Description

fig.1 - Intrgrated circuits

Integrated Circuit, tiny electronic circuit used to perform a specific electronic function, such as amplification; it is usually combined with other components to form a more complex system.

It is formed as a single unit by diffusing impurities into single-crystal silicon, which then serves as a semiconductor material, or by etching the silicon by means of electron beams. Several hundred identical integrated circuits (ICs) are made at a time on a thin wafer several centimeters wide, and the wafer is subsequently sliced into individual ICs called chips. In large-scale integration (LSI), as many as 5000 circuit elements, such as resistors and transistors, are combined in a square of silicon measuring about 1.3 cm (.5 in) on a side. Hundreds of these integrated circuits can be arrayed on a silicon wafer 8 to 15 cm (3 to 6 in) in diameter. Larger-scale integration can produce a silicon chip with millions of circuit elements. Individual circuit elements on a chip are interconnected by thin metal or semiconductor films, which are insulated from the rest of the circuit by thin dielectric layers. Chips are assembled into packages containing external electrical leads to facilitate insertion into printed circuit boards for interconnection with other circuits or components.

What can a IC do ?

In consumer electronics, ICs have made possible the development of many new products, including personal calculators and computers, digital watches, and video games. They have also been used to improve or lower the cost of many existing products, such as appliances, televisions, radios, and high-fidelity equipment.
Computer technology, in particular, has benefited greatly. The logic and arithmetic functions of a small computer can now be performed on a single VLSI chip called a microprocessor, and the complete logic, arithmetic, and memory functions of a small computer can be packaged on a single printed circuit board, or even on a single chip.

IC types

Integrated circuits are often classified by the number of transistors and other electronic components they contain:

• SSI (small-scale integration): Up to 100 electronic components per chip
• MSI (medium-scale integration): From 100 to 3,000 electronic components per chip
• LSI (large-scale integration): From 3,000 to 100,000 electronic components per chip
• VLSI (very large-scale integration): From 100,000 to 1,000,000 electronic components per chip
• ULSI (ultra large-scale integration): More than 1 million electronic components per chip

There are two major kinds of ICs:

• analog (or linear) which are used as amplifiers, timers and oscillators
• digital (or logic) which are used in microprocessors and memories

Some ICs are combinations of both analog and digital.

Description of a few types of chips

CMOS, in computer science, acronym for complementary metal-oxide semiconductor. A semiconductor device that consists of two metal-oxide semiconductor field effect transistors (MOSFETs), one N-type and one P-type, integrated on a single silicon chip. Generally used for RAM and switching applications, these devices have very high speed and extremely low power consumption. They are, however, easily damaged by static electricity.

Digital Signal Processor (DSP), an integrated circuit designed for high-speed data manipulations, used in audio, communications, image manipulation, and other data-acquisiton and data-control applications.

Dynamic RAM (DRAM) in computer science, a form of semiconductor random access memory (RAM). Dynamic RAMs store information in integrated circuits that contain capacitors. Because capacitors lose their charge over time, dynamic RAM boards must include logic to "refresh" (recharge) the RAM chips continuously. While a dynamic RAM is being refreshed, it cannot be read by the processor; if the processor must read the RAM while it is being refreshed, one or more wait states occur. Because their internal circuitry is simple, dynamic RAMs are more commonly used than static RAMs, even though they are slower. A dynamic RAM can hold approximately four times as much data as a static RAM chip of the same complexity.

EPROM, in computer science, acronym for erasable programmable read-only memory. Also called reprogrammable read-only memory (RPROM). EPROMs are nonvolatile memory chips that are programmed after they are manufactured. EPROMs are a good way for hardware vendors to put variable or constantly changing code into a prototype system when the cost of producing many PROM chips would be prohibitive. EPROMs differ from PROMs in that they can be erased, generally by removing a protective cover from the top of the chip package and exposing the semiconductor material to ultraviolet light, and can be reprogrammed after having been erased. Although EPROMs are more expensive than PROMs, they can be more cost-effective in the long run if many changes are needed.

PROM, acronym for programmable read-only memory. In computer science, a type of read-only memory (ROM) that allows data to be written into the device with hardware called a PROM programmer. After a PROM has been programmed, it is dedicated to that data, and it cannot be reprogrammed. Because ROMs are cost-effective only when produced in large volumes, PROMs are used during the prototyping stage of the design. New PROMs can be created and discarded as needed until the design is perfected.

Reduced Instruction Set Computer (RISC), a type of microprocessor that focuses on rapid and efficient processing of a relatively small set of instructions. RISC design is based on the premise that most of the instructions a computer decodes and executes are simple. As a result, RISC architecture limits the number of instructions that are built into the microprocessor but optimizes each so it can be carried out very rapidly-usually within a single clock cycle. RISC chips thus execute simple instructions faster than microprocessors designed to handle a much wider array of instructions.

ROM, acronym for read-only memory. In computer science, semiconductor-based memory that contains instructions or data that can be read but not modified. To create a ROM chip, the designer supplies a semiconductor manufacturer with the instructions or data to be stored; the manufacturer then produces one or more chips containing those instructions or data. Because creating ROM chips involves a manufacturing process, it is economically viable only if the ROM chips are produced in large quantities; experimental designs or small volumes are best handled using PROM or EPROM. In general usage, the term ROM often means any read-only device, including PROM and EPROM.
Static RAM (SRAM), in computer science, a form of semiconductormemory (RAM). Static RAM storage is based on the logic circuit known as a flip-flop, which retains the information stored in it as long as there is enough power to run the device. A static RAM chip can store only about one-fourth as much data as a dynamic RAM chip of the same complexity, but static RAM does not require refreshing and is usually much faster than dynamic RAM. It is also more expensive. Static RAMs are usually reserved for use in caches.

Useful Links:

Semiconductors | Transistor | Hardware inside your computer | VLSI Chips (Microprocessor)