Application-specific integrated circuit
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An application-specific integrated circuit (ASIC) (pronounced /ˈeɪsɪk/ ) is an integrated circuit (IC) customized for a particular use, rather than intended for general-purpose use. For example, a chip designed to run in a digital voice recorder is an ASIC. Application-specific standard products (ASSPs) are intermediate between ASICs and industry standard integrated circuits like the 7400 or the 4000 series .
As feature sizes have shrunk and design tools improved over the years, the maximum complexity (and hence functionality) possible in an ASIC has grown from 5,000 gates to over 100 million. Modern ASICs often include entire 32-bit processors , memory blocks including ROM , RAM , EEPROM , Flash and other large building blocks. Such an ASIC is often termed a SoC (system-on-chip ). Designers of digital ASICs use a hardware description language (HDL), such as Verilog or VHDL , to describe the functionality of ASICs.
History
The initial ASICs used gate array technology. Ferranti produced perhaps the first gate-array, the ULA (Uncommitted Logic Array ), around 1980. An early successful commercial application was the ULA circuitry found in the 8-bit ZX81 and ZX Spectrum low-end personal computers, introduced in 1981 and 1982. These were used by Sinclair Research (UK) essentially as a low-cost I/O solution aimed at handling the computer's graphics. Some versions of ZX81 /Timex Sinclair 1000 used just four chips (ULA, 2Kx8 RAM , 8Kx8 ROM , Z80A CPU ) to implement an entire mass-market personal computer with built-in BASIC interpreter.
Standard-cell design
In the mid 1980s, a designer would choose an ASIC manufacturer and implement their design using the design tools available from the manufacturer. While third-party design tools were available, there was not an effective link from the third-party design tools to the layout and actual semiconductor process performance characteristics of the various ASIC manufacturers. Most designers ended up using factory-specific tools to complete the implementation of their designs. A solution to this problem, which also yielded a much higher density device, was the implementation of standard cells . Every ASIC manufacturer could create functional blocks with known electrical characteristics, such as propagation delay , capacitance and inductance, that could also be represented in third-party tools. Standard-cell design is the utilization of these functional blocks to achieve very high gate density and good electrical performance. Standard-cell design fits between Gate Array and Full Custom design in terms of both its non-recurring engineering and recurring component cost.
Full-custom design
By contrast, full-custom ASIC design defines all the photolithographic layers of the device. Full-custom design is used for both ASIC design and for standard product design.
The benefits of full-custom design usually include reduced area (and therefore recurring component cost), performance improvements, and also the ability to integrate analog components and other pre-designed — and thus fully verified — components, such as microprocessor cores that form a system-on-chip.
The disadvantages of full-custom design can include increased manufacturing and design time, increased non-recurring engineering costs, more complexity in the computer-aided design (CAD) system, and a much higher skill requirement on the part of the design team.