Relaxation oscillator

Simple relaxation oscillator made by feeding back an inverting Schmitt trigger's output voltage through a RC network to its input.

In electronics, a relaxation oscillator is a nonlinear electronic oscillator circuit that produces a nonsinusoidal repetitive output signal, such as a triangle wave or square wave.[1][2][3][4] The circuit consists of a feedback loop containing a switching device such as a transistor, comparator, relay,[5] op amp, or a negative resistance device like a tunnel diode, that repetitively charges a capacitor or inductor through a resistance until it reaches a threshold level, then discharges it again.[4][6] The period of the oscillator depends on the time constant of the capacitor or inductor circuit.[2] The active device switches abruptly between charging and discharging modes, and thus produces a discontinuously changing repetitive waveform.[2][4] This contrasts with the other type of electronic oscillator, the harmonic or linear oscillator, which uses an amplifier with feedback to excite resonant oscillations in a resonator, producing a sine wave.[7]

The blinking turn signal on some motor vehicles is generated by a simple relaxation oscillator powering a relay.

Relaxation oscillators may be used for a wide range of frequencies, but as they are one of the oscillator types suited to low frequencies, below audio, they are typically used for applications such as blinking lights (turn signals) and electronic beepers, as well as voltage controlled oscillators (VCOs), inverters, switching power supplies, dual-slope analog to digital converters, and function generators.

The term relaxation oscillator, though often used in electronics engineering, is also applied to dynamical systems in many diverse areas of science that produce nonlinear oscillations and can be analyzed using the same mathematical model as electronic relaxation oscillators.[8][9][10][11] For example, geothermal geysers,[12][13] networks of firing nerve cells,[11] thermostat controlled heating systems,[14] coupled chemical reactions,[9] the beating human heart,[11][14] earthquakes,[12] the squeaking of chalk on a blackboard,[14] the cyclic populations of predator and prey animals, and gene activation systems[9] have been modeled as relaxation oscillators. Relaxation oscillations are characterized by two alternating processes on different time scales: a long relaxation period during which the system approaches an equilibrium point, alternating with a short impulsive period in which the equilibrium point shifts.[11][12][13][15] The period of a relaxation oscillator is mainly determined by the relaxation time constant.[11] Relaxation oscillations are a type of limit cycle and are studied in nonlinear control theory.[16]

  1. ^ Graf, Rudolf F. (1999). Modern Dictionary of Electronics. Newnes. p. 638. ISBN 0750698667.
  2. ^ a b c Edson, William A. (1953). Vacuum Tube Oscillators (PDF). New York: John Wiley and Sons. p. 3. on Peter Millet's Tubebooks website
  3. ^ Morris, Christopher G. Morris (1992). Academic Press Dictionary of Science and Technology. Gulf Professional Publishing. p. 1829. ISBN 0122004000.
  4. ^ a b c Du, Ke-Lin; M. N. S. Swamy (2010). Wireless Communication Systems: From RF Subsystems to 4G Enabling Technologies. Cambridge Univ. Press. p. 443. ISBN 978-1139485760.
  5. ^ Varigonda, Subbarao; Tryphon T. Georgiou (January 2001). "Dynamics of Relay Relaxation Oscillators" (PDF). IEEE Transactions on Automatic Control. 46 (1). Inst. of Electrical and Electronic Engineers: 65. doi:10.1109/9.898696. Retrieved February 22, 2014.
  6. ^ Nave, Carl R. (2014). "Relaxation Oscillator Concept". HyperPhysics. Dept. of Physics and Astronomy, Georgia State Univ. Retrieved February 22, 2014.
  7. ^ Oliveira, Luis B.; et al. (2008). Analysis and Design of Quadrature Oscillators. Springer. p. 24. ISBN 978-1402085161.
  8. ^ DeLiang, Wang (1999). "Relaxation oscillators and networks" (PDF). Wiley Encyclopedia of Electrical and Electronics Engineering, Vol. 18. Wiley & Sons. pp. 396–405. Retrieved February 2, 2014.
  9. ^ a b c Sauro, Herbert M. (2009). "Oscillatory Circuits" (PDF). Class notes on oscillators: Systems and Synthetic Biology. Sauro Lab, Center for Synthetic Biology, University of Washington. Retrieved November 12, 2019.,
  10. ^ Letellier, Christopher (2013). Chaos in Nature. World Scientific. pp. 132–133. ISBN 978-9814374422.
  11. ^ a b c d e Ginoux, Jean-Marc; Letellier, Christophe (June 2012). "Van der Pol and the history of relaxation oscillations: toward the emergence of a concept". Chaos. 22 (2): 023120. arXiv:1408.4890. Bibcode:2012Chaos..22b3120G. doi:10.1063/1.3670008. PMID 22757527. S2CID 293369. Retrieved December 24, 2014.
  12. ^ a b c Enns, Richard H.; George C. McGuire (2001). Nonlinear Physics with Mathematica for Scientists and Engineers. Springer. p. 277. ISBN 0817642234.
  13. ^ a b Pippard, A. B. (2007). The Physics of Vibration. Cambridge Univ. Press. pp. 359–361. ISBN 978-0521033336.
  14. ^ a b c Pippard, The Physics of Vibration, p. 41-42
  15. ^ Kinoshita, Shuichi (2013). "Introduction to Nonequilibrium Phenomena". Pattern Formations and Oscillatory Phenomena. Newnes. p. 17. ISBN 978-0123972996. Retrieved February 24, 2014.
  16. ^ see Ch. 9, "Limit cycles and relaxation oscillations" in Leigh, James R. (1983). Essentials of Nonlinear Control Theory. Institute of Electrical Engineers. pp. 66–70. ISBN 0906048966.