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. 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 there 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 the second an
additive part (non-LTI) from a DFE. If the part of the upstream
equalization is convolved with the output of Rx2, then both the CTLE and
DFE equalization will scale this part of the upstream equalization while
if the if all of the effects of the upstream equalization, this only the
CTLE scales all of the effects of the upstream equalization.
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:
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 give the wrong results.
* The flow in BIRD-190 does not allow the Rx2 to optimize itself
correctly.
* The flow in BIRD-190 give the wrong results.
* The flow in BIRD-166 does allow the Rx2 to optimize itself
correctly.
* The flow in BIRD-190 give the right results.
Walter
