Delay Lines
Delay lines are so called because they delay signals in a transmission line. As their name
implies they are used to delay or slow down signals for timing purposes. If two or more
signals from different sources are required to arrive at a single point at the same time
it is necessary to delay match the faster signals to the slowest. This may be achieved by
using additional lengths of cable or more conveniently by a lumped element circuit; delay
line.
Pulse Delay Lines and Video Delay Lines
Delay lines are normally divided into two groups, Pulse Delay Lines and
Video
Delay Lines. The former are specified in the time domain and used for digital pulses. The
latter are specified in the frequency domain and a typical application is in television
systems.
Pulse Delay Lines
All delay lines are specified in terms of the amount of delay they introduce and the
impedance of the circuit or line in which they are to be used. In pulse applications the
pulse shape is specified as shown below.
Fig 1. Pulse Delay Lines
diagram
Video Delay Lines
For Video Delay Lines the frequency response is specified in a similar way to that for
a filter.
In delay lines using LC lumped element technology the delay times achievable are in the
range of 1 nanosecond to a few microseconds.
Delay lines can consist
Delay lines can consist of a single delay, a single delay with taps available along the
line, or as individual delays in a single module which can be cascaded; these are normally
referred to as programmable delay lines. The latter often have delay times which follow a
binary sequence. With tapped delays the signal can be accessed at each tap with a high
impedance load of at least 10 times the characteristic impedance of the filter. The input
must be at the source and load impedance of the line.
Delay Lines FAQs
The question most often asked concerning the pulse delay lines is "how do I
specify the bandwidth of the pulse I am using from the rise time?" The formula below
gives an approximate answer.
Bandwidth = 0.35/Rise Time (10% to 90%)
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