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Getting a sine/cosine

  1. Nov 14, 2007 #1
    I have a sine wave. i want to make it 90 degrees out of phase. if i remember correctly i could use a capacitor to create a phase lag of 90 degrees (like on of those motors where they put a capacitor to create the offset so it starts to turn)

    Do you put the capacitor in series? What value? putting the cap would just make it ac coupled not sure if would do the lag
    If not, how can i create a 90 degrees phase shift

    edit: i guess a differentiator would work. any other simpler way through circuit? my op amp is configured non-inverting input

    Last edited: Nov 14, 2007
  2. jcsd
  3. Nov 15, 2007 #2


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    Staff: Mentor

    To get a -90 degree phase shift in voltage, you can run your voltage source signal through an inductor and then a resistor to ground. Well above the LR breakpoint frequency, the current through the inductor will lag the voltage across it by 90 degrees, and so the output voltage across the resistor will also lag the input voltage by 90 degrees.
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