Phase Shift Oscillator Calculator

A phase shift oscillator is a circuit that generates a continuous sine wave by passing a signal through three RC stages, each contributing a 60° phase shift to produce the 180° needed for stable oscillation. Enter your Resistance (R), Capacitance (C), and Amplifier Gain into the Phase Shift Oscillator Calculator to find the Oscillation Frequency, feedback factor, phase shift per RC stage, total phase shift, and capacitive reactance. Optionally, enter a Target Frequency to see the required R value needed to hit that frequency with your chosen capacitor.

Ω

Resistance value for each RC stage

µF

Capacitance value for each RC stage

Hz

Optional: Enter desired frequency to calculate required component values

Minimum gain of 29 required for oscillation

Results

Oscillation Frequency

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Feedback Factor (β)

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Phase Shift per RC Stage

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Total Phase Shift

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Capacitive Reactance (Xc)

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Required R for Target Frequency

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Frequently Asked Questions

What is the minimum gain required for a phase shift oscillator?

The minimum gain required is 29 (approximately 29.3). This is because the feedback factor (β) of the three-stage RC network is 1/29, so the amplifier gain must be at least 29 to satisfy the Barkhausen criterion for oscillation.

How does the RC phase shift oscillator work?

The oscillator uses an inverting amplifier (180° phase shift) combined with a three-stage RC network that provides another 180° phase shift at the oscillation frequency. This creates positive feedback (total 360°) at one specific frequency, causing sustained oscillation.

Why are three RC stages needed instead of one?

A single RC stage can only provide a maximum of 90° phase shift. Three identical RC stages are needed to achieve the required 180° phase shift at the oscillation frequency, with each stage contributing approximately 60° of phase shift.

What happens if I change the component values?

Changing R or C values will change the oscillation frequency according to f = 1/(2π√6RC). If you increase R or C, the frequency decreases. If you decrease R or C, the frequency increases proportionally.

How accurate is the phase shift oscillator frequency?

The theoretical frequency is quite accurate, but practical circuits may vary due to component tolerances, amplifier characteristics, and loading effects. Typical accuracy is within 5-10% of the calculated value.

Can I use different R and C values for each stage?

While possible, it's recommended to use identical R and C values for all three stages. This ensures equal phase contribution from each stage and simplifies the design calculations for predictable oscillation frequency.

What is the typical frequency range for RC phase shift oscillators?

RC phase shift oscillators typically work well in the audio frequency range from about 10 Hz to 100 kHz. At very high frequencies, parasitic capacitances affect performance, while at very low frequencies, large component values are required.