Thanks.. I model offset by dial ling some mismatch, so it includes
temperature effects..
I can understand Microchip having poor models.. But TI, LTC and ADI have
way too complex models for the job they seem to do.
I thought these models are simple representations of the real device
intended to give the board level designer something to simulate his
circuit with.. The way these commercial models are, it looks like they
took the schematic from the chip design engineer and did a poor job of
obscuring proprietary information.
cheers
AG
=====================================================================================================================
toggle quoted message
Show quoted text
On 9/14/2011 9:52 AM, RobertTalty wrote:
I'm not sure I understand
How do you model offset?
I model it by adding a DC source in series with the In+ or IN- gate.
some value between 100uV and 10mV depending on the expected mismatch
of the input pair.
Model PSRR requires that you model the power supply, which a simple
G/R model does not have, also the typical sources of non-ideal opamp
performance that results in power supply variation transferring to the
output signal neesd to be correctly modeled. simple things like the
variations in current sources with power supply voltage, the correct
model for this depends on weather you cascode the mirrors or not.
Same thing with Cmrr? A differential G with perfect R load has
infinite CMRR, modeling CMRR requires that you include errors that
cause CMRR. in your model. This requires some knowledge of the Input
pair type and the cascode bias levels.
BTW most commercial device level spice models are very badly written.
I mean VERY BADLY written. so they are unlikely to include these
effects, heck Microchips opamp models usually don't even converge
properly.
The Microchip opamp spic models are very complex and attempt to model
all types of errors and their Temp variations, but in the end these
models cause convergence problems, so what is the point of a complex
model that causes beginners convergence problems. Convergence can be
hard for experienced spice users to solve, so it is the last thing
that beginners need.
So if you want to see some complex models go to Microchip and download
some of their spice models.
regards
Robert
--- In LTspice@... <mailto:LTspice%40yahoogroups.com>,
Ganesan <dg1@...> wrote:
Thanks for the suggestions.. I will get back in a few days..
My more complicated models which I did not post are Gm and R based..
However my most complicated model seems to be much simpler than what is
commercially available? They also have a disclaimer that they don't
model offset, psrr, cmrr etc.? What gives..
This question still remains unanswered..
Cheers
ag
--- In LTspice@...
<mailto:LTspice%40yahoogroups.com> <mailto:LTspice%40yahoogroups.com>,
"Apparajan" <dg1@> wrote:
I have uploaded my model
Temp-->File-->>E_model_for_diffamp.asc
It is a very simple model that models the differential and common
mode loop gains. I have other more complicated models that model
slew-rate, bandwidth, etc. However my most complicated model seems
to be
much simpler than what is commercially available? They also have a
disclimer that they don't model offset, psrr, cmrr etc.? What gives...
No virus found in this incoming message.
Checked by AVG - www.avg.com
Version: 9.0.914 / Virus Database: 271.1.1/3896 - Release Date: 09/14/11 01:34:00
