delay line
Delay lines are electronic components with which signals can be delayed by a certain time. They are used wherever signals have to be provided with phase shifts or delay times. In general, a distinction is made between passive and active delay lines, and between analog and digital delay lines.
Wherever waves propagate, they are delayed by physical media. This applies equally to acoustic vibrations and optical waves, as well as to electrical and electromagnetic waves. Every transmission medium and every piece of conductor can be used as a phase shifter and delay signals. This starts with the finite transmission speed in conductors, however short they may be. Their length, inductance and capacitance cause signal delays. This also applies to low-passfilters or active components.
In some circuits, these delay times must be compensated to ensure correlation of two signals, for example. In oscilloscopes, signals must be delayed in order to display the trigger signal, and in other circuits to be able to average two signals offset in time, as in PAL television, and in phase-sensitive circuits, the phase position of one signal must be shifted by a certain phase angle relative to the other.
Passive electronic delay lines can be a combination of inductors and capacitors that delay the input signal by a fixed delay time. A well-known example is the delay line in classic color televisions according to the PAL television standard. Here, the two alternating color carrier signals, which were switched in phase in successive lines, were combined. Since delay lines attenuate the signals, active delay lines were developed to compensate for the attenuation; their active components amplified the attenuated signals. In addition to these analog delay lines, there are digital and programmable delay lines. Examples of digital delay lines are CCD sensors where the charges reach the outputs step by step according to the bucket brigade principle or shift registers like First In First Out( FIFO). With programmable delay lines, on the other hand, the delay times can be programmed.