Re: [SI-LIST] : Best type of models, edge rates & load

D. C. Sessions (dc.sessions@vlsi.com)
Mon, 26 Jul 1999 14:49:37 -0700

Adrian Shiner wrote:
>
> Surely all this data sheet spec rise & fall times info is becoming "foo dust" as switches become faster? The slew rate of a voltage waveform at a given point on a printed circuit, driven from a perfect switch (zero switch time)
> depends solely on the current source/ sink capability of the generator being switched, its approximation to a current or voltage source and the circuit impedance.

Not really. The output current doesn't go instantaneously from full-drive
sink (or off) to full-drive source, so the output waveform isn't *entirely*
a capacitive-charging curve. In fact (as we've been discussing) real loads
are close to the real axis, so the I/T curve dominates.

> Why don't the IC manufacturers defne the output driver broadly in line with the above?

Actually, that's what too many do and what we've been griping about.

-- 
D. C. Sessions
dc.sessions@vlsi.com

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