Generators can operate in self-excitation mode or standby mode, when the sawtooth voltage pulse repetition period is determined by triggering pulses.

Sawtooth voltage is called electrical oscillations (pulses), which are generated by converting the energy source direct current into the energy of electrical vibrations.

Voltage sawtooth- this is a voltage that, for a certain time, increases or decreases in proportion to time (linearly), and then returns to its original level (Fig. 1).

Rice. 1. Parameters of PN

The sawtooth voltage can be linearly increasing or linearly decreasing and is characterized by the main parameters:

The duration of the direct (working) and reverse

Output voltage amplitude

Repetition period T

Entry level U 0

The non-linearity coefficient E, characterizing the degree of deviation of the real sawtooth voltage, from the voltage changing according to a linear law.

V max = at t=0 and V min = at t= t pr - the rate of change of the sawtooth voltage, respectively, at the beginning and at the end of the forward stroke.

Regardless of the practical implementation, all types of GPN can be represented as a single equivalent circuit (Fig. 2)

It includes a power supply E, a charging resistor R, which can be considered as the internal resistance of the power supply, a capacitor C - energy storage, electronic key K and discharge resistor r with a resistance equal to the internal resistance of the closed key.

Rice. 2. Equivalent circuit of GPN

key in original state To closed and installed on the capacitor First level voltage

When the key is opened, the capacitor begins to discharge through the discharge resistor r and the voltage across it varies exponentially

,

where
is the time constant of the capacitor charging circuit.

At present, the GPN with a small value of the nonlinearity coefficient and its insignificant dependence on the load resistance is created on the basis of integrated amplifiers.

A generator based on an op-amp is usually built according to an integrator circuit (for small non-linearity coefficients and a low-resistance load).

The proposed scheme and diagrams of its work look like Fig. 2:

In this circuit, the output voltage is the opamp-amplified voltage across capacitor C. The op amp is covered by both (R1, R2, source E 0) and (R3, R4, source E 3). The operation of the GPN is controlled using the transistor VT1

The operation of the GPN is controlled using a key device (KU) on a transistor VT 1.

The key device can be implemented on a bipolar transistor, controlled by positive polarity pulses.

The transistor (KU) is saturated (open) with positive half-cycles U in, and with negative ones it is in the cut-off mode (closed), while the sawtooth voltage front will be formed at the time of the action of the negative pulse at the input (KU). In the pauses between input pulses, the transistor is closed, and the capacitor is charged with current from source E. and resistor R3.

Voltage , formed on the capacitor, is fed to the non-inverting input of the operational amplifier operating in linear mode with a gain at the non-inverting input

As a result, a voltage is generated at the output of the amplifier
, and on the resistor R4 - a voltage equal to

,

which creates a current flowing through the capacitor in the same direction as the current .

Therefore, the capacitor charging current in the pauses between input pulses is equal to

.

As the capacitor charges, the current decreases, and the voltage across the capacitor and at the input of the operational amplifier increases. If the gain at the inverting input is greater than one, then the voltage across resistor R4 and the current flowing through it are also increasing. When selecting the gain, it is possible to ensure high linearity of the sawtooth voltage.

The work of Mr.

Let's consider the operation of the GPN using the example of our circuit to form the required duration of the reverse stroke, we will supplement the emitter circuit of the transistor VT 1 with resistance R6. Resistance R5 limits the base current of the transistor in saturation mode. Consider the processes occurring in this scheme. Let a pulse of duration act at the input , leading to the unlocking of the transistor. Under the condition of a slight voltage drop across the open junctions of the transistor, the voltage across the capacitor at the initial time is approximately equal to the drop across the resistance R6

. (1)

Due to feedback, the collector current of the transistor is

. (2)

In turn, the currents through the corresponding resistances are determined by the expressions

,
. (3)

Control pulse amplitude must be greater than

. (4)

At the same time, at the output of the circuit there is a constant voltage level equal to

. (5)

At the point in time the transistor turns off and the capacitor begins to charge. The processes occurring in the circuit are described by the following equations

,

,

. (6)

From (6) we get

Let us introduce the notation
,
,
, then the resulting equation can be rewritten as

. (7)

This is an inhomogeneous first-order differential equation whose solution has the form

. (8)

We find the integration constant from the initial conditions (1). Because at the initial time
, then
, therefore, (8) can be written as

.

Then the output voltage will change according to the law

(9)

Here
has the same meaning as before.

Since the voltage at the output of the system after the working stroke should be equal to the value
, where
is the amplitude of the sawtooth voltage, then, solving (9) with respect to time, we obtain

. (10)

Similarly for the discharge circuit, taking into account that
and
.

2. Scheme calculation.



For correct operation The circuit requires the inverting input gain to be greater than one. Let
, choose a resistor R2 with a nominal value of 20 kOhm, then R1 = 10 kOhm.

Calculate the gain for the non-inverting input.

It is required to provide a coefficient of non-linearity of 0.3%, then the time constant of the capacitor charge must be not less than the value

3. 

   Then the output voltage will change according to the law:

4. ,

   So if you ask
   B, then
   = 1067

   then K \u003d \u003d \u003d 0.014 provided that the supply voltage in the transistor circuit is 15 V.

   Taking into account the notation obtained earlier, we calculate the resistance ratio of the resistances R3 and R4

   .

   Let's set the resistance in the collector circuit of the transistor R3 = 10 kOhm, then we get that R4 = 20 kOhm.

   In turn, c, therefore, the capacitance of the capacitor will be about 224 pF, we choose 220 pF.

   Let's proceed to the calculation of the discharge circuit. For the discharge circuit, it is true

   . (13)

   We substitute the formulas from (11) into (13), solve with respect to R6, and obtain

   .

   Whence it follows, when substituting numerical values, that R6 \u003d 2 mOhm.

   Get the expression for the return time

   , (11)

   where
   ,
   ,
   .

   If expression (9) is differentiated with respect to time and multiplied by C1, then the coefficient of voltage nonlinearity will be determined by the formula

   t p / ,where =RC

   Based on the studies carried out, we proceed to the calculation of parameters and the choice of circuit elements.

   The current flowing at the moment when the transistor opens through the resistance R6 will be estimated based on the following reasoning. At the moment of switching, all the voltage on the capacitor is applied to the resistance, so current will flow through it
   uA.

   As a key, you can use a transistor with suitable parameters such as KT342B. Resistor R5, which limits the base current, we choose about 1 kOhm. Since the maximum collector current is 50 mA, and the current gain is 200, then the base saturation current will be 250 μA, therefore, the voltage across the resistor will be 0.25 V. Let's assume the base-emitter saturation voltage is 1 V. The voltage drop across the resistance R6, at the maximum current flowing through R3 and R4 added to R6 will be 6.08 V. Thus, a pulse with an amplitude of 8 V is required to reliably unlock the transistor and keep it open.

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Department of Education, Science and Youth Policy

Voronezh region

GOBU SPO VO "Borisoglebsk College of Industrial and Information Technologies"

course project

discipline: "Design of digital devices"

Topic: "Sawtooth voltage generator"

Borisoglebsk 2015.

Introduction

Nowadays, television receivers occupy a large place in the world of radio-electronic equipment. Television is the widest area of ​​radio electronics. Now every home has a TV, and it is the most basic source of information. When designing a television receiver, they are consistent with dozens of sciences and topics of radio electronics. And one of the main sciences is "Pulse technology" and the topic: "Generators of sawtooth voltage or current." On a TV, these are scanners - horizontal and vertical. Sawtooth voltage generators (SPGs) are also used in oscilloscope sweepers. Generators of this type are also used in the repair, setup and adjustment of various office equipment. The topic of the course project "Sawtooth voltage generator" is extremely important and relevant, since this device necessary at every workplace of the electronic equipment adjuster.

1 . Analysis of analogues of the sawtooth voltage generator.

1.1 Analysis of analog sawtooth voltage generator 1

1.1.1 circuit diagram

As the first analogue, consider a sawtooth voltage generator on transistors

Rice. 1 - Schematic diagram of the GPN

The generator (see Figure 1) provides a sawtooth voltage with good linearity. The sawtooth voltage is taken directly from the capacitor C2. On the resistor R2, at the moments of the discharge of the capacitor, pulses appear that can be used for synchronization.

1.1.2 The principle of operation of the GPN circuit

Transistor T1 of the generator with resistor R1 in the emitter circuit is a current source with an output resistance equal to several megohms. The current of this source charges the capacitor C2.

Due to the large output impedance of the current source, good linearity of the charge voltage is ensured.

When the voltage across capacitor C2 reaches a value at which the unijunction transistor T2 opens, the capacitor rapidly discharges.

The oscillation repetition frequency is controlled by resistor R3 (by adjusting the charge current of capacitor C2). This frequency does not depend on fluctuations in the supply voltage, since both the voltage at which transistor T2 opens and the charge current change proportionally, compensating for each other's influence on the repetition frequency.

The sawtooth voltage is taken directly from the capacitor C2. On the resistor R2, at the moments of the discharge of the capacitor, pulses appear that can be used for synchronization.

With the ratings of the parts indicated in the diagram, the repetition frequency can vary within 0.1--4 kHz; the swing of the sawtooth voltage is 10 V, the amplitude of the clock pulses is 5 V.

1.1.3 Functional diagram of GPN

Analyzing the circuit diagram, functionally it can be divided into 3 main parts.

Rice. 2 - Parts of the circuit diagram

Rice. 3 - Functional diagram of the GPN

RFK - Oscillation frequency adjustment

IT - Current source with output. resistance of several MΩ

1.2 Analysis of the analogue of the sawtooth voltage generatoron the microcontroller

1.2.1 Schematic diagram of the GPN

The schematic diagram of the indicator looks like this:

Rice. 4 - Schematic diagram of the GPN

1.2.2 The principle of operation of the GPN

The sawtooth voltage is formed on the capacitor C1, the charging current of which is determined by the resistors R1-R2 and (to a much lesser extent) the parameters of the transistors of the current mirror VT1-VT2. A rather large internal resistance of the charging current source makes it possible to obtain a high linearity of the output voltage (photo below; vertical scale 10V / div).

Basic technical problem in such circuits is the discharge circuit of the capacitor C1. Usually, unijunction transistors, tunnel diodes, etc. are used for this purpose. In the above circuit, the discharge is produced ... by a microcontroller. This achieves ease of setting up the device and changing the logic of its operation, because. the selection of circuit elements is replaced by the adaptation of the microcontroller program.

Rice. 5 - Oscillograms of pulses of GPN

The voltage across C1 is monitored by a comparator built into the microcontroller DD1. The inverting input of the comparator is connected to C1, and not the inverting input to the reference voltage source on R6-VD1. When the voltage at C1 reaches the reference value (approximately 3.8V), the voltage at the output of the comparator jumps from 5V to 0.

This moment is monitored by software and leads to the reconfiguration of the GP1 port of the microcontroller from the input to the output and the supply of a logic 0 level to it. As a result, the capacitor C1 is shorted to ground through the open transistor of the port and discharges rather quickly. At the end of the C1 discharge at the beginning of the next cycle, the GP1 output is again configured to the input and a short rectangular sync pulse is generated at the GP2 output with an amplitude of 5V.

Rice. 6- Printed circuit board GPN arr. side

The duration of the discharge and synchronizing pulses is set by software and can vary over a wide range, because The microcontroller is clocked by an internal oscillator at a frequency of 4 MHz. When varying the resistance R1 + R2 within 1K - 1M, the frequency of the output pulses with the specified capacitance C1 changes from about 1 kHz to 1 Hz.

The sawtooth voltage at C1 is amplified by the op-amp DA1 up to the level of its supply voltage. The desired output voltage amplitude is set by resistor R5. The choice of the type of op-amp is due to the possibility of its operation from a 44V source.

The voltage of 40V to power the op-amp is obtained from 5V using a pulse converter on a DA2 chip connected by standard scheme from her datasheet. The operating frequency of the converter is 1.3 MHz.

The generator is assembled on a board measuring 32x36 mm.

All resistors and most capacitors are size 0603. The exceptions are C4 (0805), C3 (1206), and C5 (tantalum, frame A). Resistors R2, R5 and connector J1 are installed on the reverse side of the board (Fig. 6).

Rice. 7 - Printed circuit board of GPN persons. side

The upper frequency limit in this circuit is limited by the discharge time C1, which in turn is determined by the internal resistance of the output transistors of the port. To speed up the discharge process, it is desirable to discharge C1 through a separate low resistance MOSFET.

In this case, it is possible to significantly reduce the time of the software delay for the discharge, which is necessary to ensure full discharge capacitor and, accordingly, the saw output voltage drop to almost 0V.

To stabilize the operation of the generator, it is desirable to use an assembly of two PNP transistors in one package as VT1-VT2. At a low frequency of the generated pulses (less than 1 Hz), the final resistance of the current generator begins to affect, which leads to a deterioration in the linearity of the sawtooth voltage. The situation can be improved by installing resistors in the emitters VT1 and VT2.

1.2.3 Functional diagram of GPN

Analyzing the circuit diagram, functionally it can be divided into 4 main parts.

Rice. 8 - Functional parts of the circuit diagram of the GPN

generator voltage microcontroller indicator

Based on the analysis of the circuit (GPN), we can draw up a functional diagram of the device.

Rice. 9 - Functional diagram of the GPN

FPN - Sawtooth Voltage Shaper

M - Microcontroller

UN - Voltage amplifier

IP - Pulse Converter

2 . Development of a structural functional diagramdigital device

2.1 Construction of a functional diagram

Based on the analysis of existing devices, we will draw up our own scheme. The functional diagram will look like this

Rice. 10 - Functional diagram of the GPN

DN - Voltage divider

TG - Schmitt Trigger

DC - Diode-resistor circuit

IT - Integrator

2.2 Ffunctional parts of the device

Voltage divider

Rice. 11 - Voltage divider

The voltage divider consists of 2 resistors R1 and R2. Half the supply voltage from the voltage divider is supplied to the inverting input of the op-amp DA1 and the direct input of the op-amp DA2. It does not require an additional power supply

Schmitt trigger

The Schmitt trigger is assembled on an operational amplifier. And plays the role of a sawtooth voltage shaper

Rice. 12 - Schmitt trigger

Diode-resistor circuit

With the help of the Diode-resistor circuit, you can set the desired shape and frequency of the pulses.

Rice. 13 - Diode-resistor circuit

The integrator is assembled on an operational amplifier

Rice. 14 - Integrator

3 . Schematic diagram of a sawtooth voltage generator

3.1 Schematic diagram of the GPN generator

Based on the functional units discussed above, it is possible to draw up a schematic diagram of the GPN generator.

Rice. 15 - Schematic diagram of the GPN

Elements on the diagram

R1, R2 - Voltage divider

R4, R5, D1, D2 - Diode-resistor circuit

R6 - With the help of it, the circuit is covered by feedback

C1 - Feedback Capacitor

C2 - Filter

3.2 Description of the GPN scheme

This sawtooth voltage generator can be used in various circuits, for example, in PWM, as a sweep generator, in devices for voltage comparison, time delay and pulse extension.

The oscillator circuit is shown in Figure 15. It consists of a Schmitt trigger on the DA1 operational amplifier, and an integrator assembled on the DA2 operational amplifier. Both op-amps are connected in series through diode-resistor circuits D1, D2, R4, R5, and with the help of resistor R6, the circuit is covered by feedback.

Half of the supply voltage is supplied to the inverting input of the op-amp DA1 and the direct input of the op-amp DA2 from a voltage divider collected on resistors R1, R2, which makes it possible to get by with one power source.

Element ratings

3.3 The principle of operation of the GPN

When the power is turned on, the capacitor C1 is discharged, it starts charging through the D2R5 circuit and the output of the amplifier DA1, on which a low voltage is established, the other terminal of the capacitor C1 is connected to the output of the op-amp DA2, on which the voltage rises. As soon as this voltage reaches the switching threshold of the Schmitt trigger DA1, the trigger will switch and a certain voltage will be set at its output, which will first discharge through the diode D1 and the resistor R4 and then charge the capacitor C1 to a different polarity. Further, the process is repeated, and the circuit goes into self-oscillatory mode.

Since the resistors R4 and R5, through which the capacitor C1 is charged and discharged, have a different value, the time for charging and discharging the capacitor will be different, respectively, the sawtooth voltage at the output of the op-amp DA1 will rise for a long time and quickly fall off.

Oscillation frequency calculation

The frequency of the sawtooth signal at the output of the generator is determined by the formula

where F is the frequency in Hertz;

R3, R6, R4, R5 - resistance in ohms;

C1 is the capacitance in farads.

Conclusion

In accordance with the task, a device project was developed: "Sawtooth voltage generator", which fully meets the required parameters.

This device consists of:

DN - Voltage divider.

TG - Schmitt trigger.

DC - Diode-resistor circuit.

IT - Integrator.

In one of the nodes, the frequency of the RC circuit was calculated.

The purpose of the course project on the topic “Sawtooth generator.

voltage" was achieved by solving the tasks set, namely:

Analysis of existing analogues.

Development block diagram.

Development of a schematic diagram of the device.

The solution of the tasks was achieved using technical and reference literature, as well as Internet resources.

Bibliography

1. Directory. "Integrated circuits and their foreign analogues". Under the editorship of Nefedov A.V. - M. Radiosoft. 1994

2. Directory. "Diodes, thyristors, transistors and microcircuits for general purposes". Voronezh. 1994

3. "Electronics" V.I. Lachin, N.S. Savelov. Phoenix 2000

4. Zhmurin D.N. Mathematical foundations of systems theory: Uch. settlement - Novocherkassk, 1998.

5. Generation and signal generators. Dyakonov V.A.

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The principle of operation of the relaxation generator is based on the fact that the capacitor is charged to a certain voltage through a resistor. Upon reaching desired voltage the control opens. The capacitor is discharged through another resistor to a voltage at which the control element closes. So the voltage across the capacitor increases exponentially, then decreases exponentially.

You can read more about how a capacitor charges and discharges through a resistor at the link.

Low frequencies are designed to obtain periodic low-frequency electrical signals with specified parameters (shape, amplitude, signal frequency) at the output of the device.

KR1446UD1 (Fig. 35.1) is a general-purpose dual op-amp. Based on this microcircuit, devices for various purposes can be created, in particular, electrical oscillations, which are shown in Fig. 35.2-35.4. (Fig. 35.2):

♦ simultaneously and synchronously generates rectangular and sawtooth voltage pulses;

♦ has a single artificial middle point for both op amps, formed by the voltage divider R1 and R2 .

Built on the first of the op-amps, on the second - Schmitt with a wide hysteresis loop (U raCT \u003d U nHT; R3 / R5), accurate and stable switching thresholds. The generation frequency is determined by the formula:

f =———– and amounts to 265 Gi for the denominations indicated on the diagram. FROM

Rice. 35.7. Pinout and composition of the microcircuit KR 7446UD7

Rice. 35.2. generator of rectangular-triangular pulses on the chip KR1446UD 7

by changing the supply voltage from 2.5 to 7 V, this frequency changes by no more than 1%.

The improved one (Fig. 35.3) generates rectangular pulses, and their frequency depends on the value of the control

Rice. 35.3. controlled square wave generator

input voltage according to the law

When it changes

input voltage from 0.1 to 3 V, the generation frequency increases linearly from 0.2 to 6 kHz.

The generation frequency of the rectangular pulse generator on the KR1446UD5 chip (Fig. 35.4) is linear in the value of the applied control voltage and at R6 = R7 is determined as:

5 V generation frequency increases linearly from 0 to 3700 Hz.

Rice. 35.4. voltage controlled generator

So, when the input voltage changes from 0.1 to

Based on TDA7233D microcircuits, using the base element as a single basis, fig. 35.5, a, you can collect sufficiently powerful pulses (), as well as voltages, fig. 35.5.

The generator (Fig. 35.5, 6, top) operates at a frequency of 1 kHz, which is determined by the selection of elements Rl, R2, Cl, C2. The capacitance of the transition capacitor C sets the timbre and volume of the signal.

The generator (Fig. 35.5, b, bottom), produces a two-tone signal, subject to the individual selection of the capacitance of the capacitor C1 in each of the basic elements used, for example, 1000 and 1500 pF.

Voltages (Fig. 35.5, c) operate at a frequency of about 13 kHz (capacitor C1 is reduced to 100 pF):

♦ upper - generates negative gel voltage relative to the common bus;

♦ medium - produces a positive doubled relative to the supply voltage;

♦ lower - generates, depending on the transformation ratio, a bipolar equal voltage with galvanic (if necessary) isolation from the power source.

Rice. 35.5. abnormal use of TDA7233D microcircuits: a - basic element; b - as pulse generators; c - as voltage converters

When assembling converters, it should be taken into account that a significant part of the output voltage is lost on the rectifier diodes. In this regard, it is recommended to use Schottky as VD1, VD2. The load current of transformerless converters can reach 100-150 mA.

Rectangular pulses (Fig. 35.6) operate in the frequency range 60-600 Hz \ 0.06-6 kHz; 0.6-60 kHz. To correct the shape of the generated signals, the chain ( Bottom part rice. 35.6), connected to points A and B of the device.

Having covered the op-amp with positive feedback, it is easy to transfer the device to the mode of generating rectangular pulses (Fig. 35.7).

Variable frequency pulses (Fig. 35.8) can be made on the basis of the DA1 chip. When used as DA1 1/4 of the LM339 microcircuit, by adjusting the potentiometer R3, the operating frequency is tuned within 740-2700 Hz (the value of the capacitance C1 is not indicated in the original source). The initial generation frequency is determined by the product C1R6.

Rice. 35.8. wide-range tunable oscillator based on comparator

Rice. 35.7. generator of rectangular pulses at a frequency of 200 Hz

Rice. 35.6. LF square-wave generator

On the basis of comparators such as LM139, LM193 and the like, the following can be assembled:

♦ rectangular pulses with quartz stabilization (Fig. 35.9);

♦ pulses with electronic tuning.

Frequency-stable oscillations or the so-called “hourly” rectangular pulses can be performed on the DAI LTC1441 comparator (or similar) according to the typical circuit shown in fig. 35.10. The generation frequency is set by a quartz resonator Z1 and is 32768 Hz. When using a line of frequency dividers by 2, rectangular pulses with a frequency of 1 Hz are obtained at the output of the dividers. Within a small range, the operating frequency of the generator can be lowered by connecting a small capacity resonator in parallel.

Typically, LC and RC- are used in electronic devices. Less known are LR-, although devices with inductive sensors can be created on their basis,

Rice. 35.11. LR generator

Rice. 35.9. pulse generator on comparator LM 7 93

Rice. 35.10. "clock" pulse generator

Detectors for wiring, pulses, etc.

On fig. 35.11 shows a simple LR square-wave generator operating in the frequency range 100 Hz - 10 kHz. As inductance and for sound

the generator operation is controlled by a telephone capsule TK-67. Frequency tuning is carried out by potentiometer R3.

Operable when the supply voltage changes from 3 to 12.6 V. When the supply voltage drops from 6 to 3-2.5 V, the upper generation frequency rises from 10-11 kHz to 30-60 kHz.

Note.

The range of generated frequencies can be extended to 7-1.3 MHz (for a microcircuit) by replacing the telephone capsule and resistor R5 with an inductor. In this case, when the diode limiter is turned off, signals close to a sinusoid can be obtained at the output of the device. The stability of the generation frequency of the device is comparable to the stability of RC generators.

Sound signals (Fig. 35.12) can be performed K538UNZ. To do this, it is enough to connect the input and output of the microcircuit with a capacitor or its analogue - a piezoceramic capsule. In the latter case, the capsule also acts as a sound emitter.

The generation frequency can be changed by selecting the capacitance of the capacitor. In parallel or in series, a piezoceramic capsule can be switched on to select the optimal generation frequency. The supply voltage of the generators is 6-9 V.

Rice. 35.72. audio frequencies on a chip

For an express check of the op-amp, a generator can be used sound signals shown in fig. 35.13. The tested DA1 chip of type , or others with a similar pinout, is inserted into the socket, after which the power is turned on. If it is in good condition, the HA1 piezoceramic capsule emits a sound signal.

Rice. 35.13. sound generator- OS tester

Rice. 35.14. generator of rectangular pulses on OUKR1438UN2

Rice. 35.15. generator of sinusoidal signals on OUKR1438UN2

Rectangular signals at a frequency of 1 kHz, made on the KR1438UN2 chip, are shown in fig. 35.14. amplitude-stabilized sinusoidal signals at a frequency of 1 kHz is shown in fig. 35.15.

The generator that generates sinusoidal signals is shown in fig. 35.16. This one operates in the 1600-5800 Hz frequency range, although at frequencies above 3 kHz, the waveform is increasingly far from ideal, and the output signal amplitude drops by 40%. With a tenfold increase in the capacitances of capacitors C1 and C2, the tuning band of the generator, while maintaining the sinusoidal waveform, decreases to 170-640 Hz with an amplitude unevenness of up to 10%.

Rice. 35.7 7. generator of sinusoidal oscillations at a frequency of 400 Hz