Question about Simple RC filters

Discussion in 'General Electronics Chat' started by proland1121, Jul 17, 2014.

  1. proland1121

    Thread Starter New Member

    Jul 17, 2014

    So for a basic RC filter, the cut-off frequency is 1/2πRC. Now, for a given cut-off frequency, I can make another filter with double the resistance and half the capacitance. By the equation, the cut-off frequency is unchanged.

    My question is, how would these filters differ in performance (if at all)? Do their transient responses (overshoot and ringing) differ? Is there a general rule-of-thumb to decide which RC pair is best for a given cut-off frequency?
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    All other things being equal, the performance (should be no overshoot in a single pole filter) will be identical independent of the R/Xc ratio.

    However, other factors may dictate. For Example, could the upstream stage drive a 1 Ohm series resistance?
  3. Veracohr

    Well-Known Member

    Jan 3, 2011
    A single-pole filter shouldn't have any overshoot or ringing.

    There may be some differences due to ESR and ESL of the capacitor, but I don't know if it would be significant. If you're concerned about noise, higher resistor values introduce more noise. On the other side, smaller capacitor values can mean smaller physical size, depending on the type you're using.
  4. crutschow


    Mar 14, 2008
    For ideal components there is no difference. Any differences would be due to the value of stray impedances, non-ideal components, and the value of the input source and output load impedances.