AR# 11450: Virtex-II/-II Pro/-4/-5/-6 IBIS/SPICE models - How does an IBIS or SPICE simulation account for the DCI impedance value?
Virtex-II/-II Pro/-4/-5/-6 IBIS/SPICE models - How does an IBIS or SPICE simulation account for the DCI impedance value?
In an IBIS or SPICE simulation of any of the Virtex-II/-II Pro/-4/-5/-6 I/O standards that employ DCI (digitally controlled impedance), how does the simulation account for the impedance value?
Any IBIS or SPICE model represents a single DCI impedance setting. With the exception of 40 and 65 ohm LVDCI models in the Virtex-II FPGA IBIS release, and 25/40/65/75 ohm LVDCI models in the Virtex-II SPICE release, all Virtex-II, Virtex-II Pro, Virtex-4, Virtex-5, and Virtex-6 DCI models represent 50 ohms termination. There is not a way to change these impedance settings.
Note: DCI simulation models (besides the V-II models mentioned above) assume 50 ohms on the reference pins VRP and VRN. When using LVDCI_DV2 the effective impedance is 1/2 of what is seen on VRP/VRN, so the effective impedance will be 25 ohms in series.