ADA4941-1 introduces noise

Hello,

I am getting data from an AD7961 ADC with an ADA4941-1 in front as a single-ended-to-differential stage.

I am getting a surprising noise of +/-2mV when I short the ADA input to ground. This noise goes down to +/-0.2mV if I skip the ADA4941-1 stage and instead short both the differential inputs of the AD7961 to ground (the inputs still have their resitor-capacitor network as indicated in the part's datasheet).

I am working on home made prototyping PCB with the ICs mounted onto fine, commercial SMD-to-thru-hole adaptors. I know that this is not actually an ideal situation to get pure data in, but I can't figure out how the mV noise range is possible. I have used all the precautions, such as capacitors near the chips and precise voltage reference by ADR430. I am using this temporary solution to evaluate the circuit and move to a more professional PCB later on.

Any suggestion is appreciated.

Many thanks in advance,

Marco

Parents
  • Hi Neil,

    many thanks for your prompt answer. Please find attached the schematic.

    I need to acquire a +/-1V signal and for this reason I have setup the pair of resistor dividers respectively at the non-inverting (8) and REF (2) pins of the ADA4941-1. In this way when the INPUT range is +/-1V vs. GND, OUT+ ranges from 0 to +2V and the same does OUT- but phase-reversed.

    Best regards,

    Marco

    ADcircuit.pdf
Reply
  • Hi Neil,

    many thanks for your prompt answer. Please find attached the schematic.

    I need to acquire a +/-1V signal and for this reason I have setup the pair of resistor dividers respectively at the non-inverting (8) and REF (2) pins of the ADA4941-1. In this way when the INPUT range is +/-1V vs. GND, OUT+ ranges from 0 to +2V and the same does OUT- but phase-reversed.

    Best regards,

    Marco

    ADcircuit.pdf
Children
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