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Op amp frequency response

  1. Jun 19, 2016 #1
    Hello I am developing a low noise preamp and would like to change the roll off of my design to sharply decrease the gain for very low frequencies "1-5Hz". The results of my current design are as follows.
    upload_2016-6-19_20-1-43.png

    upload_2016-6-19_20-2-12.png

    I would need something that looked more like this..
    upload_2016-6-19_20-6-47.png

    I understand the simple equations of changing the corner frequency and gain but I am unsure how to change the roll off. I recall I may have covered some of this in control systems but that was quite some time ago.

    Ideally id like to replicate the results in the above bode plot and have good response (40db) for higher frequencies.

    Any help is greatly appreciated!
     
  2. jcsd
  3. Jun 19, 2016 #2

    Tom.G

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    Here is a two pole highpass filter ckt you may be able to use or modify. Note that the component values are for 100Hz corner frequency. For 14Hz corner freq. (1/7 freq.) multiply cap values by 7, for 10Hz (1/10 freq.) multiply cap values by 10.
    AN-31-25.jpg
     
  4. Jun 20, 2016 #3
    Thanks for the response I was looking into it today, ill need a 3rd order system to achieve the desired results... There is always a trade off though. Ill report back when I have some more information. I am hoping I can achieve this with a modification to the original circuit.
     
  5. Jun 20, 2016 #4

    Tom.G

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    If you know what output impedance it will drive, you can get a additional pole by adjusting the value of C2.
     
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