[ibis-users] Re: Model reference question

  • From: "Snith, Lars Aake" <Lars.Snith@xxxxxxxxx>
  • To: Walter Katz <wkatz@xxxxxxxxxx>, "ibis-users@xxxxxxxxxxxxx" <ibis-users@xxxxxxxxxxxxx>
  • Date: Fri, 11 Dec 2015 16:10:15 +0000

Hello Walter,

This buffer is not strong enough to fully drive/sink the 50 ohm load.
In real operation the supply on driver stage is the same. For typ: +9.9V and
-6.6V.

Best regards, Lars

From: Walter Katz [mailto:wkatz@xxxxxxxxxx]
Sent: Friday, December 11, 2015 16:55
To: Snith, Lars Aake; ibis-users@xxxxxxxxxxxxx
Subject: RE: [ibis-users] Model reference question

Lars,

According to the ramp statement:

[Ramp]
dV/dt_r 1.34464/1.03806n NA NA
dV/dt_f 1.34424/1.57929n NA NA

And the VT curves, the buffer only swings through about 2. V. The output
toggles between 7.7 and 9.7 when driving into a 9.9V load and between -6.6 and
-4.1V when driving into a -6.6 volt load. These voltages describe the unit
under test, what are the actual voltages supplied to the part in operation?

Walter





From: ibis-users-bounce@xxxxxxxxxxxxx<mailto:ibis-users-bounce@xxxxxxxxxxxxx>
[mailto:ibis-users-bounce@xxxxxxxxxxxxx] On Behalf Of Snith, Lars Aake
Sent: Friday, December 11, 2015 10:04 AM
To: ibis-users@xxxxxxxxxxxxx<mailto:ibis-users@xxxxxxxxxxxxx>
Subject: [ibis-users] Model reference question

Hello,

At the same time forced to switch IBIS development system and encountering a
new IO topology, I was (and am) skeptical to the resulting model.
The IO has an input signal that toggles between 3.3V/2.7V/3.6V and 0V/0V/0V.
Output toggles between 9.9V/6V/11.8V and -6.6V/-3V/-7.2V .

Configuring as per SW User Guide documentation gives tolerable VT curves, but
IV curves look like below, also attached as "xtf.ibs":
[cid:image001.png@01D13436.BFDC28D0]
This naturally fails IBISCHK6 and it is quite clear that curves are offset by
the negative supply. Transposing curves back to origo make the model pass
IBISCHK6.
This is acknowledged by tool supplier and will be corrected in a coming
version. Their corrected curve can be seen in attached "ibis.ibs" (typ only).

So far so good. The remaining issue concerns the GND clamp. Looking at POWER
clamp while referred to Ground makes it obvious that GND is 0V, as clamping
occurs at 9.9+0.7V:
[cid:image002.png@01D13436.BFDC28D0]

This is as expected. Now if we look at the GND clamp I would expect -6.6V-0-7V
= -7.3V. But this is not the case:
[cid:image003.png@01D13436.BFDC28D0]

Would you care to make a sanity check on these models, and perhaps comment on
the correct reference/fixture setup in a case like this?

Best regards, Lars Snith
Atmel Norway.


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