Relaxation Oscillator

relaxation oscillator [‚rē‚lak′sā·shən ‚äs·ə‚lād·ər]

(electronics)

An oscillator whose fundamental frequency is determined by the time of charging or discharging a capacitor or coil through a resistor, producing waveforms that may be rectangular or sawtooth.

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Relaxation Oscillator 

a generator of nonsinusoidal electrical oscillations that usually have a broad spectrum (seeGENERATION OF ELECTRICAL OSCILLATIONS). The two basic elements of a relaxation oscillator are (1) a passive capacitive or inductive energy storage element and (2) a nonlinear element with a volt-ampere characteristic that has a falling segment so that the element has hysteresis properties. Because of the presence of these properties, the oscillator operates alternately in regions of regeneration and relaxation. In the regeneration region, energy from the source of direct current or voltage is stored in the storage element. In the relaxation region, a substantial portion of the energy is released from the storage element. The released energy is dissipated in the nonlinear element and the other resistive elements of the relaxation oscillator, such as resistors. A characteristic feature of relaxation oscillators is that the maximum energy that can be stored by the storage unit is comparable to the maximum energy the unit can lose. Examples of devices used as nonlinear elements include gas-discharge devices (such as thyratrons and neon lamps), electron tubes, transistors, thyristors, and tunnel diodes. Transistor or electron-tube amplifiers with positive feedback are also used as nonlinear elements.

Examples of common relaxation oscillators are multivibrators, blocking oscillators, and sawtooth oscillators (including phantastrons). It is characteristic of relaxation oscillators that the oscillations are self-maintained; the period of the relaxation oscillations is determined by the parameters of the oscillator. Because of the poor stability of the frequency and, consequently, of the period of relaxation oscillators, the oscillations of such generators are often synchronized with an external source of stable oscillations. Use is also made of a slave mode of operation, in which the relaxation oscillator is turned on by the action of an external signal. Relaxation oscillators are employed in such pulse-engineering equipment as television, radar, and measuring apparatus.

REFERENCES

Andronov, A. A., A. A. Vitt, and S. E. Khaikin. Teoriia kolebannii, 2nd ed. Moscow, 1959.
Itskhoki, Ia. S., and N. I. Ovchinnikov, Impul’snye i tsifrovye ustroistva. Moscow, 1972.

IA. S. ITSKHOKI