06-25-2020 01:10 AM
In the .csv-file that contains the data of an Eye Scan there are the two values "vertical opening" and "horizontal opening". Can anybody explain how they are calculated or is there a definiton for them somewhere?
Can they be seen as rough values for the margin the system has at a certain BER?
06-26-2020 08:43 AM
The opening is the numbers of steps (vertical)or percentage of the UI horizontal that sees no errors with the current number of samples. It shows the margin that you have at the current number of samples taken. It is usually used in conjunction with an "eye mask" to qualify a channel for production. For instance, you might typically be looking for +-30 steps vertical clearance and +-.15 UI horizontal clearance at 10^9 samples to give a BER of 10^-15 over PVT. (assuming you meet and continue meeting all the data sheet specs on voltage, noise etc.)
06-28-2020 11:04 PM
A single eye scan measurement consists of accumulating the number of data samples (sample count) and the number of times that the offset sample disagreed with the data sample (error count).
The bit error ratio (BER) at the programmed vertical and horizontal offset is the ratio of the error count to the sample count. The sample count can range from tens of thousands to greater than 10^14. Which means the BER is lower if the vertical/horizontal offset is far away from the center. You can learn more from RX margin analysis, for BER calcucation, equation 4-2(LPM), equation 4-3(DFE) ug578:
06-28-2020 11:48 PM
06-29-2020 07:57 AM
Yes the margin needed across PVT is found through extensive temperature testing of worst and best case silicon.