AnsweredAssumed Answered

DDR Batch wizard monotonicity

Question asked by pjs on Apr 4, 2018
Latest reply on Apr 9, 2018 by weston_beal

Hi,

 

I'm running some DDR4 analysis and I have some DDR Writes which are failing the monotonic test. When I examine the waveform I see the following:

 

 

One thought as to why this is might be failing is that the default VINH in the IBIS is defined as 1.06V which corresponds directly with the blip we are seeing in the waveform. Having spoken briefly to the DDR chip manufacturer they suggested that in DDR4 the thresholds are dynamic and are based off the DQ Rx mask and the VcentDQ. They insinuated that the VINH value is only really there as a placeholder to meet the IBIS standard.

 

Do you know if the DDR batch wizard is using the VINH from the IBIS file or will it be using a dynamic value based off the VcentDQ? The results table suggests that the 'Reference voltage used' is 762mV and so I believe this leaves plenty of headroom. The eye density plots also show all the DQ lines meeting the Rx mask with plenty of headroom.

 

Do you have any idea what thresholds are being used during the monotonic test?

Outcomes