Re: [SI-LIST] : Package Parasitics Modelling

Christian S. Rode (csrode@mediaone.net)
Mon, 29 Mar 1999 18:17:38 -0500

Still, 3 ohms (?) is much better than 0.05 ohms. I guess I wrote that
last message from an obsolete perspective. In days gone by I think
they intentionally used to add a poly serpentine resistor (over thick
field oxide) to limit the discharged current. How they get to 10KV
input protection today is beyond my ken.

A modern model might then be 3 ohms in series with
protection diode capacitance + 100 ohms (several squares of
20 ohm /sq diffusion/poly) in series with the input gate capacitance
(negligible?)

tomda wrote:

> If there was significant resistance between the input pin and the C
> associated with the input protection devices it would show up in the input
> VI curves. We don't see any significant R in series with the protection
> devices when we make our measurement based models. The current in those
> "diodes" can easily get to over 100 mA before the voltage across the device
> is 1 volt.
>
> Tom Dagostino
>
> -----Original Message-----
> From: Christian S. Rode [SMTP:csrode@mediaone.net]
> Sent: Monday, March 29, 1999 11:16 AM
> To: si-list@silab.eng.sun.com
> Subject: Re: [SI-LIST] : Package Parasitics Modelling
>
> A question about IBIS input models. I assume a good portion of the input
> capacitance
> of these models (C_comp) is associated with the input protection structures
> and that
> there can be significant resistance between that capacitance and the pad.
> That's
> not modeled in (earlier) IBIS models (and the EIA FAQ's "it's included
> in the I-V characteristics" isn't relevant). 50 milliohms (or whatever)
> for R_pkg will
> give an unnaturally high-Q for the input model. What would be a range of
> numbers for
> R between the L and C? (I'm currently guessing 100 ohms)
>
> Chris Rode
>
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