DC blocking AC amplifying circuit

Discussion in 'General Electronics Chat' started by tenzil, Jun 16, 2016.

  1. tenzil

    Thread Starter New Member

    Jun 16, 2016
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    0
    Hello everyone,
    I need to block the DC or keep the DC at a constant level in the output of the op amp and amplify the AC using the same op amp.
    Currently the DC shift in the input is between 1.6V to 2V
    i don't need any gain for the DC and the gain required for AC is 10 and above.
    When i try to block the DC using the capacitor there is so much of noise in the output.
    I am uploading some of my test circuit and its results.
    please help me to solve this out.
     
    Last edited: Jun 16, 2016
  2. AlbertHall

    Well-Known Member

    Jun 4, 2014
    1,951
    387
    Wild guess - use a coupling capacitor?
     
  3. dl324

    Distinguished Member

    Mar 30, 2015
    3,244
    622
    Welcome to AAC!
    You didn't complete your description...

    To block DC, you can AC couple the signal. If you want a fixed or variable DC offset in the output, you can use a summing amplifier to add an offset.
     
  4. tenzil

    Thread Starter New Member

    Jun 16, 2016
    14
    0
    Thank you for your update.
    sorry that my description is not complete.
    I need to block the DC or keep the DC at a constant level in the output of the op amp and amplify the AC using the same op amp.
    Currently the DC shift in the input is between 1.6V to 2V
    i don't need any gain for the DC and the gain required for AC is 10 and above.
    When i try to block the DC using the capacitor there is so much of noise in the output.
    I am uploading some of my test circuit and its results.
    please help me to solve this out.

    Actually the signal is an output of hall effect sensor,the problem is the DC offset is varying with some sensors.So in this case will the summing amplifier work.
     
  5. dl324

    Distinguished Member

    Mar 30, 2015
    3,244
    622
    Your PDF attachment is 6.6MB. Kindly post smaller files and delete the one in your last post; only one copy is needed.
     
  6. tenzil

    Thread Starter New Member

    Jun 16, 2016
    14
    0
    Thank you for your update.
    I need to block the DC or keep the DC at a constant level in the output of the op amp and amplify the AC using the same op amp.
    Currently the DC shift in the input is between 1.6V to 2V
    i don't need any gain for the DC and the gain required for AC is 10 and above.
    When i try to block the DC using the capacitor there is so much of noise in the output.
    I am uploading some of my test circuit and its results.
    please help me to solve this out.
     
  7. tenzil

    Thread Starter New Member

    Jun 16, 2016
    14
    0
    Sure,
    please find the attachment
     
  8. dl324

    Distinguished Member

    Mar 30, 2015
    3,244
    622
    Still too large. Post JPG's of appropriate resolution to convey information.

    I question the way R2 is connected. I have never seen the gain setting resistor not having a DC path to ground.
     
  9. tenzil

    Thread Starter New Member

    Jun 16, 2016
    14
    0
    please find the attached files,
    The R2 and the capacitor will act High pass filter and block the DC.
    Amplifier circuit.png Amplifier circuit.png
     
  10. BR-549

    Well-Known Member

    Sep 22, 2013
    1,995
    388
    we need the data sheet on the sensor.......and any other components between sensor and amp.
     
  11. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,800
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    Can you post your .asc file?
     
  12. dl324

    Distinguished Member

    Mar 30, 2015
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    It doesn't work that way. R3 and R2 set the gain. DC blocking is done by putting a coupling cap on the opamp input.
     
  13. AlbertHall

    Well-Known Member

    Jun 4, 2014
    1,951
    387
    That is, between Vin and R4.
     
  14. dl324

    Distinguished Member

    Mar 30, 2015
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    622
    C1 is in parallel with R4, that's not an AC coupling cap.

    EDIT: I get it. You're not telling me where the cap is, you're telling the OP where to put it.
     
    Last edited: Jun 16, 2016
  15. tenzil

    Thread Starter New Member

    Jun 16, 2016
    14
    0
    please find the data sheet of the sensor
     
  16. tenzil

    Thread Starter New Member

    Jun 16, 2016
    14
    0
    Currently in board there is no amplifier b/w sensor and ADC,so because of the DC shift in the o/p of the sensor is different from one another the data what we got from the ADC are not proper.
    so i am thinking of blocking the dc and amplify the AC .
    please let me know if there is any circuit that will meet my requirement
    please find the datasheet of the sensor
     
  17. tenzil

    Thread Starter New Member

    Jun 16, 2016
    14
    0
    Currently in board there is no amplifier b/w sensor and ADC,so because of the DC shift in the o/p of the sensor is different from one another the data what we got from the ADC are not proper.
    so i am thinking of blocking the dc and amplify the AC .
    please find the datasheet of the sensor and the .asc file.
    please let me know if there is any circuit that will meet my requirement
     
  18. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,800
    1,103
    Try this mod of your asc file.
    Note that your circuit currently has a gain of ~100, so the amp is driven into saturation. Is that your intention?
     
  19. tenzil

    Thread Starter New Member

    Jun 16, 2016
    14
    0
    Actually i need a gain should grater than 10,
    That we can adjust
     
  20. tenzil

    Thread Starter New Member

    Jun 16, 2016
    14
    0
    Thanks a lot for you update ,
    let me rig this circuit and let you know how it is working.
     
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