Delay line oscillator
Encyclopedia
A delay line oscillator is a form of electronic oscillator
Oscillation
Oscillation is the repetitive variation, typically in time, of some measure about a central value or between two or more different states. Familiar examples include a swinging pendulum and AC power. The term vibration is sometimes used more narrowly to mean a mechanical oscillation but sometimes...

 that uses a delay line
Delay line
Delay line may refer to:* Propagation delay, the length of time taken for something to reach its destination* Analog delay line, used to delay a signal...

 as its principal timing element.

The circuit is set to oscillate by inverting
Inverter (logic gate)
In digital logic, an inverter or NOT gate is a logic gate which implements logical negation. The truth table is shown on the right.This represents perfect switching behavior, which is the defining assumption in Digital electronics. In practice, actual devices have electrical characteristics that...

 the output of the delay line and feeding that signal back to the input of the delay line with appropriate amplification. The simplest style of delay line oscillator, when properly designed, will oscillate with period exactly two times the delay period of the delay line. Additional outputs that are correlated in frequency with the main output but vary in phase can be derived by using additional taps from within the delay line

The delay line may be realized with a physical delay line (such as an LC network
LC circuit
An LC circuit, also called a resonant circuit or tuned circuit, consists of an inductor, represented by the letter L, and a capacitor, represented by the letter C...

 or a transmission line
Transmission line
In communications and electronic engineering, a transmission line is a specialized cable designed to carry alternating current of radio frequency, that is, currents with a frequency high enough that its wave nature must be taken into account...

). In contrast to a Phase-shift oscillator
Phase-shift oscillator
A phase-shift oscillator is a simple electronic oscillator. It contains an inverting amplifier, and a feedback filter which 'shifts' the phase of the amplifier output by 180 degrees at a specific oscillation frequency....

 in which LC components are lumped, the capacitances and inductances are distributed through the length of the delay line. A ring oscillator
Ring oscillator
A ring oscillator is a device composed of an odd number of NOT gates whose output oscillates between two voltage levels, representing true and false...

 uses a delay line formed from the gate delay of a cascade of logic gate
Logic gate
A logic gate is an idealized or physical device implementing a Boolean function, that is, it performs a logical operation on one or more logic inputs and produces a single logic output. Depending on the context, the term may refer to an ideal logic gate, one that has for instance zero rise time and...

s. The timing of a circuit using a physical delay line is usually much more accurate. It is also easier to get such a circuit to oscillate in the desired mode
Overtone
An overtone is any frequency higher than the fundamental frequency of a sound. The fundamental and the overtones together are called partials. Harmonics are partials whose frequencies are whole number multiples of the fundamental These overlapping terms are variously used when discussing the...

.

The delay line oscillator may be allowed to free run or it may be gated for use in asynchronous logic
Asynchronous circuit
An asynchronous circuit is a circuit in which the parts are largely autonomous. They are not governed by a clock circuit or global clock signal, but instead need only wait for the signals that indicate completion of instructions and operations. These signals are specified by simple data transfer...

.

Since the optical cavity is a delay line, a laser can be regarded as a special case of the delay-line oscillator.
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