Electronic devices and devices. Application of electronic devices and devices Main characteristics of electronic devices

Class 2lg, 13, - „

SS Wed No. 63799

4 rl I;, - ..:, and- -., „P, R ann wasp

Zar gGGslGrated in F\u003e cg.c iso, ", reteniGs of the State Planning Committee of the USSR (\\ g l.gv G.

A.G. Alexandrov

Announced on January 31, 1941 in the People's Commissariat for Electroprom ea X 40368 (304420) Published on January 31, 1945

The present invention provides a method for static characterization of electronic devices with smooth electrostatic control.

For a number of practical purposes, it may be necessary to have the characteristics of these devices, taken depending on the potential of the control electrode at constant potentials on the other electrodes. For low-power lamps, these characteristics are usually measured in a simple point-like manner. 3a, a number of special devices have recently appeared that make it possible to immediately obtain a family of static characteristics on the screen of an electronic oscilloscope.

For high-power electrode lamps, for example, powerful generator lamps, the question of removing static characteristics is more serious, since their electrodes, which are not designed for large overloads, are not able to withstand the powers that can be dissipated by them when taking full static characteristics.

Further, there is a number of such lamps that are not able to withstand even those light conditions in which they would be in special circuits for taking a family of static characteristics by the oscilloscopic method.

In a number of special physical studies of activated complex cathodes, for example, oxide ones, it is sometimes necessary to measure the electron emission current in such modes that the cathode does not noticeably heat up due to the superposition of the measured current on the filament current.

These difficulties are easily resolved using the proposed method, the essence of which can be understood from the following description and consideration of FIG. 1 - 8 drawing.

FIG. 1 shows the electron tube 1 under study, into the control electrode circuit of which narrow voltage pulses are periodically supplied from the resistance 14 connected in series with the source of the biasing grid voltage o, blocked by the capacitor 9.

Periodic narrow voltage pulses are obtained from a capacitor 25 charged from a regulated constant current source 21 through a potentiometer 22 and

¹ 63799 resistances 28 and 24. The specified capacitor is periodically forced to discharge through the thyratron

26, periodically forcedly ignited by means of a peak transformer 27, the secondary circuit of which is connected in series with the source of the mixing voltage 30 through a potentiometer 29.

To limit the grid current, a limiting resistance 28 is introduced into the grid circuit of this thyratron.

The capacitor is discharged to a non-inductive resistance

14 connected to the control electrode circuit of the investigated vacuum tube. Potentials to other electrodes are supplied from DC sources 2, 3, 4, etc., which can be adjusted. These sources are blocked by sufficiently large capacities 6, 7, 8, etc., so that when current pulses pass through the indicated electrodes, there is no noticeable decrease in the potentials on the electrodes and thereby distortion of the measured characteristics. This circumstance is of particular importance in cases where the sources supplying the electrode circuits are low-power and have large internal resistances.

The voltages of sources 2, 3, 4, 5 can be measured using DC voltmeters 31, 82, 88, 34. In the electrode circuit, pre-known non-inductive resistances 10, 11, 12, 18 are introduced, on which narrow pulses of voltage drop are obtained when passing through them narrow impulses of currents. These voltage drops are fed by the switch 15 to an auxiliary device, with which they can be measured one after the other.

The auxiliary measuring device consists of a constant current source 17, a potentiometer

16, DC voltmeter 18, valve 20 and current indicator 35.

FIG. 2, the solid line shows the time curve of the voltage present directly between the grid and the cathode of the thyratron 26. The dotted line in this figure shows the time curve of the bias voltage across the potentiometer 29.

FIG. 3 shows the time curve of the voltage across the capacitor 25, charging during time 1 from the source 21 and during time 1 discharging to the resistance 4. Thus, the period of the oscillation is t, + t, \u003d T.

This period, in turn, is equal to the period of the voltage fluctuations supplied to the transformer 27. The fluctuations are taken forced, since in this case a clearer picture is obtained and more accurate measurements are provided. Along the way, one should also point out the fact that the use of periodic oscillations has undoubted advantages over a single impulse. The point is that the method of periodic impulses certainly provides greater accuracy, discards the element of randomness and, moreover, significantly: it saves time spent on measurements.

FIG. 4 shows the time curve of the voltage present directly between the grid and the cathode of the test lamp. As you can see from this graph, the grid voltage curve looks like very narrow pulses. The maximum value of the pulse curve can be easily adjusted "either by changing the voltage using the potentiometer 22, or by changing the voltage of the source

5. Thus, you can change the "voltage of the gate (grid).

FIG. 5 shows an exemplary current pulse curve over time in a circuit of any of the electrodes. This curve corresponds to the curve in FIG. 4, FIG. 6 schematically shows an exemplary pulse curve over time in a circuit of any of the highly stretched electrodes. axis of time. The same graph shows dashed lines 2, 8, 4 „related to the voltage on the 63799 tentiometer 16. Three cases are shown here. Line 2 refers to the case when the voltage at the potentiometer 16 is greater than the maximum value at the corresponding non-inductive resistance in the circuit of one or another electrode, that is, Y „\u003e 1„, P.

In this case, the valve 20 will be closed, since its anode is negative with respect to the cathode.

Curve 2 in FIG. 6 refers to the case when „\u003d I„, b.

This case is critical, for which the measurement is made. By measuring with a voltmeter 18 the voltage across the potentiometer in this case and knowing the given resistance K in advance, it is easy to determine the value of the current pulse 1 „,.

Curve 4 in FIG. 6 refers to the case when U „(I„, Â.

In this case, the anode of the valve 20 will be positive with respect to its cathode and a current will flow through it, the average value of which will be measured by the device 85. The appearance of the current will serve as a sign that the critical mode has been passed and therefore it is required to increase the voltage at the potentiometer 16.

As a valve 20, you can take the smallest kenotron (diode), or a triode with a grid attached to the anode. The incandescence of the kenotron should be powered from a direct current source, and the common point should be made at the negative end of the incandescent source (to avoid the influence of the nonequipotentiality of the cathode and the initial electron velocities).

In addition to the compensation method for measuring current pulses, the oscilloscopic or oscillographic method can also be used. For this purpose, shown in dotted lines in FIG. 1 conductors

86 are attached to a pair of deflection plates of the oscilloscope, giving a vertical deflection of the electron beam; the other pair of deflecting plates is connected to a source with a sawtooth voltage curve, this source being synchronized with a source 27 supplying an alternating voltage to the thyratron grid circuit

26. In this case, clear pulses of voltage drop will appear on the oscilloscope screen (see Fig. 5), having measured them with the help of preliminary calibration and zn; I in advance the values \u200b\u200bof non-inductive resistances in the electrode circuits, it is possible to determine the very values \u200b\u200bof current pulses. In this measurement, it is imperative to use an electronic oscilloscope or oscilloscope. The use of a loop electromagnetic oscilloscope should give significant errors from -; -. And a large inertia of the system.

The method of supplying pulses to the control electrode circuit and measuring currents in the circuit of other electrodes has a number of significant advantages. First of all, the power of the thyratron that discharges the capacitor is greatly reduced. Then it becomes possible to measure currents in the circuit of any electrode at any potentials on other electrodes, which cannot be had in the case when the current pulse is measured in the circuit of the electrode to which the potential pulse is applied.

With the present method, the lamp is "unlocked" only at those moments when a potential pulse is applied to the control electrode, while the rest of the time, the control is controlled: the electrode has a sufficiently large (in absolute value) negative potential.

The approximate static characteristics obtained by the proposed method are shown in the figures

The subject of the invention

1. A method for recording the static characteristics of electronic devices with smooth electrostatic control, which is also different from the fact that a voltage in the form of narrow pulses from a voltage charged from an external source and periodically forcedly discharged at using a capacitor thyratron, and regulated voltages from direct current sources blocked by capacitors are applied to other electrodes of the examined electronic device through previously known non-inductive resistances, and the resulting MQKcHMBJlbHblp are obtained. The values \u200b\u200bof the pulses of currents in the circuits of these electrodes are measured by the pulses of voltage drop across the above resistances, to which an adjustable compensating voltage is applied through the valve and the current indicator.

2. A device for implementing the method according to claim 1, characterized by the use of an electronic oscilloscope or oscilloscope for measuring the maximum values \u200b\u200bof pulses in the circuits of the electrodes of the examined vacuum tube, one pair of deflecting electrodes, " and the other pair of deflecting electrodes is supplied with a sawtooth voltage synchronized with an alternating voltage source supplied to the thyratron control electrode circuit, which periodically discharges the capacitor.

Tech. editor M.V.Snolyakva

Resp. editor D. A. Mikhailov

Gosplannzdat printing house, no. Vorovskogo, Kaluga

L! 49953. Signed for printing on 25 XI 1946. Circulation 500 copies. Price 65 kopecks. Zach. 325

Electronics - the field of science and technology that studies and applies devices, the operation of which is based on the flow of electric current in a vacuum, gas and solid. The high speed and high reliability of electronic devices have led to their widespread use in computers, radio engineering, communications, navigation, industry, etc. Electronic devices are used to convert the electrical energy of the power source into the energy of a useful signal (amplifiers, signal generators, etc. .), conversion of AC to DC (rectifiers) and DC to AC (inverters), conversion of types of energy, regulation of voltage, frequency, etc.

In electronic devices conversion of electrical energy and signals is carried out using electronic devices (electronic active elements). In addition to electronic devices, they use power supplies and passive components: resistors, capacitors, inductors.

Currently, mainly semiconductor electronic devices are used. They carry electric charges occurs in a solid (semiconductor). These include diodes, transistors, thyristors, etc.

Semiconductor diode (Fig. 1) is a two-layer structure, which is formed in one crystal. One layer has n-type conductivity and the other p-type. In general, this structure is called a pn junction or an electron-hole junction. The main property of the electron-hole transition is its one-sided electrical conductivity.

Fig. 1. Semiconductor diode: a) semiconductor structure of the diode;

b) conventional graphic designation; c) volt - ampere characteristic

With direct mixing of the pn junction, its electrical conductivity increases and a current passes through the junction, which strongly depends on the applied voltage. With a reverse bias of the pn junction, the electrical conductivity of the junction decreases and electricity practically does not pass through it.

A semiconductor diode with a reverse biased pn junction, in which, with relatively small changes in the reverse voltage in the region close to the breakdown voltage, the reverse current increases sharply, is called zener diode (fig. 2). It is used to create voltage stabilizers.

Fig. 2. Semiconductor Zener diode: a) conventional graphic designation; b) volt - ampere characteristic

Varicapis called a semiconductor diode with a reverse biased pn junction, used as a variable capacitor for electronic setting frequency selective circuits (Fig. 3).

Fig. 3. Semiconductor varicap: a) conventional graphic designation;

b) volt - farad characteristic

Semiconductor triodes (transistors) are divided into bipolar and field-effect.

Bipolar transistorcalled a semiconductor device with two pn-junctions (Fig. 4). It has a three-layer structure of the n-p-n- or p-n-p-type. The middle area between two pn junctions is called the base. Its thickness is made small enough. The adjacent areas are called emitter and collector. Accordingly, the pn-junction emitter-base is called emitter, and the base-collector junction is called collector.

Fig. 4. Semiconductor structure and conventional graphic designation of bipolar transistors: a) n-p-n-type; b) p-n-p-type

Field effect transistor is called a semiconductor device, the resistance of which changes under the action of a transverse electric field created by a control electrode (gate) adjacent to the conducting volume of the semiconductor. There are two types of field-effect transistors: with a control p-n-junction (fig. 5) and insulated shutter(fig. 6).

Fig. 5. Semiconductor structure and conventional graphic designation of a field-effect transistor with a control p-n-junction: a) with an n-type channel; b) with a p-type channel

Fig. 6. Semiconductor structure and conventional graphic designation of a field-effect transistor with an insulated gate: a) with a built-in channel; b) with an induced channel

Unlike bipolar transistors, in which charge transfer is controlled by changing the base current, in a field-effect transistor, the current is controlled by changing the control voltage that regulates the width of the channel through which the current flows. The region of the channel from which the carriers begin to move is called the source, and the region to which the main carriers move is called the drain. The control area in the instrument that encloses the channel is called the gate. By changing the voltage between the gate and the source, the channel cross section is changed.

Multilayer structures with three pn junctions are called thyristors... Their main property is the ability to be in two states of stable equilibrium: maximally open (with high conductivity) and maximally closed (with low conductivity). For this reason, they function as a non-contact electronic keywith unilateral conductivity. Thyristors with two leads (two-electrode) are called diode thyristors (dinistors), and with three (three-electrode) - or triode thyristors (trinistors),or symmetric thyristors (triacs),if they are able to conduct current in both directions (fig. 7).

Fig. 7. Thyristors: semiconductor structure: a) diode thyristor (dinistor); d) trinistor; g) symmetrical thyristor (triac); conventional graphic designation: b) diode thyristor; e) trinistor; h) triac; current-voltage characteristics: c) diode thyristor; f) trinistor; i) triac

Semiconductor photocells include: photoresistor, photodiode, phototransistor, photothyristor, LED (Fig. 8).

Fig. 8. Conditional graphic designation of semiconductor photocells: a) photoresistor; b) photodiode; c) phototransistor; d) photothyristor; e) LED

Photoresistor called a semiconductor device, the resistance of which depends on the illumination. With increasing illumination, the resistance of the photoresistor decreases.

The principle of the photodiode based on increasing inverse current pn transition when illuminated. The photodiode is used without an additional power source, since it itself is a current generator, and the current strength is proportional to the illumination.

In a phototransistor pn junction collector-base is a photodiode.

LEDs emit light when a direct current passes through them. The glow intensity is proportional to the forward current.

If an LED and a photosensitive element, such as a phototransistor, are combined in one housing, then the input current can be converted into an output current with complete galvanic separation of the circuits. Such optoelectric elements are called optocouplers (fig. 9).

Fig. 9. Conditional graphic designation of semiconductor optocouplers:

a) resistor; b) diode; c) transit; d) thyristor

In addition to photoresistors, the most common semiconductor resistors include: thermistors and varistors, the resistance of which changes with temperature and applied voltage, respectively (Fig. 10).

Fig. 10. Conditional graphic designation of semiconductor resistors: a) thermistor; b) varistor

With the help of the considered electronic devices, the necessary transformations of electrical energy and signals are carried out. The simplest type of conversion is AC rectification, more complex ones are DC-to-AC inversion, amplification, generation and conversion of signals of various shapes.

Rectifiers convert the alternating voltage of the supply network into direct voltage across the load (Fig. 11). They are used as sources of secondary power supply. The alternating voltage of the mains supply using a power transformer is reduced or increased to the required value, and then rectified using a rectifier. As a result, a constant direction voltage is generated at the output of the rectifier, which is pulsating (i.e. changes in value over time) and therefore is unsuitable for powering most electronic devices.

Fig. 11 Block diagram of the rectifier

To reduce the ripple of the rectified voltage at the output of the rectifier, a smoothing filter is included, and in some cases a constant voltage stabilizer is additionally introduced.

The main rectifier circuits can be subdivided into half-wave (fig. 12) and full-wave (fig. 13).

Fig.12. Schemes and timing diagrams of half-wave rectifiers: a) single-phase; b) three-phase

Fig.13. Half-wave rectifiers: single-phase rectifiers: a) bridge circuit; b) with a withdrawal from the midpoint of the transformer winding; c) their timing diagrams; three-phase rectifier; d) three-phase bridge circuit; e) its timing diagram

Smoothing filters only the direct component of the rectified voltage is passed to the output and its variable components are weakened as much as possible. In the simplest case, the smoothing filter can contain only one element — either a high inductance choke connected in series at the rectifier output, or a large capacitor connected in parallel with the load (Fig. 14).

Fig. 14. Smoothing filters: a) inductive; b) capacitive; c) their timing diagrams

Voltage stabilizer is called a device that maintains the voltage across the load with a given accuracy when the load resistance and mains voltage change within certain limits (Fig. 15). The voltage that the stabilizer maintains is set by the reference element - the Zener diode (Fig. 2).

Fig. 15 Circuit and timing diagrams of a parametric voltage regulator

Amplifier is called a device designed to increase the amplitude and power of the input signal without changing its other parameters. The increase in the amplitude and power of the signal at the output of the amplifier is achieved by converting the energy of the DC power supply to the energy of the output AC signal. In general, electronic amplifiers are multistage devices. The individual stages are interconnected by circuits through which the alternating (amplified) signal is transmitted and the DC component of the signal is not passed through. The stages are performed according to the scheme with a common emitter and a common source, with a common collector and with a common drain, with a common base and with a common gate (Fig. 16).

Fig. 16. Switching circuits for transistors with a common (s): a) emitter;

b) a collector; c) base; d) the source; e) drain; f) shutter

The circuit of any stage consists of a power supply, a transistor, and bias circuits that provide a DC operating mode of the transistor, that is, a quiescent mode (Fig. 17).

Multi-stage amplifiers are a series connection of the same type of amplifier stages.

Integrated amplifiers use direct connection between stages. Such amplifiers can amplify arbitrarily slowly changing signals and even direct current signals, and therefore are called DC amplifiers. Modern DC amplifiers amplify signals in a very wide frequency spectrum and are classified as broadband amplifiers.

Fig. 17 Amplifier circuits: a) on a bipolar transistor; b) on a field-effect transistor

The disadvantage of direct coupled amplifiers is the change in the output voltage of the quiescent mode (zero drift) due to instability of the supply voltage, temperature, and other factors. An effective way to reduce zero drift in such amplifiers is the use of differential amplification stages.

Differential amplifier is designed to amplify the difference between two input signals and is a symmetrical two-transistor circuit with combined emitters, which has two inputs and two outputs (Fig. 18).

Fig. 18. Differential amplifier

Operational amplifier(Fig. 19), like any other amplifier, is designed to amplify the amplitude and power of the input signal. It received the name "operational" from analogs on discrete elements that performed various mathematical operations (summation, subtraction, multiplication, division, logarithm, etc.), mainly in analog computers. Nowadays, the operational amplifier is most often performed in the form of an integrated circuit.

Fig. 19 Operational amplifier

Electronic generators self-oscillating (self-excited) systems are called, in which the energy of a power source (direct current) is converted into energy of an alternating signal of the desired shape.

In sinusoidal voltage generators transistors operate in an amplifying mode. Unlike them in pulse generators transistors operate in a key mode (when the transistor is alternately in a fully open, then in a completely closed state). In the open state, the transistor passes the maximum current and has a minimum output voltage, determined by its residual voltage. In the closed state, its current is minimal, and the output voltage is maximal and close to the voltage of the power supply. Such an element is called transistor switch(fig. 20).

Fig.20. Diagrams of transistor switches: a) on a bipolar transistor; b) on a field-effect transistor; c) their timing diagrams

Multivibrators Are pulse generators with a positive feedback, in which the amplifying elements (transistors, operational amplifiers) operate in a key mode.

Multivibrators do not have a single state of stable equilibrium, therefore, they belong to the class of self-oscillating generators and are based on discrete transistors, integral logic gates and operational amplifiers (Fig. 21).

Fig. 21. Schemes of self-oscillating multivibrators: a) on discrete elements; b) on integral logic gates; c) on an operational amplifier; d) their timing diagrams

Integrated microcircuit (IC) is a collection of several interconnected transistors, diodes, capacitors, resistors, etc. It is manufactured in a single technological cycle (i.e. simultaneously), on the same supporting structure - a substrate and performs a certain function of converting electrical signals ...

The components that are part of the IC and cannot be separated from it as independent products are called IC elements or integral elements. In contrast, structurally isolated devices and parts are called discrete components, and the nodes and blocks built on their basis are called discrete schemes.

High reliability and quality in combination with small size, weight and low cost of integrated circuits ensured their wide application in many fields of science and technology.

The basis of modern microelectronics is semiconductor integrated circuits... Currently there are two classes of semiconductor integrated circuits: bipolar and MIS.

The main element of a bipolar IC is an NPN transistor: the entire technological cycle is oriented towards its manufacture. The rest of the elements are manufactured simultaneously with this transistor without additional technological operations. For example, resistors are made with an NPN base layer, so they have the same depth as the base layer. As capacitors, reverse biased pn junctions are used, in which the n-layer corresponds to the collector layer of the npn-transistor, and the p layer corresponds to the base layer.

Logical elements call electronic devices that perform the simplest logical operations: NOT, OR, AND (Fig. 22).

Fig. 22. Conventional designation and truth tables of the simplest logical elements: a) NOT; b) OR; in and

Logical functions and logical operations on them constitute the subject of logic algebra, or Boolean algebra. The algebra of logic is based on logical values, which are denoted by the Latin letters A, B, C, D, etc. A logical value characterizes two mutually exclusive concepts: is and is not, true and false, on and off, etc. If one of values \u200b\u200bof a logical value is denoted by A, then the second is denoted "not A".

For operations with logical values, it is convenient to use a binary code, assuming A \u003d 1, “not A” \u003d 0, or, conversely, A \u003d 0, “not A” \u003d 1. In the binary number system, the same circuit can perform both logical and arithmetic operations. If the concept "not A" is designated with a special letter, for example, B, then the relationship between B and A will look like: B \u003d.

This is the simplest logical function called negation, inversion, or NOT function. A circuit providing this function is called an inverter or NOT circuit.

OR (disjunctor) and AND (conjuncator) circuits can be performed on resistors (resistor logic), on diodes (diode logic), on transistors (transistor logic). Most often, these circuits are used in combination with an inverter, and then they implement the functions OR-NOT, AND-NOT (Fig. 23).

Fig. 23. Legend and truth tables:

a) Pierce's arrow; b) Schaeffer's stroke

Functions OR-NOT (Peirce's arrow) and AND-NOT (Schaeffer's stroke) are the most common, since any other logical function can be implemented on their basis. The number of variables, and hence the number of inputs for the corresponding circuits, can be equal to two, three, four or more. In logic gates, logical zeros and ones are usually represented by different voltage values: voltage (or zero level) U 0 and voltage (or one level) U 1. If the level of one is greater than the level of zero, then they say that the circuit works in positive logic, otherwise (U 1< U 0) она работает в отрицательной логике. Никакой принципиальной разницы между положительной и отрицательной логиками нет. Более того, одна и та же схема может работать и в одной, и в другой логике.

The most widely used circuit is NAND of TTL type (transistor-transistor logic).

By combining logical circuits OR-NOT or AND-NOT, you can create various devices, both with memory and without memory.

To digital devices with memory include: triggers, counters, registers.

Triggersare called devices that have two states of stable equilibrium and are capable of abruptly switching from one stable state to another each time the control input signal exceeds a certain level, called the response threshold.

There are several types of triggers: RS, D, T, JK, etc., which are produced by the industry in the form of separate microcircuits, and are also based on NAND or NOR logic gates (Fig. 24).

Fig. 24. Graphic symbols of triggers: a) RS-trigger based on logical elements OR-NOT; in the form of separate microcircuits: b) RS-trigger; c) D-trigger; d) T-trigger; e) JK flip-flop

In digital information processing devices, the measured parameter (angle of rotation, speed, frequency, time, temperature, etc.) is converted into voltage pulses, the number of which characterizes the value of this parameter. These pulses are counted pulse counters (fig. 25, and) and are expressed as numbers.

Fig. 25. Graphical symbols: a) pulse counter;

b) register; c) decoder; d) encoder; e) multiplexer;

f) arithmetic logic unit

Registers are the functional units of digital devices designed for receiving, storing, transmitting and transforming information (Fig. 25, b).

To digital devices without memory include: decoders, encoders, multiplexers, demultiplexers, etc.

Decoder is called a device that produces a single signal at only one of its outputs, depending on the code of a binary number at its n inputs (Fig. 25, at).

Scrambler (fig. 25, r) performs the function opposite to the decoder.

Multiplexer is called a device for switching one of the information inputs to one of its outputs, depending on the binary code at its m address inputs (Fig. 25, d).

Demultiplexer performs the function opposite to the multiplexer.

Depending on the number of elements on one crystal, they talk about a different degree of IC integration. Large integrated circuit (LSI) contains several million elements on one chip (in one package) and performs the functions of complex devices. It is a functionally complete product.

LSI, which includes at least the main processor units: an arithmetic logic unit (Fig. 25, e), a command decoder and a control device, is called microprocessor... It may include other blocks that expand the capabilities of the microprocessor. The microprocessor is used for logical processing, storage and transformation of data. It is a universal semiconductor device in its capabilities and can be used in control systems for complex devices.

Questions on the topic

1. What does electronics study?

2. What devices are called electronic?

3. How do semiconductor materials differ from conductors and dielectrics?

4. How is the p-n-junction structured? What is the main property of the junction that allows the manufacture of semiconductor devices on its basis?

5. How does a diode work? What is its current-voltage characteristic?

6. How does a bipolar transistor work and how does it work?

7. How does a field effect transistor work? How is it different from a bipolar transistor?

8. What are the names and what are the outputs of the bipolar and field-effect transistors?

9. What is the voltage stabilization based on with a Zener diode? What parameters are characterized by zener diodes?

10. How to convert a sinusoidal voltage to DC?

11. How do diode rectifiers work?

12. How do electrical filters work?

13. How to get a stable constant voltage?

14. What are electrical signal amplifiers used for?

15. What is the principle of amplification of current and voltage?

16. What is the difference between amplifiers on transistors and amplifiers on integrated circuits?

17. What is an integrated circuit?

18. What elements are called logical functions? How do basic (basic) logic functions work? What operations do they perform?

19. What are digital devices with memory?

20. What are digital devices without memory?

21. What is a microprocessor? What is it used for?

Similar information.

Chapter thirteen. Two-electrode lamps and their application for AC rectification

13-1. Classification and application of electronic devices

Electronics studies the principle of operation, structure and application of electronic, ionic and semiconductor devices.

Electronic devices are called devices in which the phenomenon of current is associated with the movement of only electrons in the presence of a high vacuum in the devices, which excludes the possibility of collisions of electrons with gas atoms. This group of devices includes, for example, two- and three-electrode lamps, some photocells, cathode-ray tubes, etc.

Electronic devices are used in rectifiers, amplifiers, generators, high frequency receivers, as well as in automation, telemechanics, measuring and computer technology.

Ionic devices are called devices in which the phenomenon of current is due to the movement of electrons and ions obtained by ionizing gas or mercury vapor with electrons. These include gasotrons, thyratrons, mercury valves, etc.

Ionic devices differ from electronic ones by the significant inertia of the processes due to the huge mass of the ion in comparison with the mass of the electron, therefore, ionic devices are used in installations with a frequency not exceeding several kilohertz - in rectifiers of medium and high power in circuits automatic control mechanisms, etc.

Semiconductor devices are called devices in which current is created in a solid by the movement of electrons and "holes", and the properties of semiconductors are used.

In recent years, the use of semiconductor devices has sharply increased due to a number of their advantages over electronic and ionic devices. The main ones are: low energy consumption, small size, weight and cost, significant mechanical strength, long service life and ease of use. In a number of areas of radio engineering, power engineering, automation, telemechanics and computing technology semiconductor devices are successfully replacing electronic and ionic devices.

1. Definition of electronic devices. Classification of electronic devices

Electronic devices are devices whose operation is based on the use of electrical, thermal, optical and acoustic phenomena in a solid, liquid, vacuum, gas or plasma. The most common functions performed by electronic devices are to convert information signals or energy.

The main tasks of an electronic device as a converter of information signals are: amplification, generation, transmission, accumulation and storage of signals, as well as their isolation against the background of noise.

Electronic devices can be classified according to their purpose, physical properties, basic electrical parameters, structural and technological characteristics, the nature of the working environment, etc.

Depending on the type of signals and the method of information processing, all existing electronic devices are divided into electrical conversion, electrical light, photoelectric, thermoelectric, acoustoelectric and mechanoelectric.

By the type of working environment, the following classes of devices are distinguished: semiconductor, electrovacuum, gas-discharge, chemotronic (working medium - liquid). Depending on the functions performed and the purpose, electronic devices are divided into rectifying, amplifying, generator, switching, indicator, etc.

By frequency range - low-frequency, high-frequency, ultra-high frequency; in terms of power - low power, medium power and powerful.

2. Modes and parameters of electronic devices

The concept of the mode of an electronic device includes a set of conditions that determine its operation. Any mode is determined by a set of parameters. Distinguish between electrical, mechanical, climatic modes.

Each of these modes is characterized by its own parameters.

The optimal operating conditions of the device during operation, testing or measurements of its parameters are determined by the nominal mode. Limiting parameters characterize the maximum permissible operating modes. These include the maximum allowable voltage values \u200b\u200bon the electrodes of the device, the maximum allowable power dissipated by the device, etc. There are static and dynamic modes. If the device operates at constant electrode voltages, this mode is called static. In this case, all parameters do not change over time. The operating mode of the device, in which the voltage on at least one of the electrodes changes over time, is called dynamic. In addition to the mode parameters, the parameters of the electronic device are distinguished (for example, the gain, internal resistance, interelectrode capacitances, etc.). The relationship between changes in currents and voltages on the electrodes in a static mode is described by static characteristics. The set of static characteristics at fixed values \u200b\u200bof the third parameter is called a family of characteristics.

3. Electrical conductivity of materials.

Semiconductors used in electronics have a single crystal lattice. Each atom of the crystal lattice is firmly held at the sites of the crystal lattice due to covalent bonds. In an ideal lattice, all electrons are bonded to their atoms, so this structure does not conduct electric current. However, small energetic influences can lead to the detachment of some electrons from their atoms, making them able to move around the crystal lattice. These electrons are called conduction electrons. The energy states of conduction electrons form a zone of values \u200b\u200b(levels) of energy, called the conduction band. The energy states of the valence electrons form the valence band. A forbidden band lies between the maximum energy level of the valence band W in and the minimum level of the conduction band W c. The band gap in W c determines the minimum energy required to release a valence electron, that is, the ionization energy of a semiconductor atom. The band gap for most semiconductors is 0.1 - 3 eV.

4. The concept of electrochemical potential (Fermi level).

The probability of finding a free electron in the energy state W is determined by the function

Donor doped semiconductors are called electronic semiconductors, or n-type semiconductors.

As the temperature rises, the Fermi level shifts to the middle of the band gap. In the case of a semiconductor with an acceptor impurity, electrons are minority charge carriers, holes are the majority carriers, and a semiconductor with an acceptor impurity is called a hole, or p-type semiconductor.

As the temperature rises, the Fermi level shifts to the middle of the band gap.

5. Intrinsic conductivity.

Intrinsic and impurity conductivity of semiconductors

1. Features of semiconductors

hole ". Only electrons are real particles ( e). Eelectron conductivity is due to the motion of free electrons. Hole conduction is caused by the motion of bound electrons, which pass from one atom to another, alternately replacing each other, which is equivalent to the movement of "holes" in the opposite direction. "Hole" is conventionally assigned a "+" charge. In pure semiconductors, the concentration of free electrons and “holes” are the same. Electron-hole conductivity - the conductivity caused by the formation of free charge carriers (electrons and “holes”), formed when covalent bonds are broken, is called own conductivity.

6. Impurity electrical conductivity of semiconductor materials.

Impurity conductivity - conductivity due to the formation of free charge carriers upon the introduction of impurities of a different valence (n) Donor admixture nimpurities\u003e nsemiconductor Arsenic in germanium napprox. \u003d 5; np / wire-to \u003d 4

Each impurity atom contributes a free electron

Semiconductors n - typewith donor admixture Major charge carriers electronsNon-primary carriers about - "Holes" Electronic conductivity Acceptor impurity n impurities< n полупроводник

Indium to Germanium napprox. \u003d 3; np / wire-k \u003d 4 Each impurity atom captures an electron from the main semiconductor, creating an additional hole.

7. Electrical transitions in semiconductor devices

An electrical transition is called a transition layer between regions of a solid with different types or conductivity values. The most commonly used electrical transition between n - and p-type semiconductors, called the electron-hole transition, or p-n - junction. Transitions between regions with the same type of electrical conductivity, but with different values \u200b\u200bof specific conductivity (n + -n; p + -p) are also used. The "+" sign marks an area with a higher concentration of impurities.

Metal-semiconductor transitions are widely used. Electrical junctions can be created both on the basis of semiconductors with the same band gap (homojunctions) and with different widths (heterojunctions).

Electrical junctions are used in almost all semiconductor devices. Physical processes in transitions underlie the action of most semiconductor devices.

Asymmetric p-n junctions are widely used, in which the concentration of impurities in the emitter is much higher than in the other.

area - base. In symmetric p-n junctions, the concentration of acceptors in the p-region is equal to the concentration of donors in the n-region.

8-9 Electron-hole transition in equilibrium state

Contact potential difference.

Equilibrium corresponds to zero external stress at the transition. Since the concentration of electrons in the n-region is much higher than in the p-region, and the concentration of holes in the p-region is higher than in the n-region. As a result, charges will diffuse from a region with a higher concentration to a region with a lower concentration, which will lead to the appearance of a diffusion current of electrons and holes.

At the border of the p - and n-regions, a layer depleted in mobile carriers is created. An uncompensated charge of positive ions appears in the n-type near-contact region, and an uncompensated charge of negative impurity ions appears in the hole region. Thus, the electronic semiconductor is charged positively, and the hole semiconductor - negatively.

An electric field of intensity E arises between the regions of a semiconductor with different types of electrical conductivity. The resulting double layer of electrical charges is called locking, it is depleted in basic carriers and, as a result, has a low electrical conductivity.

The field strength vector is directed in such a way that it prevents the diffusion motion of the majority carriers and accelerates the minority carriers. This field corresponds to the contact potential difference ϕ k associated with the mutual diffusion of carriers. Outside the pn junction, the semiconductor regions remain neutral. The movement of minority carriers forms a drift current directed towards the diffusion current. So, under equilibrium conditions, the counter drift and diffusion currents should be equal, i.e.

Then the expression for the contact potential difference ϕ k in the p-n-junction

10. Electron-hole transition in a nonequilibrium state

If a voltage source is connected to the p-n-junction, the equilibrium state will be violated, and current will flow in the circuit. Distinguish between direct and reverse inclusion of a p-n-junction.

10.Direct Power On... Let the external stress be applied by the plus to the p-region, and by the minus to the n-region. Moreover, it is opposite in sign of the contact potential difference. Since the concentration of mobile carriers in the p-n-junction is much lower than in the p - and n-regions, the resistance of the p-n-junction is much higher than the resistance of the p - and n-regions. It can be assumed that the applied voltage drops completely at the junction. The majority carriers will move towards the contact, reducing the deficit of carriers in the pn junction and decreasing the resistance and thickness of the pn junction. The flow of primary media through the contact will increase. The current flowing through the junction, in this case, is called direct, and the voltage applied to the junction is called forward voltage. The diffusion of holes through the junction leads to an increase in the hole concentration behind the junction. The resulting concentration gradient of holes causes their diffusion penetration deep into the n-region, where they are minority carriers. This phenomenon is called injection (injection). Hole injection does not violate electrical neutrality in the n-region, since it is accompanied by the arrival of the same number of electrons from the external circuit.

11. Reverse inclusion.

If an external voltage is applied with a plus to the n-region, and a minus to the p-region, then it coincides in sign with the contact potential difference.In this case, the voltage at the junction increases, and the height of the potential barrier becomes higher than in the absence of voltage.

The direction of the resulting current is opposite to the direction of the forward current, so it is called reverse current, and the voltage causing the reverse current is called reverse voltage. The field in the transition is accelerating only for minority carriers. Under the action of this field, the concentration of minority carriers at the transition boundary decreases and a gradient of the concentration of charge carriers appears. This phenomenon is called carrier extraction.

Since the number of minority carriers is small, the extraction current through the junction is much less than the forward current. It is practically independent of the applied voltage and is the saturation current.

Thus, the pn junction has asymmetric conductivity: the conductivity in the forward direction significantly exceeds the conductivity of the pn junction in the opposite direction, which has found wide application in the manufacture of semiconductor devices.

12. Current-voltage characteristic of the p-n-junction

The current-voltage characteristic of the p-n-junction is the dependence of the current through the p-n-junction on the magnitude and polarity of the applied voltage.

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13. Properties of p-n-junction

At large negative voltages in p-n-transition, a sharp increase in the reverse current is observed. This phenomenon is called breakdown. p-n-transition. Breakdown of the transition occurs at a sufficiently strong electric field, when minority charge carriers are accelerated so much that they ionize semiconductor atoms. During ionization, electrons and holes are created, which, while accelerating, again ionize atoms, etc., as a result of which the diffusion current through the junction increases sharply, and on the current-voltage characteristic p-n-transition in the region of large negative voltages, a jump in the reverse current is observed. It should be noted that after breakdown, the junction fails only when irreversible changes in its structure occur in the case of excessive overheating, which is observed during thermal breakdown. If the power allocated to p-n- transition is maintained at an acceptable level, it remains operational even after a breakdown. Such breakdown is called electrical (recoverable) breakdown.
276 "align \u003d" left "\u003e

Most semiconductor diodes are based on single-ended p-n junctions. As structural elements of diodes, p-i-, n-i-junctions, metal-semiconductor junctions, p + -p-, p + -n-junctions, heterojunctions are also used. Diodes with p ‑ i ‑ n‑, p + -p-n - and n + -n-p-structures are also produced. The entire electrically junction structure is enclosed in a metal, glass, ceramic or plastic body to eliminate environmental influences. Semiconductor diodes are manufactured in both discrete and integral versions. The main element of a semiconductor diode is p-n-junction, so the current-voltage characteristic of a real diode is close to the current-voltage characteristic p-n-junction shown in Figure 3.3, d. The parameters and operating mode of the diode are determined by its current-voltage characteristic, illustrating the dependence of the current flowing through the diode I on applied voltage U... The typical current-voltage characteristic of the device is shown in the figure.

504 "height \u003d" 390 "align \u003d" center "\u003e

Figure: 2. Graphic designations of semiconductor diodes.

1 - general designation (rectifier, pulse, high-frequency diode); 2 - zener diode; 3 - two-anode zener diode; 4 - tunnel diode; 5 - inverted diode; 6 - varicap; 7 - LED; 8 - photodiode

17. Rectifier diodes

Designed to convert alternating current with a frequency of 50 to 20,000 Hz into a pulsating current of one direction and are widely used in power supplies for electronic equipment for various purposes. Silicon is used as a semiconductor material for such diodes, less often germanium and gallium arsenide. The principle of operation of rectifier diodes is based on the valve property of the p-n-junction. They are divided into low, medium and high power diodes. Low power diodes are designed to rectify currents up to 300 mA, medium and high power - to rectify currents, respectively, from 300 mA to 10 A and from 10 to 1000 A. The advantages of silicon diodes: low reverse currents; the possibility of using more high temperatures environment and high reverse voltages. The advantage of germanium diodes is a low voltage drop of 0.3 - 0.6 V when a forward current flows (compared to 0.8 - 1.2 V for silicon diodes).

As rectifier diodes, planar, alloy, diffusion and epitaxial diodes are used, made on the basis of asymmetric pn junctions. The barrier capacity of the junction is large due to its large area and reaches tens of picofarads. Germanium diodes can be used at temperatures not exceeding 70 - 80 ° C, silicon diodes - up to 120 - 150 ° C, gallium arsenide - up to 150 ° C.

The maximum reverse voltage of low-power low-frequency rectifier diodes ranges from several tens to 1200 V. For higher voltages, the industry produces rectifier poles using a series connection of diodes. Reverse currents do not exceed 300 μA for germanium diodes and 10 μA for silicon ones.

Powerful (power) diodes differ in frequency properties and operate at frequencies ranging from tens of hertz to tens of kilohertz and are made mainly of silicon.

Operation at high currents and high reverse voltages is associated with the release of significant power in the pn junction. Therefore, in installations with diodes of medium and high power, coolers are used - radiators with air and liquid cooling. With air cooling, heat is removed by means of a radiator. In this case, cooling can be natural (due to air convection) or forced (using the blowing of the device body and radiator with a fan). With liquid cooling, a heat-removing fluid (water, antifreeze, transformer oil, synthetic dielectric fluids) is passed through special channels into the radiator.

The main parameters of rectifier diodes are:

maximum permissible forward current Ipr max;

forward voltage drop across the diode Upr (at Ipr max);

maximum allowable reverse voltage Urev max;

reverse current at a given reverse voltage Iobr (at Uobr max);

operating temperature range of the environment;

rectification coefficient Kv;

limiting frequency of rectification, corresponding to a decrease in the rectification factor by 2 times.

18. Zener Diodes

Semiconductor zener diodes are diodes designed to stabilize the voltage level in a circuit. The principle of operation of zener diodes is based on the use of the electrical type of breakdown of the pn junction with reverse bias.

On the reverse branch of the I - V characteristic, there is a section with a weak dependence of the voltage on the magnitude of the reverse current (a section with an electrical breakdown of the pn junction). Plane silicon diodes are used as zener diodes. The I - V characteristic of the zener diode is shown in Fig. 5. The magnitude of the reverse voltage at which electrical breakdown begins to develop depends largely on the resistivity of the starting material, which is determined by the impurity concentration.

At a voltage less than 6 V, tunnel breakdown prevails in the pn junction of the diode. In the range from 6 to 12 V, both types of electrical breakdown are observed - tunneling and avalanche, and above 12 V avalanche breakdown prevails. With a change in temperature, the stabilization voltage Ust changes. Low and high voltage zener diodes have opposite stabilization voltage changes with increasing temperature. With a tunnel breakdown, Ust decreases with increasing temperature, and with an avalanche breakdown, it increases. For voltages from 6 to 12 V, the effect of temperature is insignificant, since both types of breakdown exist in the junction.

The main parameters of the zener diode are:

stabilization voltage Ust - voltage drop across the zener diode when a given stabilization current flows;

minimum Ict min and maximum Ict max zener diode currents;

temperature coefficient of stabilization voltage

;

Semiconductor diodes used to stabilize voltages less than 1 V using the forward branch of the I - V characteristic are called stabilizers.

19. Varikapi

Varicaps use the dependence of the barrier capacitance of the pn junction on the reverse voltage. They are divided into trimmers, or varicaps, and multipliers, or varactors. Varicaps are used to change the resonant frequency of vibrating systems. Varactors are used to multiply frequency.

The main special parameters of varicaps are:

rated capacity Sv, measured at a given reverse voltage Urev;

capacitance overlap coefficient https://pandia.ru/text/78/661/images/image028_13.gif "width \u003d" 79 "height \u003d" 52 "\u003e is the ratio of the reactance of the varicap at a given frequency of the alternating signal to the loss resistance;

temperature coefficient of capacitance - the ratio of the relative change in capacitance to the absolute change in the ambient temperature that caused it.

In addition to the considered diodes, tunnel diodes, Gunn diodes, avalanche-transit diodes, successfully operating in the microwave range (0.3 ... 300 GHz), as well as photo and emitting diodes used in photoelectric and optoelectronic devices and as indicator devices, are produced.

20. Pulse diodes

Designed to work in digital and other devices of impulse technology. They are designated in the same way as rectifiers, have a short duration of transient processes. They differ from rectifier diodes in small capacities of the p-n-junction (fractions of picofarads) and a number of parameters that determine the transient characteristics of the diode. A decrease in capacities is achieved by reducing the area of \u200b\u200bthe p-n-junction, therefore, their allowable dissipation powers are low (30 - 40 mW).

The operation of pulse diodes is influenced by the effects of accumulation and resorption of charge carriers. When the diode is exposed to short-term pulses, the inertia of the processes of resorption of carriers and overcharge of its capacitance begins to affect. The time to establish the resistance of the directly connected p-n-junction of the diode tust is determined by the injection of charge carriers, their diffusional movement into the depth of the base, which reduces the volume resistance of the diode base to its stationary state. After the end of the rectangular pulse, when the p-n junction is turned back on, the reverse current initially sharply increases due to the intense resorption of nonequilibrium carriers with its subsequent exponential decrease to the stationary value of the thermal current I0.

, where vdr and vrec are the rates of drift and recombination of carriers in the structure, which determine the rate of absorption of carriers, W is the length of the diode structure between its terminals. The carrier drift velocity depends on the field strength, is relatively small and has its own limit vsat. To decrease tbos, it is necessary to reduce the volume of the semiconductor structure and increase the recombination rate of minority carriers, which is achieved by the technology of manufacturing pulsed diodes: introducing neutral impurities, most often gold (Au) into the initial material, to create so-called "traps" - recombination centers. The parameters of the pulse diodes are the same as for the high-frequency diodes. In addition, specific parameters are added to them:

ü total capacity of the diode SD (tenths of a picofarad unit);

ü maximum impulse forward voltage Upr max and;

o maximum allowable impulse current Ipr max and;

ü the time to establish the forward voltage tust - the time interval from the moment the forward current pulse is applied to the diode until the specified forward voltage is reached (fractions of nanoseconds fractions of microseconds);

ü diode reverse recovery time tvos - the time of switching the diode from a given forward current to a given reverse voltage from the moment the current passes through zero until the reverse current reaches a given value (fractions of nanoseconds ¼ fractions of microseconds).

To reduce tvos, special types of pulse diodes are used: diodes with a Schottky barrier (DBSh), diodes with a charge accumulation (DNZ). In the SDS, the junction is made on the basis of a rectifying metal-semiconductor contact, in which the work function from the metal is greater than the work function from the semiconductor. These diodes do not waste time on the accumulation and resorption of charges in the base, their speed depends only on the speed of the process of recharging the barrier capacitance. Structurally, SDBs are made in the form of a low-resistance silicon plate, on which a high-resistance epitaxial film with electrical conductivity of the same type is applied. A metal layer is applied to the film surface by vacuum deposition. The inertia of the LBS is mainly determined by the capacity of the rectifying contact, which can be less than 0.01 pF.

DNZ - used to form short rectangular pulses. This is achieved by uneven doping of the diode area. For the manufacture of such diodes, mesa and epitaxial technology are used.

21. Diodes with charge storage (DNZ).

In DNZ, the base is made unevenly alloyed along its length. In such diodes, the concentration of impurities in the base decreases when approaching the p-n junction; therefore, the concentration of the majority carriers of the base, electrons, is also nonuniform if the base has n-type conductivity. Due to this, electrons diffuse towards the p-n-junction, leaving in the depth of the base an excess positive charge of donor atoms.

impurity, and near the transition there is an excess charge of electrons. An electric field arises between these charges, directed towards the transition. Under the action of this field, holes injected into the base during direct switching on of the diode are concentrated (accumulated) in the base at the junction boundary. When the diode is switched from forward to reverse direction, these holes under the action of the field inside the junction quickly leave the base to the emitter, and the recovery time of the reverse resistance decreases.

For the manufacture of such diodes, mesa and epitaxial technology are used.

22. Diodes with a Schottky barrier.

diode reverse recovery time tvos - the time of diode switching from a given forward current to a given reverse voltage from the moment the current passes through zero until the reverse current reaches a given value (fractions of nanoseconds… fractions of microseconds). To reduce tvos, special types of pulse diodes are used: diodes with a Schottky barrier (DBSh), diodes with charge storage (DCC). In the SDS, the junction is made on the basis of a rectifying metal-semiconductor contact, in which the work function from the metal is greater than the work function from the semiconductor. These diodes do not spend time on the accumulation and resorption of charges in the base, their speed depends only on the speed of the process of recharging the barrier capacitance. Structurally, SDBs are made in the form of a low-resistance silicon plate, on which a high-resistance epitaxial film with electrical conductivity of the same type is applied. A metal layer is applied to the film surface by vacuum deposition. The inertia of the LBS is mainly determined by the capacity of the rectifying contact, which can be less than 0.01 pF.

23 Tunnel and inverted diodes

The principle of operation of a tunneling diode (TD) is based on the phenomenon of the tunneling effect in a pn junction formed by degenerate semiconductors. This leads to the appearance on the current-voltage characteristic of a section with a negative differential resistance at forward voltage. It is known that a particle with insufficient energy to overcome a potential barrier can pass through it if there is a free energy level on the other side of this barrier, which it occupied in front of the barrier. This phenomenon is called the tunnel effect. The narrower the potential barrier and the lower its height, the greater the probability of a tunnel junction. The tunnel crossing takes place without energy consumption. The current-voltage characteristic of the tunnel diode is shown in Fig. 2.26, a.

2.17. Tunnel diode parameters

Peak current I p (from hundreds of microamperes - up to hundreds of milliamperes).

Peak voltage U p - forward voltage corresponding to current p I.

The current of the depression I in, corresponding to the voltage U in.

The trough voltage is the forward voltage corresponding to the current in I. The solution voltage U p is the forward voltage corresponding to the typical current on the second ascending branch of the I – V characteristic determines the possible voltage jump across the load when the tunnel diode is operating in the switching circuit.

24. A variety of tunnel diodes are inverted diodes, manufactured on the basis of a semiconductor with impurity concentrations in the p - and n - regions of the diode, less than in tunneling ones, but larger than in conventional rectifier diodes.

The current-voltage characteristic of the inverted diode is shown in Fig. 2.28.

The forward branch of the I - V characteristic of a reversed diode is similar to the forward branch of a conventional rectifier diode, and the reverse branch is analogous to the reverse branch of the I - V characteristic of a tunnel diode, since at reverse voltages, electrons tunnel from the valence band of the p-region to the conduction band of the n-region and at low reverse voltages (tens of millivolts) reverse currents are large. Thus, inverted diodes have a rectifying effect, but the conducting direction in them corresponds to the reverse connection, and the blocking direction corresponds to the direct connection. Due to this, they can be used in microwave detectors and mixers as switches.

Back in the 19th century, a number of physical phenomena were discovered, the nature of which is due to the interaction of free electrons with an electromagnetic field and matter. Such phenomena are called electromagnetic. These include:

- emission of electrons by a heated body - thermionic emission;

- the emission of electrons by a substance under the influence of photons (photoelectric effect);

- emission of photons by a substance under the influence of electrons (luminescence);

- dependence of the electronic conductivity of a circuit consisting of heated and unheated electrodes, separated by a vacuum gap, on the direction of the current;

- ionization of a rarefied gas during the passage of a stream of rapidly moving electrons, accompanied by a sharp increase in the electrical conductivity of the medium;

- the presence of two types of semiconductor conductivity (electron and hole), depending on the predominance of one or another type of charge carriers (electrons or holes);

The listed and many other electronic phenomena are well studied and have practical application. Devices whose principle of operation is based on physical phenomena associated with the movement of electrically charged particles in a vacuum, gas or in a solid are called electronic. The field of science and technology, which deals with the study and development of electronic devices and devices, is called electronics.

The most common classification feature is the working environment in which the main physical processes take place in the device. Thus, a distinction is made between electrovacuum, ionic (gas-discharge) and semiconductor devices.

In electrovacuum devices, the working space is isolated from the environment by a gas-tight shell - a cylinder. Electrical processes in these devices take place in a highly rarefied gas environment with a pressure of about 10-6 mm Hg. Art. Electrovacuum devices include electronic lamps, electron-beam, photoelectronic and microwave devices.

Ionic (gas-discharge) devices are called devices, the cylinders of which are filled with inert gases (argon, neon, krypton, etc.), their mixture, hydrogen or mercury vapor. The gas pressure in the cylinder is not great: 10-10-5 mm Hg. Art. Filling the devices with gas allows a much higher current to pass through them than is possible in an electric vacuum device with the same power consumption, which is explained by the low internal resistance of the device, and, consequently, by a small voltage drop between the anode and cathode.

The design and purpose of ionic devices are very diverse. Most of their types are used for rectifying alternating current (gasotrons, ignitrons, thyristors, mercury valves, etc.). They are also used to stabilize constant voltages (zener diodes), as electronic relays, switching devices (ion dischargers).

The most common functions performed by electronic devices are to convert information signals or energy.

The very name "electronic devices" indicates that all processes of conversion of signals and energy occur either due to the movement of electrons, or with their direct participation. The main tasks of an electronic device as a converter of information signals are: amplification, generation, transmission, accumulation and storage of signals, as well as their isolation against the background of noise.

Electronic devices can be classified according to their purpose, physical properties, basic electrical parameters, structural and technological characteristics, the nature of the working environment, etc.

Depending on the type of signals and the method of information processing, all existing electronic devices are divided into electrical conversion, electrical light, photoelectric, thermoelectric, acoustoelectric and mechanoelectric.

Electrical converting devices represent the largest

group of electronic devices. These include various types of diodes and transistors, thyristors, gas-discharge, vacuum devices.

Electric light includes LEDs, fluorescent capacitors, lasers, cathode-ray tubes.

Photovoltaic - photodiodes, phototransistors, photothyristors, solar batteries.

Thermoelectric - semiconductor diodes, transistors, thermistors.

Acoustoelectric amplifiers, generators, filters, delay lines on surface acoustic waves belong to acoustic devices. Recently, at the junction of electronics and optics, a new field of technology has been formed - optoelectronics, which attracts the methods of electronics and optics to solve problems of formation, storage and processing of signals.

Depending on the functions performed and the purpose, electronic devices are divided into rectifying, amplifying, generator, switching, indicator, etc.

By frequency range - low-frequency, high-frequency, ultra-high frequency; in terms of power - low power, medium power and powerful.

The concept of the mode of an electronic device includes a set of conditions that determine its operation. Any mode is determined by a set of parameters. Distinguish between electrical, mechanical, climatic modes. Each of these modes is characterized by its own parameters. The optimal operating conditions of the device during operation, testing or measurements of its parameters are determined by the nominal mode.

Limiting parameters characterize the maximum permissible operating modes. These include the maximum allowable voltage on the electrodes of the device, the maximum allowable power dissipated by the device, etc. Distinguish between static and dynamic modes. If the device operates at constant electrode voltages, this mode is called static. In this case, all parameters do not change over time. The operating mode of the device, in which the voltage on at least one of the electrodes changes over time, is called dynamic.

In addition to the parameters of the mode, the parameters of the electronic device are distinguished (for example, the gain, internal resistance, interelectrode capacities, etc.). The relationship between changes in currents and voltages on the electrodes in a static mode is described by static characteristics. The set of static characteristics at fixed values \u200b\u200bof the third parameter is called a family of characteristics.

Topic 2. Physical phenomena of semiconductor electronics

Semiconductors in physics are usually called materials with resistivity r \u003d 10 3 - 10 9 Ohm × cm, in contrast to conductors (metals), which have r< 10 4 Ом×см, и диэлектриков - материалов с r >10 10 Ohm × cm.

Semiconductors have owneh electrical conductivity,which is called impurity when making impurities.By introducing various impurities, it is possible to form semiconductors with desired properties.

The operation of most semiconductor devices and active elements of integrated circuits is based on the use of electrical junctions, the common property of which is the presence of a potential barrier at the interface between semiconductors. Semiconductors can differ in the type of conductivity (p or n), or have different physical characteristics, for example:

Electrical transition - a transition layer in a semiconductor material between two regions with different types of electrical conductivity or different values \u200b\u200bof electrical conductivity (one of the regions can be a metal).

Depending on the functional purpose, the level of the required electrical parameters in the diodes, the following types of rectifying and ohmic electrical junctions are used.

Straightening transition - electrical junction, the electrical resistance of which in one direction of the current is greater than in the other.

Ohmic transition - electrical junction, the electrical resistance of which does not depend on the direction of the current in a given range of current values.

Electron-hole junction (p-n-junction) Is an electrical transition between two regions of a semiconductor, one of which has n-type conductivity, and the other p-type.

Heterogeneous transition (heterojunction) Is an electrical junction formed as a result of the contact of semiconductors with different bandgap widths.

Homogeneous transition (homojunction) Is an electrical junction formed as a result of the contact of semiconductors with the same band gap.

Schottky transition - an electrical junction formed by contact between a metal and a semiconductor.

Electronic-electronic transition (n-n + -junction) Is an electrical transition between two regions of an n-type semiconductor with different values \u200b\u200bof electrical conductivity.

Hole-hole junction (p-p + -junction) Is an electrical transition between two regions of a p-type semiconductor with different values \u200b\u200bof electrical conductivity. The "+" sign conventionally denotes an area with a higher electrical conductivity

The formation of an electron-hole junction occurs upon contact of semiconductors without applying an external voltage. The impurity conduction atoms located along the interfaces are rigidly bound to the crystal lattice and are immobile.

As a result, the diffusion current between the regions, which is formed at the moment of contact, will transfer electrons from the outer electron shells of atoms in the region n to the unfilled outer shells of impurity atoms in the region p type. This process can be considered as instantaneous ionization of all boundary impurity atoms on both sides of the interface, which will lead to the formation of two boundary charged layers of opposite sign with respect to impurity conductivity in each of the regions.

These two boundary layers form the region of e electron-hole junction,depleted in basic carriers. The field formed by the pn junction is directed against the main field formed by the initial p - and n - conductivity atoms, which causes the formation of a drift current of holes and electrons directed opposite to the initial diffusion current. An equilibrium state arises, which is characterized by a certain value of the field E, the width of the pn junction w, the capacitance C and the contact potential difference φc.

Such transitions can be symmetrical or asymmetrical. In symmetric transitions, the semiconductor regions have the same impurity concentration, and in asymmetric transitions, they differ (the impurity concentrations differ by several orders of magnitude - thousands and tens of thousands of times).

The boundaries of the transitions can be smooth or sharp, and with smooth transitions it is technologically difficult to provide high-quality valve properties that are necessary for the normal operation of diodes and transistors, therefore, the sharpness of the boundary plays an essential role; in a sharp transition, the concentration of impurities at the interface of the regions change at a distance commensurate with the diffusion length L.

When an external voltage is applied, three states are characteristic of the electron-hole p-n junction: equilibrium; forward biased); reverse biased).

Equilibrium state of the pn junction considered in the absence of voltage at the external terminals. In this case, the potential barrier arising at the boundary of the two regions prevents the uniform distribution of carriers over the entire volume of the semiconductor. Only those main carriers are able to overcome this barrier, which have enough energy and they form through the transition diffusion current I diff. In addition, in each region there are minority carriers, for which the field of the pn junction will be accelerating, these carriers form through the transition

drift current I dr, which is more often called thermal or saturation current I 0. The total current through the equilibrium p-n-junction will be equal to zero: Free movement of carriers through the electron-hole junction is possible when the potential barrier of the p-n junction is lowered. When this happens injectioncharge carriers, i.e. their transition from the emitter region to the base region to another under the action of an external voltage. The emitter region is doped with impurity atoms much more strongly than the base. Due to the different concentrations of impurity atoms in asymmetric transitions, one-way injection takes place: the carrier flux from the region with a low concentration of impurity atoms (from the base) is very weak and can be neglected.

With direct polarity of the external source the equilibrium state of the transition is violated, since the field of this source, superimposed on the field of the pn-junction, weakens it, the forbidden zone of the transition decreases, the potential barrier decreases, the resistance of the transition decreases sharply, the diffusion component of the current increases by a factor of "e u / jt" and is a function of the applied voltage

where j t \u003d kT / q - temperature potential (at room temperature j t \u003d 0.025V);

k is the Boltzmann constant;

T is the temperature;

q is the electron charge.

Current component I about in an idealized junction when exposed to a direct external voltage remains practically unchanged. Therefore, the direct net current through an ideal pn junction

(2.2.)

and finally

(2.3)

Equation (2.1) of an ideal pn junction determines the main volt-ampere characteristics of semiconductor devices.

When plotting the I - V characteristic of the junction according to (2.1), it can be seen that for an ideal pn junction at voltages greater than zero, the mode of a given forward current, and not voltage, is characteristic. For a real I – V characteristic, taking into account the ohmic voltage drop in the base layer, the external voltage is distributed between the pn junction and the base layer (the base resistance r b with a small junction area can be tens of Ohms), therefore, equation (1.1) describing the static I – V characteristic (Fig. 2.1 ) of a real transition can be written as follows:

(2.4)

When the polarity of the external source is reversed, the polarity of the external voltage source coincides with the polarity of the contact potential difference, the potential barrier of the p-n-junction increases, and the transition gap expands. At low values \u200b\u200bof the reverse voltage through the p-n-junction, the motion of the majority carriers will also be observed, forming a current opposite to the drift current:

(2.5)

The resulting current through the pn junction under the action of a reverse voltage

(2.6)

Equation (1.4) describes the reverse branch of the reverse-biased transition (Fig. 22.1).

At U arr greater than 3j t, the diffusion current through the junction stops. In this case, the minority carrier current continues to flow through the junction.

The ratio of forward and reverse current is called the rectification ratio.

K rec \u003d I pr / I arr \u003d exp U / j t, (2.7)

Obviously, K recp has a very large value and characterizes the rectifying properties of the pn junction

The reverse current is generally called the thermogeneration current and has a large value; while the thermal current at room temperature is not taken into account at all (in the Si p-n junction), since it is 2-3 orders of magnitude less than the reverse current. The thermal current of germanium junctions is 6 orders of magnitude higher than that of silicon junctions; therefore, this current cannot be neglected in germanium structures.

In a real junction, a significant dependence of the minority carrier current on the applied voltage is observed. Under the action of a reverse voltage, when the forbidden band expands, the transition region is greatly depleted in carriers, while the recombination process slows down and the generation process turns out to be unbalanced. The excess of generated carriers is captured by the electric field and transferred to neutral layers (electrons to the n-region, and holes - to the p-region). These streams form the thermogeneration current. This current is weakly temperature dependent and highly dependent on the magnitude of the applied reverse voltage; it is appropriate to recall the simplified formula for the dependence of the speed of motion of an electron in an accelerating electric field on the applied voltage

(2.8)

With an increase in the applied voltage, the electron velocity increases, the number of its collisions with atoms in the lattice sites (impact ionization) increases, which leads to the appearance of new charge carriers. An increase in the number of charges leads to an increase in the current of minority carriers, the transition temperature increases, and this, in turn, leads to disruption of covalent bonds and growth of carriers. The process can take on an avalanche-like nature and lead to a breakdown of the p-n-junction (Fig. 1.1). The following types of breakdowns are distinguished:

tunnel (with a transition field strength over 10 6 V / cm, up to point "a");

electric (caused by impact ionization, after point "a"), this type of breakdown is sometimes called avalanche, while reversible processes take place in the transition and after removing the reverse voltage, it restores its working properties. With an electrical breakdown, an increase in current almost does not cause a voltage change, which made it possible to use this characteristic feature for voltage stabilization;

thermal arises as a result of strong heating of the transition (after point "b"); the processes that take place in the junction are irreversible, and the working properties of the junction are not restored after the voltage is removed (this is why the reverse voltage at the junctions of diodes and transistors is strictly limited in the reference literature).

Figure: 2.1. I - V characteristic of a real electron-hole p-n junction

Analyzing the forward and reverse branches of the current-voltage characteristic, we come to the conclusion that the pn-junction conducts current well in the forward-biased state and very poorly in the reverse-biased state, therefore, the pn-junction has gate properties and can be used to convert an alternating voltage to a constant voltage, for example, in rectifying devices in power supplies.