Delay line memory

Delay lines ( english delay line, Correct: delay line ) are used to time shift or temporary storage ( run-time memory ) of a serial signal ( analog or digital) by means of the signal propagation delay in an electrical cable of a certain length, or even in an acoustic transmission path.

The delay time can be set from the quotient of length and wave velocity.

• 2.1 TV reception technology
• 2.2 Audio Technology
• 2.3 Scientific equipment and high frequency

Principle of operation

Electromagnetic delay line

The delay occurs without signal conversion by an electric line or an equivalent arrangement of a certain length. On the line / structure to a wired electromagnetic wave propagates. The geometrical length may be significantly less than the electrically effective length of the signal delay, for example:

• A dielectric with a dielectric constant ( ε ) greater than 1 causes a so-called reduction factor.
• A ferromagnetic material with permeability ( μ ) > 1, also causes a reduction.
• Over the length Coupled inductance causes a geometric shortening ( wire coil, see picture, but also in traveling wave tubes ).
• The " line " can be built in concessions to the signal bandwidth also of discrete inductors and capacitors to achieve a high level of maturity.
• The conduit may consist of resonators ( cavity resonators, comb-like structures ); it is then only in a narrow frequency band effectively and serves mostly the speed of adjustment ( delay ) of the wave at an electron current (examples: undulators in the free-electron laser, slot anode of the magnetron )

A combination of the above measures is also possible.

Electronic delay line

An electronic form of a delay line is of the so-called bucket brigade, wherein the charges of a plurality of capacitors to a clock signal to be passed through to the next. The principle is in the form of integrated circuits as a bucket brigade (English charge-coupled device, CCD) known. Since this principle operates in discrete time, the bandwidth is limited to half the clock frequency. Digital form are FIFO memory, it is implemented with DRAMs.

Acoustic delay line

In acoustic delay lines, the electric signal is converted by piezoelectric transducers in the ultrasonic is passed through a medium with a defined speed of sound, and then converted back into an electrical signal.

The accompanying chart shows a PAL ultrasonic delay line: the two piezoelectric transducers are bonded in the form of narrow strips on the front sides of a glass plate to see only the aluminum connector wires. In order to limit the size of the glass plate being worked with reflections at the edges of the glass medium. In order wave propagation and the signal defined narrow, square cushion pads are applied to the glass plate. Is used by potassium lead glass which glass has a lighter weight compared to lower sound speed (about 2500 to 2540 m / s ), and also has a low temperature coefficient of the propagation speed.

Early forms were made of magnetostrictive wires excited.

Mechanical delay line

Mechanical reverbs ( spring reverb ) are delay lines in principle.

Application

Television reception equipment

Ultrasonic delay lines were up to about 1995 used in color television sets by the television standards PAL and SECAM, to delay the color carrier signal to the running time of one image line. This allows for PAL using the alternating in phase color carrier signal phase errors which manifest themselves in hue errors are efficiently suppressed by averaging the color signals of two consecutive image lines (the phase errors cancel each other out ); SECAM at which each image line each transfers only one of the two color difference signals, the circuit can access only through the use of a delay line at all to the other of the color difference signal ( from the previous line). Therefore, on the other hand, the use of a delay line for PAL only desirable for increased image quality, with SECAM is imperative. The third analog color television system, NTSC, the color signal in each line is independent of the neighboring lines; NTSC receiver therefore does not use delay line. After demodulation of the chrominance signals YR ( Rotdifferenz ) and YB ( blue differential ) from the carrier chrominance signal from all three systems together with the luminance signal Y, the three RGB components (red, green, blue) for controlling the three electron guns of the color picture tube, won.

In ultrasonic delay lines, the signal delay of the quadrature amplitude modulated PAL carrier chrominance signal is performed with a carrier frequency of 4.43361875 MHz band-pass position. Subtracting the modulated color components is achieved by a delay of a non-integer number of periods of the color carrier frequency, and is 283.5 periods. With the period of the color subcarrier frequency by:

There is a delay of ultrasonic delay line of ≈ 63.943 microseconds.

In later PAL color television receivers, the delay of the two has already been demodulated color subcarrier signals YR and YB in baseband with a delay of exactly one image line of 64 microseconds using two synchronized SC filter performed. Delay chains in the form of switched-capacitor filter chains are in contrast to the ultrasonic delay line to produce an integrated circuit, smaller, and mechanically robust.

Since 2000 use standard digital television equipment for reception of analogue television signals multi-standard decoder with integrated delay chains.

Audio Technology

Electronic signal delays after the bucket principle, so-called bucket brigade (English bucket brigade memory (BBM ) or Bucket Brigade Device ( BBD) ) can be used to identify and blank noise good time or to the sense of spatial hearing, by adding the delayed signal components influence.

Also, echo and reverb units are in principle coupled delay lines. Previously it also came with a mechanical method acoustically excited coil spring for use ( spring reverb ).

Scientific equipment and high frequency

In research it is often necessary to delay signals or pulses to compensate for time shifts, to allow for the detection or synchronized trigger time points.

Delay times in the nanosecond and sub- nanosecond range are often ensured by defined cable lengths. This can be fixed lines or coaxial cable laboratory.

In the high-frequency technology and antenna construction, it is often necessary to distribute or combine signals in phase. The delay lines used for this purpose are also called bypass line.

History

In early computers such as ACE, UNIVAC I or EDSAC was used delay lines as a dynamic main memory. In contrast to a random access memory (RAM ) could not be accessed randomly each data item, but it had to wait until it reappeared at the end of the run-time memory.

Mercury - term memory consisted of a mercury -filled tube, at whose two ends a quartz oscillator was mounted. One of the two quartz crystals was excited to mechanical vibrations by an electrical signal and led to ultrasonic waves in the mercury, which continue with the propagation speed of 2 km / s, and after appropriate delay time to put the other quartz crystal to generate a turn electrical signal. In sync with the clock of the arithmetic unit, the corresponding bit signals either sent back to the run-time memory or replaced by other bits. So you could circulate a serial bit pattern of a certain length and thus save. In this way, the storage being alone in the mercury by the signal propagation time of the acoustic wave in the ACE, these were 1024 bits at a clock rate of 1 MHz, so a duration of 1 ms.

Mercury delay lines have been previously used in RADAR technology in World War II for analog signals.

Another variant of the delay line delay memory used for nickel wire - in this, the effect of magnetostriction in nickel for writing / reading, and a long rolled nickel wire was utilized for storage. Such delay lines were used in particular in desktop computers, where core memory too expensive and the lower processing speed was not a problem.

A third variant uses glass as a medium for the acoustic wave. It was used in color television sets for the ( analog ) storage of the signal lines by using the method SECAM and PAL for the correction of chromatic aberrations. By use of reflections in the glass body which originally 15cm long unit could be substantially reduced.