Guest @m@ Posted September 2, 2009 Report Share Posted September 2, 2009 hey people !! I have designed a low pass filter in stimulation program , but the point which annoying me is that my low pass circuit have c= 10uF and r=500 ohms so the Fc becomes 31.83Hz but my circuit passes a huge amount of large frequency after this range i.e after 31.83 Hz I further increases my frequency by function generator then at kHz it start showing DC at output why it is like that ? ??? why its doesn't stop signal after 31.83 HZ pllz help me Quote Link to comment Share on other sites More sharing options...
Hero999 Posted September 2, 2009 Report Share Posted September 2, 2009 A simple first order low pass filter will do that.Above twice the cut-off frequency, the roll-off will be 6dB/octave. Quote Link to comment Share on other sites More sharing options...
audioguru Posted September 2, 2009 Report Share Posted September 2, 2009 The lowpass filter reduces frequencies above its cutoff frequency, it does not eliminate them.At double the cutoff frequency, the output of your simple first-order filter is -6dB which is half.At double the cutoff frequency, the output of a second-order lowpass filter is -12dB which is 1/4.At double the cutoff frequency, the output of a third-order lowpass filter is -18dB which is 1/8th.At double the cutoff frequency, the output of a fourth-order lowpass filter is -24dB which is 1/16th.Higher frequencies are reduced more. Quote Link to comment Share on other sites More sharing options...
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