How to create opamp models with the software OpAmp-Modell

Only in a bundle with the AktivFilter 3 Professional Edition we ship the tool OpAmp-Modell. The software OpAmp-Modell enables you to extend AktivFilter 3'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. Any user defined model is stored in one single textfile "opamps.txt", which is loaded whenever you start AktivFilter.

How to extract the opamp parameters

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

Gain at two frequencies
Gain-Bandwidth-Product

We will show you how to apply both approaches.

Approach: Extracting parameters from gain at two frequencies

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

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 und f2 = 100 kHz, A2 = 20 dB.

Now lets start OpAmp-Modell and insert the following data for the new opamp, in this example called "UA4711":

Extracting opamp parameters at two frequencies

We click on OK and get a message box, saying that the opamp has been stored to the file. If we now start AktivFilter 3, 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

Approach: Extracting parameters from gain-bandwidth-product (GBP)

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

The DC-gain, i.e. the open-loop-gain at 0 Hz
The gain-bandwidth-product (GBP)

We have an opamp, in that example called "LM4711", with 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 and insert 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 file, you must do this: Start OpAmp-Modell and insert the name of the opamp. Insert no parameters, but click on OK. In the next dialog you must confirm that the opamp should be deleted.

Changing an opamp model

If you need to change an opamp model, which has already been stored to the file, you simply have to insert the new data of the opamp. When you finish the session of OpAmp-Modell, the opamp model in the file is updated.