Help with phase shift oscillator

Discussion in 'Homework Help' started by testing12, Nov 12, 2012.

  1. testing12

    Thread Starter Member

    Jan 30, 2011
    Hello everyone,
    I need some help with the circuit below. Im trying to create a phase shift oscillator but i get nothing at the output or if i start fiddling with the gain on the last stage it just saturates. Im aiming for a frequency of 900 Hz.

    I know w = (sqrt(3)) / RC
    Where R is 30.63KOhms and C = 0.01uF

    I also know the gain on the final stage must be 8, which I have. (i have also adjusted for a gain slightly higher then 8)

    The loop gain is 1 and the overall phsae shift is 0. (60 + 60 + 60 - 180 = 0)

    Does anyone notice anything im doing wrong, I have been at this for awhile.
    Any suggestions are greatly appreciated,
    Kind Regards.

  2. Audioguru


    Dec 20, 2007
    The output from U4 is a saturated squarewave.
    The output from U2 is a good sinewave and its output can be amplified if you want.
    testing12 likes this.
  3. testing12

    Thread Starter Member

    Jan 30, 2011
    it turns out the circuit was fine... i just needed to let the simulation run for about 60 seconds before i was able to obtain the clean sine wave.