Editing Delay-line memory (section)

===Piezoelectric delay lines===
[[File:ultrasonicdelayline.jpg|thumb|An ultrasonic [[analog delay line]] from a [[PAL]] color TV; it delays the color signal by 64&nbsp;μs. Manufacturer: VEB ELFEMA Mittweida ([[East Germany|GDR]]) in 1980]]
A similar solution to the magnetostrictive system was to use delay lines made entirely of a [[piezoelectric]] material, typically quartz. Current fed into one end of the crystal would generate a compressive wave that would flow to the other end, where it could be read. In effect, piezoelectric material simply replaced the mercury and transducers of a conventional mercury delay line with a single unit combining both. However, these solutions were fairly rare; growing crystals of the required quality in large sizes was not easy, which limited them to small sizes and thus small amounts of data storage.<ref>{{cite book |title=Glass Memories |publisher=Corning Electronics |date=1963 |id=RRP 8/63 5M |url=https://archive.org/details/TNM_Glass_computer_memories_-_Corning_Electronics_20171206_0185}}</ref>

A better and more widespread use of piezoelectric delay lines was in European television sets. The European [[PAL]] standard for color broadcasts compares the signal from two successive lines of the image in order to avoid color shifting due to small phase shifts. By comparing two lines, one of which is inverted, the shifting is averaged, and the resulting signal more closely matches the original signal, even in the presence of interference. In order to compare the two lines, a piezoelectric delay unit to delay the signal by a time that is equal to the duration of each line, 64&nbsp;μs, is inserted in one of the two signal paths that are compared.<ref>{{cite thesis |first=F.T. |last=Backers |title=Ultrasonic delay lines for the PAL colour-television system |date=1968 |type=Ph.D. |location=Eindhoven, Netherlands |publisher=Technische Universiteit |url=https://pure.tue.nl/ws/files/3648245/161551.pdf |pages=7–8 }}<br/>{{cite journal |first=F. Th. |last=Backers |title=A delay line for PAL colour television receivers |journal=Philips Technical Review |volume=29 |issue= |pages=243–251 |date=1968 |doi= |url=http://www.extra.research.philips.com/hera/people/aarts/_Philips%20Bound%20Archive/PTechReview/PTechReview-29-1968-243.pdf }}{{Dead link|date=May 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> In order to produce the required delay in a crystal of convenient size, the delay unit is shaped to reflect the signal multiple times through the crystal, thereby greatly reducing the required size of the crystal and thus producing a small, rectangular-shaped device.