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AD538 Two Quadrant Division

Question asked by lbandre on Jul 31, 2017
Latest reply on Aug 2, 2017 by lbandre

I am building a detector that has two output voltages that I need to divide. The numerator could have positive or negative voltage depending on the location of a laser beam on the detector. The denominator will always be positive. 


I have been trying to build a circuit to divide two voltages using the AD538 Real-Time Analog Computational Unit (ACU). The circuit diagram for two quadrant division using the AD538 is shown below and the data sheet is attached.


Two Quadrant Division Circuit Figure

The trimming potentiometer labeled R2 10kOhms, should this have a center at 10kOhms or a maximum at 10kOhms? In the data sheet it says that the center of the trimming potentiometer should give a gain of 1.4, and I am not sure if that means set the resistance to 5kOhms or 10kOhms. 


Further, I have tried many values for the R2 potentiometer, but have not been able to accurately divide two voltages consistently. I am able to get a correct value for negative numerator voltages when I adjust R2, but when I change the fraction I do not get the correct value. And when I test with positive numerator voltages, I am never able to get an accurate value. The output voltage is a small negative value (I don't know why it would be negative if both voltages in the fraction are positive?) and doesn't change when I vary the input voltage values. 


Any help with the two quadrant division circuit would be greatly appreciated.


Thank you!