Application-specific integrated circuit

An application specific integrated circuit ( English application-specific integrated circuit , ASIC , even custom chip ) is an electronic circuit , which as an integrated circuit has been realized. The function of an ASIC can therefore no longer be changed, but the manufacturing costs are lower with high one-off costs (e.g. photo masks ). ASICs are manufactured worldwide by many manufacturers according to customer requirements and usually only supplied to them. This is how the ASIC differs from other microchips. If a component developed as an ASIC is sold on the market, it is often referred to as an application-specific standard product (ASSP).

description

ASIC on a printed circuit board .

Purely digital ASICs integrate a large number of logic functions that would otherwise have to be put together from various standard components such as processors , logic families (e.g. 74xx ) or similar components. Mixed-signal ASICs consist of digital and analog functions. The analog circuits such as B. analog-to-digital converters , PLLs , low-noise amplifiers, high-current drivers , etc. the target technology ( structure size ).

ASICs are mainly used for devices built in large series to reduce costs. Most of the chips manufactured today are application-specific, such as the processors in cell phones for coding signals or for processing data. The difference to PLDs and Field Programmable Gate Arrays is that the functionality of the application-specific IC must be clearly defined by the manufacturer and is therefore firmly specified. The internal circuit can no longer be changed by the user. There are also ASIC variants on which microprocessors or signal processors are integrated ( system-on-a-chip ), whereby a certain flexibility for the user can be achieved through the software running on them.

Today, EDA software (EDA = Electronic Design Automation ) is used to design ASICs .

The well-known CPUs ( Intel Pentium , AMD Athlon etc.), on the other hand, are universal integrated circuits that can handle a variety of different tasks. However, this has the disadvantage that these tasks are not processed optimally: Energy consumption, chip area, clock frequency and other target parameters are higher in certain applications than with a specialized component, and the data throughput is lower.

A CPU that is only manufactured for a specific task is called an application-specific instruction-set processor (ASIP).

Classification

Various solutions for ASICs are available on the market. The concepts can be roughly divided into the following groups:

Fully customer-specific ASIC: Use of customer-specific logic blocks that are designed by the customer at transistor level. These are placed and linked specifically for the product, so all structuring levels are product-specific.
partially customer-specific ASIC: like completely customer-specific ASIC supplemented by standard or macro cells (e.g. SRAM blocks) from the manufacturer.
Standard cell ASIC: a customer-specific circuit design consisting only of logic cells provided by the manufacturer
Megacell ASIC: They are similar to the standard cell ASIC, but are significantly more complex and larger. Usually they fulfill standard functions, e.g. B. RAM blocks, MPEG coder
Gate array ASIC: preconfigured standard gates or cells that are only linked in the metallization level at the customer's request.
- Sea-of-Gates -ASIC: They are similar to gate arrays, but have several (customer-specific) metallization levels, which enables more complex interconnection of the cells and denser transistor arrangements.

What these groups have in common is that at least a more or less large part of the circuits is specified during manufacture according to customer specifications. They differ in terms of the possible configuration options by the customer, space requirements, available housing, complexity of the circuit, switching speed, power consumption, etc. which ultimately is reflected in the costs of production or the individual chip. The largely prefabricated ones are one of the most cost-effective ways to manufacture ASIC. However, they are not optimized for their application. Completely customer-specific ASICs, on the other hand, are optimized for the respective application through the circuit design (usually at the customer's) and the appropriate choice of production technology. However, they require a great deal of effort in terms of creation and verification.

In addition, FPGAs are sometimes referred to as ASICs. An FPGA is usually associated with the fact that the customer-specific circuit is only brought into the component at the customer. However, there are also FPGAs that are partially adapted at the customer's request, in which certain assemblies are already customized during manufacture. This usually restricts the range of use of the customer-specific FPGA, but enables faster and cheaper circuits for the corresponding application.

Advantages and disadvantages

Due to the adaptation of their architecture to a specific problem, ASICs work very efficiently and a lot faster than a functionally equivalent implementation via software in a microcontroller . In a mobile phone, for example, this has the advantage that the battery lasts longer and the device is more compact.

Due to their exclusivity, ASICs prevent replicas. ASICs are often a major problem for hobbyists and service workshops, as they are usually no longer produced after a device has been discontinued. If the remaining stocks are used up, a repair is usually only possible by removing the ASICs from devices with other defects.

The major disadvantages of ASICs are the high investment costs, especially in the case of small and medium-sized quantities, and in any case the longer development time compared to solving the same task with discrete components and standard ICs or with programmable components such as FPGAs .

application

ASICs are used in many different electronic devices, from clock radios to high-performance computers. The reason for the development of such ICs, which are often only designed for a single specific model series, is the cost savings compared to the construction with standard modules, especially with high production numbers. In the early days of integrated circuits, ASICs were an alternative to implementation using individual transistors or TTL modules. Digital ASICs are ICs that have been designed for a specific purpose. In most cases, these modules work either in terms of space, consumption, costs or performance.

Examples:

Graphics processors
Agnus (ASIC in the Commodore Amiga )
Sinclair Computer Logic
Application of cryptographic algorithms in computer systems, (see also: Mining Rig )

literature

G. Hermann, D. Müller : ASIC - Design and Test. Carl-Hanser-Verlag, 2004, ISBN 3-446-21709-6 .
Peter Ammon: Development process for ASIC circuits. In: Electronics. No. 7, 1987.
J. Tatje: ASIC high tech for everyone with LOGiC. In: Design & Electronics. No. 19 1986.
K. Reindl: Customized ICs with analog circuit functions. In: Design & Electronics. 1986.

Individual evidence

↑ Lexicon Electronics and Microelectronics . Second, updated and expanded edition. Springer, Berlin / Heidelberg 1993, ISBN 3-642-58006-8 , keyword: ASIC , p. 45-46 .
^ SK Tewksbury: Application-Specific Integrated Circuits . In: Richard C. Dorf (Ed.): The electrical engineering handbook . 2nd edition. CRC Press, Boca Raton 1997, ISBN 0-8493-8574-1 .

[1] Lexicon Electronics and Microelectronics . Second, updated and expanded edition. Springer, Berlin / Heidelberg 1993, ISBN 3-642-58006-8 , keyword: ASIC , p. 45-46 .

[2] SK Tewksbury: Application-Specific Integrated Circuits . In: Richard C. Dorf (Ed.): The electrical engineering handbook . 2nd edition. CRC Press, Boca Raton 1997, ISBN 0-8493-8574-1 .