RE: Open drain model

The rise time for an open drain or open collector device is a function of:

How fast the device turns off
The Load R to Vcc
The parasitic C at the node

Zero is not an acceptable answer, there will always be some kind of limiting
factor on the risetime of an open drain. Usually R load and C_comp are the
limiting factors, the turn off time of the transistor is usually relatively
fast.

Tom Dagostino
IBIS and Tau Modeling Manager
SDD
Mentor Graphics Corp.
503-685-1613
tom_dagostino@mentor.com

-----Original Message-----
From: Olli Timonen [mailto:Olli.Timonen@tellabs.com]
Sent: Thursday, November 09, 2000 5:42 AM
To: IBIS
Subject: Open drain model

Hi,

How should be the [Ramp] risetime dV/dt_r defined for an open drain
model because pad cell cannot produce a rise transition? I turned into a
model with open drain model and the rise time was defined as zero.
ibischk3 says it's OK but the parser of Interconnect Synthesis (ICX)
doesn't accept it.

regards,
Olli

 
Received on Thu Nov 9 09:57:15 2000