Gate array: Difference between revisions

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Revision as of 23:06, 16 June 2022

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[[File:ZX81 ULA.jpg|thumb|Sinclair ZX81 ULA]]

A '''gate array''' is an approach to the design and manufacture of [[application-specific integrated circuit]]s (ASICs) using a [[semiconductor device fabrication|prefabricated]] chip with components that are later interconnected into logic devices (e.g. [[NAND gates]], [[Flip-flop (electronics)|flip-flops]], etc.) according to a custom order by adding metal interconnect layers in the factory. It was popular during upheaval in semiconductor industry in 80s and its usage declined by end of 90s.

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=== Development ===

Gate arrays had several concurrent development paths. [[Ferranti]] in the UK pioneered commercializing [[bipolar transistor|bipolar]] ULA technology,<ref name="bteng198307">{{ cite journal | url=https://archive.org/details/bte-198307/page/n19/mode/2up | title=The Use of Gate Arrays in Telecommunications | journal=British Telecommunications Engineering | last1=Grierson | first1=J. R. | date=July 1983 | access-date=26 February 2021 | volume=2 | issue=2 | pages=78-80 | issn=0262-401X | quote=In the UK, Ferranti, with their bipolar collector diffused isolation (CDI) arrays, pioneered the commercial use of gate arrays and for many years this was by far the most widely used technology. }}</ref> offering circuits of "100 to 10,000 gates and above" by 1983.<ref name="btj198301">{{ cite news | url=https://archive.org/details/btj-198301/page/n71/mode/1up | title=Everybody's talking about Ferranti ICs. | work=British Telecom Journal | volume=3 | issue=4 | date=January 1983 | access-date=23 January 2021 }}</ref><ref name="ferranti_quickref">{{ cite book | url=https://archive.org/details/FerrantiQ.RefULA1984/page/n1/mode/1up | title=Ferranti Discrete and Integrated Circuits Quick Reference Guide | publisher=Ferranti plc. | date=1982 | access-date=23 February 2021 | pages=IC4 }}</ref> The company's early lead in semi-custom chips, with the initial application of a ULA integrated circuit involving a camera from [[Rollei]] in 1972, expanding to "practically all European camera manufacturers" as users of the technology, led to the company's dominance in this particular market throughout the 1970s. However, by 1982, as many as 30 companies had started to compete with Ferranti, reducing the company's market share to around 30 percent. Ferranti's "major competitors" were other British companies such as Marconi and Plessey, both of which had licensed technology from another British company, Micro Circuit Engineering.<ref name="heidelberg19821006_ics">{{ cite magazine | url=https://archive.org/details/jprs-report_jprs-82727/page/10/mode/2up | title=Great Britain Develops Semicustom and Custom ICs | magazine=Heidelberg Elektronik Industrie | date=6 October 1982 | access-date=4 March 2022 | last1=Turmaine | first1=Bradley | pages=43-46 }}</ref> A contemporary initiative, UK5000, also sought to produce a CMOS gate array with "5,000 usable gates", with involvement from [[British Telecom]] and a number of other major British technology companies.<ref name="bteng198610_silicon">{{ cite journal | url=https://archive.org/details/bte-198610/page/n41/mode/2up | title=Silicon Micro-Electronics at British Telecom Research Laboratories | journal=British Telecommunications Engineering | date=October 1986 | access-date=4 March 2022 | pages=230-236 }}</ref>

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=== Alternatives ===

Indirect competition arose with the development of the [[field-programmable gate array]] (FPGA). [[Xilinx]] was founded in 1984 and its first products were much like early gate arrays, slow and expensive, fit only for some niche markets. However, [[Moore's law|Moore's Law]] quickly made them a force and by the early 1990s were seriously disrupting the gate array market.

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=== Decline ===

While the market boomed, profits for the industry were lacking. Semiconductors underwent a series of rolling [[List of recessions in the United States|recessions]] during the 1980s that created a boom-bust cycle. The 1980 and 1981-1982 general recessions were followed by high interest rates that curbed capital spending. This reduction played havoc on the semiconductor business that at the time was highly dependent on capital spending. Manufacturers desperate to keep their fab plants full and afford constant modernization in a fast moving industry became hyper-competitive. The many new entrants to the market drove gate array prices down to the marginal costs of the silicon manufacturers. Fabless companies such as LSI Logic and CDI survived on selling design services and computer time rather than on the production revenues.<ref name=":1" />

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== Design ==

A gate array is a prefabricated silicon chip with most [[transistor]]s having no predetermined function. These transistors can be connected by metal layers to form standard [[Negated AND gate|NAND]] or [[NOR gate|NOR]] [[logic gate]]s. These logic gates can then be further interconnected into a complete circuit on the same or later metal layers. Creation of a circuit with a specified function is accomplished by adding this final layer or layers of metal interconnects to the chip late in the manufacturing process, allowing the function of the chip to be customized as desired. These layers are analogous to the copper layers of a [[printed circuit board]].

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== Uses ==

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Gate arrays were used widely in the [[home computer]] market in the United Kingdom in the early 1980s, including in the [[Sinclair ZX81]] and [[Sinclair Spectrum]], the [[BBC Micro]] and [[Acorn Electron]], and the [[Commodore Amiga]].

== References ==

{{Reflist}}

{{refs}}

== External links ==

* {{Commons category-inline|Gate arrays}}