Re: Re[1]: Draft IBIS 2.0 specification - Modelling of Ac Ramp Parasitics

I am posting this at the suggestion of Will hobbs.

I had discussions with Stephen Peters of Intel
recently regarding the modelling of ramp
ac parasitics. I am arguing for switching the location of L_fixture as shown in
the Ibis 2.0(1) draft specification. Since we are dealing with "effective"
parasitic values , this change may not have any adverse effect on modelling.
My case for this change is mainly one of consistency with the way Ldut and
Cdut is shown. A bonus , atleast in my view is that the new scheme is even simpler
to model.

I may not be able to attend tomorrow's session and Stephen has gracefully
consented to raise this one. If there are any takers , I will be glad!!

- kumar

Stephen:

My guess is that most of the parasitics in the model represent some "effective" value and may not be purely physical. That is why I prefer a representation which gives higher priority to consistency and simplicity. In my view Cfixture before
Lfixture is more consistent and is even simpler to model.

Most likely I will not be able to attend the forum this Friday. How do
you propose we handle this issue? Can You raise this on my behalf if I am
not there?

Thanx and regards

kumar
>
> Hello Kumar:
>
> When I came up with the test fixture R and C I was tring to
> match the data book load most TTL and CMOS devices use when specifing
> Tco -- a capacitor to ground and a pullup resistor to some voltage.
> The L-fixture was an attempt to account for pin inductances due to
> sockets, wire, etc. I thought the right order (physically) was an 'L',
> in series with the R/C combination. Is a better representation the
> C before the L? If it needs to be changed we can, but it should be
> brought before the fourum soon before the spec gets approved.
>
> Regards,
> Stephen
>
>
>
> Stephen:
>
> I have question regarding the text fixture waveform models
>
> $|
> $| PACKAGE | TEST FIXTURE
> $| _________ |
> $| | DUT | L_dut R_dut | L_fixture R_fixture
> *| | die |---@@@@@--/\/\/\--o-----|--@@@@---o---/\/\/\----- V_fixture
> *| |_________| | | |
> *| | | |
> *| | | |
> $| C_dut === | === C_fixture
> *| | | |
> *| | | |
> $| GND | GND
>
>
> Do you know the text fixture in such a detail to model its parastics
> differently from the device
> output? If you do not I suggest we use a model like the following
> which models the parasitics of the text fixture in the same way as the device.
>
> If Lfixture is large these two models will produce different results. For small
> Lfixture the question is academic and is one of consistency in modelling.
>
>
> - kumar
>
>
> $|
> $| PACKAGE | TEST FIXTURE
> $| _________ |
> $| | DUT | L_dut R_dut | L_fixture R_fixture
> *| | die |---@@@@@--/\/\/\--o-----|-o--@@@@------/\/\/\----- V_fixture
> *| |_________| | | |
> *| | | |
> *| | | |
> $| C_dut === | === C_fixture
> *| | | |
> *| | | |
> $| GND | GND
>

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Received on Thu Nov 17 06:31:36 1994