RE: [802.3ae_Serial] Application of power budget model
Juergan -
I was away on vacation last week and unable to respond until today.
See responses beginning with "**TL -" below.
Thanks, Tom
-----Original Message-----
From: Rahn, Juergen (Juergen) [mailto:krahn@xxxxxxxxxx]
Sent: Monday, July 23, 2001 7:28 AM
To: Lindsay, Tom
Cc: stds-802-3-hssg-serialpmd@xxxxxxxx
Subject: AW: [802.3ae_Serial] Application of power budget model
Hi,
just for clarification :
The value "Tx_OMA_min_yz " is for the 1310 nm interface the value I find
in
the triple tradeoff table?
**TL - that was my intent.
If I look through the calculations you made up I find:
> Tx_OMA_min_yz = Tx_OMA_min+ (Various penalties) + (passive loss
variation)
and
**TL - I also included P_isi variation.
> Tx_OMA_min_yz = Rx_stress_OMA+ (Various penalties)+ (passive loss
> variation)+ Passive Loss
with (passive loss variation)=passive_loss_yz - passive_loss
with(Various penalties)= P_mpn_yz + P_rin_yz + P_mn_yz +
P_refl_yz+P_isi_yz
- P_isi+ etc.)
**TL - ok, but the last 2 terms are P_isi variation, which I would not
lump under "Various penalties".
This gives me:
> Tx_OMA_min =Rx_stress_OMA+ Passive Loss+ (passive loss variation)
>
**TL - If I did my algebra correctly, Tx_OMA_min = Rx_stress+
Passive_loss. See #1 under Stressed sensitivity values in standard.
This however would mean that the stressed sensitivity does not consider
penalties (only the wavelength independent P_isi). Is this correct?
**TL - per my equations, you are correct, but all other penalties and
wavelength variations would show up in the Tx triple trade-off curves.
As I mentioned before, they could possibly be applied in the stressed
sensitivity values instead or some other mix of the two.
Looking now through the Tables on the base of with my first
understanding,
I find the Tx_OMA_min_yz the stressed sensitivity and the informative
path
data. I cannot find in 1310nm the Tx_OMA_min which should be the input
value
to the triple tradeoff calculation. This means the calculation is done
on a
mixture out of informative and normative parameters and even parameters
which are given at no place as the wavelength dependence of the path
loss
(should by minor but if used to be defined).
**TL - I do NOT think that all informative or other behind-the-scenes
values need to be in the standard. However, I do believe they should be
documented somewhere in a upload or something equivalent, even if it's
to the private site. The way I would like to do this is to record the
"final" spreadsheet tool and the process by which it is used to generate
the standard's values. My email was a proposal on the process.
The TX_OMA is defined as a
function of spectral behavior in the 1300 nm case (if my first statement
is
correct) while the penalties are not given the same way. In order to
make
the standard understandable I think modifications are required, as it is
extremely difficult even to understand what the meaning of which figure
is.
**TL - per above, I don't see the need to show penalties, even at any
wavelength. However, see the 2nd paragraph under Stressed sensitivity
values in standard.
In the 1550 case the parameters are given in a different way.:
Given is a generic transmitter OMA value :
Launch power (min) in OMA minus TDP of -1.39 dBm (OMA)
This means using the systematic from above here the other value , namely
Tx_OMA_min is given as this implies the following:
> Tx_OMA_min_yz- Penalties = Tx_OMA_min.This this understanding correct?
So the above means in the parameters have to follow the equation:
> Tx_OMA_min = Rx_stress_OMA+ Passive Loss+ (passive loss variation)
The loss is defined to be 13 dB (neglecting the loss variation, not
given
anyway), and the stressed sensitivity is given with (-11.40)dBm in OMA.
This
means the Tx_OMA_min is in minimum +1.6 dBm OMA if we follow this
equation.
To compensate for the penalties in practice this has to be increased by
the
penalties , which are not explicitly stated in the transmitter table
however
a penalty is given in the receiver table. This is a vertical eyemask
penalty
as a test condition so at a test the receiver has to be verified with a
signal that shows 3 dB eye penalty. I am struggling in this respect a
bit
as I cannot find the minimum requirement for the transmitter stated
explicitly in the transmitter table only a 3 dB penalty as stated in the
receiver table is near to the difference out of the +1.6 dBm I calculate
out
of loss and stressed sensitivity and the value given in the table.
This leads to two questions:
1. Is the understanding in the above correct, should we add the eye
penalty
to the transmitter power or has the receiver to show higher sensitivity?
2. Should the presentation of those figures (if the consideration is
covert)
not modified a bit, as (at least for me and some systems engineers in my
organization) it is very confusing and not clear what meaning the values
have (what is also indicated by this discussion).
**TL - I apologize - my original email was focused on 850 and 1310 nm
systems. If we can get through my issues with those, then we can decide
if they are appropriate for 1550 nm.
Thanks,
Tom Lindsay
425/672-8003
Regards Juergen
> ----------
> Von: Tom Lindsay[SMTP:tlindsay@xxxxxxxxxxxxxxxxxxxx]
> Antwort an: Tom Lindsay
> Gesendet: Sonntag, 22. Juli 2001 03:36
> An: stds-802-3-hssg-serialpmd@xxxxxxxx
> Betreff: [802.3ae_Serial] Application of power budget model
>
> PMD'rs -
>
> There is consensus that all of the power budgeting numbers in clause
52
> (and 53?) need to be reviewed and updated. Also, one of the topics
kicking
> around is how the power budgeting values in the standard should be
related
> to the spreadsheet model. Clearly, the latter must be understood as
part
> of the process of doing the former. So, following on from Pier's
slides in
> Portland as a starting point for discussion, this email proposes my
> understanding of how the values and the model should be related. The
real
> goal is to come to agreement on a process and get it documented.
>
>
> Basis values - these values form the basic budget and parametric spec
> limits. These values appear to include worst-case Tx and cable and
nominal
> Rx parameter values.
>
> 1. Determine Tx_max based on Rx overload and/or laser safety
requirements.
> Typically an average power, but overload may want to consider peak (up
to
> 2x Tx_max).
> 2. Tx_min=Tx_max-Tx_range. Tx_range is typically 5-7 dB. If Tx_min is
in
> average power, then
> Tx_OMA_min = Tx_min + 3dB
> 3. Inherent Rx_sensitivity_OMA = Tx_OMA_min - budget
> 4. As a committee, iterate through steps 2-3, trading budget vs. all
other
> values such that achievable values are determined and constraints are
met
> (margin>=0 & P_isi<=3.6 dB).
>
>
> Stressed Rx sensitivity values in standard - based on the final basis
> values above
>
> 1. Rx_stress_OMA = Tx_OMA_min
> minus passive_loss
>
> In actual Rx stressed sensitivity testing, Rx_stress_OMA can be
increased
> by the portions of P_mpn, P_rin, P_mn, P_refl, etc. that are included
in
> the test setup.
>
> 2. Vertical_closure = P_isi.
>
> Note - to calculate P_isi, use a value for Rx BW that is equal to that
of
> the calibration filter used (7500 MHz, etc.).
>
>
> 3-tradeoff values in standard - for each spectral center y and width z
>
> Tx_OMA_min_yz = Tx_OMA_min
> plus (passive_loss_yz - passive_loss)
> plus (P_mpn_yz)
> plus (P_rin_yz)
> plus (P_mn_yz)
> plus (P_refl_yz)
> plus (P_isi_yz - P_isi)
> etc.
>
> Expressed differently,
> Tx_OMA_min_yz = Rx_stress_OMA
> plus (passive_loss_yz + P_mpn_yz + P_rin_yz + P_mn_yz + P_refl_yz,
> etc.)
> plus (P_isi_yz - P_isi)
>
> The variables without _yz are the basis values determined earlier.
>
> This treatment of the "other" penalties (P_mpn, etc.) is debatable,
but
> they must be accounted for somewhere in the standard. Otherwise it
will
> have negative margin per the spreadsheet. An option is to subtract
some or
> all of them in derivation of the stressed Rx sensitvity value. This
> general area is at the root of my desire to get this process
documented.
>
>
> Other questions
> 1. Should basis budget analysis include worst case Rx values (e.g.,
min
> BW), for example to ensure P_isi<=3.6 dB?
> 2. Should P_cross be included anywhere in Stressed Rx sensitivity
specs,
> or is it truly a Rx property?
> 3. Should there be any margin for unknowns, or is the conservatism in
the
> spreadsheet adequate? Since many of the penalties are uncorrelated,
they
> are overstated by linear addition in the model.
> 4. Per the model, "budget" is from TP2 to TP4, whereas system folks
will
> think of it as being from TP2 to TP3. Is this a concern?
> 5. Vertical_closure is calibrated on a scope, placing cursors at the
> innermost trace "means" per Figure 52-15 in draft 3.1 (non
change-bar).
> a. While this is clear using something like K28.5s, this probably
won't be
> clear with our 64/66B test patterns. This is its own issue, but it
raises
> another question:
> b. Which test pattern should be used during calibration - Typical or
> Jitter?
>
>
> Sorry to be only the question-guy and not doing more to provide
answers. I
> will not be able to join the conference call 7/24, but I should be
able to
> join 7/31.
>
> Thanks,
> Tom Lindsay
> Stratos
> 425/672-8005
>
>