How to create opamp models with OpAmp-Modell software

Only in a bundle with AktivFilter 3.2 Professional Edition and AktivFilter 3.2 Campus Edition we ship the tool OpAmp-Modell. OpAmp-Modell software enables you to extend AktivFilter 3.2's built-in database of operational amplifiers. Furthermore, you can overwrite AktivFilter's built-in models by your own models, which you have created with OpAmp-Modell software. Any user defined opamp model for AktivFilter 3.2 is stored in a data file "opamps.txt", a text file, which is loaded whenever you start AktivFilter.

How to extract the opamp parameters

OpAmp-Modell software offers two approaches for extracting the opamp parameters:

We will show you how to apply both approaches.

1st approach: Extract parameters from gain at two frequencies

You have a diagram with the gain depending on frequency ("Open-loop gain"), e.g. from a datasheet:

Open-loop gain of the opamp

For creating a model of that opamp, we need to know the gain at two frequencies. Therefore, we choose one very low frequency and a second frequency, which is higher but is located on the straigh part of the curve in the diagram. From the diagram above we take e.g. the values: f1 = 1 Hz, A1 = 115 dB and f2 = 100 kHz, A2 = 20 dB.

Now lets start OpAmp-Modell software and enter the following data for a new opamp, in this example called "UA4711" (a fictive opamp type):

Extracting opamp parameters at two
frequencies

We click on OK and get a message box, saying that the opamp has been stored to the data file. If we now start AktivFilter 3.2, we can use the new created opamp model of the UA4711 when designing a filter:

The new created opamp model is available
for a filter design with AktivFilter

2nd approach: Extract parameters from gain-bandwidth product (GBP)

For this method, we need the following data of the opamp:

In this example we will create an opamp model for a (fictive) opamp type "LM4711". From the data sheet we know, that this opamp type has a DC-gain of 102 dB and a gain-bandwidth product of 4.7 MHz. For creating a model of the opamp with that data, we start OpAmp-Modell software and enter the following data:

Extracting opamp parameters from the
gain-bandwidth product

Deleting an opamp model from the file

If you need to remove a self-created opamp model from the data file, you simply need to do this: Start OpAmp-Modell software and enter the name of the opamp. Enter no parameters, but click on OK. In the next dialog you confirm that the opamp shall be deleted.

Changing an opamp model

If you need to change an opamp model, which has already been stored to the data file, you simply need to enter the new data of the opamp. When you finish the session of OpAmp-Modell software, the updated opamp model will be written to the data file.



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