[IBIS] [Composite Current] with series termination

I would like to ask the simulator gurus out there how the BIRD95
[Composite Current] waveform would be used with series termination, ie.
reflective switching. With a 2.5V series terminated 0.5ns buffer
driving, say, a 2ns, 50 ohm transmission line, the pad voltage rises to
1.25V, stays there for quite a while, then completes the rise to 2.5V.
During the 1.25V period the pad current will be flat at about 1.25/50 =
25mA. This pad current flattening begins about half way through the
"normal" rise time, as measured using the standard test fixtures. At
that point the pad current flattens out at 25mA, but the [Composite
Current] is telling the simulator the VDDQ current needs to continue
dropping to zero.

Here are the 3 currents I see in a rising edge simulation of such a test
fixture. Sorry, I can't make the 3 curves add up to zero at all points
using ASCII graphics:

Pad current  :

-50 ---                                  reflection back to driver here
                                                     |

                                                     v

            _______________________________________/\

           /                                         \

          /                                           \

  0 ___  /                                             \_____________

 


VDDQ current  :

          /\
50 ---   | |                                                    
         | |

         | |

         | \_______________________________________/\

         |                                           \

         |                                            \

  0 ___  /                                             \_____________



GND current  :

              
-50 ---                                                         
          /\

         | |

         | |

         | |

         | |

  0 ___  /  \_______________________________________/\_______________



[Composite Current] probably looks like this  :

          /\
50 ---   | |                                                    
         | |

         | |

         | |

         | |

         | |

  0 ___  /  \________________________________________________________   
      

My question is, will the simulator deliver the constant 25mA current at
the pad for several nanoseconds if it is being told that VDDQ current is
a spike that drops to zero at the end of the 0.5ns "normal" rise time?
This may have come up before, but if so I haven't heard it put quite
this way.

Mike LaBonte

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