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?
If I look through the calculations you made up I find:
> Tx_OMA_min_yz = Tx_OMA_min+ (Various penalties) + (passive loss variation)
and
> 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.)
This gives me:
> Tx_OMA_min =Rx_stress_OMA+ Passive Loss+ (passive loss variation)
>
This however would mean that the stressed sensitivity does not consider
penalties (only the wavelength independent P_isi). Is this correct?
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). 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.
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).
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
>
>