***Choice of op-amp for butterworth filter***

Discussion in 'General Electronics Chat' started by artmaster547, Oct 10, 2016.

  1. artmaster547

    Thread Starter Member

    Jan 6, 2016
    89
    1
    Hi All
    I'm trying to design a low pass butterworth filter, which I wish to add a stage to follow a differential amplifier and there will be four of these connected stages on one PCB, I have come up with a design using a Texas Instruments TL071 amplifier however I feel like this is a little accessive and I will then require multiple physical opamp packages (x4). Whereas with my differenital amplifier stage there were 4 opamps in one package, would it be suitable to also use this same opamp for the butterworth filter that would be STMICROELECTRONICS MC3317D Op Amp Quad, I'm just thinking about trying to save on board estate.

    Kind Regards
    Jonathan Sundaram
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,152
    1,793
    I don't clearly understand your problem. You can get the same opamp in singles, duals and quads. Look for TL071, TL072, TL074. What are the specifications of the Butterworth filter?
     
  3. artmaster547

    Thread Starter Member

    Jan 6, 2016
    89
    1
    oh wait is for example tl074 a quad? The spec for it is cutoff of 1kHz and gain of 1 V/V
     
  4. Papabravo

    Expert

    Feb 24, 2006
    10,152
    1,793
    Unless there is something else you haven't mentioned, you should be fine. Don't forget the decoupling caps on the PCB.
     
  5. artmaster547

    Thread Starter Member

    Jan 6, 2016
    89
    1
    By decoupling do you mean the capacitors that I already had in the design or do I need to include more sorry if these questions are super stupid I'm a beginner and want to learn as much as possible
     
  6. Papabravo

    Expert

    Feb 24, 2006
    10,152
    1,793
    Yes those capacitors on the power supply rails. I'm not a mind reader -- how would I know you had them since you did not provide a schematic. They are often overlooked in first designs.
     
  7. artmaster547

    Thread Starter Member

    Jan 6, 2016
    89
    1
    I apologise the following is a photo of the circuit, I was simulating it first just make sure I was getting the correct waveforms:
     
  8. artmaster547

    Thread Starter Member

    Jan 6, 2016
    89
    1
    just to confirm that this is what you were referring to?
     
  9. Papabravo

    Expert

    Feb 24, 2006
    10,152
    1,793
    I don't see any bypass capacitors on the power rails labeled Vcc and Vee. What does the 3MHz. refer to in the drawing?
     
  10. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,061
    3,830
    3MHz GBW

    upload_2016-10-10_17-0-7.png
     
  11. Veracohr

    Well-Known Member

    Jan 3, 2011
    552
    76
    With a gain of 1 at 1kHz, either is fine. TL074 has lower specified distortion though, if that's an issue.
     
  12. Papabravo

    Expert

    Feb 24, 2006
    10,152
    1,793
    GopherT likes this.
  13. artmaster547

    Thread Starter Member

    Jan 6, 2016
    89
    1
    oh wait I have done that in the actual eagle schematic sorry, I understand what you meant now, so a decoupling in between the positive and negative supply right?
     
  14. Papabravo

    Expert

    Feb 24, 2006
    10,152
    1,793
    Not quite. Decoupling should provide a low impedance path to GND for each supply. It is usually done with multiple capacitors in parallel for each supply.
     
  15. artmaster547

    Thread Starter Member

    Jan 6, 2016
    89
    1
    Hmm ok I've never seen that done before I will definitely try this out then, I'm modifying a design that was given to me by an experienced engineer I'm surprised that they didn't implement this feature with their op-amps. Would you mind drawing up a schematic quickly just to ensure I do this correctly thanks J
     
Loading...