What is the best way!! to Filter-out DC component of a signal?

Discussion in 'General Electronics Chat' started by richiechen, Jan 12, 2012.

  1. richiechen

    Thread Starter Member

    Jan 1, 2012
    Hey everyone!

    I am thinking a question,
    What is the best way to filter out the DC component of a signal?

    A single capacitor? It distorts other frequency signals, however.
    Build a high-pass filter? It is more complex and actually we only need to filter-out the DC part.

    Let's discuss!!

  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    Discuss what ?

    Show me some values and signals to start with.
  3. wmodavis

    Well-Known Member

    Oct 23, 2010
    The best way is the simplest way and that is a capacitor which will block the DC and pass the AC. The value of the capacitor and the load resistance are key to selecting the value of C to not cause unwanted attenuation of the low end of the spectrum your dealing with. I presume (because you did not clearly state otherwise) that the attenuation of lower frequencies is what you meant by 'distortion of other frequency signals'. You did not mention what actual frequencies you want/need to pass (other than DC vs other frequency signals) and with what amplitude precision. A capacitor, in conjuction with its load IS a high pass filter. Any other configuration of high pass signal will do the same but likely with more ripple in the pass band. It would be more helpful if you supplied more information.
  4. jimkeith

    Well-Known Member

    Oct 26, 2011
    If the DC component is stable, it may be nulled via an op amp summing amplifier--may require test and adjustment.

    Also, what frequency response are you looking for?
  5. wmodavis

    Well-Known Member

    Oct 23, 2010

    Freq range he intimated:
    Block 0Hz
    Pass 0.000001Hz and above

    Sounds like a properly spec'd capacitor to me.
  6. MrChips


    Oct 2, 2009
    He said block DC but did not specify the minimum frequency.
    But you are correct, spec the capacitor properly:

    What is your minimum frequency?
    What is the impedance of the load?
    From this you can determine the appropriate value of the DC blocking capacitor. That is the simplest solution.

    A DC difference amplifier will also do the job as in post #4.
    You can also build a DC detect circuit and use this as the DC reference in the difference amplifier if you want to push the frequency limit to very low frequencies.