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OPA171 RFI filter

Other Parts Discussed in Thread: OPA171, OPA333


In the datasheet for OPAx171 is mentioned that device has RFI filtered inputs. In the mean time there is no any information about performance of this RF filter.

From fig.19  (Open loop gain vs Frequency) it seems that RF filter has cutof higher than 10MHz. Is it possible to obtain frequency response of the amplifier for frequencies above 10MHz to predict impact of the RF signal to the  signal chain.

As well it will be useful to have information about EMI/RFI capability of the OPAx171 which frequencies and how they impact to the voltage offset.

best regards,


  • Oleksiy,

    The measured EMI rejection ratio of the OPA171 is shown in the graph below:

    EMI rejection ratio is a measure of how frequencies above the amplifier's bandwidth are rectified into a DC offset. The formula used for this calculation is:

    This equation can be rearranged to calculate the amount of shift in the offset voltage due to an input EMI signal of known frequency and amplitude:

     More information on our testing methods can be found in:

    Right now we are working to test the bulk of our amplifier portfolio and generate test reports that are added to the product page on our website. An example test report can be seen on the OPA333 page: and we'll be uploading many more of these reports in the near future.

  • Hi John,

    Thanks for the answer.

    Just to be sure about your answer in the equiation for Vos value of the EMIRR_IN should be taken from the figure (EMI rejaection)?

    Concerning RF filter features what exact bandwidth it has? How far it from GBW of opperational amplifier&

    best regards,


  • Oleksiy,

    That is correct, the value for the EMIRR IN+ (dB) term is taken from the above plot at your desired frequency. The EMI filter is a single-pole lowpass filter with a corner frequency between 40 and 50 MHz.