SAWTOOL VOLTAGE GENERATOR- generator of linearly changing voltage (current), electronic device, forming a periodic fluctuations in voltage (current) of a sawtooth shape. Main The purpose of H. p. n. is to control the time sweep of the beam in devices using cathode ray tubes. G. p. n. also used in devices for comparing voltages, time delay and pulse expansion. To obtain a sawtooth voltage, the process of charging (discharging) a capacitor in a circuit with a large time constant is used. The simplest G. p. (Fig. 1, a) consists of integrating circuit RC and a transistor that performs the functions of a key controlled periodically. impulses. In the absence of pulses, the transistor is saturated (open) and has a low resistance of the collector-emitter section, capacitor FROM discharged (Fig. 1, b). When a switching pulse is applied, the transistor turns off and the capacitor is charged from a power source with a voltage of - E to- direct (working) course. Output voltage G. p. n., removed from the condenser FROM, changes according to the law. At the end of the switching pulse, the transistor opens and the capacitor FROM quickly discharges (reverse) through a low resistance emitter - collector. Main characteristics G. p. n.: sawtooth voltage amplitude, coefficient. nonlinearity and coefficient. using the power supply voltage. When in this scheme

Forward run time T p and the frequency of the sawtooth voltage are determined by the duration and frequency of the switching pulses.

The disadvantage of the simplest G. p. is small k E at small. The required values ​​of e lie in the range of 0.0140.1, with the smallest values ​​related to the comparison and delay devices. The non-linearity of the sawtooth voltage during the forward stroke occurs due to the decrease in the charging current due to the decrease in the voltage difference . An approximate constancy of the charging current is achieved by including a non-linear current-stabilizing two-terminal device (containing a transistor or a vacuum tube) in the charge circuit. In such G. p. and . In G. p. with positive voltage feedback, the output sawtooth voltage is fed into the charging circuit as a compensating emf. In this case, the charging current is almost constant, which provides the values ​​\u200b\u200b1 and \u003d 0.0140.02. G. p. n. used for scanning in cathode ray tubes with e-magn. beam deflection. To obtain a linear deviation, a linear change in current in the deflection coils is necessary. For a simplified equivalent coil circuit (Fig. 2, a), the current linearity condition is satisfied when a trapezoidal voltage is applied to the coil terminals. Such a trapezoidal stress (Fig. 2, b) can be obtained in G. p. when included in the charging circuit will add. resistance R e (shown in Fig. 1, a dotted line). The deflecting coils consume high currents, so the trapezoidal voltage generator is supplemented with a power amplifier.

The generator is a self-oscillatory system that generates impulses electric current, in which the transistor plays the role of a switching element. Initially, since the invention, the transistor was positioned as an amplifying element. The presentation of the first transistor took place in 1947. The presentation of the field-effect transistor took place a little later - in 1953. In pulse generators, it plays the role of a switch and only in generators alternating current it implements its amplifying properties while simultaneously participating in the creation of positive feedback to support the oscillatory process.

A visual illustration of the division of the frequency range

Classification

Transistor generators have several classifications:

• by the frequency range of the output signal;
• by type of output signal;
• according to the principle of action.

The frequency range is a subjective value, but for standardization the following division of the frequency range is accepted:

• 30 Hz to 300 kHz – low frequency(LF);
• from 300 kHz to 3 MHz - middle frequency (MF);
• 3 MHz to 300 MHz - high frequency (HF);
• above 300 MHz - ultra high frequency (SHF).

This is the division of the frequency range in the field of radio waves. There is an audio frequency range (AF) - from 16 Hz to 22 kHz. Thus, wanting to emphasize the frequency range of the generator, it is called, for example, a high-frequency or low-frequency generator. The frequencies of the sound range, in turn, are also divided into HF, MF and LF.

According to the type of output signal, generators can be:

• sinusoidal - for generating sinusoidal signals;
• functional - for self-oscillation of signals of a special form. A special case is a rectangular pulse generator;
• noise generators - generators of a wide frequency spectrum, in which, in a given frequency range, the signal spectrum is uniform from the lower to the upper section frequency response.

According to the principle of operation of generators:

• RC generators;
• LC generators;
• Blocking generators - short pulse shaper.

Due to fundamental limitations, RC oscillators are usually used in the low and audio ranges, and LC oscillators in the HF frequency range.

Generator circuitry

RC and LC sine wave generators

The generator on a transistor is most simply implemented in a capacitive three-point circuit - the Kolpitz generator (Fig. below).

Transistor oscillator circuit (Colpitz generator)

In the Kolpitz circuit, elements (C1), (C2), (L) are frequency-setting. The remaining elements are a standard transistor piping to provide the necessary DC operation. The same simple circuitry has a generator assembled according to the inductive three-point circuit - the Hartley generator (Fig. below).

Diagram of a three-point generator with inductive coupling (Hartley generator)

In this circuit, the oscillator frequency is determined by a parallel circuit, which includes elements (C), (La), (Lb). Capacitor (C) is needed to form a positive feedback on the alternating current.

The practical implementation of such a generator is more difficult, since it requires an inductor with a tap.

Both self-oscillation generators are mainly used in the MF and HF ranges as carrier frequency generators, in frequency-setting local oscillator circuits, and so on. Radio regenerators are also based on oscillators. This application requires high frequency stability, so the circuit is almost always supplemented with a quartz oscillation resonator.

The master current generator based on a quartz resonator has self-oscillations with a very high accuracy in setting the frequency value of the RF generator. Billionths of a percent is far from the limit. Radio regenerators use only quartz frequency stabilization.

The operation of generators in the field of low-frequency current and audio frequency associated with the difficulties of implementing high values ​​of inductance. To be more precise, in the dimensions of the required inductor.

The Pierce oscillator circuit is a modification of the Kolpitz circuit, implemented without the use of inductance (Fig. below).

Pierce generator circuit without the use of inductance

In the Pierce scheme, the inductance is replaced by a quartz resonator, which made it possible to get rid of the laborious and bulky inductor and, at the same time, limited the upper oscillation range.

Capacitor (C3) does not pass the DC component of the base bias of the transistor to the quartz resonator. Such a generator can generate oscillations up to 25 MHz, including audio frequency.

The operation of all of the above generators is based on the resonant properties of an oscillatory system composed of capacitance and inductance. Accordingly, the oscillation frequency is determined by the values ​​of these elements.

RC current generators use the principle of phase shift in an RC circuit. The most commonly used circuit with a phase-shifting chain (Fig. below).

Schematic of an RC oscillator with a phase-shifting chain

Elements (R1), (R2), (C1), (C2), (C3) perform a phase shift to obtain the positive feedback necessary for the occurrence of self-oscillations. Generation occurs at frequencies for which the phase shift is optimal (180 deg). The phase-shifting circuit introduces a strong attenuation of the signal, therefore, such a circuit has increased requirements for the gain of the transistor. The Wien bridge circuit is less demanding on the parameters of the transistor (Fig. below).

Diagram of an RC generator with a Wien bridge

The Wien double T-bridge consists of elements (C1), (C2), (R3) and (R1), (R2), (C3) and is a narrow-band notch filter tuned to the generation frequency. For all other frequencies, the transistor is covered by a deep negative connection.

Functional current generators

Function generators are designed to generate a sequence of pulses of a certain shape (a certain function describes the shape - hence the name). The most common generators are rectangular (if the ratio of the pulse duration to the oscillation period is ½, then such a sequence is called a “meander”), triangular and sawtooth pulses. The simplest generator rectangular pulses- a multivibrator, served as the first scheme for beginner radio amateurs to assemble with their own hands (Fig. below).

Scheme of a multivibrator - a generator of rectangular pulses

A feature of the multivibrator is that almost any transistor can be used in it. The duration of the pulses and pauses between them is determined by the values ​​of the capacitors and resistors in the base circuits of the transistors (Rb1), Cb1) and (Rb2), (Cb2).

The frequency of current self-oscillation can vary from units of hertz to tens of kilohertz. RF self-oscillations on a multivibrator cannot be realized.

Triangular (sawtooth) pulse generators are usually built on the basis of rectangular pulse generators (master oscillator) by adding a corrective chain (Fig. below).

Triangular pulse generator circuit

The shape of the pulses, close to triangular, is determined by the charge-discharge voltage on the plates of the capacitor C.

Blocking generator

The purpose of blocking generators is to generate powerful current pulses with steep fronts and low duty cycle. The duration of the pauses between pulses is much longer than the duration of the pulses themselves. Blocking oscillators are used in pulse shapers, comparators, but the main area of ​​application is a horizontal scanning master generator in information display devices based on cathode ray tubes. Blocking generators are also successfully used in power conversion devices.

FET generators

A feature of field-effect transistors is a very high input resistance, the order of which is commensurate with the resistance electronic tubes. The circuit solutions listed above are universal, they are simply adapted for use various types active elements. Colpitz, Hartley and other generators made on a field-effect transistor differ only in the ratings of the elements.

Frequency-setting circuits have the same ratios. To generate high-frequency oscillations, a simple generator made on a field-effect transistor according to an inductive three-point circuit is somewhat preferable. The fact is that the field-effect transistor, having a high input resistance, practically does not have a shunting effect on the inductance, and, therefore, the high-frequency generator will work more stable.

Noise generators

A feature of noise generators is the uniformity of the frequency response in a certain range, that is, the amplitude of oscillations of all frequencies included in a given range is the same. Noise generators are used in measuring equipment to assess the frequency characteristics of the tested path. Audio range noise generators are often supplemented with a frequency response equalizer to adapt to subjective loudness to human hearing. Such noise is called "gray".

Video

Until now, there are several areas in which the use of transistors is difficult. These are powerful microwave range generators in radar, and where it is required to receive especially powerful high-frequency pulses. Not yet developed power transistors microwave range. In all other areas, the vast majority of generators are made exclusively on transistors. There are several reasons for this. First, the dimensions. Secondly, power consumption. Thirdly, reliability. On top of that, transistors, due to the peculiarities of their structure, are very easy to miniaturize.

Good day dear radio amateurs! I welcome you to the site ""

We assemble a signal generator - a functional generator. Part 1.

In this lesson Beginner radio schools we will continue to fill our radio laboratory with the necessary measuring instruments. Today we will start collecting function generator. This device is necessary in the practice of a radio amateur to set up various amateur radio circuits - amplifiers, digital devices, various filters and many other devices. For example, after we assemble this generator, we will take a short break during which we will make a simple light and music device. So, in order to properly adjust the frequency filters of the circuit, this device is just very useful to us.

Why is this device called a functional generator, and not just a generator (low frequency generator, high frequency generator). The device that we will make generates three different signals at its outputs at once: sinusoidal, rectangular and sawtooth. As a basis for the design, we will take the scheme of S. Andreev, which is published on the website in the section: Circuits - Generators.

To begin with, we need to carefully study the circuit, understand the principle of its operation and collect the necessary details. Thanks to the use of a specialized microcircuit in the circuit ICL8038 which is just designed to build a function generator, the design is quite simple.

Of course, the price of a product depends on the manufacturer, on the capabilities of the store, and on many other factors, but in this case we are pursuing one goal: to find the necessary radio component that would be of acceptable quality and, most importantly, affordable. You probably noticed that the price of a microcircuit is highly dependent on its marking (AC, BC and SS). The cheaper the chip, the worse its characteristics. I would recommend opting for the “BC” chip. Her characteristics are not very different from the “AC”, but much better than that of the “SS”. But in principle, of course, this microcircuit will also work.

We assemble a simple function generator for the laboratory of a beginner radio amateur

Good day to you dear radio amateurs! Today we will continue to collect our function generator. So that you do not jump through the pages of the site, I post it again circuit diagram function generator, the assembly of which we are engaged in:

I also post the datasheet technical description) chips ICL8038 and KR140UD806:

(151.5 KiB, 6,245 hits)

(130.7 KiB, 3,611 hits)

I have already collected the necessary parts to assemble the generator (I had some of them - constant resistances and polar capacitors, the rest were bought at a radio parts store):

The most expensive parts were the ICL8038 chip - 145 rubles and switches for 5 and 3 positions - 150 rubles. In total, this scheme will have to spend about 500 rubles. As you can see in the photo, the five-position switch is two-section (there was no one-section), but this is not scary, more is better than less, especially since the second section may come in handy for us. By the way, these switches are exactly the same, and the number of positions is determined by a special stopper, which can be set to the desired number of positions yourself. In the photo I have two output connectors, although in theory there should be three: common, 1:1 and 1:10. But you can put a small switch (one output, two inputs) and switch the desired output to one connector. In addition, I want to pay attention to the constant resistor R6. There is no rating of 7.72 MΩ in the line of megaohm resistances, the nearest rating is 7.5 MΩ. In order to get the desired value, you will have to use a second 220 kOhm resistor, connecting them in series.

I also want to draw your attention to the fact that we will not finish the assembly and adjustment of this circuit to assemble the functional generator. For comfortable work with the generator, we must know what frequency is generated in this moment work, or we may need to set a certain frequency. In order not to use additional devices for these purposes, we will equip our generator with a simple frequency meter.

In the second part of the lesson, we will study another method of manufacturing printed circuit boards - the LUT method (laser ironing). We will create the board itself in the popular amateur radio program for creating printed circuit boards – SPRINT LAYOUT.

How to work with this program, I will not explain to you yet. In the next lesson, in a video file, I will show you how to create our printed circuit board in this program, as well as the entire process of manufacturing the board using the LUT method.

An electronic generator is a device for the formation of undamped electrical oscillations of various shapes, frequencies and powers. Very often, generators are made on the basis of an op-amp.

multivibrator

multivibrator called a voltage generator with a shape close to rectangular. Its name reflects the fact that such a voltage, when expanded in a Fourier series, is represented by a series containing many higher harmonics (multi - a lot of).

According to the characteristics of the OS (see Fig. 2.13, b) it can be seen that the output voltage of the amplifier linearly depends on the input voltage only in a very narrow range - hundreds of microvolts. If the input voltage is outside this range, then the output signal can only take on two values: +UВЬ1Х (≈ +12 V) and -UВЬ1Х (≈ -12 V). This feature of the operational amplifier is based on the principle of forming a rectangular voltage of a multivibrator (Fig. 2.20, a).

Rice. 2.20. multivibrator(a) and graphs explaining its operation (b)

Suppose that at the moment of switching on between the inputs of the amplifier there is a small (a few millivolts is enough) negative potential difference. In this case, a voltage + UOUT will be generated at the output, and the non-inverting input from the divider R 1, R 2 positive potential will be applied +U n. The capacitor will begin to charge along the "Uout-R3-C-case" circuit, trying to reach the potential + Uout. The potential at the inverting input will begin to rise until it exceeds the potential at the non-inverting input +U D. At this point, the amplifier will output a negative voltage -U vyx and will create a negative potential at the non-inverting input -U D. The capacitor will now begin to recharge, seeking to reach its potential -U vyx. However, as soon as the potential at the inverting input drops below the potential at the non-inverting input -U D, the amplifier will output a positive voltage +U vyx. Such an abrupt process of changing the output voltage from + U out to -U the output and vice versa will be repeated until the supply voltage is removed from the operational amplifier. Graphs demonstrating the described processes are shown in fig. 2.20, b. The period of G-oscillations is determined by the time constant of the capacitor charge τ = R 3c, as well as the extent to which the potential formed by the divider R 1, R 2, less voltage Uout.

Sawtooth voltage generator

The voltage across the capacitor rises in a straight line when it is charged. direct current, independent of the voltage on it, and prevent the influence of the load resistance on this current, i.e. the condition must be met R n >>R. Integrating over time the expression

Condition I c = const in the circuit of the sawtooth voltage generator (SPG) based on the OU (Fig. 2.21, a) provided with constant voltage Uin. As long as the transistor is off, during the time t n the capacitor is charging and the voltage across it increases in a straight line. The amplifier, trying to make the potential difference at its inputs close to zero, generates an output voltage that repeats the voltage across the capacitor. When a pulse Udis is applied, the transistor opens, and the capacitor quickly discharges through it in a time t discharge, after which the charging process is repeated. The output voltage of the circuit acquires a sawtooth shape, which is maintained as long as the voltage value is within the range from -Uout to +Uout.

Personnel development. The driving sawtooth voltage generator (Fig. 11.4) is assembled on transistors VT1 and VT2. When the supply voltage is turned on, the capacitors C1 and C2 are charging. Currents flow through the base circuits of the transistors, which bring the transistors into saturation mode. After some time, the charging current of the capacitors will decrease and reach a value at which one of the transistors will come out of saturation. Change in voltage in the collector circuit of the transistor VT1 close the transistor VT2. As a result, the capacitor C1, included in the OOS circuit, will slowly discharge through the collector circuit of the transistor VT1. Since the negatively charged capacitor plate C1 connected to the base of the transistor VT1, when the capacitor is discharged, the base current decreases and as a result, such a ratio between the collector and base currents is automatically set, which is exactly equal to the current transfer coefficient of the transistor. During the entire time of the discharge of the capacitor, the base current and the base voltage change insignificantly. Current through resistors R1 and R2 remains constant and does not depend on the processes occurring in the device. Thus, during the forward run, the generator has a deep OOS that maintains a constant capacitor discharge current C1, and hence the high linearity of the sawtooth voltage. Since the current transfer coefficient of the transistor varies depending on the applied voltage (at the initial moment by 1 - 2%), then the non-linearity of the signal will be characterized by the same value. The process of discharging the capacitor stops at such voltages on the collector, which require a significant increase in the base current to control the collector current. The current transfer coefficient of the transistor drops sharply. In this case, based on the transistor VT2 closing signal is significantly reduced. Transistor VT2 opens. A positive voltage appears in its collector, opening the transistor. An avalanche-like process occurs. Both transistors are open. The cycle of work is repeated.

Rice. 11.4

The values ​​of the elements shown in the diagram form an output signal with an amplitude of more than 10 V and a frequency of 50 Hz. Resistors are used to regulate the amplitude of the output signal and its linearity. R7 and R8 respectively. Resistor R1 changes the frequency of the master oscillator.

Bipolar generator sawtooth signal. The adjustable slope sawtooth generator (Figure 11.5) consists of two integrating chains R5, C1 and R2, C2 and a threshold element built on transistors VT1 and VT2. When the power is turned on based on the transistor VT2 a 10 V signal occurs. As the capacitor charges C1 tension decreases. At this time, the voltage at the base of the transistor VT1 increases. At different ends of the potentiometer, there are signals with different fronts. When the voltage at the bases of the transistors VT1 and VT2 equals, they open and the capacitors are discharged. After that, a new generator cycle will begin. The slope of the output sawtooth signal can be adjusted over a wide range using a potentiometer.

Rice. 11.5

Rice. 11.6

controlled generator. The sawtooth signal generator (Fig. 11.6, a) is built according to the integrator circuit with a large time constant, which is determined by the expression t \u003d h 21 E C 1 R 4 where h 21e is the current transfer coefficient of the transistor VT1. Transistor VT1 slowly opening: condenser C1 included in the OOS circuit. The voltage in the collector circuit decreases. At some point, the diode opens VD2 and shunts the input of the transistor VT2. transistor VT2 closes. To speed up the closing process, a dynamic load is included in its collector - a transistor VT3. Through the emitter of the transistor VT3 capacitor C1 fast charging. As a result, sawtooth backlash is minimized. Its duration is less than 5 x. The duration of the sawtooth signal can be adjusted using the base current of the transistor VT1(Fig. 11.6,6).

Sawtooth signal generator on the integrator. The basis of the generator (Fig. 11.7) is an integrator on a transistor. The K122UD1 integrated circuit is used as threshold and amplifying elements. The threshold of the microcircuit, equal to 3 V, is set by the divider Rl, R2. When the power is turned on in the collector of the transistor, the voltage cannot change abruptly. negative Feedback forms a linearly increasing signal at the output through the capacitor. The time constant is t=h 21E R 3 C 2 , where h 21E is the current transfer coefficient of the transistor. When the collector voltage reaches 3V, the IC will switch. The positive voltage at pin 5 will pass through the diode and turn on the transistor. The capacitor will discharge C2. The collector will return to zero potential.

Rice. 11.7

The circuit will start a new cycle of work. The circuit with the specified ratings of the elements generates an output signal with an amplitude of 3 V, a repetition rate of 100 Hz and a trailing edge duration of 0.1 ms.

Triggered bipolar signal generator. To obtain a high-voltage sawtooth signal in the generator (Fig. 11.8), two stages are used, at the outputs of which falling and rising signals are formed. Each stage consists of two transistors. transistors VT2 and VT4 are dropping, a VT1 and VT3- active elements, in the collectors of which output signals are formed. After turning on the power, the voltage at the collector of the transistor VT3 cannot change abruptly. This is prevented by OOS through a capacitor C2. The collector voltage will rise slowly. The rate of voltage increase is determined by the time constant t \u003d L 2 1E Cz(Ru-(-+Rt), where hzi e- current transfer coefficient of the transistor. resistor R7 is limiting. In the other stage, at the first moment, a voltage of 100 V appears. Then the voltage decreases and tends to zero. Reset voltage in the collector of the transistor VT1 occurs at the moment when the input pulse arrives. At this time, the transistor opens VT4. Pulse signal from capacitor C4 passes to the base of the transistor VT2 and opens it. Capacitors are reset at the same time C1 and C2.

Rice. 11.8

Sawtooth signal generator with adjustable linearity. The generator (Fig. 11.9) is based on the principle of charging a capacitor C2 stabilized current. The current stabilizer is built on a transistor VT2. Capacitor signal C2 goes to the input of the emitter follower. When a sawtooth signal is formed, the voltage across the capacitor increases. Simultaneously with an increase in the voltage across the capacitor, the base current of the transistor increases VT3. As a result, the capacitor is charged not by a direct current, as required by a linear increase in voltage, but by a current that decreases with time. The charge of the capacitor is affected by the input impedance of the emitter follower. To obtain a sawtooth voltage, it is necessary to compensate for the base current of the transistor. This can be achieved by an OS circuit connecting the emitters of transistors VT2 and VT3. With an increase in the output signal of the emitter follower, the emitter current of the transistor increases VT2. Changing the resistance of the resistor R9 in the feedback circuit, we can achieve rising or falling output waveform.

Rice. 11.9

To discharge the capacitor in the circuit, a blocking generator is used. During the charging of the capacitor, the diode is closed by the supply voltage. When the transistor VT1 open, capacitor C2 discharged through a diode VD1. The amplitude of the output signal is regulated by a resistor R5, and the frequency is a resistor R1. The maximum amplitude is 15 V.

CONTROLLED GENERATORS

Field effect transistor generator. The basis of the generator (Fig. 11.10) is the charge of the capacitor-direct current, which is given by field effect transistor VT4. The charge rate of the capacitor is determined by the resistor R10. The rising voltage is applied to the base of the emitter follower transistor, the output of which is connected to the flip-flop - transistors VT1 and VT2. The output of the trigger goes to the base of the transistor VT3 to relieve the voltage on the capacitor.

Initial state transistors VT2 and VT3 closed. As soon as the voltage on the capacitor reaches 6 V, the trigger fires and the transistor opens. VT3. The capacitor is discharged through an open transistor. When the voltage on the capacitor drops to 1 V, the trigger returns to the initial state. A new capacitor charge cycle begins.

The ratings of the elements shown in the diagram allow you to adjust the output signal frequency from 15 to 30 kHz. If you put a capacitor with a capacity of 0.033 microfarads, then the frequency of the output signal is 1 kHz.

Rice. 11.10 Fig. 11.11

Triangular signal generator on the op-amp. In the scheme of Fig. 11.11 on the condenser FROM a triangular signal with an amplitude of 0.6 V is generated. The charge and discharge of the capacitor are carried out by the output signal of the op-amp, which automatically changes at the moment when the voltage across the capacitor reaches the opening threshold. The opening threshold is set by the divider R2 and R3. The repetition rate of the output signal is determined by the expression f=l/4R 1 C. A resistor is used to equalize the slopes of the front and the decay of the output signal. R6.

Triangular signal shaper. Shaper fig. 11.12 allows you to get a triangular signal at the output. The signal amplitude reaches 90% of the supply voltage with sufficiently high edge linearity.

The shaper is based on the principle of charging and discharging a capacitor through current generators built on transistors. The collector currents of the transistors are determined by the reference voltages of the zener diodes and the emitter resistors. In the absence of an input signal, equal currents must flow through the transistors. If the equality of the currents is not satisfied due to the spread of the values ​​​​of the zener diodes and resistors, then you should adjust the resistor R4. The appearance of the input signal with amplitude more tension breakdown of the zener diodes will cause an imbalance in the collector currents. The positive half wave of the input signal will reduce the current of the transistor VT2. transistor current VT1 will remain unchanged. The differential collector current will charge the capacitor. With the advent of the negative half-wave, the collector current of the transistor will decrease VT1. transistor current VT2 set to nominal. The capacitor will be discharged by the current of the transistor VT2. If the input signal amplitude is less than the supply voltage, then there is a direct relationship between the amplitudes of the input and output signals, and if the supply voltage is greater, then the output signal amplitude is constant.

The capacitance of the capacitor is calculated by the formula C \u003d 10 3 I / 2fU m ah (μF), where I is the current of the transistor; f is the frequency of the input signal; U max - amplitude of the output signal.

Rice. 11.12 Fig. 11.13 Fig. 11.14

Rice. 11.15

Wide range triangular waveform generator. The triangular signal generator (Fig. 11.13) allows you to get a frequency from 0.01 Hz to 0.1 MHz. 20 V output signal is formed on the capacitor C4 collector currents of transistors VT4, VT6. When the capacitor is charged, the transistors VT4 and VT5 open, and the transistors VT3 and VT6 closed. When the voltage on the capacitor rises to the level determined by the divider R1 - R3 transistor VT1 will open. The transistors will open after it. VT3 and VT6, that turn off the transistors VT4 and VT5 The process of discharging the capacitor through the transistor will begin VT6 When the low level is reached, the transistor will open VT2. This process returns the circuit to its original state. The capacitor starts charging again. The output signal frequency can be linearly changed with a resistor R5 overlapping 20 times. For a capacitor with a capacity of 1 nF and at R5 = 510 kΩ, the frequency is 001 Hz

Step signal shaper. In the initial state (Fig. 11-14), the capacitor is charged to the supply voltage. All transistors are closed. Input pulse of positive polarity turns on the transistor VT1. A current flows through this transistor, which discharges the capacitor. The voltage across the capacitor decreases. The second input pulse will also discharge the capacitor by a discrete voltage value. As a result of this, each pulse will reduce the voltage across the capacitor in steps. As soon as the voltage across the capacitor equals the voltage across the divider R4, R5, transistor opens VT2 and a relaxation process begins in a composite cascade. transistors VT2 and VT3 open. There is a process of charging the capacitor. After that, a new cycle of discharging the capacitor begins.

Trapezoidal signal generator with adjustable rise time. The generator (Fig. 11.15) is based on a multivibrator that controls the operation of current-setting transistors VT3 and VT4. When the transistor VT2 open, through transistor VT3 capacitor charging current flows SZ. The rate of rise of the voltage on the capacitor (or the edge of the output signal) depends on the charging current, which is regulated by a resistor R12 The maximum voltage across the capacitor is limited by the zener diode VD2. When switching the transistors of the multivibrator to another state, the process of discharging the capacitor begins. Transistor VT3 closes, and the transistor VT4 opens. Transistor discharge current VT4 adjustable with a resistor R15. The value of this current determines the slope of the output signal. The frequency and duty cycle of the output signal are regulated by resistors R2 and R4. The generator can operate in a wide frequency range, up to 1 MHz. With large changes in the frequency of the output signal, it is necessary to change the values ​​​​of the capacitances of the capacitors C1 and C2.

OS GENERATORS

Controlled sawtooth signal generator. The generator (Fig. 11.16) consists of a threshold device and an integrator. The output voltage of the negative polarity of the threshold device built on the op-amp DA1, applied to the input of the integrator. Capacitor C, included in the OOS circuit, is gradually charged. At the output of the OU DA2 a linearly increasing signal is formed. When at the non-inverting input of the op-amp DA1 will be zero potential, it will switch. The positive polarity output signal passes through the diode and discharges the capacitor. When the capacitor is completely discharged, the op amp DA1 will return to its original state and a new cycle of generating the output signal will begin. The repetition rate of the output signal is determined by the expression f = 3/C(R 3 + R 4).

Generator at OS K153UD1. The triangular pulse generator (Fig. 11.17, a) is built on two op-amps. The first op-amp performs the functions of an integrator, and the second is a threshold element. Op-amp output voltage DA1 increases (decreases) linearly. When it is equal in absolute value to the output voltage of the op-amp DA2, the second op-amp will switch and on the divider R5, R6 voltage polarity will change. In this case, the output signal of the op amp DA1 will decrease (increase) linearly. At the next moment, the output signal of the op-amp will be compared DA1 with OS closing threshold DA2. Secondary switching of the op-amp will take place DA2. The dependence of the period of the signal of a triangular shape on the gain of the op-amp DA2 shown in fig. 11.17.6.

Unijunction transistor generator with amplifier. Sawtooth signal generator (Fig. 11.18, a) built on an op-amp that performs the functions of an integrator. The slew rate of the output signal depends on the input voltage. When the voltage at the output of the op-amp reaches 8 V, the unijunction transistor opens. Positive pulse across the resistor R2 passes through the diode, and the integrating capacitor is discharged. The dependence of the output signal frequency on the input voltage is shown in fig. 11.18, b.

Rice. 11.16 Fig. 11.17

Generator with double pic. Generator (Fig. 11.19, a) consists of an integrator made on the op-amp DA2. When oh DA2 switches, its non-inverting input is supplied with a POS voltage, which determines the threshold for the circuit to operate. With potentiometer R4 to the non-inverting input of the op-amp DA1 the second POS is in effect. If the value of this connection is less than the opening threshold of the OS DA2, then the leading edge of the pulse signal at the output of the op-amp DA1 will pass through the condenser C1 to its inverting input. From this moment, the process of charging the capacitor C1 begins. Op-amp output voltage DA1 increases slowly. When it reaches the opening threshold of the OS DA2, switching occurs DA2. Capacitor discharge process begins C1. The pulse repetition rate of the output signal is determined by the expression f=K 2 /4RC(K 1 -K 2);

Rice. 11.18

Rice. 11.19

Rice. 11.20

K 1 \u003d R 2 / (R 2 + R 3); K 2 \u003d R "4 / (R" 4 + R "4). Depending on the level of the POS signal in the OS DA1 You can adjust the output level. The maximum value, DE is determined by the voltage on the divider R2, R3. On fig. 11.19.6 shows voltage diagrams in circuit races.

A triggered signal generator. Output voltage (Fig. 11.20, a), formed on the capacitor NW, equal to U 3 \u003d \u003d (t / C 3) I 2. The capacitor is charged with a linearly increasing current I 2 \u003d U 2 / R 5 of the transistor VT2. Transistor Collector Current Control VT2 carried out by the voltage across the capacitor C2 (U 2 \u003d (t / C 2) I 3). This voltage depends on the current of the transistor VT3 (l 3 \u003d U B / R 4). As a result, U 3 \u003d U b t 2 / C 2 C 3 R 4 R 5 . For the ratings of the elements indicated in the diagram, the output signal frequency is 5 kHz. Reset capacitors C2 and NW carried out by an external signal through transistors VT4 and VT1. On fig. 11.20.6 shows voltage diagrams at different points in the circuit.

sec signal conditioner x . Function formation secx is carried out from the input harmonic signal. The circuit (Fig. 11.21, a) can operate from units of hertz to hundreds of kilohertz. In the first transistor, the input signal is limited with an amplitude of 2.5 V. The second transistor increases the steepness of the edges of the rectangular signal and changes its phase. Collector signal of the transistor VT2 summed with the input signal at the resistor R6. The output signal is selected at a certain point on the potentiometer so that a certain value for the depth of the valley of the sec function can be set. It should be noted that this formation scheme can give an error of up to 10% at some points. With an increase in the amplitudes of the meander and harmonic signals, the error decreases. To increase the accuracy of the formation of the function sec a; you can put a diode limiting circuit at the input (Fig. 11.21.6). The role of this circuit is to smooth out the peaks of the harmonic signal. With the help of an additional circuit, the simulation accuracy can be increased up to 5%.

Rice. 11.21

COMPLEX SIGNAL GENERATORS

Diode generator of complex signals. Complex waveforms are formed (Fig. 11.22) as a result of changing the gain of a differential amplifier. With small input signals, all diodes are closed. Gain determined by resistors R2, R3 and R11, R12, close to unity. With an increase in the input signal level, diodes begin to conduct in the emitter circuits of transistors. This leads to an increase in the gain. The output signal becomes steeper. Three levels of gain change are used for both positive and negative polarities of the input signal. Each circuit, consisting of diodes and a potentiometer, determines a different opening threshold. The exact shape of the output signal is adjusted by the appropriate potentiometer.

Discrete shaper of signals of special forms. The generator (Fig. 11.23) is based on a multi-phase multivibrator, which is triggered by a pulse of positive polarity. The transistors will turn on one by one in the circuit. VT3. Only one transistor is open. The transistor will go into a conducting state. VT2, which is in the emitter of the transistor VT1 will direct the current determined by the resistor R5. If the resistances of the resistors change according to a certain law, then the amplitude of the output signal changes according to the same law. With resistors R5 you can get any law of change of the output signal. The frequency of switching channels is determined by the time constant R 6 C 2 .

Rice. 11.22 Fig. 11.23

Rice. 11.24

Function generator. A pulse signal of positive polarity is applied to the generator input (Fig. 11.24). Logic circuit 2I - NOT integrated circuit K133LAZ is closed. At output 1, a signal of negative polarity appears with a duration equal to the duration of the input signal. This signal on the RC chain is differentiated, and a positive pulse closes the second logic circuit. At the output of this circuit, a pulse of negative polarity with a duration of 5 μs appears. All subsequent chains work in the same way. At outputs 1 - 7, pulse signals appear one after the other. All these signals are summed through certain weight resistors at the input of the op-amp. Depending on the sequence of the accepted resistances of the weight resistors, a signal of any complexity can be formed at the output of the op-amp. The amplitude of the output signal is determined by the resistance of the resistor R4. To balance the op-amp, the resistance of the resistor R3 is selected for the total resistance of weight resistors.