Re: [BP] how to evaluate signaling method
mike,
First to comment on your possible responses:
1) If the interference is a fairly large fraction of the baud rate
the adaptation will not be able to track it directly and it tries
to chop out that frequency it will miss any data in that range.
2) Slightly re-worded: it may be much more sensitive to some
frequencies. So far at Agilent we have not seen this, but it
might happen. We will have to remain alert.
3) If the effective Rx EYE is very sharp, with very small difference
between the minimum EYE opening and the maximum amplitude this
will happen. In the real world noise will prevent it from
happening. In any event the amplitude just below where failure
will be the interference tolerance.
The reasons for using a constant frequency are:
1. It spends a lot of time near its peak therefore doing a good job
providing worst case interference.
2. In actual measurements the interfering signal cannot be injected
right at the Rx and will pass through some dispersive elements.
A single frequency sine wave is the only signal which will not
have its wave shape altered by the path.
For simulation purposes, we could use some sort of PRBS signal since it
need not suffer degradation. It will have many frequency components and
remain at its peak value (+/-) essentially all the time.
charles
> Charles,
>
> It seems that if the interference is a single frequency interferer, then
> we need to consider the possible responses of a PHY to the interference:
> 1) it might, in the case of an adaptive PHY, track some of it out
> 2) it might fail at one frequency, where at another it might pass
> 3) If might pass until a defined amplitude, then fail totally (likely)
>
> In all of these cases, however, a single frequency test ignores the
> effect of the frequency distribution of real interferers. Some
> frequency components will be tracked out (by CDRs and adaptive
> equalizers, etc), while others will not. The real-world performance of
> the PHY will be a combination of these. I think, for this reason, that
> we need to consider the interferer frequency distribution in this test.
> Can this test be modified to account for this? Can we use measured
> NEXT/FEXT response to
>
> .../Mike
>
> -----Original Message-----
> From: owner-stds-802-3-blade@LISTSERV.IEEE.ORG
> [mailto:owner-stds-802-3-blade@LISTSERV.IEEE.ORG] On Behalf Of Charles
> Moore
> Sent: Tuesday, August 24, 2004 2:16 PM
> To: STDS-802-3-BLADE@LISTSERV.IEEE.ORG
> Subject: Re: [BP] how to evaluate signaling method
>
> john,
>
> 1. a. In measurement we pick one frequency and sweep the amplitude
> of interference. By plotting BER vs interference amplitude
> at the we can find the Rx noise. Knowing Rx noise we can
> compute an adder to the speced Xtalk tolerance to
> extrapolate
> from a measurable BER to the BER we want. This really
> should
> only need to be done at one frequency.
>
> b. The xtalk to use is the upper bound of the Xtalk which the
> system specs allow. The amount of Xtalk will depend on the
> channel, the Tx low pass characteristics, Tx equalization,
> and signaling type. All these need to be taken into account
> but some things like Tx equalization may be hard to know
> a-priori and worst case values need to be used.
>
> c. We do not have much comparison.
>
> 2 Hspice allows elements which are defined in terms of
> S-parameters
> in touchstone (s4p) files. You measure them, we will use them
> in
> simulation, and that will be real data.
>
> 3. The number of bits used a trace off between simulation time and
> confidence. Maybe we should hunt for the interference
> tolerance
> limit using a small number of bits, then use a larger number to
> confirm it. Also, by worst-casing the interfering signal we
> enormously reduce the amount of simulation needed.
>
> 4. The PWL will be complex but manageable i think. I should have
> a
> start at it to show by next meeting.
>
> charles
>
>> Charles,
>> Some questions for you.
>> 1. I have gone back and reviewed your presentation, and it looks to me
>
> for
>
>> crosstalk that you are proposing for a given frequency doing an
>
> amplitude
>
>> sweep then plotting the BER versus the Interference amplitude.
>> a. I assume for multiple frequencies this process has to be
>> repeated?
>> b. This process seems to look at the xtalk performance of the
>> channel
>> only, rather than the product of the Tx spectrum and channel.
>> Can
>> you comment?
>> c. Have you compared the summation of signal and proposed xtalk
>> procedure against signal and broadband xtalk generation to
>
> see
>
>> how
>> they compare? Can you share results?
>>
>> 2. You are proposing modeling the channel in HSPICE? Why would we do
>
> this
>
>> as opposed to use of real data?
>>
>> 3. The number of bits being proposed to run is 127 * 4 = 508 plus some
>> offset bits. This seems like a very small number of bits to consider,
>> especially in light of the BER we are trying to achieve.
>>
>> 4. Won't the PWL become complex pending the Tx solution being
>
> proposed?
>
>>
>> John
>>
>>
>>
>> -----Original Message-----
>> From: owner-stds-802-3-blade@listserv.ieee.org
>> [mailto:owner-stds-802-3-blade@listserv.ieee.org] On Behalf Of Charles
>
> Moore
>
>> Sent: Monday, August 23, 2004 6:11 PM
>> To: STDS-802-3-BLADE@listserv.ieee.org
>> Subject: [BP] how to evaluate signaling method
>>
>> guys,
>>
>> What i propose for signaling evaluation is an extension of
>> ideas i presented at the July meeting in Portland in the talk
>> "Receiver Testing Using Interference Tolerance Measurements".
>>
>> The basic idea is to do a time domain simulation of the Tx,
>> channel, and Rx using a standard, generally available simulator.
>> To provide a simple and reproducible model of cross talk, a
>> sinusoidal interfering signal will be added at the input to the
>> receiver. The amplitude of the interfering signal will be
>> increased until the signal at the output of the Rx is deemed to
>> be no longer usable. The highest level of interference at which
>> the Rx provides a usable output will be called the interference
>> tolerance. If the interference tolerance is below a specified
>> (and perhaps signaling method dependent) value the simulated data
>> path is non-compliant. If the interference tolerance is above
>> the specified value, it is compliant and has a margin which is
>> equal to the difference between the simulated tolerance and the
>> spec. In general more margin is better.
>>
>> This is the basic idea. Details which i suggest be adopted as
>> part of the method but which can be changed without altering the
>> basic idea include:
>>
>> 1. Use hspice as the simulator.
>>
>> 2. Model the transmitter as:
>> a. 1 or 2 piecewise linear (PWL) current sources:
>> i. 1 current source with NRZ encoded data for NRZ
>
> signaling.
>
>> ii. 1 current source with precoded data for duo-binary
>> signaling.
>> iii. 2 current sources with 1/3 and 2/3 NRZ amplitude with
>
> LSB
>
>> and MSB data respectively, for PAM4 signaling.
>> b. Rise times of PWL current sources set at about 30ps for NRX
>
> or
>
>> duo-binary or 60ps for PAM4
>> c. R,L,C network between current source and Tx pins to provide
>> reasonable return loss vs frequency
>>
>> 3. Include signaling method dependent Tx equalization in PWL current
>> source model. Control equalization with hspice parameters.
>>
>> 4. Include some modeled Tx Jitter in PWL current sources.
>>
>> 5. Use hspice S-parameter network modeling capabilities to model
>> channel.
>>
>> 6. Allow proprietary Rx models by Encryption.
>>
>> 7. Add interference signal at Rx with sinusoidal current source.
>>
>> 8. Allow for Rx input noise in the minimum interference tolerance
>
> spec.
>
>>
>> 9. Determine that the Rx provides a usable output by:
>> a. showing that data out of Rx gives the correct bits.
>> b. If Rx does not include re-clocking, show that output eye is
>> wide enough
>> c. If Rx does not include a limiting stage, show that the output
>> eye has enough amplitude.
>>
>> 10. Use 127 bit long PRBS pattern for data. Offset a few bits between
>> pattern for MSB and LSB to give PAM4 pattern or use shorter PRBS
>> pattern for LSB. Repeat PRBS pattern at least 4 times to allow
>> interference to "walk through" the data.
>>
>> 11. Test with more than one interfering rate. Interesting rates
>> should include:
>> a. For NRZ or PAM4, (1+.2/127)*(baud rate)/2
>> b. For duo-binary, (1+.2/127)*(baud rate)/4
>>
>> charles
>>
>> --
>> |--------------------------------------------------------------------|
>> | Charles Moore
>> | Agilent Technologies
>> | ASIC Products Division
>> | charles_moore@agilent.com
>> | (970) 288-4561
>> |--------------------------------------------------------------------|
>
>
>
> --
> |--------------------------------------------------------------------|
> | Charles Moore
> | Agilent Technologies
> | ASIC Products Division
> | charles_moore@agilent.com
> | (970) 288-4561
> |--------------------------------------------------------------------|
--
|--------------------------------------------------------------------|
| Charles Moore
| Agilent Technologies
| ASIC Products Division
| charles_moore@agilent.com
| (970) 288-4561
|--------------------------------------------------------------------|