RU2790608C1 - Method of amplification of sine and quasi-sine signals - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: invention allows creating broadband amplifiers with a uniform amplitude-frequency response designed to work with sinusoidal, quasi-sinusoidal, and narrowband signals. To this end, a method for amplifying signals is proposed, which consists in continuous monitoring of the frequency of the input amplified signal and correction, based on the results of measuring the frequency, the gain of the controlled amplifying unit so that the gain remains constant when the frequency of the input sinusoidal or quasi-sinusoidal signal changes. This is possible with a priori known form of the amplitude-frequency characteristic of the amplifying unit, information about which is used to convert the measured frequency into gain control signals. Devices that implement the method are also proposed.

EFFECT: reduced frequency distortion that occurs when amplifying sinusoidal and quasi-sinusoidal signals in a relatively wide frequency band.

16 cl, 5 dwg

Description

The invention relates to the field of radio engineering and allows you to create broadband amplifiers with a uniform amplitude-frequency response, designed to work with sinusoidal, quasi-sinusoidal, and narrowband signals.

For many years, a method has been used to amplify signals of various spectral composition, according to which, in order to obtain a relatively uniform amplification of signals in a given frequency range, the frequency correction of amplifying paths is carried out, which from a physical point of view consists in changing the inertial properties of amplifying paths in those parts of the frequency range where it is required to change frequency-dependent gain, see for example [Nikolaenko N.S. Design of transistor amplifiers. - M: Energy, 1965, pp. 304-307; Pat. RU 2568314, publ. 11/20/2015; Pat. RU 2669075, publ. 08.10.2018]. The advantages of this approach are simplicity and the possibility of amplifying signals with a relatively wide continuous spectrum. The disadvantage is the difficulty of obtaining a smooth amplitude-frequency response (AFC) in those areas where the correction is carried out

The closest in its technical essence to the claimed solution is a method that involves supplying an amplified signal to the amplifier input, removing the amplified signal from its output and controlling the gain of the amplifier depending on the result of comparing the output signal with the input [US Pat. RU 2556392, publ. 07/10/2015]. To implement the method, a device is used that contains an amplifying unit with a controlled gain, a nonlinear distortion meter, a comparison unit and a control unit, the output of which is connected to the control input of the amplifying unit, the input and output of which are, respectively, the input and output of the device.

A feature of the method chosen as a prototype is the change in the gain of the amplifying unit depending on the input signal and, as a result, on the non-linear distortions that occur during its amplification. Despite the presence with the claimed method of amplifying sinusoidal and quasi-sinusoidal signals of general action, the prototype method was developed to amplify signals with a relatively wide continuous spectrum, with the possibility of reducing non-linear distortion by controlling the gain. It is not focused on reducing frequency distortions belonging to the class of linear distortions and, therefore, its use will not improve the degree of gain uniformity in a given frequency range.

The technical result achieved by using the present group of inventions is to reduce the frequency distortion that occurs when amplifying sinusoidal and quasi-sinusoidal signals in a relatively wide frequency band.

The technical result is achieved by the fact that in the method of amplifying sinusoidal and quasi-sinusoidal signals, which consists in applying to the input of an amplifier with a frequency-dependent characteristic of the amplified signal, removing the amplified signal from the output of the amplifier, according to the invention, the amplitude-frequency characteristic of the amplifier is preliminarily determined, the signal frequency is measured, and then the obtained frequency value is used to correct the gain by establishing a functional relationship with the frequency response of the amplifier.

In addition, to achieve a technical result, according to the invention, a functional relationship with the amplitude-frequency characteristic of the amplification path is established by changing the gain by a factor proportional to the value of the inverse amplitude-frequency characteristic at the point corresponding to the measured signal frequency.

In addition, to achieve the technical result, according to the invention, the measurement of the signal frequency is carried out by preliminary frequency division by n times (n≥ 2), after which the measurement result is increased by n times.

In addition, to achieve the technical result according to the invention, the frequency of the signal is measured before it is amplified.

In addition, to achieve the technical result according to the invention, the frequency of the signal is measured after its amplification.

The technical result is also achieved by the fact that the amplifier with auto-correction (option 1), containing an amplifying unit with a controlled gain and a control unit, the output of which is connected to the control input of the amplifying unit, the input and output of which are, respectively, the input and output of the amplifier with auto-correction, according to the invention , contains a frequency meter and a functional converter, the input of the frequency meter is combined with the input of an auto-correction amplifier, the output of the frequency meter is connected to the input of the functional converter, the output of which is connected to the input of the control unit.

The technical result is also achieved by the fact that the amplifier with auto-correction (option 2), containing an amplifying unit with a controlled gain and a control unit, the output of which is connected to the control input of the amplifying unit, the input and output of which are, respectively, the input and output of the amplifier with auto-correction, according to the invention , contains a frequency meter and a functional converter, the input of the frequency meter is combined with the output of an amplifier with auto-correction, the output of the frequency meter is connected to the input of the functional converter, the output of which is connected to the input of the control unit.

The technical result is also achieved by the fact that the amplifier with auto-correction (option 3), containing an amplifying unit with a controlled gain and a control unit, the output of which is connected to the control input of the amplifying unit, the input and output of which are, respectively, the input and output of the amplifier with auto-correction, according to the invention , contains a frequency divider, a frequency meter and a functional converter, the input of the frequency divider is combined with the input of an amplifier with auto-correction, the output of the frequency divider is connected to the input of the frequency meter, the output of the frequency meter is connected to the input of the functional converter, the output of which is connected to the input of the control unit.

The technical result is also achieved by the fact that the amplifier with auto-correction (option 4), containing an amplifying unit with a controlled gain and a control unit, the output of which is connected to the control input of the amplifying unit, the input and output of which are, respectively, the input and output of the amplifier with auto-correction, according to the invention , contains a frequency divider, a frequency meter and a functional converter, the input of the frequency divider is combined with the output of an amplifier with auto-correction, the output of the frequency divider is connected to the input of the frequency meter, the output of the frequency meter is connected to the input of the functional converter, the output of which is connected to the input of the control unit.

The essence of the invention is illustrated by graphic material. In FIG. 1 shows a functional diagram of the first version of the amplifier with auto-correction. In FIG. 2 shows frequency response graphs illustrating the invention. In FIG. 3 shows a functional diagram of the second version of the amplifier with auto-correction, in Fig. 5 is a functional diagram of the third version of the amplifier with auto-correction. In FIG. 4 shows a functional diagram of a possible implementation of the control unit.

Functional diagram according to Fig. 1 contains a frequency meter 1, a functional converter 2, a control unit 3 and an amplifying unit 4. The input and output of the amplifying unit 4 are, respectively, the input and output of an amplifier with auto-correction, the output of unit 3 is connected to the control input of the amplifying unit 4, the input of the frequency meter 1 is combined with the input of the amplifier with auto-correction, the output of the frequency meter 1 is connected to the input of the functional converter 2, the output of which is connected to the input of the control unit 3.

In FIG. 2, as an example, in the upper part is a graph of the frequency response of a real input amplifier, in the lower part is a graph of the inverse frequency response of this amplifier. The plots are shown as gain K versus frequency ƒ of the input signal. Points (k ₁ , ƒ ₁ ), (k ₂ , ƒ ₂ ), (k ₃ , ƒ ₃ ), (k ₄ , ƒ ₄ ) are highlighted on the upper graph, which serve to designate the boundaries of the operating frequency range (points ƒ ₁ , ƒ ₄ ) and areas of uniform amplification (points ƒ ₂ , ƒ ₃ ).

Functional diagram according to Fig. 3 contains a frequency meter 5, a functional converter 6, a control unit 7 and an amplifying unit 8. The input and output of the amplifying unit 8 are, respectively, the input and output of an amplifier with auto-correction, the output of the unit 7 is connected to the control input of the amplifying unit 8, the input of the frequency meter 1 is connected to the output of the amplifier with auto-correction, the output of the frequency meter 5 is connected to the input of the functional converter 6, the output of which is connected to the input of the control unit 7.

Functional diagram according to Fig. 4 contains a buffer register 9, an adder 10 and a digital-to-analog converter (DAC) 11, the output of which is the output of the control unit, the input of which is the information input of the register 9, the output of which is connected to the first input of the adder 10, the second input of which is the input of the reference voltage code U ₀ , the output of the adder 10 is connected to the input of the DAC 11, the clock input of the register 9 is the clock input of CLK (the clock circuit is not shown in the diagram).

Functional diagram according to Fig. 5 contains a frequency divider 12, a frequency meter 13, a functional converter 14, a control unit 15 and an amplifying unit 16. The input and output of the amplifying unit 16 are, respectively, the input and output of an auto-correcting amplifier, the output of unit 15 is connected to the control input of the amplifying unit 16, the input of the divider 12 frequency is combined with the input of the amplifier with auto-correction, the output of the frequency divider 12 is connected to the input of the frequency meter 13, the output of which is connected to the input of the functional converter 14, the output of which is connected to the input of the control unit 15.

The idea underlying the considered method of amplifying signals is to continuously monitor the frequency ƒ of the input amplified signal and correct, based on the results of measuring the frequency ƒ, the gain of the amplifying unit so that the gain remains constant when the frequency of the input sinusoidal or quasi-sinusoidal signal changes. This is possible with a known form of frequency response, that is, if the function K(ƒ) is given a priori in any form. At the same time, if the value of the inverse function K(ƒ) is determined from the measured frequency ƒ*, and the frequency-dependent value K(ƒ) is changed by 1/K(ƒ*) times, then it is easy to see that the voltage at the output of the amplifying unit can remain constant regardless of the frequency ƒ:

where U _out , U _{in x} are the amplitudes of the signals, respectively, at the output and input of the amplifying unit. In the above expression, the * sign in the frequency designation ƒ indicates the frequency estimate obtained by the hardware.

Let us explain the foregoing on the example of one of the possible options for implementing the method (see Fig. 1). The input signal of the form u(t)=Usin2πƒt is fed to the input of the amplifying unit 4, which has the ability to change the gain under the action of the voltage U _control applied to its control input. At the same time, the input signal is fed to the input of the frequency meter 1, from the output of which the code of the measured frequency ƒ* is taken, which in the functional converter 2 is converted into the reciprocal of the frequency response at the point ƒ*, that is, it implements a function of the form 1/K(ƒ*). The digital code, which is the result of calculating the above function (inverse frequency response) is then fed to the control unit 3, in which the value 1/K(ƒ*) is translated into the control signals of the amplifying unit 4 - into the voltage U _control proportional to the value 1/K( ƒ*). As an example of a real frequency response in Fig. 2 shows the experimentally obtained characteristic of the amplifying unit, designed to operate in the frequency range from 1 to 200 MHz. From the general view of the frequency response, it follows that the correction of the frequency response - a change in the gain of block 4 - will be required in the initial section from ƒ ₁ to ƒ ₂ and in the section from ƒ ₃ to the upper limit of the range ƒ ₄ . For clarity, in the lower Fig. Figure 2 shows a graph of the inverse frequency response 1/K(ƒ), where you can see how the gain of block 4 should be changed: in particular, at the boundaries of the range, lower and upper, the gain should be increased, respectively, by 1/ _k1 and 1/ _k4 times. In the middle part of the operating range, the gain does not change, since the frequency response in this region has the form of a horizontal straight line (here it is necessary to clarify that, to simplify the presentation of the material, Fig. 2 shows a graph of the frequency response of a voltage follower amplifier).

Thus, automatic gain correction is carried out, aimed at obtaining a uniform gain in a given frequency range.

Moreover, the accuracy of the gain correction is affected by the error Δƒ of determining the frequency ƒ, since in the ideal case the condition

или

or

which in practice cannot be performed with mathematical accuracy, since it is impossible to reduce the error Δƒ to zero. In this regard, it is advisable to evaluate the consequences of the gain correction error, assuming that the main contribution to its formation is made by the error in determining the frequency of the amplified signal. To do this, we represent the absolute error of amplifying the amplitude of the output voltage _Uout after auto-correction in the form:

будет тем ближе к единице, чем меньше производная Ф(K) функции K(ƒ) в окрестности ƒ. Полагая, что указанная производная на участке Δƒ не меняется можно записатьIt is easy to understand that for a fixed value of Δƒ, the ratio

will be the closer to unity, the smaller the derivative Ф(K) of the function K(ƒ) in the vicinity of ƒ. Assuming that the indicated derivative in the section Δƒ does not change, we can write

hence,

The last expression connects ΔU _out not only with the error in determining the frequency Δƒ, but also with the rate of change in the frequency response in the selected section, which allows us to evaluate possible errors in different sections of the frequency response, and based on the general rule, according to which the smaller Ф (K), the less the error Δƒ has an effect on the accuracy of auto-correction.

Returning to the device diagram shown in Fig. 1, we note that if necessary, for example, to reduce the impact on the input of the device of indoor units or to supply amplified signals to the input of the frequency meter, the frequency meter can be connected directly to the output of the controlled amplifying unit. Such an option is shown in the functional diagram of Fig. 3, here blocks 5-8 perform the same functions as blocks 1-4 in the device of FIG. 1.

In practice, situations are possible in which the limited operating frequency range of the frequency meter does not allow measuring with the necessary error the frequencies that are in the operating frequency band of the controlled amplifying unit of the device. In such cases, to eliminate such a limitation, the circuit can be supplemented with a high-frequency frequency divider with a division factor of n (n≥2), for example, a frequency divider 12 (prescaler), as shown in FIG. 5. In the presented device, a signal is supplied to the input of the meter 13, the frequency of which is reduced by n times, while the result of the frequency measurement in the meter 13 should be increased by the same number of times, which is necessary for the correct execution of further operations to control the amplifying unit 16. Otherwise the operation of the auto-correction amplifier shown in the diagram of FIG. 5 does not differ from previously presented amplifiers. In a variant version, the input of the frequency divider can be connected to the output of a controlled amplifying unit, while the principle of operation of the device, in terms of auto-correction, gain, does not change (a diagram of such an option, due to its obviousness, is not given).

Concerning the issues of building individual blocks that are part of the considered amplifiers with auto-correction, we note the following.

может быть построен на основе программируемого постоянного запоминающего устройства, реализующего аппаратно-табличный способ вычислений. В этом случае в память запоминающего устройства заносят ранее вычисленные значения

которые извлекаются из памяти при поступлении на адресный вход соответствующих операндов ƒ_i. Здесь индекс i указывает на дискретный характер частоты. Разумеется, количество значений ƒ_i выбирают не только исходя из диапазона рабочих частот, но и из требований, предъявляемых к точности автокоррекции (разность ƒ_i - ƒ_i+1 должна быть меньше допустимой погрешности Δƒ). Что же касается блока 3 (7, 15), сопрягаемого с функциональным преобразователем, то его схемотехника определяется как особенностями функционального преобразователя, так и управляемой частью усилительного блока 4 (8, 16). Один из возможных вариантов реализации блока 3 управления, в предположении, что управление усилительным блоком осуществляется в аналоговой форме, показан на схеме по фиг. 4. В настоящей схеме входные данные, представляющие собой цифровые коды величин

поступают через буферный регистр 9 на первый вход сумматора 10, в котором складываются с фиксированным значением U₀ и далее преобразуются в ЦАП 11 в напряжение U_yпр, непосредственно подаваемое на управляющий вход усилительного блока 4 (8, 16). Регистр 9 необходим для хранения цифрового кода и обеспечивает независимость блока управления от времени нахождения результата измерения частоты на его выходе. Обновление данных в регистре 9 происходит под действием тактовых импульсов CLK, период следования которых определяется требуемым быстродействием цепей автокоррекции, а именно возможной (допустимой условиями применения) скоростью изменения частоты усиливаемых сигналов. Добавление постоянной величины U₀, которая в частном случае может принимать значение, равное нулю, может быть необходимо для управления усилительным блоком, в котором требуется задание некоторой начальной точки, отличной от нуля. Для изменения коэффициента пропорциональности между входной величиной блока управления и выходной, в простейшем случае может использоваться известный прием управления опорным напряжением ЦАП 11, которое формируется стабилизированным источником (на схеме по фиг. 4 цепи опорного напряжения не показаны).Functional converter 2 (6, 14) used to calculate a function of the form

can be built on the basis of a programmable read-only memory device that implements a hardware-table method of calculations. In this case, the previously calculated values are entered into the memory of the storage device.

which are retrieved from memory when the corresponding operands ƒ _i arrive at the address input. Here the index i indicates the discrete nature of the frequency. Of course, the number of values ƒ _i is chosen not only on the basis of the operating frequency range, but also from the requirements for auto-correction accuracy (the difference ƒ _i - ƒ _i+1 must be less than the permissible error Δƒ). As for block 3 (7, 15) interfaced with the functional converter, its circuitry is determined both by the features of the functional converter and by the controlled part of the amplifying block 4 (8, 16). One of the possible implementations of the control unit 3, assuming that the amplifying unit is controlled in analog form, is shown in the diagram of FIG. 4. In this scheme, the input data, which are digital codes of values

come through the buffer register 9 to the first input of the adder 10, in which they are added with a fixed value U ₀ and then converted to the DAC 11 into a voltage U _ypr directly applied to the control input of the amplifying unit 4 (8, 16). Register 9 is necessary to store the digital code and ensures the independence of the control unit from the time the frequency measurement result is found at its output. The data in register 9 is updated under the action of clock pulses CLK, the repetition period of which is determined by the required speed of the auto-correction circuits, namely, the possible (permissible conditions of use) rate of change in the frequency of the amplified signals. The addition of a constant value U ₀ , which in a particular case can take on a value equal to zero, may be necessary to control the amplifying unit, which requires the setting of some starting point other than zero. To change the proportionality factor between the input value of the control unit and the output value, in the simplest case, the well-known method of controlling the reference voltage of the DAC 11, which is formed by a stabilized source, can be used (the circuit of the reference voltage is not shown in the diagram of Fig. 4).

Comparing the technical solutions considered in this paper with the devices known in this field, first of all, it is necessary to point out that the presented amplifiers with auto-correction can provide fairly uniform amplification of signals in a very wide frequency band, provided that the amplified signals have a narrow spectrum with a pronounced center. From the description of the signal amplification method and the principle of operation of the amplifiers, it can be seen that the correction occurs in a specific narrow frequency band for a signal located in a given frequency zone, and in the absence of a signal it is also absent. That is, the correction is dynamic in nature, and in the absence of an input signal, the amplifying unit retains the original uneven frequency response characteristic of it without external control.

Claims (16)

1. A method for amplifying sinusoidal and quasi-sinusoidal signals, consisting in applying an amplified signal to the input of an amplifier with a frequency-dependent characteristic of the amplified signal, removing the amplified signal from the output of the amplifier, characterized in that the amplitude-frequency characteristic of the amplifier is preliminarily determined, the signal frequency is measured, and then the obtained frequency value is used to correct the gain by changing the gain by a factor proportional to the value of the inverse frequency response at the point corresponding to the measured signal frequency. 2. The method according to claim 1, characterized in that the measurement of the signal frequency is carried out by preliminary frequency division by n times (n≥2), after which the measurement result is increased by n times. 3. The method according to claim 1, characterized in that the frequency of the signal is measured before it is amplified. 4. The method according to p. 1, characterized in that the frequency of the signal is measured after its amplification. 5. An auto-correction amplifier implementing the method according to claim 1, comprising an amplifying unit with a controlled gain and a control unit, the output of which is connected to the control input of the amplifying unit, the input and output of which are, respectively, the input and output of the auto-correction amplifier, characterized in that a frequency meter and a functional converter are introduced into it, which serves to obtain the value of the inverse amplitude-frequency characteristic at a point corresponding to the measured signal frequency, the input of the frequency meter is combined with the input of an auto-correction amplifier, the output of the frequency meter is connected to the input of the functional converter, the output of which is connected to the input a control unit that serves to generate control signals for the gain of the amplifying unit. 6. The amplifier according to claim 5, characterized in that the functional converter is made in the form of a programmable read-only memory device that implements a hardware-table calculation method. 7. Amplifier according to claim 5, characterized in that the control unit is made in the form of a device that converts digital signals received at its input into analog signals for controlling the gain of the amplifying unit. 8. Amplifier with auto-correction, implementing the method according to claim 1, containing an amplifying unit with a controlled gain and a control unit, the output of which is connected to the control input of the amplifying unit, the input and output of which are, respectively, the input and output of the amplifier with auto-correction, characterized in that a frequency meter and a functional converter are introduced into it, the input of the frequency meter is combined with the output of an amplifier with auto-correction, the output of the frequency meter is connected to the input of a functional converter, the output of which is connected to the input of the control unit, which serves to generate control signals for the gain of the amplifying unit. 9. The amplifier according to claim 8, characterized in that the functional converter is made in the form of a programmable read-only memory device that implements a hardware-table calculation method. 10. Amplifier according to claim 8, characterized in that the control unit is made in the form of a device that converts digital signals received at its input into analog signals for controlling the gain of the amplifying unit. 11. An auto-correction amplifier implementing the method according to claim 1, comprising an amplifying unit with a controlled gain and a control unit, the output of which is connected to the control input of the amplifying unit, the input and output of which are, respectively, the input and output of the auto-correction amplifier, characterized in that a frequency divider, a frequency meter and a functional converter are introduced into it, the input of the frequency divider is combined with the input of an amplifier with auto-correction, the output of the frequency divider is connected to the input of the frequency meter, the output of the frequency meter is connected to the input of the functional converter, the output of which is connected to the input of the control unit, which serves to generating control signals for the gain of the amplifying unit. 12. The amplifier according to claim 11, characterized in that the functional converter is made in the form of a programmable read-only memory device that implements a hardware-table calculation method. 13. Amplifier according to claim 11, characterized in that the control unit is made in the form of a device that converts digital signals received at its input into analog signals for controlling the gain of the amplifying unit. 14. An auto-correction amplifier implementing the method according to claim 1, comprising an amplifying unit with a controlled gain and a control unit, the output of which is connected to the control input of the amplifying unit, the input and output of which are, respectively, the input and output of the auto-correction amplifier, characterized in that a frequency divider, a frequency meter and a functional converter are introduced into it, the input of the frequency divider is combined with the output of an amplifier with auto-correction, the output of the frequency divider is connected to the input of the frequency meter, the output of the frequency meter is connected to the input of the functional converter, the output of which is connected to the input of the control unit, which serves to generating control signals for the gain of the amplifying unit. 15. The amplifier according to claim 14, characterized in that the functional converter is made in the form of a programmable read-only memory device that implements a hardware-table calculation method. 16. The amplifier according to claim 14, characterized in that the control unit is made in the form of a device that converts digital signals received at its input into analog signals for controlling the gain of the amplifying unit.

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