[ibis-macro] Re: Query on AMI BIRD

  • From: Huang chunxing <huangchunxing@xxxxxxxxxx>
  • To: Mike Steinberger <msteinb@xxxxxxxxxx>
  • Date: Sat, 21 Jul 2007 10:45:42 +0800

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?
    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

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? 

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 
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> >    above. It may be privileged and confidential. If you have received this 
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> >    in error, please destroy any and all copies of this message including 
> > attached 
> >    files in your possession.
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