Hi All,
I'd like to share some thoughts on the recent discussion about Rx GetWave
output waveform.
1. If the standard or Rx model specifies a threshold that EDA tool uses to
perform NRZ logic decision on the Rx GetWave output, then there is no need to
ask whether the Rx GetWave output is single-ended or differential, or whether
it should be centered at 0 V, or whether it should be decomposed into DC and AC
components. All EDA tool needs is to compare the GetWave output to the
threshold. In the PAM4 case, we don't need to ask these questions because PAM4
thresholds are defined.
2. There are two approaches to define the NRZ threshold.
* Approach 1: the standard specifies that the NRZ threshold used by EDA
tool is always at 0 V. The Rx model internally positions its GetWave output
according to this convention. Note that in theory the standard can use any
value for the threshold. For example, we can even define the value to be 1
million V.
* Approach 2: introduce a new threshold parameter. Its Usage is Out, and
its value is returned by the Rx mode. This is the approach we took in the PAM4
case.
3. These two approaches are mathematically equivalent
Regards,
Fangyi
