Re[2]: BIRD24 COMMENT

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You are correct in observing that there is no V_load specified in IBIS2.0 with
the key word Ramp. To explain what happened here requires a little history.

In IBIS1.1 R_load was a fixed 50 Ohm resistor, which was connected to Vcc or
GND. (See "Notes on data derivation method" section of IBIS1.1). In IBIS2.0 we
added the sup-parameter R_load to the Ramp keyword, because a ramp measurement
with a very weak buffer could result in a very small voltage swing which
significantly reduces the accuracy of the measurement. Using a different R_load
overcomes this problem. This sub-parameter was added for those who want to
continue to use the ramp keyword rather than the [Rising Waveform] and [Falling
Waveform] keywords provided by IBIS2.0.

However, when using the waveform keywords, which are a superset of the Ramp
definition, you can have an arbitrary waveform with any R_load and V_load
specified. Since a ramp can be considered a special case of a waveform (or V-T)
curve (which replace the Ramp keyword), I do not see any reason to retroactively
add a V_load specification for Ramp.

Arpad Muranyi
Intel Corporation

This raises an interesting point. How reliable is the value of C_comp itself?

Anyway I am not in favor any "implied" quantities associated with waveform
tables. Every parasitc associated with that wave should be explicitly
stated. So for example C_dut can include the effects of C_comp.

While I am at it I also want to raise another point regarding ky word Ramp.
That specification includes R_load. But there is no provisison for V_load.

If we look at the notes on Ramp rates there are situations in which V_load is
vendor specified and there is no place in IBIS models where thie information
is
carried.

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Subject: Re: BIRD24 COMMENT
To: ibis@vhdl.org, bob@icx.com
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