Ring Oscillator Calculator

A ring oscillator is a circuit made of an odd number of inverter stages wired in a loop, where the signal endlessly chases its own tail to produce a clock-like oscillating frequency. Enter your propagation delay per stage, number of stages, load capacitance, supply voltage, and temperature into the Ring Oscillator Calculator, then choose a calculation method (propagation delay or RC time constant) to get the oscillation frequency in MHz. Secondary outputs include the period, total delay, and frequency in Hz. Also try the Colpitts Oscillator Calculator.

ps

Delay through each inverter stage

Must be odd number (3, 5, 7, etc.)

pF

Capacitive load on each stage

V

Circuit supply voltage

°C

Operating temperature

ps

Used when RC method is selected

Results

Oscillation Frequency

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Period

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Total Delay

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Frequency (Hz)

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Results Table

Frequently Asked Questions

What is a ring oscillator and how does it work?

A ring oscillator is a device composed of an odd number of NOT gates in a ring. The output oscillates between high and low states due to the propagation delay through each stage, creating a continuous clock signal. See also our Wien Bridge Oscillator Calculator.

Why must the number of stages be odd?

An odd number of inverter stages ensures there's always an inversion in the feedback loop, which is necessary for oscillation. Even numbers would create a stable state rather than oscillation.

How does propagation delay affect oscillation frequency?

The oscillation frequency is inversely proportional to the total propagation delay. Higher delays result in lower frequencies, while faster switching elements increase the oscillation frequency.

What factors influence the propagation delay in CMOS ring oscillators?

Key factors include supply voltage, load capacitance, temperature, and process variations. Higher voltage and lower capacitance typically reduce delay and increase frequency. You might also find our Phase Shift Oscillator Calculator useful.

How does temperature affect ring oscillator performance?

Temperature affects carrier mobility and threshold voltages in CMOS devices. Generally, higher temperatures increase propagation delay and reduce oscillation frequency.

What are typical applications of ring oscillators?

Ring oscillators are used in PLLs, clock generators, random number generators, and as test structures for process monitoring in semiconductor manufacturing.

How accurate are ring oscillator frequency calculations?

Calculations provide good estimates but actual frequencies may vary due to process variations, parasitic effects, and non-linear dependencies that simple models don't capture.

What is the minimum number of stages for a ring oscillator?

The minimum is 3 stages. While single-stage oscillators exist, they require additional feedback elements. Three stages is the simplest configuration for a pure inverter-based ring oscillator.