Solution ID: rd09112003_4753
Last Modified: Feb 09, 2006
Product Category: Devices
Product Area: I/O
Product Sub-area: IBIS Models

Problem

Do Vref, Rref, and Cref values have any correspondence to V_fixture, R_fixture ,and C_fixture parameters in the [Rising Waveform] and [Falling Waveform] section of the IBIS file?

Solution

The *ref and *fixture parameters are two different things: according to IBIS Specification 4.0, the *ref parameters are the test load that the semiconductor vendor uses when specifying the propagation delay and/or output switching time of the model. At that load, Vmeas is where Tco is valid. These numbers help to facilitate board-level timing simulations; on the other hand, the *fixture parameters describe how the buffer was loaded when generating the waveforms. These numbers are useful in calculating the current during HIGH to LOW or LOW to HIGH transitions.

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