1、Integrated circuit (IC) IntroducionIntegrated circuit also called microelectronic circuit or chip an assembly of electronic components, fabricated as a single unit, in which miniaturized active devices (e.g., transistors and diodes) and passive devices (e.g., capacitors and resistors) and their inte
2、rconnections are built up on a thin substrate of semiconductor material (typically silicon). The resulting circuit is thus a small monolithic “chip,” which may be as small as a few square centimetres or only a few square millimetres. The individual circuit components are generally microscopic in siz
3、e.Integrated circuits have their origin in the invention of the transistor in 1947 by William B. Shockley and his team at the American Telephone and Telegraph Companys Bell Laboratories. Shockleys team (including John Bardeen and Walter H. Brattain) found that, under the right circumstances, electro
4、ns would form a barrier at the surface of certain crystals, and they learned to control the flow of electricity through the crystal by manipulating this barrier. Controlling electron flow through a crystal allowed the team to create a device that could perform certain electrical operations, such as
5、signal amplification, that were previously done by vacuum tubes. They named this device a transistor, from a combination of the words transfer and resistor (see photograph). The study of methods of creating electronic devices using solid materials became known as solid-state electronics. Solid-state
6、 devices proved to be much sturdier, easier to work with, more reliable, much smaller, and less expensive than vacuum tubes. Using the same principles and materials, engineers soon learned to create other electrical components, such as resistors and capacitors. Now that electrical devices could be m
7、ade so small, the largest part of a circuit was the awkward wiring between the devices. In 1958 Jack Kilby of Texas Instruments, Inc., and Robert Noyce of Fairchild Semiconductor Corporation independently thought of a way to reduce circuit size further. They laid very thin paths of metal (usually al
8、uminum or copper) directly on the same piece of material as their devices. These small paths acted as wires. With this technique an entire circuit could be “integrated” on a single piece of solid material and an integrated circuit (IC) thus created. ICs can contain hundreds of thousands of individua
9、l transistors on a single piece of material the size of a pea. Working with that many vacuum tubes would have been unrealistically awkward and expensive. The invention of the integrated circuit made technologies of the Information Age feasible. ICs are now used extensively in all walks of life, from
10、 cars to toasters to amusement park rides.Basic IC types Analog versus digital circuitsAnalog, or linear, circuits typically use only a few components and are thus some of the simplest types of ICs. Generally, analog circuits are connected to devices that collect signals from the environment or send
11、 signals back to the environment. For example, a microphone converts fluctuating vocal sounds into an electrical signal of varying voltage. An analog circuit then modifies the signal in some useful waysuch as amplifying it or filtering it of undesirable noise. Such a signal might then be fed back to
12、 a loudspeaker, which would reproduce the tones originally picked up by the microphone. Another typical use for an analog circuit is to control some device in response to continual changes in the environment. For example, a temperature sensor sends a varying signal to a thermostat, which can be prog
13、rammed to turn an air conditioner, heater, or oven on and off once the signal has reached a certain value.A digital circuit, on the other hand, is designed to accept only voltages of specific given values. A circuit that uses only two states is known as a binary circuit. Circuit design with binary q
14、uantities, “on” and “off” representing 1 and 0 (i.e., true and false), uses the logic of Boolean algebra. The three basic logic functionsNOT, AND, and ORtogether with their truth tables are given in the figure. (Arithmetic is also performed in the binary number system employing Boolean algebra.) The
15、se basic elements are combined in the design of ICs for digital computers and associated devices to perform the desired functions.Microprocessor circuitsMicroprocessors are the most complicated ICs. They are composed of millions of transistors that have been configured as thousands of individual dig
16、ital circuits, each of which performs some specific logic function. A microprocessor is built entirely of these logic circuits synchronized to each other. Just like a marching band, the circuits perform their logic function only on direction by the bandmaster. The bandmaster in a microprocessor, so
17、to speak, is called the clock. The clock is a signal that quickly alternates between two logic states. Every time the clock changes state, every logic circuit in the microprocessor does something. Calculations can be made very quickly, depending on the speed (“clock frequency”) of the microprocessor
18、. Microprocessors contain some circuits, known as registers, that store information. Registers are predetermined memory locations. Each processor has many different types of registers. Permanent registers are used to store the preprogrammed instructions required for various operations (such as addit
19、ion and multiplication). Temporary registers store numbers that are to be operated on and also the result. Other examples of registers include the “program counter,” the “stack pointer,” and the “address” register. Microprocessors can perform millions of operations per second on data. In addition to
20、 computers, microprocessors are common in video game systems, televisions, cameras, and automobiles.Memory circuits Microprocessors typically have to store more data than can be held in a few registers. This additional information is relocated to special memory circuits. Memory is composed of dense
21、arrays of parallel circuits that use their voltage states to store information. Memory also stores the temporary sequence of instructions, or program, for the microprocessor. Manufacturers continually strive to reduce the size of memory circuitsto increase capability without increasing space. In add
22、ition, smaller components typically use less power, operate more efficiently, and cost less to manufacture.Digital signal processors A signal is an analog waveformanything in the environment that can be captured electronically. A digital signal is an analog waveform that has been converted into a se
23、ries of binary numbers for quick manipulation. As the name implies, a digital signal processor (DSP) processes signals digitally, as patterns of 1s and 0s. For instance, using an analog-to-digital converter, commonly called an A-to-D or A/D converter, a recording of someones voice can be converted i
24、nto digital 1s and 0s. The digital representation of the voice can then be modified by a DSP using complex mathematical formulas. For example, the DSP algorithm in the circuit may be configured to recognize gaps between spoken words as background noise and digitally remove ambient noise from the wav
25、eform. Finally, the processed signal can be converted back (by a D/A converter) into an analog signal for listening. Digital processing can filter out background noise so fast that there is no discernible delay and the signal appears to be heard in “real time.” For instance, such processing enables
26、“live” television broadcasts to focus on a quarterbacks signals in an American gridiron football game. DSPs are also used to produce digital effects on live television. For example, the yellow marker lines displayed during the football game are not really on the field; a DSP adds the lines after the
27、 cameras shoot the picture but before it is broadcast. Similarly, some of the advertisements seen on stadium fences and billboards during televised sporting events are not really there.Application-specific ICsAn application-specific IC (ASIC) can be either a digital or an analog circuit. As their na
28、me implies, ASICs are not reconfigurable; they perform only one specific function. For example, a speed controller IC for a remote control car is hard-wired to do one job and could never become a microprocessor. An ASIC does not contain any ability to follow alternate instructions.Radio-frequency IC
29、s Radio-frequency ICs (RFICs) are rapidly gaining importance in cellular telephones and pagers. RFICs are analog circuits that usually run in the frequency range of 900 MHz to 2.4 GHz (900 million hertz to 2.4 billion hertz). They are usually thought of as ASICs even though some may be configurable
30、for several similar applications. Most semiconductor circuits that operate above 500 MHz cause the electronic components and their connecting paths to interfere with each other in unusual ways. Engineers must use special design techniques to deal with the physics of high-frequency microelectronic in
31、teractions.Microwave monolithic ICs A special type of RFIC is known as a microwave monolithic IC (MMIC). These circuits run in the 2.4- to 20-GHz range, or microwave frequencies, and are used in radar systems, in satellite communications, and as power amplifiers for cellular telephones. Just as soun
32、d travels faster through water than through air, electron velocity is different through each type of semiconductor material. Silicon offers too much resistance for microwave-frequency circuits, and so the compound gallium arsenide (GaAs) is often used for MMICs. Unfortunately, GaAs is mechanically m
33、uch less sound than silicon. It breaks easily, so GaAs wafers are usually much more expensive to build than silicon wafers.Basic semiconductor design Any material can be classified as one of three types: conductor, insulator, or semiconductor. A conductor (such as copper or salt water) can easily co
34、nduct electricity because it has an abundance of free electrons. An insulator (such as ceramic or dry air) conducts electricity very poorly because it has few or no free electrons. A semiconductor (such as silicon or gallium arsenide) is somewhere between a conductor and an insulator. It is capable
35、of conducting some electricity, but not much.Basic semiconductor designDoping siliconMost ICs are made of silicon, which is abundant in ordinary beach sand. Pure crystalline silicon, as with other semiconducting materials, has a very high resistance to electrical current at normal room temperature.
36、However, with the addition of certain impurities, known as dopants, the silicon can be made to conduct usable currents. In particular, the doped silicon can be used as a switch, turning current off and on as desired.The process of introducing impurities is known as doping or implantation. Depending
37、on a dopants atomic structure, the result of implantation will be either an n-type (negative) or a p-type (positive) semiconductor. An n-type semiconductor results from implanting dopant atoms that have more electrons in their outer (bonding) shell than silicon, as shown in the figure. The resulting
38、 semiconductor crystal contains excess, or free, electrons that are available for conducting current. A p-type semiconductor results from implanting dopant atoms that have fewer electrons in their outer shell than silicon. The resulting crystal contains “holes” in its bonding structure where electro
39、ns would normally be located. In essence, such holes can move through the crystal conducting positive charges.Basic semiconductor design The p-n junction A p-type or an n-type semiconductor is not very useful on its own. However, joining these opposite materials creates what is called a p-n junction
40、. A p-n junction forms a barrier to conduction between the materials. Although the electrons in the n-type material are attracted to the holes in the p-type material, the electrons are not normally energetic enough to overcome the intervening barrier. However, if additional energy is provided to the
41、 electrons in the n-type material, they will be capable of crossing the barrier into the p-type materialand current will flow. This additional energy can be supplied by applying a positive voltage to the p-type material,as shown in the figure. The negatively charged electrons will then be highly att
42、racted to the positive voltage across the junction. A p-n junction that conducts electricity when energy is added to the n material is called forward-biased because the electrons move forward into the holes. If voltage is applied in the opposite directiona positive voltage connected to the n side of
43、 the junctionno current will flow. The electrons in the n material will still be attracted to the positive voltage, but the voltage will now be on the same side of the barrier as the electrons. In this state a junction is said to be reverse-biased. Since p-n junctions conduct electricity in only one
44、 direction, they are a type of diode. Diodes are essential building blocks of semiconductor switches.Basic semiconductor design Field-effect transistors Bringing a negative voltage close to the centre of a long strip of n-type material will repel nearby electrons in the material and thus form holest
45、hat is, transform some of the strip in the middle to p-type material. This change in polarity utilizing an electric field gives the field-effect transistor its name. (See animation.) While the voltage is being applied, there will exist two p-n junctions along the strip, from n to p and then from p b
46、ack to n. One of the two junctions will always be reverse-biased. Since reverse-biased junctions cannot conduct, current cannot flow through the strip. The field effect can be used to create a switch (transistor) to turn current off and on, simply by applying and removing a small voltage nearby in o
47、rder to create or destroy reverse-biased diodes in the material. A transistor created by using the field effect is called a field-effect transistor (FET). The location where the voltage is applied is known as a gate. The gate is separated from the transistor strip by a thin layer of insulation to pr
48、event it from short-circuiting the flow of electrons through the semiconductor from an input (source) electrode to an output (drain) electrode. Similarly, a switch can be made by placing a positive gate voltage near a strip of p-type material. A positive voltage attracts electrons and thus forms a r
49、egion of n within a strip of p. This again creates two p-n junctions, or diodes. As before, one of the diodes will always be reverse-biased and will stop current from flowing. FETs are good for building logic circuits because they require only a small current during switching. No current is required for holding the transistor in an on or off state; a voltage will maintain the state. This type of switching helps preserve battery life. A field-effec
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