[802.3ae_Serial] Application of power budget model

Thread Links	Date Links
Thread Prev	Thread Next	Thread Index	Date Prev	Date Next	Date Index

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.