Lmf100 noise issues

Discussion in 'The Projects Forum' started by chunkmartinez, Sep 9, 2015.

  1. chunkmartinez

    Thread Starter Senior Member

    Jan 6, 2007
    I have been trying to use an lmf100 IC as a notch filter with as much attenuation as possible but at the notch I get a bit of noise. My scope shows about 30mV of noise. The IC seems to be limited to an input voltage of about 1.4vrms before it starts to clip the peak of the waveform....and this is with a supply voltage as high as it will take. So I can't just use a higher voltage.

    I am wanting to get rid of this noise. I am using my cars 12v system for the supply, when I start the car is when I get the noise on the supply lines(car +\-). This noise is also present on the output of the IC with no input signal but power applied.

    I already have .1uf caps right next to the ics supply pins and I recently added 100uf caps to the supply aswell.

    Any idea what I can do? The circuit is to null a sinewave input so I can compare remaining harmonics to the original fundamental.
  2. bertus


    Apr 5, 2008

    What kind of noise do you see?
    Is it the sampling noise as given in the picture on page 26 of the datasheet?


  3. chunkmartinez

    Thread Starter Senior Member

    Jan 6, 2007
    No, it's different. At the notch frequency I will see a different signal that doesn't look like the original signal, should I try and measure the frequency with my scope?