Application-Specific Integrated Circuits (ASIC's)


The term 'ASIC' stands for 'application-specific integrated circuit'.  An ASIC is basically an integrated circuit designed specifically for a special purpose or application. Strictly speaking, this also implies that an ASIC is built only for one and only one customer. An example of an ASIC is an IC designed for a specific line of cellular phones of a company, whereby no other products can use it except the cell phones belonging to that product line. The opposite of an ASIC is a standard product or general purpose IC, such as a logic gate or a general purpose microcontroller, both of which can be used in any electronic application by anybody.


Aside from the nature of its application, an ASIC differs from a standard product in the nature of its availability.  The intellectual property, design database, and deployment of an ASIC is usually controlled by just a single entity or company, which is generally the end-user of the ASIC too.  Thus, an ASIC is proprietary by nature and not available to the general public.  A standard product, on the other hand, is produced by the manufacturer for sale to the general public.  Standard products are therefore readily available for use by anybody for a wider range of applications.


The first ASIC's, known as uncommitted logic array or ULA's, utilized gate array technology.  Having up to a few thousand gates, they were customized by varying the mask for metal interconnections. Thus, the functionality of such a device can be varied by modifying which nodes in the circuit are connected and which are not. Later versions became more generalized, customization of which involve variations in both the metal and polysilicon layers. 


ASIC's are usually classified into one of three categories: full-custom, semi-custom, and structured.


Full-custom ASIC's are those that are entirely tailor-fitted to a particular application from the very start.  Since its ultimate design and functionality is pre-specified by the user, it is manufactured with all the photolithographic layers of the device already fully defined, just like most off-the-shelf general purpose IC's. The use of predefined masks for manufacturing leaves no option for circuit modification during fabrication, except perhaps for some minor fine-tuning or calibration. This means that a full-custom ASIC can not be modified to suit different applications, and is generally produced as a single, specific product for a particular application only.  


Semi-custom ASIC's, on the other hand, can be partly customized to serve different functions within its general area of application. Unlike full-custom ASIC's, semi-custom ASIC's are designed to allow a certain degree of modification during the manufacturing process.   A semi-custom ASIC is manufactured with the masks for the diffused layers already fully defined, so the transistors and other active components of the circuit are already fixed for that semi-custom ASIC design. The customization of the final ASIC product to the intended application is done by varying the masks of the interconnection layers, e.g., the metallization layers. 


Structured or Platform ASIC's, which belong to a relatively new ASIC classification, are those which have been designed and produced from a tightly defined set of: 1) design methodologies; 2) intellectual properties (IP's); and 3) well-characterized silicon, aimed at shortening the design cycle and minimizing the development costs of the ASIC.  A platform ASIC is built from a group of 'platform slices', with a 'platform slice' being defined as a pre-manufactured device, system, or logic for that platform.  Each slice used by the ASIC may be customized by varying its metal layers.  The 're-use' of pre-manufactured and pre-characterized platform slices simply means that platform ASIC's are not built from scratch, thereby minimizing design cycle time and costs.


Examples of ASIC's include: 1) an IC that encodes and decodes digital data using a proprietary encoding/decoding algorithm; 2) a medical IC designed to monitor a specific human biometric parameter; 3) an IC designed to serve a special function within a factory automation system;  4) an amplifier IC designed to meet certain specifications not available in standard amplifier products; 5)  a proprietary system-on-a-chip (SOC); and 6) an IC that's custom-made for a particular automated test equipment. 




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