RC Phase Shift Oscillator Calculator (Frequency & Gain)
By Santaji GadepatilinUpdated November 5, 2026
An RC phase shift oscillator uses three RC sections to shift the signal by 180°, and an inverting amplifier to supply the other 180° and make up the loss. This RC phase shift oscillator calculator gives the oscillation frequency and the gain resistor needed — one of the types of transistor oscillators, and a cousin of the Wien bridge oscillator.
How to use the RC phase shift oscillator calculator
Enter the resistance and capacitance used in each of the three identical RC sections. The calculator returns the oscillation frequency and the minimum feedback resistor for an inverting op-amp stage. To design for a frequency, clear R or C and enter the frequency.
RC phase shift oscillator formula
f = 1 ÷ (2π R C √6) · |A| ≥ 29 → Rf ≥ 29 R
Worked example
R = 10 kΩ, C = 10 nF in each section:
- f = 1 ÷ (2π × 10,000 × 10 × 10⁻⁹ × 2.449) = 649.7 Hz
- Rf ≥ 29 × 10 kΩ = 290 kΩ (use 300–330 kΩ)
Frequency for common R and C values
| R | 1 nF | 10 nF | 100 nF | 1 µF |
|---|---|---|---|---|
| 1 kΩ | 64,974.7 Hz | 6,497.5 Hz | 649.7 Hz | 65.0 Hz |
| 4.7 kΩ | 13,824.4 Hz | 1,382.4 Hz | 138.2 Hz | 13.8 Hz |
| 10 kΩ | 6,497.5 Hz | 649.7 Hz | 65.0 Hz | 6.5 Hz |
| 47 kΩ | 1,382.4 Hz | 138.2 Hz | 13.8 Hz | 1.4 Hz |
| 100 kΩ | 649.7 Hz | 65.0 Hz | 6.5 Hz | 0.6 Hz |
Notes
- The formula assumes the ladder is not loaded — drive it from a low impedance and let the last R go to the op-amp virtual ground.
- For a transistor version the √6 factor changes slightly with the loading of the transistor’s input.
Frequently asked questions
What is the frequency of an RC phase shift oscillator?
For three identical RC sections, f = 1 ÷ (2π R C √6) ≈ 0.065 ÷ (RC). With 10 kΩ and 10 nF it oscillates at about 650 Hz.
Why must the gain be 29?
At the frequency where the three-section ladder shifts the phase by 180°, it attenuates the signal to 1/29. The amplifier needs a gain of at least 29 to sustain oscillation.
How do I set the gain with an op-amp?
Use an inverting amplifier whose input resistor is the last R of the ladder, and a feedback resistor Rf ≥ 29R. Use slightly more (about 30–32R) for reliable start-up.
Why is the output not a perfect sine wave?
Excess gain drives the amplifier into clipping. Amplitude stabilisation with diodes or a thermistor in the feedback path keeps distortion low.