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AD8137 output problem

Question asked by Gellert90 on Apr 10, 2017
Latest reply on May 2, 2017 by Gellert90

Dear All!

 

I have just started working with AD8137 as the following (Vs+ = 5V, Vs- = 0V, Vocm = 2.5V).

During the tests i tried removing R13 (letting the IC make Vocm to half supply) and replacing it to 0R as well. R12 was also tried to be removed.

My problem is that i expect both outputs moving from Vocm in 180 degree to each other as the simulation result on the next picture shows it. The simulation model of the amplifier was downloaded from here: http://www.analog.com/en/products/amplifiers/differential-amplifiers/fully-differential-amplifiers/ad8137.html . The input signal (10kHz, 400mVpp, 0V offset) was placed to IN+ referred to IN-.

Doing the same in the lab, i have measured different signals.

The yellow is OUT- and blue is OUT+. They are aligned symmetrically from 2.5V but with and offset like there were some common mode amplificaton too. The input configuration was the same as above.

 

Please give me some advice what i have misunderstood or where have been mistaken.

 

Thanks,

Gellert

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