Phase Shift Oscillator with non-inverting input not tied to ground

Discussion in 'Homework Help' started by favner85, Mar 7, 2013.

  1. favner85

    Thread Starter New Member

    Nov 4, 2012
    In the following Phase Shift Oscillator ¿What is the purpose of the 2.5[V] at the non-inverting terminal?

    I already developed the equations for almost the same circuit except that the non-inverting terminal is tied to ground.

    I've found that the gain A = 29 so that the circuit oscillates at a frequency of f= 1 / sqrt(6)*R*C

    The simulations are not consistent, as for the current circuit the sine wave seems at the output to be shifted 2.5[V] but when I put 1[V] for example the signal fades over time.
    Do the 2.5[V] affect the gain or frequency? If so how?
    Are those 2.5[V] just for to shift the signal? Thank you.

  2. antonv


    Nov 27, 2012
    What was the power supply arrangement for the circuit with the non-inverting input grounded?
  3. ScottWang


    Aug 23, 2012
    The TLV2471 is a Rail-To-Rail Input/Output OpAmp, so when the power is +5V, then using 2.5V can be the virtual ground for the sine wave.

    The original circuit at here.
  4. crutschow


    Mar 14, 2008
    For a sine-wave, the output needs to swing evenly plus and minus around the bias point of the op amp. If the op amp is powered from a single supply and ground then the op amp output has to be biased a 1/2 the supply voltage to avoid clipping the bottom half of the sinewave. This is accomplished by biasing the plus (+) input at 1/2 the supply voltage.
  5. ramancini8

    Active Member

    Jul 18, 2012
    When I wrote this app note I had a dog named Bubba who constantly chased his tail; hence, the Bubba oscillator. The 2.5 volts is for biasing as previously mentioned.