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Application-specific integrated circuits are integrated circuits made for specific users or specific electronic systems. The versatility and mass production of digital integrated circuits have greatly reduced the cost of electronic products and promoted the popularization of computer communications and electronic products. However, at the same time, it has also created the problem of the contradiction between general-purpose and special-purpose, and the disconnection between system design and circuit production.
Application-specific integrated circuits refer to integrated circuits with special specifications that are customized according to different product requirements; on the contrary, non-customized ones are integrated circuits that apply specific standard products.
ASIC is designed and manufactured by specific user requirements and specific electronic system requirements. Since the production cost of a single ASIC chip is very high, if the shipment volume is small, the use of ASICs is not economically affordable. In this case, programmable logic devices (such as field programmable logic gate arrays) can be used as target hardware to implement integrated circuit design. In addition, programmable logic devices have user-programmable features, so they are suitable for prototypes before mass production of large-scale chips for debugging and other tasks. However, programmable logic devices are not as optimized as fully customized integrated circuits in terms of area and speed.
Generally, the ROM and RAM of the ASIC are masked (MASK) before leaving the factory, such as the commonly used infrared remote control transmitter chip is this kind of chip.
ASICs are characterized by the needs of specific users, with more varieties, fewer batches, and short design and production cycles. As a product of integrated circuit technology and specific user’s complete machine or system technology, it is a product of close integration with general integrated circuits. It has the advantages of smaller size, lighter weight, lower power consumption, improved reliability, improved performance, enhanced confidentiality, and reduced cost. At the same time, the larger the scale of the integrated circuit, the more difficult it is to change the special requirements when building a system. In order to solve these problems, an application-specific integrated circuit characterized by user participation in the design has emerged, which can realize the optimized design of the whole machine system, with superior performance and strong confidentiality.
The design process generally can be divided into full custom design and semi-custom design. The former is to complete the various stages of the design in sequence according to the process shown in the figure, and the latter is to use the existing results in a certain stage of the design to carry out a more effective design. For example, a semi-customized design of a module circuit that has a reasonable layout structure and proved to be practical after actual use can save layout or manufacturing time. Standard cell method, gate array method, and programmable logic array method are all common methods for a semi-custom design using modular circuits.
In the computer-aided design system, the more abundant the basic cells developed in the form of cell circuit library and macrocell library, the more conducive to circuit design. These libraries include basic gates, flip-flops, decoders, microprocessor core circuits, ROM, RAM, and analog circuit modules. Usually, the description of the library unit includes the name, function, Boolean expression, logic diagram, circuit diagram, electrical parameters, layout frame, input, output port, and layout structure:
(1) The purpose of functional design is to prepare for circuit design, use system functions for system implementation, and facilitate hierarchical design according to the level of systems, circuits, and components.
(2) The result of the logical design is to give a logical composition that satisfies the logical relationship required by the functional block. It is implemented by gate-level circuits or functional module circuits, expressed in tables, Boolean formulas, or specific languages.
(3) The purpose of circuit design is to determine the circuit structure (component connection relationship) and component characteristics (component value, transistor parameters) to meet the required functional circuit characteristics while considering power supply voltage fluctuations, temperature fluctuations, and manufacturing errors caused Performance changes.
(4) Layout design directly serves process manufacturing. It determines the configuration of components and functional modules on the chip according to the logic circuit diagram or the electronic circuit diagram, and the wiring path between them. In order to save the chip area, a variety of schemes are compared until they are satisfied.
(5) Verification is the process of designing circuit functions, logic, and layout with the aid of a computer-aided design system, as well as analyzing the possible delays and failures of the actual product. Revise the design parameters on the basis of simulation analysis.
In order to strive for a successful product launch, each stage of the design work must repeatedly compare the results to obtain the best design results.
The basic process of ASIC is CMOS, bipolar, BiCMOS, etc. BiCMOS is a kind of mixed craft, it has the dual characteristics of bipolar and CMOS, it is convenient to increase the working speed, reduce the power consumption, improve the integration level and realize the mixing of the analog-digital circuit. The use of gallium arsenide (GaAs) semiconductor materials not only improves the working speed of the circuit but also consumes less power.
As the required functions become more complex, the size of the device gradually decreases, and the number of pins increases. In order to meet the number of leads, volume, and heat dissipation performance, the ASIC will automate the pressure welding process of the chip and inner leads. When the device is mounted on the printed circuit board In terms of convenience and other requirements, packaging processes such as a square shell with leads on all four sides or two rows of outer leads arranged side by side are used. For electronic systems that require high-density assembly, strong vibration resistance, and harsh temperature and humidity environments, chip carrier packaging and tape automatic bonding packaging have been adopted to improve the automation of their mounting operations on printed circuit boards. Reduced volume and weight.
Application-specific integrated circuits also adopt multi-chip technology, using a variety of processes and circuit technologies to prepare individual chips, making it easier to design, manufacture and test multi-functional application-specific integrated circuits.
Application-specific integrated circuits require circuit designers to closely participate in testing, and product testing programs and methods need to be considered from the beginning of circuit design. Test design is an important design content in the development of application-specific integrated circuits.
When designing the circuit, design some additional automatic test circuits and integrate them on the same chip with the designed functional circuits. After the chip is processed, these additional circuits automatically complete the function test of the chip with the support of the software. This test method tests the internal nodes without restriction, can work synchronously with the circuit under test, improves the test quality, and saves time.
The traditional test method is still one of the main methods used in the production of ASICs. It is hoped that the input excitation, output response sampling, and test process will be controlled on automatic test equipment, otherwise, it will be difficult to cope with the ever-expanding circuit scale and functions.
Material defects, processing deviations, poor working conditions, and especially design errors can all cause circuit failure. Circuit designers use the computer-aided design system to simulate possible faults during the circuit design process, analyze the fault attributes, detect and determine the fault location to improve the circuit design and make it easy to detect these faults in the production process.
In this type of design, all logic cells are tailored for specific applications, that is, the designer must manufacture logic cells specifically for the circuit. All mask layers used for interconnection are customized. Therefore, the programmer cannot change the interconnection of the chip and must understand the circuit layout when programming.
One of the best examples of a fully customized ASIC is a microprocessor. This type of customization allows designers to build various analog circuits, optimized memory cells, or mechanical structures on a single IC. The ASIC is expensive and time-consuming to manufacture and design. The time required to design these ICs is approximately eight weeks.
These are usually used for advanced applications. Maximum performance, smallest area, and highest flexibility are the main features of a fully customized design. Ultimately, the risk in the design is high because the circuit components used in logic cells, resistors, etc. are not pre-tested.
In this type of design, the logic units are obtained from the standard library, that is, they are not hand-made as in a fully customized design. Some are customized, and some are drawn from pre-designed libraries. Based on the types of logic cells obtained from the library and the amount of customization allowed for interconnection, these ASICs are divided into two types: ASICs based on standard cells and ASICs based on gate arrays.
1) ASIC based on standard cells
2) ASIC based on gate array
This type of semi-custom ASIC has predefined transistors on the silicon wafer, that is, the designer cannot change the position of the transistors present on the die. The basic array is a predefined pattern of the gate array, and the basic unit is the smallest repeating unit in the basic array.
The designer is only responsible for using the first few metal layers of the die to change the interconnection between the transistors. The designer chooses from the gate array library. These are commonly referred to as "screened gate arrays." There are three types of ASICs based on gate arrays. They are channelized channeled gate arrays, channel-less gate arrays, and structured gate arrays.
a) Channeled gate array
In this type of gate array, there is space for wiring between rows of transistors. These are similar to CBIC in that space for interconnection is reserved between the blocks, but the height in the channel gate array unit row is fixed, while in CBIC, this space can be adjusted.
b) Channel-less gate array
c) Structured gate array
The structured gate array has high CBIC area efficiency. Like shielded gate arrays, they have lower costs and faster turnaround times. Here, the fixed size of the embedded function limits the structured gate array.
Digital, analog or digital-analog hybrid application-specific integrated circuits have been widely used in various communication systems, image and signal processing fields, high-quality audiovisual products, electromechanical controls, measurement circuits, and computers. In the military and aerospace sectors, application-specific integrated circuits have received special attention, and many key electronic systems have already used their own products. With the emergence of new materials and new processes, the application areas of application-specific integrated circuits are constantly expanding and extending.
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