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Definition: ASIC

(Application Specific Integrated Circuit) Pronounced "A sik," an ASIC is a chip that is custom designed for a specific purpose, and it is typically used by the company that created it. However, a chip that is custom designed for sale is called an "application specific standard part" (see ASSP).

Full Custom ASIC
A full custom ASIC means the designers have total control over every transistor and can fine tune the logic to perform operations as fast as possible. Today, this is rarely done for an entire chip unless it is a small one. However, as part of a large chip, a single circuit or small number of circuits can be custom designed.

Standard Cells
Most ASICs are designed by selecting and connecting standard cells from libraries that contain predefined elements such as registers, logic gates, flip-flops and latches. Standard cells may also include larger functions (see standard cell).

Gate Arrays and Structured ASICs
An older ASIC technology, gate arrays involved pre-creating a "sea of gates" (or "sea of cells") across the surface, each gate/cell containing a handful of transistors. The design was mapped onto these silicon structures by wiring them together. See gate array.

Structured ASICs were a later variation that used the same concept, but each cell consisted of slightly more complex functions. Rarely used today, gate arrays and structured ASICs allowed devices to reach the market faster but sacrificed performance. See structured ASIC, FPGA, PLD, adaptive computing and CSIC.

Types of Chips
ASICs are made in a semiconductor fab and are contrasted here with the programmable logic market. (Diagram courtesy of Clive "Max" Maxfield, www.clivemaxfield.com)