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ADA4940-2, issue on creating 2 differential signals around 0V

Dr Mr or Mrs,


I have designed and built a differential amplifier around the ADA4940-2.My goal is to convert two single ended signals (“deltaTune_ana” and “deltaLoad_ana”) :  each one from a dynamic of 0 to 0.4V to a dynamic of -0.2 to 0.2V.So the aim is to get  two differential signals centered around the ground with a gain of 1 and an offset of -0.2V from 2 single-ended signals. The circuit has been simulated on ADI DiffAmpCalc and then built.


Results on the circuit are not in accordance with the simulation : the negative supply falls in short circuit on the pcb.

I have then tried to use the ada4940-2 on your evaluation boad, with the same goals : gain of 1,offset of -0.2V and differential signals. The  positive power supply (3.3V), the negative one (-3V) and Vocm1=Vocm2=-0.2V are provided by external, low impedance and regulated power supplies. I noticed a gain of nearly one but an offset of approx -30 mV instead of -0.2V wanted.

I do not know the possible reason of this difference against the simulation. Do you have an idea ?

Extract of the scheme:

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