ALD SPICE Macromodel Advanced Linear Devices
POTENTIAL PROBLEMS
With any computer models there are difficulties encountered that would not be present in the use of as actual physical device.
These difficulties can range from a missing period in the circuit file to limitations of the simulators ability to adequately simulate
complex systems. The ALD macromodels do represent typical device behavior and they do not model every op amp parameter.
Consequently care must be taken during simulation. Most problems that occur can be placed under one of three categories.
1. Hardware or software problems related to the user's system
Such problems would include improper SPICE configuration and errors in the circuit file.
2. Problems related to the simulation application
These problems are sometimes very complex. Such problems include: failure of simulation to converge,
simulation does not model a certain parameter or the simulation behaves incorrectly. These problems involve the
simulator, the model and the application of the model in a very interrelated way.
3. Problems with the model itself
It can be difficult to distinguish these problems from type 2. It includes only model errors, not slight model
inaccuracy or the failure of a model to model certain parameters.
Because ALD is in the business of supplying integrated circuits, not SPICE macromodels, we only provide limited support for
our models. Obviously ALD cannot be responsible for case 1 errors. Case 3 errors( should any exist) will be addressed by ALD
at our discretion. The most difficult errors to address are those which come under case 2 It is crucial that all customers isolate
the source of such errors before contacting ALD. Although the company believes the models will be more than adequate for
almost all simulation needs, they are supplied on an "as is" basis and we do not guarantee the models will model every possible
operational amplifier behavior with accuracy. We do guarantee the model to have been thoroughly tested by our engineering
staff and we have encountered no errors. If a model is not to your liking, it can be easily modified by the user. Of course,
simulation problems can be tricky and elusive. However, ALD recommends using the simulator and various system simulations
as guidelines for engineering evaluation prior to building a breadboard where the "true" system parametric and performance
can be verified.
DETAILS OF THE MACROMODEL
PSPICE contain a program called Parts. Parts can create a macromodel given operational amplifier parameters. Our
macromodels began with the Parts model, but were extensively modified to provide a more accurate model of the attributes
for each ALD op amp.
An example of the circuit ALD macromodel is shown on previous page.
The following parameter are modeled with ALD's macromodels:
VOM+, VOM-, AV, CMRR, IOSAT, slew rate, rise and fall times, overshoot, output resistance, bandwidth, phase margin,
common mode input voltage range, output voltage range, input diode clamping and input capacitance.
Some of the parameters not modeled include:
VOS, IOS, noise and PSRR.
CONCLUSION
For the designer interested in off-the -shelf parts, this provides a powerful design simulation tool. For those involved in ASIC
design with our Function-Specific program these macromodels add yet another level of power, flexibility and convenience.