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R-C Phase shift Oscillator

R-C Phase shift Oscillator

R-C Phase shift Oscillator

  • RC phase shift oscillator basically consists of an amplifier and a feedback network consisting of resistors and capacitors arranged in ladder fashion. Hence such an oscillator is also called ladder type RC phase shift oscillator

    • The basic RC circuit which is used in the feedback network of oscillator

  • The total impedence of the circuit is,
    • Z = R - j Xc = R - j[1/2πfc] Ω = |Z| ∠-φ Ω
  • In such a RC circuit, current I leads input voltage Vi by angle φ where the angle φ is decided by the components R and C which is given by
  • The drop Vr is in phase with current I while the drop Vc lags current I by 90* i.e. I leads Vc by 90*.

    • Phasor Diagram

  • Such 3 R-C sections are used, each contributing 60* phase shift hence the total phase shift contributed by the feedback network(3*60*)=180*
  • All the resistance values and all the capacitors values are same, so that for a particular frequency, each section of R and C produces a phase shift of 60*

    • feedback network Diagram in ladder fashion

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