Just wondering if anyone has any thoughts on this one?
I didn't have a test case to test this. I looked at the user guide and found this description.
For single-ended nets, the monotonicity threshold check is performed while the waveform is between VIL(DC) and VIH(DC). Simulation uses the following receiver threshold information from the IBIS model (highest priority first):
- [Receiver Thresholds] keyword, Vth - Vinl_dc subparameter
- [Model Spec] or [Model] keyword, Vinl subparameter
- [Receiver Thresholds] keyword, Vth + Vinh_dc subparameter
- [Model Spec] or [Model] keyword, Vinh subparameter
It makes sense to use the Vin[l,h]_dc subparameters, and I hoped that it would make the actual thresholds from the calculated Vref value reported in the DDR report.
I made a small DDR4 test and adjusted the [Receiver Thresholds] subparameters to get some monotonicity errors. It appears that the monotonicity check uses all the values (including Vth) from the IBIS receiver. It appears that the check does not use the calculated Vref value. What does the DDR4 specification say about monotonicity requirements?