Re: The voltage range

Vincent,

A diode has a V/I curve that characterizes the clamping
characteristic of that device. Discrete diodes tend to
have extramely strong clamping characteristics, and so
appear to have one particular Vf. However, a real diode
actually has a finite resistance. That resistance constitutes
what the V/I curve of the device will look like after the
diode has reached its Vf clamping voltage. Most CMOS
clamp diodes are actually ESD structures on the die, and
are designed to have fairly large losses. As a result,
the V/I curve should be extended in IBIS modeling to account
for the large real resistance of the device, and the imperfect
clamping that will occur as a result.

regards,

--scott

Scott McMorrow
SiQual/Stramond

> Hi all,

> I have a question on the range of the voltage for Power and
> Gnd clamps. The question is why do we need such wide range.

> Is it not true that on an actual PCB, even if the voltage
> at any pin tends to go higher than Vcc (due to L-C
> effects etc.), the clamping diodes will allow it to go only
> till Vcc+Vf, where Vf is the forward voltage of the clamping
> diode? Basically that's what the diodes are for.

> What is going to happy if we do provide that wide range of
> data? Is it going to fail on QC check?

> --
> Best Regards,

> Vincent Chang
>
 
Received on Thu Jul 3 12:17:27 1997