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WEBENCH® Tools/OPA1632: webench filter desing tool differential filter

Carlos Munoz
Prodigy 85 points
Part Number: OPA1632

Tool/software: WEBENCH® Design Tools

Hi, 

I have designed a filter with filter design Tool and implement it in a differential filter with the OPA1632 as follows: Gain = 1, fc=500, fs=2000 At_stop = -20 dB

The simulation has more attenuation than expected. I have realized the filter in a PCB with the OPA1632 and I get around -6dB at the passband. I am missing something? Is it a problem of the IC? should I look for another amplifier? How to translate the designs from the Webench filter design tool to a differential amplifier? 

  • 0
    TI__Expert 8365 points

    Hi Carlos,

    We have forwarded your query to the concerned team. The team will get back to you soon.

    Thanks &Regards,

    Praveen

  • 0
    TI__Expert 3482 points

    Carlos

    I converted a single-ended lowpass filter to fully differential lowpass filter with MFB topology.

    I managed to get the expected results which the attenuation is -3dB at 500Hz as shown in below figure.

    I spotted from your schematic that you used the default power supply connection, which is in opposite polarity with the OPA1632.

    I changed my connection to match yours which the positive terminal is connected to -5V and negative is connected to 5V.

    I found that the attenuation is -16dB at 500Hz.

    I hope this addresses your issue.

    Regards,

    Alfred

  • 0
    TI__Expert 7875 points

    Hi Carlos, 

    You've translated the filter properly to the FDA. I've noticed that on the FDA model that the supply voltages are connected inverted (positive supply is at the bottom). I think that is likely your issue. I often get caught off guard by some of the models that have the VS+ pin at the bottom by default. 

    Regards, 

    Jacob 

  • 0 in reply to Jacob Freet
    Prodigy 85 points

    Thank you very much! sorry for the mistake. 

    Best regards