWave function is free to model nonlinear and time varying
behaviors of the pin electronics.
As regards DCD in particular, there are two entirely satisfactory ways
to model the effects of this impairment using models which are compliant
with this standard:
1. The DCD can be imposed on the data signal that is input into the
transmitter model. In order to do this, the data signal must have finite
rise and fall times, preferably greater than the DCD to be imposed;
however, that is entirely consistent with the real world that is being
modeled. Every data generator has a finite rise and fall time.
2. The DCD can be imposed internal to the transmitter model. This is
probably more appropriate and more accurate since in the real world the
DCD will be caused by circuit effects internal to the transmitter.
Similarly, a real receiver can introduce DCD as well, and that DCD will
have a different effect than DCD at the transmitter. It may therefore be
appropriate for receiver models to implement DCD as well.
The problem may do not belong to AMI category and maybe I missed something
here. I hope some experts could help clarify it. Thanks in advance.
Regards,
Huang
Huawei Technologies Co.,Ltd.
Tel: 86 755 28976229
FAX: 86 755 28976758
Email: huangchunxing@xxxxxxxxxx
Web: http://www.huawei.com
Warning: The information contained in electronic mail message is intended
only for the personal and confidential use of the designated recipient(s)
named
above. It may be privileged and confidential. If you have received this
communication
in error, please destroy any and all copies of this message including attached
files in your possession.
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