Ring Oscillator

What is Ring oscillator ?

Ring oscillator comprises an odd number of CMOS inverters in a ring manner. The output of each inverter is used as input for the next one. The final output is fed back to the first inverter.  The first principle of the ring oscillator is logical instability. The noise in the circuit spontaneously starts the oscillation. The delay of each stage sets the overall oscillation frequency.

The ring oscillator is one of the most simple, effective, and reliable oscillatory topologies and is widely implemented in the industry.

ring oscillator 1 e1725555476392

Advantages of ring oscillators

  1. It has a wide tuning range.
  2. It has the smallest footprint among all oscillators.
  3. It provides multiple phase outputs.
current starved ring osc 1 e1725555600766

Disadvantages of ring oscillator

  1. It has higher phase noise because of complete dependence on active elements for oscillation.
  2. The output is not sinusoid.

Applications of ring oscillator

  1. The voltage-controlled oscillator in most phase-locked loops is built from a ring oscillator.
  2. A ring oscillator is used to demonstrate a new hardware technology.
  3. Ring oscillators are used to characterize the variation of each wafer. The fab adds it as a test structure in the scribe line of a wafer.
  4. Ring oscillators can also measure voltage and temperature effects on a chip.

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