[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
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