[ibis-macro] Re: Query on AMI BIRD
- From: Mike Steinberger <msteinb@xxxxxxxxxx>
- To: huangchunxing@xxxxxxxxxx
- Date: Wed, 18 Jul 2007 09:12:58 -0500
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
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