Re: High freq effects in i/o mo

Ravender,

Yes, whole heartedly! Way back when, when I first started using
Quad, the one question I had in mind was freqency dependent char-
acteristics of the output drivers and input receivers. All mea-
surements are done at DC, without any jw effects taken into ac-
count. And in doing so, as you have stated below, this would
lead to an understanding of the modelization or internal char-
acteristics of those devices looking into the output of a driver
or into the input of a receiver.

I feel it is necessary to take the imaginary component into effect,
and not rely simply on a lumped capacitance to a pin are some
"equivalent" series inductance of an io pin. The modeling becomes
even more important at higher frequencies, as you mentioned.

I did not fully get your drawings, with the BLA K. I was trying
to make sense, and thought perhaps the L meant inductance, etc.,
but lost it in the BA and K. A FAX with a sketch would do me
fine, and would be much appreciated.

I read with much interest your work on producing more accurate closed
form equations for characteristic impedance, etc. I think you are
doing an excellent job, and I am glad we have the right person at
the helm of this 'high-speed' ship. I have a lot of respect for you.

Any and all inputs with respect to Quad, IBIS modeling, XFX3D and other
new developments, as well as research you are conducting, is much appreciated.

   Take care,
- Chuck Catto -

****************

On Jan 6, 9:43am, "Ravender Goyal" wrote:
> Subject: High freq effects in i/o mo
> High freq effects in i/o modeling 9:07 AM 1/6/94
> Dear IBISers,
>
> I am starting this discussion to get your inputs on including the high
> frequency effects (4- 5 GHz) in IBIS models.
> As we know the signal integrity analysis accuracy depends as much on
> accurately evaluating the electrical characterisitcs (characteristic
> impedance, trace velocity, dispersion, to name a few) of interconnects,
> as it depends on the accuracy of evaluating or specifying the
> terminating impedances- i.e. the i/o models.
> For EMI (Electromagnetic Interference) analysis, the frequency of
> analysis is upto several GHz, as required by the FCC, European FCC etc.
> guidelines. Hence, for EMI analysis upto what ever frequency of
> interest, it is critical to have i/o model that is valid at that
> frequency, else results from EMI analysis could be grossly inaccurate.
> In order to include the high frequency effects, it is general
> impression (as I have heard in the past) that one may have to give up
> the proprietary information about the process. However, just for
> accurate impedance presentation, that may not be necessary. To give an
> example:
> 1- Today the i/o model is represented as follows:
>
> | Vcc/ Vdd/ etc.
> ____|____
> | B |
> | L |
> | A |
> input o--------| C |---------o output
> | K | |
> | | |
> | BOX | === pin
> capacitance
> -------------------- |
> | |
> Ground
> The black box today is an i/v curve which results in a real impedance
> only. The imaginary part of the impedance is contributed by the pin
> parasitics only. We all know that the semiconductor devices have
> capcitance that will also contribute to the imaginary part of the
> impedance.
> 2- At higher frequencies (5- 6 GHz), the device capacitances can be
> accounted for, as a first order approximation, as follows:
>
> --------------- | Vcc/ Vdd/ etc.
> | ____|____
> | | B |
> == | L |
> | | A |
> input o--------| C |---------o output
> | | K | |
> | | | |
> | | BOX | === pin
> capacitance
> == -------------------- |
> | | |
> ------------ Ground
>
> There may be another feedback capacitance from supply to ground. How
> these capcitances can be estimated, or measured are to be addressed.
> Also, what will be the optimum model to include the device
> capacitances, needs to be discussed.
> However, the primary question to address is, are these effects
> important to take into account for signal integrity/ EMI analysis?
> Secondly, is it within IBIS's charter to address such effects in the
> models?
> Thanks & look forward to hear from fellow IBISians......
>
>
> Ravender
>
>
>-- End of excerpt from "Ravender Goyal"
Received on Thu Jan 6 10:44:06 1994