Classification of integrated circuits. Large integrated circuits

In early electrical computers, the circuit components that performed the operations were vacuum tubes. These tubes, which resembled light bulbs, consumed a lot of electricity and generated a lot of heat. Everything changed in 1947 with the invention of the transistor. This small device used a semiconductor material, named for its ability to both conduct and trap electrical current, depending on whether there was electrical current in the semiconductor itself. This new technology made it possible to build all kinds of electrical switches on silicon chips. Transistor circuits took up less space and consumed less power. For more powerful computers, integrated circuits, or ICs, were created.

Nowadays, transistors have become microscopically small, and the entire IC circuit fits on a 1-inch square piece of semiconductor. Small blocks mounted in rows on a computer circuit board are integrated circuits enclosed in plastic cases. Each microcircuit contains a set of simple circuit elements, or devices. Most of them are occupied by transistors. An IC may also include diodes, which allow electrical current to flow in only one direction, and resistors, which block the current.
Fixed parts. In the interior of a computer, rows of integrated circuits in protective housings, as shown below, are mounted on the computer's circuit board (green). Each pale green line represents a path along which electric current flows; together they form “highways” through which electric current is carried from circuit to circuit.

Tiny messengers. Along the edge of the chip, highly magnetized wires, reminiscent of human hairs, send electrical signals from the electrical circuit (named above). These gold or aluminum wires are virtually resistant to corrosion and are good conductors of electricity.

Anatomy of a transistor
Transistors, the basic microscopic elements of an electronic circuit, are switches that turn electrical current on and off. Small metal tracks (gray) conduct current (red and green) from these devices. Organized into a combination called logic gates, transistors respond to electrical impulses in a variety of preset ways, allowing the computer to perform a wide range of tasks.

Logic diagram. If the incoming electrical current (red arrows) activates the base of each transistor, the supply current (green arrows) will rush to the output wiring.

Large integrated circuit

Modern integrated circuits designed for surface mounting.

Soviet and foreign digital microcircuits.

Integral(engl. Integrated circuit, IC, microcircuit, microchip, silicon chip, or chip), ( micro)scheme (IS, IMS, m/skh), chip, microchip(English) chip- sliver, chip, chip) - microelectronic device - an electronic circuit of arbitrary complexity, made on a semiconductor crystal (or film) and placed in a non-separable case. Often under integrated circuit(IC) refers to the actual crystal or film with an electronic circuit, and by microcircuit(MS) - IC enclosed in a housing. At the same time, the expression "chip components" means "surface mount components" as opposed to traditional through-hole soldered components. Therefore, it is more correct to say “chip microcircuit”, meaning a surface-mount microcircuit. Currently (year) most microcircuits are manufactured in surface-mount packages.

Story

The invention of microcircuits began with the study of the properties of thin oxide films, which manifest themselves in the effect of poor electrical conductivity at low electrical voltages. The problem was that where the two metals touched, there was no electrical contact or it was polar. Deep studies of this phenomenon led to the discovery of diodes and later transistors and integrated circuits.

Design Levels

• Physical - methods of implementing one transistor (or a small group) in the form of doped zones on a crystal.
• Electrical - circuit diagram (transistors, capacitors, resistors, etc.).
• Logical - logical circuit (logical inverters, OR-NOT, AND-NOT elements, etc.).
• Circuit and system level - circuit and system design (flip-flops, comparators, encoders, decoders, ALUs, etc.).
• Topological - topological photomasks for production.
• Program level (for microcontrollers and microprocessors) - assembler instructions for the programmer.

Currently, most integrated circuits are developed using CAD, which allows you to automate and significantly speed up the process of obtaining topological photomasks.

Classification

Degree of integration

Purpose

An integrated circuit can have complete, no matter how complex, functionality - up to an entire microcomputer (single-chip microcomputer).

Analog circuits

• Signal generators
• Analog multipliers
• Analog attenuators and variable amplifiers
• Power supply stabilizers
• Switching power supply control chips
• Signal converters
• Timing circuits
• Various sensors (temperature, etc.)

Digital circuits

• Logic elements
• Buffer converters
• Memory modules
• (Micro)processors (including the CPU in a computer)
• Single-chip microcomputers
• FPGA - programmable logic integrated circuits

Digital integrated circuits have a number of advantages over analog ones:

• Reduced power consumption associated with the use of pulsed electrical signals in digital electronics. When receiving and converting such signals, the active elements of electronic devices (transistors) operate in the “key” mode, that is, the transistor is either “open” - which corresponds to a high-level signal (1), or “closed” - (0), in the first case at There is no voltage drop in the transistor; in the second, no current flows through it. In both cases, power consumption is close to 0, in contrast to analog devices, in which most of the time the transistors are in an intermediate (resistive) state.
• High noise immunity digital devices is associated with a large difference between high (for example 2.5 - 5 V) and low (0 - 0.5 V) level signals. An error is possible with such interference when a high level is perceived as low and vice versa, which is unlikely. In addition, in digital devices it is possible to use special codes to correct errors.
• The large difference between high and low level signals and a fairly wide range of their permissible changes makes digital technology insensitive to the inevitable dispersion of element parameters in integrated technology, eliminating the need to select and configure digital devices.

Just twenty-five years ago, radio amateurs and older generation specialists had to study new devices at that time - transistors. It was not easy to give up the vacuum tubes that we were so accustomed to and switch to the crowding and ever-expanding “family” of semiconductor devices.

And now this “family” has increasingly begun to give way in radio engineering and electronics to the latest generation of semiconductor devices - integrated circuits, often called ICs for short.

What is an integrated circuit

Integrated circuit is a miniature electronic unit containing in a common housing transistors, diodes, resistors and other active and passive elements, the number of which can reach several tens of thousands.

One microcircuit can replace an entire unit of a radio receiver, an electronic computer (computer) and an electronic machine. The “mechanism” of a digital wristwatch, for example, is just one larger chip.

According to their functional purpose, integrated circuits are divided into two main groups: analog, or linear-pulse, and logical, or digital, microcircuits.

Analog microcircuits are intended for amplification, generation and conversion of electrical oscillations of different frequencies, for example, for receivers, amplifiers, and logical ones - for use in automation devices, in devices with digital timekeeping, in computers.

This workshop is devoted to familiarization with the device, operating principle and possible application of the simplest analog and logical integrated circuits.

On an analog chip

Of the huge “family” of analogue ones, the simplest are the twin microcircuits K118UN1A (K1US181A) and K118UN1B (K1US181B), which are part of the K118 series.

Each of them is an amplifier containing... However, it’s better to talk about the electronic “stuffing” instead. For now, we will consider them “black boxes” with pins for connecting power supplies, additional parts, input and output circuits to them.

The difference between them lies only in their amplification factors for low-frequency oscillations: the gain factor of the K118UN1A microcircuit at a frequency of 12 kHz is 250, and the K118UN1B microcircuit is 400.

At high frequencies, the gain of these microcircuits is the same - approximately 50. So, any of them can be used to amplify oscillations of both low and high frequencies, and therefore for our experiments. The appearance and symbols of these amplifier microcircuits on the circuit diagrams of the devices are shown in Fig. 88.

They have a rectangular plastic body. On the top of the case there is a mark that serves as a reference point for the pin numbers. The microcircuits are designed for power supply from a DC source with a voltage of 6.3 V, which is supplied through pins 7 (+Upit) and 14 (— U Pete).

The power source can be an AC power supply with adjustable output voltage or a battery made up of four cells 334 and 343.

The first experiment with the K118UN1A (or K118UN1B) microcircuit was carried out according to the diagram shown in Fig. 89. As a mounting board, use a cardboard plate measuring approximately 50X40 mm.

Microcircuit pins 1, 7, 8 And 14 solder to wire staples passed through holes in the cardboard. All of them will act as stands holding the microcircuit on the board, and the pin brackets 7. and 14, in addition, connecting contacts with the battery G.B.1 (or mains power supply).

Between them, on both sides of the microcircuit, strengthen two or three more contacts, which will be intermediate for additional parts. Mount capacitors on the board C1(type K50-6 or K50-3) and C2(KYAS, BM, MBM), connect headphones to the output of the microcircuit AT 2.

Connect to the input of the microcircuit (through a capacitor C1) electrodynamic microphone IN 1 any type or DEM-4m telephone capsule, turn on the power and, pressing the phones more tightly to your ears, tap lightly on the microphone with a pencil. If there are no errors in the installation, sounds resembling clicks on a drum should be heard in the phones.

Ask a friend to say something in front of the microphone - you will hear his voice on the phones. Instead of a microphone, you can connect a radio broadcast (subscriber) loudspeaker with its matching transformer to the input of the microcircuit. The effect will be about the same.

Continuing the experiment with a single-acting telephone device, connect between the common (negative) conductor of the power circuit and the output 12 microcircuit electrolytic capacitor NW, indicated on the diagram by dashed lines. At the same time, the sound volume on phones should increase.

Telephones will sound even louder if the same capacitor is connected to the output circuit 5 (in Fig. 89 - capacitor C4). But if the amplifier is excited, then between the common wire and pin 11 you will have to connect an electrolytic capacitor with a capacity of 5 - 10 uF. nominal voltage 10 V.

Another experiment: turn it on between the pins 10 And 3 microcircuits ceramic or paper capacitor with a capacity of 5 - 10 thousand picofarads. What happened? An incessant medium-pitched sound appeared on phones. As the capacitance of this capacitor increases, the sound tone in telephones should decrease, and with decrease, it should increase. Check this.

Now let’s open this “black box” and look at its “filling” (Fig. 90). Yes, this is a two-stage amplifier with direct coupling between its transistors. Silicon transistors, structures n -R-n. The low-frequency signal generated by the microphone is supplied (via capacitor C1) to the input of the microcircuit (pin 3).

Voltage drop created across the resistor R6 in the emitter circuit of the transistor V2, through resistors R4 And R5 supplied to the base of the transistor VI and opens it. Resistor R1 — load of this transistor. The amplified signal taken from it goes to the base of the transistor V2 for additional gain.

In an experimental amplifier with a transistor load V2 there were headphones included in its collector circuit, which converted the low-frequency signal into sound.

But its load could be a resistor R5 microcircuits, if you connect the leads together 10 And 9. In this case, the telephones must be connected between the common wire and the connection point of these terminals through an electrolytic capacitor with a capacity of several microfarads (the positive plate to the microcircuit).

When connecting a capacitor between the common wire and the terminal 12 microcircuit, the sound volume has increased, Why? Because he is shunting the resistor R6 microcircuit, weakened the negative feedback on alternating current operating in it.

The negative feedback became even weaker when you included a second capacitor in the base circuit of the transistor V1. And the third capacitor connected between the common wire and the output 11, formed with a resistor R7 microcircuit decoupling filter that prevents excitation of the amplifier.

What happened when you connected a capacitor between the terminals 10 and 5? He created a positive feedback between the output and input of the amplifier, which turned it into an audio frequency oscillator.

So, as you can see, the K118UN1B (or K118UN1A) microcircuit is an amplifier that can be low-frequency or high-frequency, for example, in a receiver. But it can also become a generator of electrical oscillations of both low and high frequencies.

Microcircuit in a radio receiver

We propose to test this microcircuit in the high-frequency path of a receiver assembled, for example, according to the circuit shown in Fig. 91. The input circuit of the magnetic antenna of such a receiver is formed by a coil L1 and a variable capacitor C1. High-frequency signal from the radio station to which the circuit is tuned, through a communication coil L2 and coupling capacitor C2 arrives at the input (output 3) microcircuits L1.

From the output of the microcircuit (output 10, connected to output 9) the amplified signal is fed through a capacitor C4 for detector, diodes VI And V2 which are switched on according to the voltage multiplication circuit, and the low-frequency signal allocated to it is telephone IN 1 converted to sound. The receiver is battery powered G.B.1, composed of four elements 332, 316 or five D-01 batteries.

In many transistor receivers, the high-frequency amplifier is formed by transistors, but in this one it is a microcircuit. This is the only difference between them. Having the experience of previous workshops, I hope you will be able to independently mount and G set up such a receiver and even, if you wish, supplement it with a low-frequency amplifier for loud-speaking radio reception.

On a logic chip

An integral part of many digital integrated circuits is the AND-NOT logical element, the symbol of which you see in Fig. 92, A. Its symbol is the "&" sign placed inside a rectangle, usually in the upper left corner, replacing the conjunction "AND" in English. There are two or more inputs on the left, one output on the right.

The small circle that begins the communication line of the output signal symbolizes the logical Negation “NOT” at the output of the microcircuit. In the language of digital technology, “NOT” means that the NAND element is an inverter, that is, a device whose output parameters are opposite to the input ones.

The electrical state and operation of a logic element are characterized by the signal levels at its inputs and output. A small (or zero) voltage signal, the level of which does not exceed 0.3 - 0.4 V, is usually called (in accordance with the binary number system) logical zero (0), and a higher voltage signal (compared to logical 0), the level of which can be 2.5 - 3.5 V, - logical unit (1).

For example, they say: “the output of the element is logical 1.” This means that at the moment a signal has appeared at the output of the element, the voltage of which corresponds to the logical level 1.

In order not to delve into the technology and structure of the NAND element, we will consider it as a “black box”, which has two inputs and one output for an electrical signal.

The logic of the element is that when logical O is applied to one of its inputs, and logical 1 is applied to the second input, a logical 1 signal appears at the output, which disappears when signals corresponding to logical 1 are applied to both inputs.

For experiments that memorize this property of the element, you will need the most common K155LAZ microcircuit, a DC voltmeter, a fresh 3336L battery and two resistors with a resistance of 1...1.2 kOhm.

The K155LAZ microcircuit consists of four 2I-NOT elements (Fig. 92, b), powered by one common 5 V DC source, but each of them operates as an independent logic device. The number 2 in the name of the microcircuit indicates that its elements have two inputs.

In appearance and design, it, like all microcircuits of the K155 series, does not differ from the already familiar analog microcircuit K118UN1, only the polarity of connecting the power source is different. Therefore, the cardboard board you made earlier is suitable for experiments with this microcircuit. The power source is connected: +5 V - to pin 7" — 5 B - to conclusion 14.

But these conclusions are not usually indicated on a schematic diagram of the microcircuit. This is explained by the fact that on circuit diagrams the elements that make up the microcircuit are depicted separately, for example, as in Fig. 92, v. For experiments, you can use any of its four elements.

Microcircuit pins 1, 7, 8 And 14 solder to the wire posts on the cardboard board (as in Fig. 89). One of the input pins of any of its elements, for example, an element with pins 1 — 3, connect through a resistor with a resistance of 1...1.2 kOhm to the output 14, the output of the second input is directly with the common (“grounded”) conductor of the power circuit, and connect a DC voltmeter to the output of the element (Fig. 93, A).

Turn on the power. What does the voltmeter show? A voltage of approximately 3 V. This voltage corresponds to a logic 1 signal at the output of the element. Using the same voltmeter, measure the voltage at the output of the first input. And here, as you can see, it is also logical 1. Therefore, when one of the inputs of the element is logical 1, and the second is logical 0, the output will be logical 1.

Now connect the output of the second input through a resistor with a resistance of 1...1.2 kOhm to the output 14 and at the same time a wire jumper - with a common conductor, as shown in Fig. 93, b.

In this case, the output, as in the first experiment, will be logical 1. Next, watching the voltmeter needle, remove the jumper wire so that a signal corresponding to logical 1 is sent to the second input.

What does a voltmeter record? The signal at the output of the element is converted to logical 0. This is how it should be! And if any of the inputs are periodically shorted to a common wire and thereby simulate the supply of a logical 0 to it, then current pulses will appear at the output of the element with the same frequency, as evidenced by fluctuations in the voltmeter needle. Check this out experimentally.

The property of the NAND element to change its state under the influence of input control signals is widely used in various digital computing devices. Radio amateurs, especially beginners, very often use a logic element as an inverter - a device whose output signal is opposite to the input signal.

The following experiment can confirm this property of the element. Connect the terminals of both inputs of the element together and, through a resistor with a resistance of 1...1.2 kOhm, connect them to the output 14 (Fig. 93, V).

This way you will apply a signal corresponding to logical 1 to the common input of the element, the voltage of which can be measured with a voltmeter. What is the output?

The voltmeter needle connected to it slightly deviated from the zero scale mark. Here, therefore, as expected, the signal corresponds to logical 0.

Then, without disconnecting the resistor from the output 14 microcircuits, connect the element input to the common conductor several times in a row with a wire jumper (in Fig. 93, V shown by a dashed line with arrows) and at the same time follow the voltmeter needle. So you will be convinced that when the inverter input is logical 0, the output is logical 1 and, conversely, when the input is logical 1, the output is logical 0.

This is how an inverter works, especially often used by radio amateurs in the pulse devices they construct.

An example of such a device is a pulse generator assembled according to the circuit shown in Fig. 94. You can verify its functionality right away, spending just a few minutes on it.

The output of element D1.1 is connected to the inputs of the element D1.2 the same microcircuit, its output is with the inputs of the element DJ.3, and the output of this element (output 8) - with element input D1.1 through variable resistor R1 . To element output D1.3 (between output 8 and a common conductor) connect the headphones B1, a parallel to elements D1.1 and D1.2 electrolytic capacitor C1.

Set the variable resistor motor to the right (according to the diagram) position and turn on the power - you will hear a sound in the phones, the tone of which can be changed with a variable resistor.

In this experiment the elements D1.1, D1.2 andD1.3, connected to each other in series, like the transistors of a three-stage amplifier, they formed a multivibrator - a generator of rectangular electrical pulses.

The microcircuit became a generator thanks to a capacitor and resistor, which created frequency-dependent feedback circuits between the output and input of the elements. Using a variable resistor, the frequency of the pulses generated by the multivibrator can be smoothly varied from approximately 300 Hz to 10 kHz.

What practical application can such a pulse device find? It can become, for example, an apartment bell, a probe for checking the performance of the receiver and low-frequency amplifier cascades, a generator for training in listening to the telegraph alphabet.

Homemade slot machine on a chip

Such a device can be turned into a slot machine “Red or Green?” The diagram of such an impulse device is shown in Fig. 95. Here are the elements D1.1, D1.2, D1.3 the same (or the same) K155LAZ microcircuit and capacitor C1 form a similar multivibrator, the pulses of which control transistors VI And V2, connected according to a common emitter circuit.

Element D1.4 works like an inverter. Thanks to it, the multivibrator pulses arrive at the bases of the transistors in antiphase and open them alternately. So, for example, when the logical level is 1 at the input of the inverter, and the logical level is 0 at the output, then at these moments, the transistor IN 1 open and light bulb HI in its collector circuit is lit, and the transistor V2 closed and its light bulb H2 does not burn.

With the next pulse, the inverter will change its state to the opposite. Now the transistor will open V2 and the light comes on H2, and the transistor VI the light bulb will close H1 will go out.

But the frequency of the pulses generated by the multivibrator is relatively high (at least 15 kHz) and light bulbs, naturally, cannot respond to every pulse.

That's why they glow dimly. But it’s worth pressing the S1 button to short-circuit the capacitor with its contacts C1 and thereby disrupt the generation of the multivibrator, when the light bulb of the transistor on the basis of which at that moment there will be a voltage corresponding to logical 1 immediately lights up brightly, and the other light bulb goes out completely.

It is impossible to say in advance which of the bulbs will continue to light after pressing the button - one can only guess. This is the point of the game.

The slot machine along with the battery (3336L or three 343 elements connected in series) can be placed in a small box, for example, in the case of a “pocket” receiver.

Incandescent light bulbs HI And H2(MH2.5-0.068 or MH2.5-0.15) place under the holes in the front wall of the case and cover them with caps or organic glass plates of red and green colors. Here also strengthen the power switch (toggle switch TV-1) and the push-button switch §1(type P2K or KM-N) stopping the multivibrator.

Setting up a slot machine involves carefully selecting a resistor R1. Its resistance should be such that when you stop the multivibrator with the button S1 at least 80 - 100 times the number of lights on each of the bulbs was approximately the same.

First check if the multivibrator is working. To do this, parallel to the capacitor C1, e, the capacitance of which can be 0.1...0.5 µF, connect an electrolytic capacitor with a capacity of 20...30 µF, and headphones to the output of the multivibrator - a low-pitched sound should appear in the phones.

This sound is a sign of the multivibrator working. Then remove the electrolytic capacitor, resistor R1 replace with a tuning resistor with a resistance of 1.2...1.3 kOhm, and between the terminals 8 and 11 elements D.I..3 And D1.4 turn on the DC voltmeter. By changing the resistance of the trimming resistor, achieve a position such that the voltmeter shows zero voltage between the outputs of these elements of the microcircuit.

There can be any number of players. Each person takes turns pressing the multivibrator stop button. The winner is the one who, with an equal number of moves, for example, twenty presses of a button, guesses the colors of the light bulbs that light up more times after the multivibrator stops.

Unfortunately, the frequency of the multivibrator of the simplest slot machine described here changes somewhat due to battery discharge, which, of course, affects the equal probability of lighting different light bulbs, so it is better to power it from a stabilized voltage source of 5 V.

Literature: Borisov V.G. Workshop for a beginner radio amateur. 2nd ed., revised. and additional - M.: DOSAAF, 1984. 144 p., ill. 55k.

INTEGRATED CIRCUIT
(IC), a microelectronic circuit formed on a tiny wafer (crystal or "chip") of semiconductor material, usually silicon, that is used to control and amplify electrical current. A typical IC consists of many interconnected microelectronic components, such as transistors, resistors, capacitors and diodes, fabricated at the surface layer of the chip. The sizes of silicon crystals range from about 1.3-1.3 mm to 13-13 mm. Advances in integrated circuits have led to the development of large-scale and very large-scale integrated circuits (LSI and VLSI) technologies. These technologies make it possible to obtain ICs, each of which contains many thousands of circuits: a single chip can contain more than 1 million components.
see also SEMICONDUCTOR ELECTRONIC DEVICES. Integrated circuits have a number of advantages over their predecessors - circuits that were assembled from individual components mounted on a chassis. ICs are smaller, faster and more reliable; They are also cheaper and less susceptible to failures caused by vibration, moisture and aging. The miniaturization of electronic circuits was made possible due to the special properties of semiconductors. A semiconductor is a material that has much greater electrical conductivity (conductivity) than a dielectric such as glass, but significantly less than conductors such as copper. The crystal lattice of a semiconductor material such as silicon has too few free electrons at room temperature to provide significant conductivity. Therefore, pure semiconductors have low conductivity. However, introducing an appropriate impurity into silicon increases its electrical conductivity.
see also TRANSISTOR. Dopants are introduced into silicon using two methods. For heavy doping or in cases where precise control of the amount of introduced impurity is not necessary, the diffusion method is usually used. Diffusion of phosphorus or boron is usually carried out in an atmosphere of a dopant at temperatures between 1000 and 1150 ° C for from half an hour to several hours. In ion implantation, silicon is bombarded with high-velocity dopant ions. The amount of implanted impurity can be adjusted with an accuracy of several percent; accuracy is important in some cases, since the gain of the transistor depends on the number of impurity atoms implanted per 1 cm2 of base (see below).

Production. Manufacturing an integrated circuit can take up to two months because certain areas of the semiconductor must be precisely doped. In a process called crystal growing, or crystal pulling, a cylindrical slab of high-purity silicon is first produced. From this cylinder, plates with a thickness of, for example, 0.5 mm are cut. The wafer is eventually cut into hundreds of small pieces called chips, each of which is transformed into an integrated circuit through the process described below. The chip processing process begins with the production of masks for each layer of the IC. A large-scale stencil is made, shaped like a square with an area of ​​approx. 0.1 m2. A set of such masks contains all the components of the IC: diffusion levels, interconnect levels, etc. The entire resulting structure is photographically reduced to the size of a crystal and reproduced layer by layer on a glass plate. A thin layer of silicon dioxide is grown on the surface of the silicon wafer. Each plate is coated with a light-sensitive material (photoresist) and exposed to light transmitted through masks. Unexposed areas of the photosensitive coating are removed with a solvent, and with the help of another chemical reagent that dissolves silicon dioxide, the latter is etched from those areas where it is no longer protected by the photosensitive coating. Variations of this basic process technology are used in the fabrication of two main types of transistor structures: bipolar and field-effect (MOS).
Bipolar transistor. Such a transistor has an n-p-n type structure or, much less commonly, a p-n-p type. Typically the process starts with a wafer (substrate) of heavily doped p-type material. A thin layer of lightly doped n-type silicon is epitaxially grown on the surface of this wafer; thus, the grown layer has the same crystalline structure as the substrate. This layer must contain the active part of the transistor - individual collectors will be formed in it. The plate is first placed in a boron vapor furnace. Boron diffusion into the silicon wafer occurs only where its surface has been etched. As a result, regions and windows of n-type material are formed. A second high-temperature process, which uses phosphorus vapor and another mask, serves to form contact with the collector layer. By carrying out successive diffusions of boron and phosphorus, the base and emitter are formed, respectively. The thickness of the base is usually several microns. These tiny islands of n- and p-type conductivity are connected into a common circuit through interconnects made of aluminum vapor deposited or vacuum sputtered. Sometimes noble metals such as platinum and gold are used for these purposes. Transistors and other circuit elements, such as resistors, capacitors, and inductors, along with associated interconnects, can be formed in the wafer by diffusion techniques through a series of operations, ultimately creating a complete electronic circuit. See also TRANSISTOR.
MOSFET transistor. The most widely used is MOS (metal-oxide-semiconductor) - a structure consisting of two closely spaced regions of n-type silicon implemented on a p-type substrate. A layer of silicon dioxide is built up on the surface of the silicon, and on top of this layer (between the n-type regions and slightly capturing them) a localized layer of metal is formed, which acts as a gate. The two n-type regions mentioned above, called source and drain, serve as connecting elements for the input and output, respectively. Through windows provided in the silicon dioxide, metal connections are made to the source and drain. A narrow surface channel of n-type material connects the source and drain; in other cases, the channel may be induced - created by voltage applied to the gate. When a positive voltage is applied to the gate of an induced channel transistor, the p-type layer underneath the gate is converted to an n-type layer, and a current controlled and modulated by the signal entering the gate flows from source to drain. The MOSFET consumes very little power; It has high input impedance, low drain current and very low noise. Because the gate, oxide, and silicon form a capacitor, such a device is widely used in computer memory systems (see below). In complementary, or CMOS, circuits, the MOS structures are used as loads and do not consume power when the main MOS transistor is in the inactive state.

After processing is completed, the plates are cut into pieces. The cutting operation is performed with a circular saw with diamond edges. Each crystal (chip, or IC) is then enclosed in one of several types of housing. 25 micron gold wire is used to connect the IC components to the package lead frame. Thicker frame pins allow the IC to be connected to the electronic device in which it will operate.
Reliability. The reliability of an integrated circuit is approximately the same as that of an individual silicon transistor, equivalent in shape and size. Theoretically, transistors can last thousands of years without failure - a critical factor for applications such as rocketry and space technology, where a single failure can mean complete failure of the project.
Microprocessors and minicomputers. First introduced publicly in 1971, microprocessors performed most of the basic functions of a computer on a single silicon IC, implemented on a 5-5 mm chip. Thanks to integrated circuits, it became possible to create minicomputers - small computers where all functions are performed on one or more large integrated circuits. This impressive miniaturization has led to a dramatic reduction in the cost of computing. The minicomputers currently produced, priced at less than $1,000, are as powerful as the first very large computers, which cost up to $20 million in the early 1960s. Microprocessors are used in communications equipment, pocket calculators, and wristwatches. watches, television channel selectors, electronic games, automated kitchen and banking equipment, automatic fuel control and exhaust gas aftertreatment in passenger cars, as well as many other devices. Much of the $15 billion global electronics industry relies on integrated circuits in one way or another. Around the world, integrated circuits are used in equipment with a total value of many tens of billions of dollars.
Computer storage devices. In electronics, the term "memory" usually refers to any device designed to store information in digital form. Among the many types of storage devices (MSDs), we consider random access memory (RAM), charge-coupled device (CCD), and read-only memory (ROM). For RAM, the access time to any memory cell located on the chip is the same. Such devices can store 65,536 bits (binary units, typically 0 and 1), one bit per cell, and are a widely used type of electronic memory; on each chip they have approx. 150 thousand components. RAMs are available with a capacity of 256 Kbit (K = 210 = 1024; 256 K = 262,144). In memory devices with sequential access, the circulation of stored bits occurs as if along a closed conveyor (CCDs use exactly this type of sampling). A CCD, a specially configured IC, can place packets of electrical charges under closely spaced tiny pieces of metal that are electrically isolated from the chip. Charge (or lack thereof) can thus move throughout the semiconductor device from one cell to another. As a result, it becomes possible to store information as a sequence of ones and zeros (binary code), and access it when required. Although CCDs cannot compete with RAM memory in terms of speed, they can process large amounts of information at a lower cost and are used where random access memory is not required. The RAM, made on such an IC, is volatile, and the information recorded in it is lost when the power is turned off. Information is entered into ROM during the production process and is stored permanently. The development and release of new types of IP does not stop. Erasable programmable ROMs (EPROMs) have two gates, one on top of the other. When voltage is applied to the upper gate, the lower one can acquire a charge, which corresponds to 1 in the binary code, and when switching (reversing) the voltage, the gate can lose its charge, which corresponds to 0 in the binary code.
see also
OFFICE EQUIPMENT AND OFFICE EQUIPMENT;
COMPUTER ;
ELECTRONIC COMMUNICATIONS;
INFORMATION ACCUMULATION AND SEARCH.
LITERATURE
Meizda F. Integrated circuits: technology and applications. M., 1981 Zi S. Physics of semiconductor devices. M., 1984 VLSI technology. M., 1986 Maller R., Keimin S. Elements of integrated circuits. M., 1989 Shur M.S. Physics of semiconductor devices. M., 1992

Collier's Encyclopedia. - Open Society. 2000 .

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A solid-state device containing a group of devices and their connections (connections), made on a single plate (substrate). In I. s. Passive elements (capacitances, resistances) and active elements are integrated, the action of which is based on various. physical... ... Physical encyclopedia

- (IC, integrated circuit, microcircuit), microminiature device with a high packing density of elements (diodes, transistors, resistors, capacitors, etc.), inextricably linked (united) with each other structurally, technologically... ... Modern encyclopedia

- (IC integrated circuit, microcircuit), a microminiature electronic device, the elements of which are inextricably linked (united) structurally, technologically and electrically. IS are divided: according to the method of combining (integrating) elements into... Big Encyclopedic Dictionary

integrated circuit- (ITU T Q.1741). Topics: telecommunications, basic concepts EN integrated circuitIC... Technical Translator's Guide

The "BIS" request is redirected here; see also other meanings. Modern integrated circuits designed for surface mounting Integrated (micro)circuit (... Wikipedia

- (IS). integrated circuit (IC), microcircuit, microminiature electronic device with a high packing density of interconnected (usually electrically) elements (diodes, transistors, resistors, capacitors, etc.),... ... Big Encyclopedic Polytechnic Dictionary

- (IC, integrated circuit, microcircuit), a microminiature electronic device, the elements of which are manufactured in a single technological cycle and are inextricably linked (united) structurally and electrically. Integrated circuits are divided into: ... encyclopedic Dictionary

The development of microelectronics led in the early 70s to the emergence of highly specialized LSIs containing hundreds and thousands of logic elements and performing one or a limited number of functions. The variety of types of digital equipment required expanding the range of LSIs, which was associated with costs that were unacceptable from an economic point of view. The way out of this situation was the development and large-scale production of a limited range of LSIs that perform various functions depending on external control signals. Sets of such LSIs form microprocessor kits and make it possible to build a variety of digital equipment of any complexity. The most important supercomponent of the BIS kit is microprocessor(MP): universal standard LSI, the functions of which are determined by a given program.

A qualitative feature of MPs is the possibility of their functional restructuring by changing the external program. In essence, MPs are the central processing elements of a computer, made in the form of one or more LSIs.

The main difference between MP and other types of integrated circuits is the ability to program the sequence of functions performed, i.e., the ability to work according to a given program.

Table 4.1

Designation	technology	Number of ICs	Bit capacity,	Performance,
	R-TIR
	n-TIR
	n-TIR
	n-TIR
	n-TIR
	p-TIR
	n-TIR
	R-TIR
	R-TIR
	n-TIR

The introduction of microprocessors makes it possible to change the design principle of digital equipment. Previously, implementing a new algorithm required new hardware development. Now, when using MP, new equipment is not required to implement a new algorithm; it is enough to change its operating program accordingly. This feature explains the enormous interest shown in our country and abroad in microprocessor devices.

A short time interval (1971-1975) is characterized by the appearance of MPs of a wide variety of modifications. Currently, the number of MP types in the world exceeds 1000.

The parameters of the main types of domestic microprocessor kits (MPCs) are given in Table. 4.1.

4.2. Microprocessor structures

A simplified block diagram of the MP is shown in Fig. 4.1.

Figure 4.1

Figure 4.2

The microprocessor contains an arithmetic-logical device ALU, storage devices for random access (RAM) and read-only (ROM) information storage, a control device that receives, decodes commands and sets the sequence of their execution, as well as input-output devices (I/O) for information, with with the help of which the initial data is entered and the data obtained as a result of the operation of the MP is output.

Microprocessors process 2-, 4-, 8-, 16-, 32-bit numbers, perform 30...500 commands of addition, subtraction, shift, and logical operations. Four- and eight-bit MPs are LSIs with crystal dimensions of 5 x 5 x 0.2 mm.

A generalized block diagram of the MP is shown in Fig. 4.2. Arithmetic logic unit The ALU performs various arithmetic and logical operations on numbers and addresses represented in binary code. The composition of operations performed by the ALU is determined by a list of instructions (set of commands). The set of commands usually includes arithmetic and logical additions and multiplications, shifts, comparisons, etc. Arithmetic operations are performed in accordance with the rules of binary arithmetic. Logical operations are performed according to the rules of Boolean algebra.

The ALU includes an adder, shifters, registers and other elements.

Control device controls the operation of the ALU and all other MP blocks. The control unit receives commands from the memory block. Here they are converted into binary control signals to execute a given command. The operation of the control unit is synchronized by a timer, which distributes the process of command execution over time. An instruction is a binary word of 8, 16, 24 bits or more (up to 64), some of which represent the operation code, and the rest are distributed between data addresses (operands) in memory. An instruction with a 16-bit address part allows you to access 2 16 -1 = 65635 memory cells. This quantity, as a rule, is quite sufficient for the problems solved by MP. This kind of memory access is called direct addressing.

However, indirect addressing is more often used, which is necessary when the bit width of the address part is less than required. In this case, addressing is carried out in two stages. At the first stage, using the address contained in the command, a cell is selected containing the address of another cell, from which the operand is selected at the second stage. The command with the indirect addressing method must contain one bit of the operand attribute, the state of which determines what is selected at this stage: the address of the operand or the operand itself? Of course, the indirect addressing method is slower than the direct one. It allows, by increasing the address memory capacity, to access the number of operands 2 n times (where n is the size of the address part of the command) greater than with the direct method.

The control device distributes any operation according to the code specified by the command word into a sequence of phases (addressing phases and execution phases), called a cycle. Due to the limited capacity of the MP, operations on large-width operands can be performed in two or more cycles. Obviously, this reduces the performance of the MP by 2 or more times. This leads to an interesting and practically important conclusion: the speed of the MP is inversely dependent on the accuracy, which is uniquely determined by the bit capacity of the operands.

The microprocessor contains register block(R). MP working registers physically represent identical memory cells used for super-operative storage of current information (SRAM). According to the functions performed, P contains groups associated with certain elements of the MP structure.

Two operand register(O) During the execution of an operation, the ALU stores two binary numbers. At the end of the operation in the first register, the number is replaced by the result, i.e., it accumulates, as it were (hence the name of the register “accumulator”). The contents of the second operand register are replaced in the next operation by another operand, while the contents of the accumulator can be stored by a number of special instructions.

Command register(K) stores during the execution of the operation several bits of the command word, which represent the code for this operation. The address portion of the command word is contained in address register A.

After implementing any operation, the bit width of the result may be greater than the bit width of each of the operands, which is registered by the state of a special flag register, sometimes called overflow trigger. During the process of debugging the compiled program, the programmer must monitor the state of the flag register and, if necessary, eliminate the overflow that has occurred.

Very important in the MP command system are transition commands to execute a given section of the program according to certain characteristics and conditions, the so-called commands conditional transitions. The presence of such teams determines the level of “intelligence” of the MP, as it characterizes its ability to make alternative decisions and choose different paths depending on the conditions arising during the decision. To determine such conditions, a special status register(C), fixing the state of the MP at each moment of program execution and sending to the control unit a transition signal to the command, the address of which is contained in a special register called program counter(SK). Commands in memory are written in a certain program sequence at addresses that form a natural series, i.e., the address of the next command differs from the address of the previous one by one. Therefore, when implementing a continuous sequence of commands, the address of the next command is obtained by adding one to the contents of the CS, i.e., it is formed as a result of counting. The purpose of the IC is to find the necessary command addresses, and if there are jump commands in the program, the next command may not have the next address. In this case, the address part of the transition command is written to the CS.

General purpose registers(RON) are used to store intermediate results, addresses and commands that arise during program execution, and can communicate via common buses with other working registers, as well as with program counters and an input/output information block. An MP usually contains 10...16 RONs of 2...8 bits each. The number of RON indirectly characterizes the computing capabilities of the MP.

Of particular interest is the presence in many MP models of a group of registers that have a store or stack organization - the so-called stacks. The stack allows you to organize the correct sequence of execution of various sequences of arithmetic operations without exchanging memory. An operand or other information can be pushed onto the stack without specifying an address, since each word placed on it first occupies the first register, then is “pushed” by subsequent words each time a register deeper. Information is output in reverse order, starting with the first register, which stores the last word pushed onto the stack. In this case, the last registers are cleared.

Blocks ALU, UU, P form CPU(CPU) included in any computer: highlighted in Fig. 4.2 with a dashed line. The composition of the MP may include timer(T), using a suspended timing capacitor or a quartz resonator. The timer is the heart of the MP, since its operation determines the dynamics of all information, address and control signals and synchronizes the operation of the control unit, and through it, other elements of the structure. The clock frequency, called clock, is selected as maximum and is limited only by signal delays, determined mainly by LSI manufacturing technology. The speed at which a microprocessor executes a program is directly proportional to the clock frequency.

The MP may include input/output device(UVV) for the exchange of information between the MP and other devices.

Signals of three types - information, address and control - can be transmitted over one, two or three buses. Tire is a group of communication lines, the number of which determines the bit depth of binary information simultaneously transmitted through it.

The number of information bus (IB) lines determines the amount of information received or transmitted by the MP in one access to memory, input or output device. Most MPs have an 8-bus information highway. This allows eight binary units of information (1 byte) to be received at a time. One byte of information can contain one of 256 possible characters of the alphabet of the information source or one of 256 possible operation codes. This number of valid characters and operation types is sufficient for most applications.

There are MPs containing 16 and 32 buses in the information highway.

The number of lines in the control bus (VIII) depends on the order of interaction between the MP, memory, and external airborne information. Typically control buses contain 8... 16 lines.

4.3. Microcomputer

An important result of the development of programmable LSIs was the development of microcomputers. If a microcomputer is created on a single integrated circuit, then it is called single-chip. A simplified block diagram of a microcomputer is shown in Fig. 4.3.

Figure 4.3

As you can see, it contains a central processing unit (CPU) (which has a structure similar to the MP discussed above), ROM, RAM, and input and output devices. The input device contains address selector and the so-called input ports for reading information from a floppy disk, ADC, teletype, punched tape. The output device also contains an address selector and information output ports (display, printing device, punched tape output device, DAC).

Data received by the input device is transmitted to the address bus, usually in the form of 8-bit parallel or serial code signals through the input port. The address selector specifies the input port that transmits data on the information highway at some point in time. Main memory consists of ROM and RAM. The permanent memory is used as a program memory that the microcomputer developer has pre-programmed in accordance with the user's requirement. Different programs use different parts of ROM.

The data memory in a microcomputer is RAM. Information stored in RAM is erased when the power supply is turned off. Data entering the RAM is processed by the CPU according to the program stored in the ROM. The results of operations in the CPU are stored in a special drive information called battery or RAM. They can be output by command through one of the output ports to output devices connected to that port. The required output port is selected using an address selection circuit.

4.4. Storage devices

The most important blocks of digital equipment are storage devices (memory blocks), which are divided into external and internal. External Memory devices are still implemented on magnetic tapes and magnetic disks. They provide indefinitely long-term storage of information in the absence! power supply, as well as almost any necessary memory capacity. Domestic Memory devices are an integral part of digital equipment. Previously, they were based on ferrite cores with a rectangular hysteresis loop. Now, in connection with the development of ICs, there are ample opportunities for creating semiconductor memory devices.

Memory devices include the following types of storage devices:

Random access storage devices, performing recording and storage of arbitrary binary information. In digital systems, RAM stores arrays of processed data and programs that determine the process of current information processing. Depending on the purpose and structure, RAM has a capacity of 10 2 ... 10 7 bits.

Read-only storage devices serving to store information, the content of which does not change during system operation, for example, standard subroutines and microprograms used during operation, tabular values ​​of various functions, constants, etc. Information is written to ROM by the LSI manufacturer.

Programmable Read Only Memory Devices are a type of ROM, characterized by the possibility of one-time recording of information according to the customer’s instructions.

Reprogrammable ROMs, differing from conventional ones by the possibility of multiple electrical changes of information carried out by the customer. The volume of the EEPROM is usually 10 2 ... 10 5 bits.

Read-only memory devices (ROM, PROM, RPZU) are required to retain information when the power is turned off.

The main parameters of the memory are: information capacity in bits; minimum circulation period; the minimum acceptable interval between the beginning of one cycle and the beginning of the second; maximum circulation frequency is the reciprocal of the minimum circulation period; specific power - the total power consumed in storage mode, per 1 bit; The specific cost of one bit of information is the total cost of the crystal divided by the information capacity.

4.5. Random access storage devices

The typical structure of LSI RAM is shown in Fig. 4.4.

Figure 4.4

Figure 4.5

The main node is a matrix of memory cells (MCM), consisting of n lines with T storage cells (forming a bit word) in each line. The information capacity of LSI memory is determined by the formula N= nm bit.

The inputs and outputs of memory cells are connected to the address ASH and bit RH buses. When writing and reading, one or simultaneously several memory cells are accessed (selected). In the first case, use two-coordinate matrices(Fig. 4.5, a), in the second case matrices with word-by-word sampling(Fig. 4.5,6).

Address signal decoder(DAS) when submitting the appropriate address signals, selects the required memory cells. With the help of the RS, the MNP is connected with buffered recording amplifiers(BUZ) and reading(BMS) information. Recording Control Scheme(CPS) determines the operating mode of the LSI (writing, reading, storing information). Crystal selection scheme(SVK) allows the execution of write-read operations on this microcircuit. The crystal sampling signal ensures the selection of the required LSI memory in a memory consisting of several LSIs.

Applying a control signal to the CPS input in the presence of a crystal sampling signal at the SVK input performs a write operation. The signal at the information input BUZ (1 or 0) determines the information written to the memory cell. The output information signal is removed from the BUS and has levels consistent with serial digital information systems.

Large integrated circuits of RAM tend to be based on the simplest elements TTL, TTLSh, MDP, KMDP, I 2 L, ESL, modified taking into account the specifics of specific products. In dynamic memory cells, storage capacitors are most often used, and MOS transistors are used as key elements.

The choice of element base is determined by the requirements for information capacity and performance of LSI memory. The highest capacity is achieved when using logic elements that occupy a small area on the chip: 2 L, MIS, dynamic SJ. LSIs with logical elements that have small differences in logical levels (ESL, I 2 L), as well as TTLSH logical elements, have high performance.

Frequency applications of LSI , using various basic technical solutions, illustrates Fig. 4.6.

Figure 4.6

Thanks to the development of technology and circuitry, the performance of elements is continuously increasing, so the boundaries between these areas shift over time to the region of higher operating frequencies.

4.6. Read-only storage devices

The ROM circuit is similar to the RAM circuit (see Fig. 4.4). The only differences are as follows:

ROMs are used to read information;

in the ROM, several bits of one address are sampled simultaneously (4, 8, 16 bits);

information written in ROM cannot be changed, and in sampling mode only it is read.

Large ROM integrated circuits are classified into factory programmable(using special photo templates) and customer programmable(electrically).

Figure 4.7

The ROM uses a matrix structure: the rows are formed by the address buses of the DS, and the columns are formed by the bits of the RS. Each AS stores a specific code: a given set of logical 1s and 0s. In the MLP shown in Fig. 4.7, a, a single write of the code is carried out using diodes that are connected between the ASC and those RCs on which there should be a logical 1 when reading. Usually the customer is supplied with a ROM with a matrix, in all nodes of which there are diodes.

The essence of one-time electrical programming of the PROM is that the user (using a special programmer device) burns out the terminals - jumpers of those diodes that are located at the locations of logical 0. Burnout of the terminals is carried out by passing a current through the corresponding diode that exceeds the permissible value.

Diode ROMs are simple, but have a significant drawback: they consume significant power. To facilitate the operation of the decoder, bipolar (Fig. 4.7,6) and (Fig. 4.7, c) transistors are used instead of diodes.

When using bipolar transistors, the AS ensures the flow of a base current, which in β b.t. +1 times less than the emitter supplying the RS. Consequently, the required decoder power is significantly reduced.

An even greater gain is provided by the use of MOS transistors, since the gate circuit consumes virtually no power. What is used here is not the burning of the terminals, but the absence of gate metallization in the transistors that ensure reading logical 0s in the bit bus.

4.7. Programmable read-only memories

Flashable ROMs are the most versatile memory devices. The block diagram of the RPOM is similar to that of RAM (see Fig. 4.4). An important distinctive feature of the ROM is the use of a specially designed transistor with a metal-nitride-oxide-semiconductor (MNOS) structure in the MNP. The operating principle of such a memory cell is based on a reversible change in the threshold voltage of the MNOS transistor. For example, if you make U ZIPor >U AS, then the transistor will not be unlocked by address pulses (i.e., it will not participate in the operation). At the same time, other MNOS transistors with U

Structure of a MNOS transistor with an induced channel R-type shown in Fig. 4.8, a.

Figure 4.8

Here the dielectric consists of two layers: silicon nitride (Si 3 N 4) and silicon oxide (SiO 2). The threshold voltage can be changed by applying short (about 100 μs) voltage pulses of different polarities to the gate, with a large amplitude of 30...50 V. When a +30 V pulse is applied, the threshold voltage U ZIPor = -5 V is set. This voltage is maintained if use a transistor or gate voltage U ZI =±10V. In this mode, the MNOS transistor operates like a regular MOS transistor with an induced channel R-type.

When a pulse of -30 V is applied, the threshold voltage takes on the value USIpore ~20 V, as shown in Fig. 4.8, 6 and V. In this case, signals at the input of the transistor U ZI ± 10 V cannot bring the transistor out of the closed state. This phenomenon is used in EPROM.

The operation of MNOS transistors is based on the accumulation of charge at the boundary of the nitride and oxide layers. This accumulation is the result of unequal conduction currents in the layers. The accumulation process is described by the expression dq/ dt= I sio 2 - I si 3 n 4 . At high negative voltage U A positive charge accumulates at the boundary. This is equivalent to the introduction of donors into the dielectric and is accompanied by an increase in the negative threshold voltage. At high positive voltage U A negative charge accumulates at the interface. This results in a decrease in the negative threshold voltage. At low voltages U SI currents in dielectric layers are reduced by 10...15 orders of magnitude, so the accumulated charge is retained for thousands of hours, and, consequently, the threshold voltage is preserved.

Another possibility is known for constructing a memory cell for ROM based on MIS transistors with a single-layer dielectric. If you apply a sufficiently high voltage to the gate, you will see avalanche breakdown dielectric, as a result of which electrons will accumulate in it. In this case, the threshold voltage of the transistor will change. The charge of the electrons is maintained for thousands of hours. In order to rewrite information, it is necessary to remove electrons from the dielectric. This is achieved by illuminating the crystal with ultraviolet light, which causes a photoelectric effect: knocking electrons out of the dielectric.

Using UV erase it is possible to significantly simplify the RPOM circuit. The generalized block diagram of an RPOM with ultraviolet erasure (Fig. 4.9) contains, in addition to the MAP, an address signal decoder (DAS), a crystal selection device (CSD) and a buffer amplifier (BU) for reading information.

Figure 4.9

According to the given block diagram, in particular, an LSI RPOM with ultraviolet erasure of the K573RF1 type with a capacity of 8192 bits is made.

4.8. Digital to Analogue Converters

The purpose of the DAC is to convert a binary digital signal into an equivalent analog voltage. Such a conversion can be made using resistive circuits shown in Fig. 4.10.

Figure 4.10

A DAC with binary weight resistors (Figure 4.10a) requires fewer resistors, but requires a range of precision resistance values. Analog output voltage U The DAC is defined as a function of two-level input voltages:

U an =( U A+2 U B+4 U C +…)/(1+2+4+...).

On digital inputs U A , U B, U C, ... voltage can take only two fixed values, for example, either 0 or 1. For a DAC that uses resistors R And R/2, More resistors are required (Fig. 4.10.6), but with only two values. The analog voltage at the output of such a DAC is determined by the formula

U an =( U A+2 U B+4 U C +…+m U n)/2 n

where n - number of DAC bits; T - coefficient depending on the number of DAC bits.

To ensure high accuracy, DAC resistive circuits must operate with a high-resistance load. To match resistive circuits with low-impedance loads, operational amplifier-based buffer amplifiers are used, shown in Fig. 4.10, a, b.

4.9. Analog-to-digital converters

The purpose of the ADC is to convert analog voltage into its digital equivalent. Generally, ADCs have more complex circuitry than DACs, with the DAC often being a subset of the ADC. A generalized block diagram of an ADC with a DAC in the feedback circuit is shown in Fig. 4.11.

Figure 4.11

ADCs made using this design are widely used due to their good accuracy, speed, comparative simplicity and low cost.

The ADC includes n-bit trigger register of conversion results DD 1 - DD n, DAC bit manager; a comparator connected to the control device of the control unit and containing a clock frequency generator. By implementing different ADC operating algorithms in the VCU, different characteristics of the converter are obtained.

Using fig. 4.11, let us consider the principle of operation of the ADC, assuming that an up/down counter is used as a trigger register. The reversible counter has a digital output, the voltage on which increases with each clock pulse when the voltage level at the “Direct Count” counter input is high, and the “Down Count” input is low. Conversely, the digital output voltage decreases with each clock pulse when the Count Up input is low and the Count Down input is high.

The most important component of the ADC is the comparator (K), which has two analog inputs U DAC and U an and a digital output connected through the control unit to a reversible counter. If the voltage at the output of the comparator is high, the level at the input of the Direct Count counter will also be high. Conversely, when the comparator output voltage is low, the Up Count input will also be low.

Thus, depending on whether the output level of the comparator is high or low, the up/down counter counts in the forward or reverse direction, respectively. In the first case, at the entrance U The comparator DAC shows a stepwise increasing voltage, and in the second one a stepwise decreasing voltage.

Since the comparator operates open-loop, its output voltage level goes high when the voltage at its input U an will become slightly more negative than at the input U DAC. Conversely, its output voltage level becomes low as soon as the input voltage U an will become slightly more positive than the input voltage U DAC.

At the entrance U The comparator DAC receives the output voltage of the DAC, which is compared with the analog input voltage supplied to the input U en .

If analog voltage U an exceeds the voltage removed from the output of the DAC, the reversible counter counts in the forward direction, increasing the voltage at the input in steps U DAC to input voltage value U an. If U en<U The DAC or becomes one during the counting process, the voltage at the output of the comparator is low and the counter counts in the opposite direction, again leading U DAC to U en . Thus, the system has a feedback loop that keeps the DAC output voltage approximately equal to the voltage U en . Therefore, the output of the up/down counter is always the digital equivalent of the analog input voltage. The digital equivalent of the analog input signal of the ADC is read from the output of the up/down counter.

4.10. Digital and analogue multiplexers

In microprocessor systems, ADCs, DACs, as well as in electronic switching systems, multiplexers are widely used: multichannel switches (having 4, 8, 16, 32, 64 inputs and 1-2 outputs) with a digital control device. The simplest multiplexers of digital and analog signals are shown in Fig. 4.12, a and b respectively.

Figure 4.12

A digital multiplexer (Fig. 4.12, a) allows for sequential or random interrogation of the logical states of signal sources X 0 , X 1 , X 2 , X 3 and transmitting the poll result to the output

According to this principle, multiplexers are built for any required number of information inputs. Some types of digital multiplexers allow switching of analog information signals.

However, the best performance is achieved by analog multiplexers containing a matrix of high-quality analog switches (AK 1 ... AK 4) operating on an output buffer amplifier, a digital control unit. The connection of the nodes to each other is illustrated in Fig. 4.12.6.

An example of an analog multiplexer LSI is a K591KN1 type microcircuit, made on the basis of MOS transistors. It provides switching of 16 analog information sources per output, allowing both addressing and sequential sampling of channels. When developing LSI analog multiplexers, the need for their compatibility with the command system of microprocessors is taken into account.

Analog multiplexers are very promising products for electronic switching fields and multi-channel electronic switches for communications, radio broadcasting and television.