In what part of the waveform are they different?? Transient part
(rise/fall edges) or the dc level or both?? How much is the difference??
If you are having problem with the dc level, here are some possible
causes:
1. The pullup and/or pulldown resistor value that you specify in SPI2MOD
is not the same value to that you use in generating the pullup and/or
pulldown data in HSPICE.
2. The pullup voltage that you specify in SPI2MOD is not the same value
to that you use in HSPICE.
2. The buffer might use a master-slave technique. If this is the case, you
want to generate model seperately for each set of the output
transistors. And then use the master-slave feature in QUAD to merge
them into a single driver.
3. If the buffer uses some sort of voltage feedback control, you won't be
able to model this accurately in any of behavioural level modeling
(QUAD, IBIS).
If you are having problem with the transient part:
1. We found that adjusting pullup and pulldown resistor value such that
the 2 waveforms don't overlap improve the resulting model quality.
2. We found that SPI2MOD doesn't generate the PVPT correctly if the buffer
has small voltage swing, feedback controlled edge rate, or significant
edge rate difference between the pullup and the pulldown transistors.
We have some luck with generating the PVPT manually, specially for
cause #1 and #3.
3. In general, we found that buffer with fast edge rate is easier to
model. Fast part would yeild more accurate QUAD model than its slow
model.
4. Try putting the right value of input capacitance in SPI2MOD.
That's all what I could think of. I hope it helps!!
Sincerely,
Adrianus
-- *********************************************************************** ** Adrianus Djohan ** ** Analog and Signal Integrity Engineer ** ** STRATUS COMPUTER ** ** Mail Stop: M3-2-EN3 email :[email protected] ** ** 55 Fairbanks Boulevard phone : (508) 490-6611 ** ** Marlborough, MA 01752 fax : (508) 480-8219 ** ** USA ** ***********************************************************************
On Wed, 28 Jan 1998, Mark Nass wrote:
> Date: Wed, 28 Jan 1998 19:29:29 -0800 > From: Mark Nass <[email protected]> > To: [email protected] > Subject: [SI-LIST] : HSPICE to QUAD models > > I have generated some QUAD models using HSPICE generated data. I used > the SPI2MOD program and have found some problems and wanted to know if > anybody has a similar experience, or a better method. > I got my rise/fall data, vol & voh data. With SPI2MOD I generated a > PVPT QUAD model. Then I ran the model in QUAD connected to the same > pullup resistor I had used to generate the HSPICE data with, connected > directly to the buffer. The two wave forms were different, by a lot. > The two solutions I came up with were > > 1.) Take the Time & voltage data generated from the HSPICE run and adjust > the time zero to be right at the time when the output buffer starts > turning on. As opposed to when SPICE time zero started, which is on the > input side of the buffer with a PWL model. > > 2.) Use the 10290 option when generating a model. This seemed to be a more > accurate model, and didn't require any data manipulation. > > Any comments? > > Mark Nass >