Delay Line Memory - Electric Delay Lines

Electric Delay Lines

Electric delay lines are used for shorter delay times (ns to several µs). They consist of a long electric line or are made of discrete inductors and capacitors, which are arranged in a chain. To shorten the total length of the line it can be wound around a metal tube, getting some more capacitance against ground and also more inductance due to the wire windings, which are lying close together.

Other examples are:

• short coaxial or microstrip lines for phase matching in high frequency circuits or antennas
• hollow resonator lines in magnetrons and klystrons as helices in travelling wave tubes to match the velocity of the electrons to the velocity of the electromagnetic waves
• undulators in free electron lasers

Another way to create a delay time is to implement a delay line in an integrated circuit storage device. This can be done digitally or with a discrete analogue method. The analogue one uses bucket-brigade devices or charge coupled devices (CCD), which transport a stored electric charge stepwise from one end to the other. Both digital and analog methods are bandwidth limited at the upper end to the half of the clock frequency, which determines the steps of transportation.

In modern computers operating at gigahertz speeds, millimeter differences in the length of conductors in a parallel data bus can cause data-bit skew, which can lead to data corruption or reduced processing performance. This is remedied by making all conductor paths of similar length, delaying the arrival time for what would otherwise be shorter travel distances by using zig-zagging traces.