Ambrish,
Got time to review my response to BIRD 190, and would like to correct what
I wrote. Changes made in line.
Walter
Ambrish,
Can you please comment on the following statements.
This discussion is limited to statistical simulations of Redriver channels
with Tx1, Rx1, Tx2, Rx2 all Init-Only or Dual models.
1. BIRD 190 states:
a. The impulse response of the Rx2 model will not include all of the
effects of the upstream equalization, and therefore the Rx2 AMI_Init will
not be able to perform an accurate equalization, and therefore to ensure
successful simulations, the user should be allowed to turn off any
automatic equalization in Rx2.
2. As Fangyi so aptly demonstrated, the Rx2 equalization will include
two parts, one is a scaling (LTI) part from a CTLE and AGC, and the second
an additive part (non-LTI) from a DFE.
a. If the part of the upstream equalization that is excluded in the
input to Rx2 (as specified in IBIS 6.1 and BIRD 190) is convolved with the
output of Rx2, then both the CTLE and DFE equalization will scale this
part of the upstream equalization
b. If this part is not excluded from the input to the Rx2 then only
the CTLE scales the effects of the upstream equalization.
c. In case 2.a. the DFE is (incorrectly) added twice
3. For those of us that find this argument unconvincing, then
consider the solution space that the user must explore to find a "best"
solution if automatic optimization is disabled as proposed in BIRD 190.
a. Let us assume that the user has set all of the upstream
co-efficient to their optimum setting, and the Rx2 automatic equalization
is turned off by the user in accordance with BIRD-190.
b. How many simulations would the user be required to run to find the
"best" solution.
i.
Case 1
1. Assume that the Rx2 model has the following controls (typical
PCIeG4, IEEE 802.3bj)
a. 10 CTLE settings
b. 10 AGC settings
c. 4 DFE taps each having 10 tap setting
2. The answer is 10^6 simulations
ii. Case
2
1. Assume that the Rx2 model has the following controls (IEEE 802.3
400Gj)
a. 10 CTLE settings
b. 10 AGC settings
c. 14 DFE taps each having 10 tap setting
2. The answer is 10^16 simulations
b. It is a requirement of our customers that our tool determine the
AMI settings that give the "best" solution. Sweeping these setting in the
Rx2 as BIRD-190 requires is unacceptable.
In conclusion:
* The flow in IBIS 6.1 does not allow the Rx2 to optimize itself
correctly.
* The flow in IBIS 6.1 gives the wrong results even when Rx2
optimization is turned off.
* The flow in BIRD-190 does not allow the Rx2 to optimize itself
correctly.
* The flow in BIRD-190 give the wrong results even when Rx2
optimization is turned off.
* The flow in BIRD-166 does allow the Rx2 to optimize itself
correctly.
* The flow in BIRD-166 give the right results.
Walter
