[SI-LIST] Hspice simulation in relates with capacitor

Hi.everyone
Now I'm making simulation with hspice.
Here are two cases and both AC coupling:
1.transmitter(88e1043)----||-------receiver(HDMP1636)
2.transmitter(HDMP1636)---||-------reciver(88e1043)

Stimulus :1.25Gbps,LVPECL
Termination as per vendor's recommendation.

For case1,when we use 10000pf capacitor,the eye diagram crossing point is abt 
200mv.(eye diagram amplitude is 400mv)
and we try 400pf capacitor again,the eye diagram opening and amplitude same as 
10000pf,but the crossing point is 0mv.
That means the differential signal's common mode voltage is changed.

For case2,the simulation result is almost no difference between 10000pf and 
400pf. 

Question is:
What on earth does the common mode voltage change with coupling capacitor for 
case1 ?
is it due to hspice simulator or there is some problem in 88e1043 model? and 
some other reasons? 

Thanks 


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