In what cases is the rc type oscillator used. RC generators

RC-generator is called a generator of harmonic oscillations, in which instead of an oscillatory system containing elements L and WITH, a resistive-capacitive circuit is used ( RC-chain), which has frequency selectivity.

The exclusion of inductors from the circuit makes it possible to significantly reduce the dimensions and weight of the generator, especially at low frequencies, since the dimensions of the inductors sharply increase with decreasing frequency. An important advantage RC-generators compared to LC- generators are the ability to manufacture them using integral technology. but RC- generators have a low stability of the frequency of the generated oscillations due to the low quality factor RC- circuits, as well as a bad form of oscillations due to poor filtering of higher harmonics in the spectrum of the output oscillation.

RC- generators can operate in a wide frequency range (from fractions of a hertz to tens of megahertz), however, they have found application in communication equipment and measuring equipment mainly at low frequencies.

Foundations of the theory RC-generators were developed by Soviet scientists V.P. Aseev, K.F. Teodorchik, E.O. Saakov, V.G. Kriksunov, and others.

RC- the generator usually includes a broadband amplifier, made on a lamp, transistor or integrated circuit, and RC- a feedback circuit with selective properties and determining the frequency of oscillations. The amplifier compensates for energy losses in passive elements and ensures the fulfillment of the amplitude self-excitation condition. The feedback loop ensures that the self-excitation phase condition is fulfilled only at one frequency. By the type of feedback circuit RC-generators are divided into two groups:

with zero phase shift in the feedback loop;

with a phase shift in the feedback circuit by 180.

To improve the shape of the generated vibrations in RC-generators use elements with nonlinearity, which limit the increase in the amplitude of oscillations. The parameters of such an element change depending on the amplitude of the oscillations, and not on their instantaneous values ​​(a thermistor, the resistance of which depends on the degree of heating by the current passing through it). With such a limitation, the form of oscillations does not change; they remain harmonic even in a stationary mode.

Consider both types RC- autogenerators.

Oscillator with 180 phase shift in the feedback circuit.

Such an autogenerator is also called an autogenerator with a three-link chain. RC.

In the schemes RC- generators with a phase shift in the feedback circuit by 180, amplifiers are used that invert the phase of the input voltage. Such an amplifier can, for example, be an inverting-input operational amplifier, a single-stage amplifier, or a multi-stage amplifier with an odd number of inverting stages.

In order for the phase balance equation to be fulfilled, the feedback circuit must provide a phase shift OC = 180.

To substantiate the structure of the feedback loop, let us reproduce the phase-frequency characteristics of the simplest RC-links (Fig. 3.4).

Rice. Option 3 RC-link and its FFC

Rice. Option 4 RC-link and its FFC

It can be seen from the graphs that one simplest RC-link introduces a phase shift not exceeding 90. Therefore, a phase shift of 180 can be carried out by cascading three elementary RC-links (fig. 5).

Rice. 5 Schemes and phase characteristics of three-link RC-chains

The elements RC-circuits are calculated so as to obtain a phase shift of 180 at the generation frequency. One of the variants of the generator with a three-link circuit RC shown in Figure 6

Rice. 6 Generator with three-link chain RC

The generator consists of a resistive transistor amplifier and a feedback circuit. A single-stage amplifier with a common emitter carries out a phase shift between the voltage on the collector and the base K = 180. Therefore, in order to perform the phase balance, the feedback circuit must provide at the frequency of the generated oscillations OC = 180.

Let's analyze the feedback loop, for which we will compose a system of equations using the loop current method.

Solving the resulting system with respect to the feedback coefficient, we obtain the expression

It follows from the expression that the 180 phase shift is obtained in the case when it is a real and negative value, i.e.

therefore, generation is possible at a frequency

At this frequency, the module of the feedback coefficient

This means that in order to excite self-oscillations, the amplifier coefficient must be greater than 29.

The generator output voltage is usually taken from the collector of the transistor. To obtain harmonic oscillations, a thermistor is included in the emitter circuit R T with a positive temperature coefficient of resistance. With an increase in the amplitude of oscillations, the resistance R T increases and the depth of negative feedback in the AC amplifier increases, respectively, the gain decreases. When a stationary oscillation mode occurs ( TO= 1), the amplifier remains linear and there is no distortion of the collector current waveform.

Oscillator with zero phase shift in the feedback circuit.

A characteristic feature of the circuits RC-generators with zero phase shift in the feedback loop is the use of amplifiers in them that do not invert the phase of the input signal. Such an amplifier can be, for example, an operational amplifier with a non-inverting input or a multistage amplifier with an even number of inverting stages. Let's consider some possible options for feedback circuits providing zero phase shift (Fig. 7).

Rice. 7 Variants of feedback circuits providing zero phase shift

They consist of two links, one of which represents RС- a link with a positive phase shift, and the second - with a negative phase shift. As a result of the addition of the phase response at a certain frequency (generation frequency), a phase shift of zero can be obtained.

In practice, the most often used as a selective circuit with a zero phase shift is a phase-balanced bridge, or, in another way, a Wien bridge (Fig. 7 c), the application of which is shown in the diagram RC-generator with zero phase shift, made on the operational amplifier (Fig. 8).

Rice. eight RC- generator with zero phase shift in the OS circuit

In this circuit, the voltage from the output of the amplifier is applied to its non-inverting input through the feedback circuit formed by the elements of the Wien bridge R 1 C 1 and R 2 C 2. Resistor chain RR T forms another feedback - negative, which is designed to limit the increase in the amplitude of oscillations and preserve their harmonic form. The negative feedback voltage is applied to the inverting input of the operational amplifier. Thermistor R T must have a negative temperature coefficient of resistance.

Feedback Loop Gain

must be real and positive, and this is possible when the equality

From here the frequency of the generated oscillations is determined. If R 1 = R 2 =R, C 1 = C 2 = C, then

The amplitude condition for self-excitation at frequency 0 requires the fulfillment of the inequality

With equality R 1 = R 2 = R and C 1 = C 2 = C gain TO > 3.

The vibration frequency can be changed by changing the resistances R or capacitors WITH, which are part of the Wien bridge, and the amplitude of the oscillations is regulated by the resistance R.

Main advantage RC-generators before LC-generators lies in the fact that the former are easier to implement for low frequencies. For example, if in a generator circuit with zero phase shift in the feedback circuit (Fig. 8) R 1 = R 2 = 1 MOhm, C 1 = C 2 = 1 μF, then the generated frequency

.

To get the same frequency in LC-generator, inductance would be required L= 10 16 H at WITH= 1 μF, which is difficult to implement.

V RC-generators it is possible by simultaneously changing the values ​​of the capacities WITH 1 and WITH 2, obtain a wider frequency tuning range than is the case in LC-generators. For LC-generators

while for RC-generators, at WITH 1 = WITH 2

To the disadvantages RC-generators should be attributed to the fact that at relatively high frequencies they are more difficult to implement than LC-generators. Indeed, the value of the capacitance cannot be reduced to less than the mounting capacitance, and a decrease in the resistances of the resistors leads to a drop in the gain, which makes it difficult to fulfill the amplitude condition for self-excitation.

The listed advantages and disadvantages RC-generators caused their use in the low-frequency range with a large frequency overlap coefficient.

The most widespread are two types of phase-shifting circuits: the so-called ladder (Figure 3, a, b) and the Wien bridge (Figure 3, c).

Rice. 3. Three-link RС circuits (a, b) and Wien bridge circuit (c)

Ladder chains represent a series connection of usually three RC links, each of which with the same elements ( R 1 = R 2 = R 3 = R and C 1 = C 2 = C 3 = C ) provides a 60 ° phase shift of the signal. As a result, the output voltage will be shifted in relation to the input voltage by 180 °. Depending on which of the chain elements is final, they are named either WITH -parallel (Figure 3, a), or R -parallel (Figure 3, b). To excite oscillations, the amplifier must also have a phase shift of 180 °, i.e. it must be inverting. The ladder circuit must be connected to the inverting input of the amplifier.

The generator frequency is determined by the time constant RC chains. The frequency of the generated sinusoidal oscillations for these circuits under the condition R 1 = R 2 = R 3 = R and C 1 = C 2 = C 3 = C calculated by the following formulas:

For the scheme WITH -parallel

for the scheme R -parallel

To ensure the balance of amplitudes, the gain of the amplifier must be equal to the attenuation introduced by the phase-shifting circuit through which the voltage from the output enters the input of the amplifier, or exceed it. Calculations show that for the above circuits, the attenuation is 210. Therefore, circuits using three-link phase-shifting chains with the same links can generate sinusoidal oscillations with a frequency only if the amplifier gain exceeds 210. Bridge (chain) Wines (Figure 3 , c) consists of two RС links. The first link consists of a serial connection R and WITH and has resistance

The second link consists of a parallel connection of the same R and WITH and has resistance

The transfer ratio of the positive feedback link is determined by the expression

whence after substitution Z1 and Z2 , find

If the condition is met

then the phase shift will be zero as well.

In this case, the frequency of the generator can be determined by the formula

Thus, the Wien bridge at the “quasi-resonance” frequency does not create a phase shift and has an attenuation equal to 1/3. Therefore, the Wien bridge must be included in the positive feedback circuit in the amplifier, the amplification factor of which when the circuit is open is OS must be at least 3. The use of single-stage amplifier circuits in this case is impossible. In stages with a common emitter or common source, the phase shift between the input and output signals is 180 ° , which excludes their use, because in this case, the phase balance condition is violated. Circuits with a common collector or a common source, although they do not reverse the signal phases, have a voltage gain of less than unity, as a result of which it is impossible to fulfill the amplitude balance condition. Amplifier stages with a common base or common gate have a very low input impedance, which, when feedback is introduced, shunts its output, reducing its gain. Therefore, the fulfillment of the balance condition turns out to be very difficult. Therefore, when constructing a generator based on discrete elements, a two-stage amplifier is used.

The most simple is to build an oscillator on the Wien bridge using an operational amplifier. There is a chain in it Pic formed by the Wien bridge can be connected to a direct, non-inverting input, and the desired gain can be set with a resistive divider in the circuit OOS connected to the inverting input (Figure 4).

Rice. 4. Generator based OU

The ratio of resistors in the circuit OOS, ensuring the fulfillment of the condition of the balance of amplitudes, must correspond to the ratio, since the gain for the signal applied to the non-inverting input is one greater than the ratio of the indicated resistors.

Oscillating circuit generators are irreplaceable as sources of sinusoidal high-frequency oscillations. To generate oscillations with frequencies less than 15 ... 20 kHz, they are inconvenient, since the oscillatory circuit is too cumbersome.

Another disadvantage of low-frequency LC - generators is the difficulty of tuning them in the frequency range. All this has led to the widespread use of RC generators at the above frequencies, in which frequency electric RC filters are used instead of an oscillatory circuit. Generators of this type can generate fairly stable sinusoidal oscillations over a relatively wide frequency range from fractions of a hertz to hundreds of kilohertz. They are small and lightweight, and these advantages of RC-generators are most fully manifested in the low-frequency region.

4.2 Block diagram of the rc-generator

This circuit is shown in Fig. No. 7.

Fig. No. 7. Block diagram of the RC autogenerator.

The circuit contains an amplifier 1, loaded with a resistor and receiving power from a constant voltage source 3. For self-excitation of the amplifier, i.e. to obtain sustained oscillations, it is necessary to supply to its input a part of the output voltage that exceeds the input voltage (or equal to it) and coincides with it in phase. In other words, the amplifier must be covered with positive feedback, and the four-pole feedback 2 must have a sufficient transmission coefficient. This problem is solved in the case when the bipolar 2 contains a phase-shifting circuit consisting of resistors and capacitors, the phase shift between the input and output voltages is 180 0.

4.3 The principle of operation of the phase-shifting circuit

The diagram of which is shown in Fig. No. 8a, illustrated using the vector diagram in Fig. No. 8b.

Fig. 8. Phase-shifting circuits: a - schematic diagram; b - vector diagram; c, d - three-link chains

Let the voltage U1 be applied to the input of this RC circuit. It causes a current I in the circuit, which creates a voltage drop across the capacitor

(where ω is the frequency of the voltage U1) and across the resistor U R = IR, which is simultaneously the output voltage U2. In this case, the phase shift angle between the current I and the voltage Uc is equal to 90 0, and between the current I and the voltage U R - zero. The voltage vector U1 is equal to the geometric sum of the vectors U C and U R and makes an angle φ with the vector U2. The smaller the capacitance of the capacitor C, the closer the angle φ to 90 0.

4.4 Conditions for self-excitation of rc - self-oscillator

The largest angle φ, which can be obtained by changing the values ​​of the elements of the RC-circuit, is close to 90 0. In practice, circuit elements R and C are selected as follows. So that the angle φ = 60 0. Therefore, to obtain the phase angle φ = 180 0, which is necessary to fulfill the phase balance condition. It is required to connect three RC links in series.

In fig. No. 8 c, d shows two variants of three-link phase-shifting circuits. The phase shift between the output and input voltages by an angle of 180 0 at R1 = R2 = R3 = R and C1 = C2 = C3 = C is provided at frequencies: f 01 ≈ (in the circuit in Fig. 8c) and f 02 ≈ (in the circuit 8d), where R is expressed in ohms, C- in farads, and f 0 - in hertz. The values ​​of f 01 and f 02 are simultaneously the frequency of self-oscillations.

To ensure the balance of amplitudes, the gain of the amplifier K us should not be less than the transmission coefficient of the feedback circuit K o.s. =. Calculations show that for the given schemes K o.c =. Thus, self-oscillations in RC-generators containing three-link phase-shifting circuits with the same links are possible only if the conditions

f auto = f 01 (or f auto = f 02); K mustache ≥29.

RC generators belong to the class of self-oscillating systems

relaxation type. The main elements of such a generator are

amplifier and aperiodic links composed of resistors and

capacitors. Not having an oscillating circuit in its composition, such

generators, however, make it possible to obtain oscillations close in shape to

harmonic. However, with strong regeneration of the system, when used

substantially nonlinear regions of amplifier characteristics, vibration mode,

due to the absence of an oscillating circuit, it is highly distorted. That's why

the generator should operate at a slight excess of the threshold

self-excitation.

The main advantages of RC-type generators are simplicity and

small dimensions. These advantages are especially pronounced when

generating low frequencies. To generate frequencies of the order of 100 Hz in

LC generators (Thomson generators) would require very large

values ​​of inductances and capacitances

In the previous chapter, LC autogenerators were considered. They are used at high frequencies. If it is necessary to generate low frequencies, the use of LC generators becomes difficult. Why? Everything is very simple. Since the formula for determining the frequency of generating oscillations looks like this:

it is easy to see that in order to decrease the frequency, it is necessary to increase the capacitance and inductance of the circuit. And an increase in capacitance and inductance directly leads to an increase in overall dimensions. In other words, the dimensions of the contour will be gigantic. And with frequency stabilization, the situation will be even worse.

Therefore, we came up with RC-oscillators, which we will consider here.

The simplest RC generator is the so-called three-phase phasing circuit, which is also called a circuit with reactive elements of the same sign. It is shown in fig. 1.

Rice. 1 - RC-oscillator with a phase-shifting chain

It can be seen from the diagram that this is just an amplifier, between the output and the input of which a circuit is connected, which reverses the phase of the signal by 180º. This circuit is called phase-shifting. The phase-shifting chain consists of the elements C1R1, C2R2, C3R3. With the help of one chain from a resik and a conder, a phase shift of no more than 90º can be obtained. In reality, the shift is close to 60º. Therefore, to obtain a 180º phase shift, three chains have to be installed. From the output of the last RC circuit, the signal is fed to the base of the transistor.

Work starts at the moment the power supply is turned on. The resulting pulse of the collector current contains a wide and continuous spectrum of frequencies, in which there will necessarily be the required generation frequency. In this case, the oscillations of the frequency to which the phase-shifting circuit is tuned will become undamped. For oscillations of the remaining frequencies, the self-excitation conditions will not be met and, accordingly, they quickly decay. The vibration frequency is determined by the formula:

In this case, the following condition must be met:

R1 = R2 = R3 = R
C1 = C2 = C3 = C

Such generators are only capable of operating at a fixed frequency.

In addition to the considered generator using a phase-shifting circuit, there is another interesting, incidentally, the most common, option. Let's look at fig. 2.

Rice. 2 - Passive RC bandpass filter with frequency-independent divider

So, this very structure is the so-called Wien-Robinson bridge, although the most common name is simply the Wien bridge. Some other scholars write a bridge of Wine with two "n".

The left side of the ento design is a passive bandpass RC filter; the output voltage is removed at point A. The right side is nothing more than a frequency-independent divider. It is generally accepted that R1 = R2 = R, C1 = C2 = C. Then the resonant frequency will be determined by the following expression:

In this case, the modulus of the gain is maximum and is equal to 1/3, and the phase shift is zero. If the transfer coefficient of the divider is equal to the transfer coefficient of the bandpass filter, then at the resonant frequency the voltage between points A and B will be equal to zero, and the phase response at the resonant frequency jumps from -90º to + 90º. In general, the following condition must be met:

Of course, everything is considered as usual in ideal or close to ideal cases. But in reality, the situation, as always, is a little worse. Since each real element of the Wien bridge has a certain scatter of parameters, even a slight violation of the condition R3 = 2R4 will lead either to an increase in the amplitude of oscillations up to saturation of the amplifier, or to damping of oscillations or their complete impossibility.

In order to make it completely clear, we will insert an amplifying cascade into the Vina bridge. For simplicity, let's plug in an operational amplifier (op-amp).

Rice. 3 - The simplest generator with a Wine bridge

In general, this is not the way to use this scheme, since in any case there will be a scatter in the parameters of the bridge. Therefore, instead of the R4 resistor, some non-linear or controlled resistance is introduced. For example, a non-linear resistor, controlled resistance using transistors, both field-effect and bipolar, and other crap. Very often, the R4 cutter in the bridge is replaced with a micropower incandescent lamp, the dynamic resistance of which increases with increasing current amplitude. The filament has a sufficiently large thermal inertia, and at frequencies of several hundred hertz, it practically does not affect the operation of the circuit within one period.

Generators with a Wien bridge have one good property: if the R1 and R2 resistors are replaced with alternating ones, but only with a dual one, then the generation frequency can be regulated within certain limits. It is possible to divide the conductors C1 and C2 into sections, then it will be possible to switch ranges, and with a double variable resistor, smoothly adjust the frequency in the ranges. For those in the tank, an almost practical diagram of a Wien bridge generator is shown in Figure 4.

Rice. 4 - RC-generator with Wine bridge

So, the Vin bridge is formed by C1-C8 condensers, R1 double resist and R2R3 resiks. The SA1 switch is used to select the range, with the R1 cutter - smooth adjustment in the selected range. Op-amp DA2 is a voltage follower to match the load.

RCoscillator with a matching stage and a phase-shifting circuit

The main advantage of RC oscillators is the ability to generate stable low-frequency oscillations (up to 20 kHz). The disadvantage of such generators is that they are not economical compared to LC autogenerators, since RC autogenerators operate in a soft self-excitation mode.

In RC oscillators, RC filters are used to build a selective circuit. In the oscillator under consideration, a positive feedback circuit is built by connecting several RC filters in series.

Consider the processes occurring in the RC filter shown in Figure 16, a. For clarity, the explanation will be explained using a vector diagram (Figure 16, b). When voltage Uin is applied to the input, current i flows in the circuit. This current creates a voltage drop across the capacitor U C and the resistor U R. The voltage U R is simultaneously the output voltage Uout. The voltage Uout is in phase with the current i, and the voltage U C is shifted relative to Uout by 90 °. The voltage at the input of the circuit is equal to the geometric sum of the vectors Uout and U C and corresponds to the vector Uin. The vectors Uin and Uout are phase shifted relative to each other by an angle j.

Figure 16 - A schematic diagram of an RC filter and a vector diagram explaining the processes occurring in it.

The angle j can be increased by decreasing the capacitance of the capacitor. As seen from the diagram j<90°. Поэтому для выполнения баланса фаз необходимо последовательное включение нескольких фильтров. При этом главным условием является равенство сдвига фаз каждым из фильтров, в противном случае каждый из фильтров будет иметь свою резонансную частоту, отличную от других фильтров и колебания будут отсутствовать. На практике используют последовательное включение трех фазосдвигающих звеньев, каждое из которых дает сдвиг фазы 60°, или четырех звеньев, каждое из которых дает сдвиг фазы 45°. На рисунке 17 приведены две возможные трехзвенные фазосдвигающие цепи. Временные диаграммы напряжений на выходе каждого звена этих цепей приведены на рисунке 18.

Figure 17 - Basic electrical diagrams of three-link phase-shifting circuits

The frequency of the generated oscillations when using these schemes is determined by the expressions:

for the circuit shown in Figure 17, and

fg = 0.065 /RC (27)

Figure 18 - Timing diagrams of voltages at the output of the links of the phase-shifting circuit

for the circuit shown in Figure 17, b

fg = 0.39 /RC (28)

where R = R 1 = R 2 = R 3 and C = C 1 = C 2 = C 3

Thus, the filters in the generator under consideration perform several functions at once: they determine the frequency of the generated oscillations, determine the shape of the oscillations, and participate in the implementation of the phase balance.

A schematic diagram of an RC oscillator with a matching stage and a phase-shifting circuit is shown in Figure 19.

In this generator, the amplifier stage is assembled on a VT1 transistor. The amplifier is loaded with resistor R3. The three-link phase-shifting circuit consists of elements C4 C5 C6 and R4 R5 R6. To match the low input resistance of the transistor VT1 with the resistance of the phase-shifting circuit, is a matching stage used? emitter follower. This stage is assembled on a VT2 transistor connected according to a circuit with a common collector. In the absence of this stage, the low input impedance VT1 will bypass the feedback circuit and significantly reduce the feedback coefficient, and this

Figure 19 - Schematic electrical diagram of an RC oscillator with a matching stage and a phase-shifting circuit

will lead to non-observance of the amplitude balance condition. Resistor R9 serves as the load for the emitter follower. Voltage bias to the transistors is supplied by voltage dividers R1 R2 and R7 R8. Elements C1 R10 are a power filter. C2 C3 C7 are decoupling capacitors. The feedback factor of such a generator is 1/29, therefore, to balance the amplitudes, the amplifier gain must be Cus? 29.

RC oscillator with phase-balanced circuit

In generators with an even number of amplifier stages, there is no need to use phase-shifting circuits in the positive feedback circuit. To select the oscillations of the required frequency in the output voltage of such generators, a four-pole device with frequency-selective properties (phase-balanced circuit) is included in the feedback circuit. A schematic diagram of such a two-port network is shown in Figure 20.

To generate oscillations, it is necessary that this four-pole device does not introduce a phase shift between the input voltage Uin and the output voltage Uout, i.e. j in must be equal to j out. The frequency at which j in = j out is determined by the expression

Figure 20 - Schematic electrical diagram of a frequency-selective four-port network

fr = 1/2p ? R 1 C 1 R 2 C 2 (29)

It is convenient to choose R 1 = R 2 = R, C 1 = C 2 = C then expression 26 will take the form

fr = 1/2p RC (30)

At all other frequencies, a phase shift will occur, which means that at these frequencies the phase balance condition will not be met and there will be no oscillations with these frequencies.

The feedback coefficient in this case will be equal to 1/3, and therefore, in order to balance the amplitudes, the amplification factor of the oscillator amplifier must be at least 3.

A schematic electrical diagram of an RC oscillator with a phase-balanced circuit is shown in Figure 21.

Figure 21 - Schematic diagram of an RC oscillator with a phase-balanced circuit

In this generator, the amplifier is assembled on two amplifying stages assembled on transistors VT1 and VT2. These stages are loaded by resistors R3 and R5. The bias voltage is applied to the transistors with a fixed base current through resistors R2 and R4. Elements C1 R1 C2 R2 form a phase-balanced circuit in a positive feedback circuit. Elements C4 C5 are decoupling capacitors. R6 C3 power filter elements. The condition for the balance of amplitudes in this circuit is fulfilled due to two amplifying stages, with the help of which a gain of 3 is easily achieved. The phase balance is achieved by switching on two transistors according to a circuit with a common emitter (the total phase shift in this case is 180 ° + 180 ° = 360 °) ...

RC Oscillator with Wine Bridge

The advantage of this generator is the ability to change the frequency of the generated oscillations. The schematic diagram of this generator is shown in Figure 22.

Figure 22 - Schematic electrical diagram of an RC oscillator with a Wien bridge

In this generator, the amplifier also has two amplifying stages assembled on transistors VT1 and VT2. These stages are loaded by resistors R4 and R9. The bias voltage is supplied to the resistors through voltage dividers R2 R3 and R7 R8.

The output voltage is fed to the amplifier input through the phase-balanced circuit C1 R1 C2 R3, which is one of the arms of the Wien bridge, the second arm is formed by the elements R6 R5. The second branch is connected to the output of the amplifier through a large capacitor C5, so that the R5 R6 circuit does not create a noticeable phase shift. Along with the positive feedback, the negative feedback formed by the elements R5 R10 C5 R6 is introduced. Negative feedback, by lowering the gain, significantly reduces the nonlinear distortion of the generated oscillations. A decrease in the gain does not lead to an imbalance of the amplitudes, since a real two-stage amplifier has a gain much greater than 3. In addition, the elements R5 R10 provide temperature stabilization of the operating point of the transistors. The frequency of the generated oscillations in the generator under consideration is controlled by the simultaneous adjustment of the resistances of the resistors R1 to R3, however, it can also be carried out by the simultaneous adjustment of the capacitances of the capacitors C1 C2.