RU2573221C2 - Method and shaper of amplitude-frequency characteristic with high squareness ratio of paths of frequency-modulated signals with pulse modulation - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: method of shaping of the amplitude-frequency characteristic (AFC) with high squareness ratio of paths of frequency-modulated signals with pulse modulation is characterized by that the amplitudes of pulsed-frequency-modulated (PFM) oscillations are normalized, then - the value of deviation of PFM of oscillations are converted to values of instant signal amplitude, the instant signal amplitude is tracked in such a way that at drop of amplitude below the pre-set threshold U₀ the control signal for decrease of transfer ratio is generated, and at return of the value of instant signal amplitude in the limits above the pre-set triggering threshold U₀ the control signal is registered. AFC shaper comprises the threshold device and, at least, one circuit with variable transfer ratio, the amplifier limiter, the reference loop, the threshold device through the control circuit is connected to the circuit with variable transfer ratio.

EFFECT: increase of attenuation behind the pass-band of the amplitude-frequency characteristic.

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Description

The group of inventions relates to the field of radio electronics, namely to selective devices, and is intended for use in a wide class of electronic devices.

A device for obtaining the desired amplitude-frequency characteristics based on the use of concentrated selection filters, which are at least two coupled oscillatory circuits (Bug NN and other radio receivers: Textbook for universities. - M.: Radio and communications, 1986, p. 83). The required frequency response of this device depends on the choice of the resonant frequencies of the circuits, the depth of connection of the circuits, their quality factor.

However, the implementation of such a filter is a difficult technical task because it requires the manufacture of high-precision elements for these filters or requires careful tuning.

A device is also known for obtaining the required amplitude-frequency characteristic, based on the use of quartz filters, which are a circuit consisting of quartz resonators made with high accuracy and interconnected, usually by means of capacitors (Golovin O.V. Professional decameter radio receivers band. - M .: Radio and communications, 1985, p. 49). The circuit can be performed on discrete high-precision components or in the form of a hybrid integrated circuit.

However, such industrial products are expensive due to the complexity of manufacturing and fitting the nominal values of the elements of the circuit in production.

Closest to the claimed device is a gain control for a receiver in a multi-carrier communication system, which can be used as a device for generating an amplitude-frequency characteristic with a high coefficient of squareness (patent for invention RU 2389131). The controller comprises means for detecting the total power of the received modulated signal, as well as means for adjusting the gain of the receiver in one direction, from the lowest gain to the highest gain, based on the detected total power of the received signal.

This device is taken as a prototype. The disadvantage of the prototype is the design complexity of the means for detecting the total power and means for regulating the gain.

путем определения разностного сигнала $$\Delta X_i=X_i-X_{i-1}^{ф}$$

, выходной цифровой сигнал $$X_i^{ф}$$

формируют в виде суммы предыдущего значения $$X_{i-1}^{ф}$$

и дополнительного сигнала Δ_i, причем дополнительный сигнала Δ_i выбирают равным заданному значению Δ, если ΔX_i≥Δ, значение минус Δ, если ΔX_i≤-Δ, и нулю, если -Δ<ΔX_i<Δ, где Δ соответствует максимально допустимому превышению сигнала помехи над полезным сигналом.A known method of digital filtering of signals, which allows to obtain a filter characteristic characterized by a high coefficient of squareness (patent for invention RU 2188499). A method of digitally filtering signals includes converting the input signal X to digital form X _i (i = 1, 2, 3, ...), comparing the converted input signal _i with the output digital signal $$X_i^f$$

by determining the difference signal $$\Delta X_i=X_i-X_{i-\mathrm{one}}^f$$

digital output $$X_i^f$$

form as the sum of the previous value $$X_{i-\mathrm{one}}^f$$

and an additional signal Δ _i , and the additional signal Δ _{i is} chosen equal to a predetermined value Δ if ΔX _i ≥Δ, the value is minus Δ if ΔX _i ≤-Δ, and zero if -Δ <ΔX _i <Δ, where Δ corresponds to the maximum permissible excess of the interference signal over the useful signal.

However, digital filtering of signals is complicated; it requires a number of mathematical operations to be performed on a signal converted to a digital form.

A known method of demodulating and filtering phase-modulated signals (patent RU 2491711), which is closest to the claimed method due to the presence of the processing stage of the signal on the circuit with a given quasilinear slope and frequency response form. The method of demodulating and filtering phase-modulated signals is that the demodulator is turned on between the source of phase-modulated signals and the low-frequency load and is made of a four-terminal, two-pole non-linear element, a low-pass filter and a separation capacitance, the phase-modulated signal is converted into an amplitude-phase-modulated signal by applying it to the right or the left slope of the amplitude-frequency characteristic, using a non-linear element, destroy the spectrum of the amplitude-phase modulated signal to high-frequency and low-frequency components, using the low-pass filter, the information low-frequency signal is extracted, the dc component of the information low-frequency signal is eliminated with the help of a separation capacitance, the amplitude of which changes according to the law of phase change of the phase-modulated input signal, the information low-frequency signal is applied to the low-frequency selective load in the form of a differentiating or integrating circuit, respectively, characterized in that between the output of four a high-frequency load, a bipolar nonlinear element is connected between the phase-modulated signal source and the input of the four-terminal into the longitudinal circuit, the dependences of the elements of the four-terminal resistance matrix on the frequency are selected from the conditions for the formation of a given shape and the left quasilinear slope of the amplitude-frequency characteristic of the high-frequency part demodulator using certain mathematical expressions.

This method is adopted as a prototype. However, the known method is very complicated.

The objective of the technical solution is to create a frequency selection device for frequency-pulse-modulated (PFM) oscillations having a reference oscillating circuit and a threshold device having at least one circuit with a controlled transmission coefficient.

The technical result consists in increasing the squareness coefficient of the amplitude-frequency characteristic (AFC), improving attenuation behind the passband, simplifying the design by eliminating expensive quartz filters or difficult filters of concentrated selection.

The specified technical result is achieved by the fact that, according to the method for generating an amplitude-frequency characteristic with a high coefficient of squareness of the paths of frequency-modulated signals with pulse modulation, the amplitude of the PFM oscillations is normalized first, then the deviation of the PFM oscillations is converted to the values of the instantaneous signal amplitude, while tracking for the instantaneous signal amplitude so that the amplitude decreases below a predetermined threshold U ₀ outputs a control signal to reduce the gain, and if the return value of the instantaneous signal amplitude at the limits above the set threshold U ₀ control signal is removed.

The specified technical result is achieved by the fact that the device for generating the amplitude-frequency characteristic with a high coefficient of rectangularity of the paths of frequency-modulated signals with pulse modulation, including a threshold device, at least one circuit with a variable transmission coefficient, according to the solution contains an amplifier-limiter, a reference loop , while the input of the claimed device is connected to the amplifier-limiter, and the output of the amplifier-limiter is connected to a circuit with a variable coefficient per and with a reference circuit connected to a threshold device, which, in turn, is connected via a control circuit to a circuit with a variable transmission coefficient, and ensuring the implementation of the method according to claim 1.

The inventive device is illustrated by figures, where in FIG. 1 shows its structural diagram, in FIG. 2 shows the resonance curve of the reference contour. The positions in the drawing indicate:

1 - amplifier limiter;

2 - a circuit with a variable transmission coefficient;

3 - reference contour;

4 - threshold device.

The claimed group of inventions is characterized by the use of a new method of frequency selection using a reference circuit and a threshold device that controls at least one circuit with a variable transmission coefficient. The property of selective conductivity is obtained not due to the properties of the filtering device, but due to the selective processing of the initial signal by the device. Moreover, the signal itself controls the operation of the device. In this case, the property of the signal to change its frequency is used. Like all frequency selection devices, including the devices mentioned above, the proposed device has the property of selective conductivity at different frequencies. The difference of the claimed device is that the property of selective conductivity is obtained not due to the properties of the filtering device, but due to the selective processing of the original signal by the device. Moreover, the signal itself controls the operation of the device. In this case, the property of the signal to change its frequency is used.

The essence of the method

A method for generating a frequency response with a high coefficient of squareness consists in tracking the deviation of the frequency-modulated (FM) signal relative to its carrier frequency and, when the frequency deviates above a certain value (below f _min or above f _max ), an abrupt decrease in the signal conductivity. The inventive method is applicable only to frequency-pulse-modulated (hereinafter - PFM) oscillations, i.e. oscillations modulated in frequency by a pulse signal. In this case, a pulse signal is understood as a discrete two-level signal. To ensure tracking of the deviation relative to the carrier frequency of the FM signal is converted into amplitude-modulated so that its amplitude is inversely proportional to the magnitude of the deviation. Thus, f _min and f _max corresponds to one threshold value of the amplitude of the signal U ₀ . The instantaneous values of the amplitude are monitored, and when it decreases below the threshold U ₀ , the transmission coefficient is sharply reduced, and when it is increased above the threshold U _{0, it is} sharply increased, which is equivalent to the synthesis of the rectangular frequency response of the device. Thus, the actual algorithm for processing PFM oscillations looks like this:

1) normalization of the amplitude of the PFM oscillations;

2) the conversion of the deviation of the PFM oscillations into the values of the instantaneous amplitude of the signal;

3) tracking the instantaneous amplitude of the signal, when the amplitude decreases below a predetermined threshold U ₀ - issuing a control signal to reduce the transmission coefficient;

4) when the value of the instantaneous amplitude of the signal returns above the set threshold of operation U ₀ - removal of the control signal.

Device essence

In the claimed device, the functional analogue of the means for detecting the total power of the received modulated signal is a threshold device, which, however, detects not the total but the instantaneous power, which makes it much simpler: the power of only one carrier is measured in the claimed device, unlike the prototype, where the power of multiple carriers is measured. A functional analogue of the means for adjusting the gain in one direction is a circuit with a variable transmission coefficient, however, the direction of regulation in a circuit with a variable coefficient from the largest to the smallest gain, i.e. back to the direction of the means for adjusting the gain, in addition, in the inventive device, the circuit with a variable transmission coefficient has, in contrast to the prototype, only two gain steps - the minimum and maximum. The inventive device consists of an amplifier-limiter 1, a circuit with a variable transmission coefficient 2, a reference circuit 3 and a threshold device 4. The input of the inventive device is connected to an amplifier-limiter 1, necessary to eliminate possible stray amplitude modulation of a frequency-modulated signal. It can be an amplifier covered by nonlinear feedback, or an amplifier connected in series with a diode limiter. The output of the amplifier-limiter is connected to a circuit with a variable transmission coefficient 2. At the same time, the output of the amplifier-limiter 1 is connected to a reference circuit 3. The reference circuit 3 is connected to a threshold device 4, which, in turn, is connected to the circuit 2 through the control circuit. 2 is an actuator. It provides two gain modes: high gain and low. The implementation of the circuit is possible in various ways: on p-i-n diodes, on double-gate field-effect transistors, on modulator microcircuits, etc. A threshold device 4 is necessary for detecting a state of low instantaneous signal power. The reference circuit, due to its frequency-selective properties, serves as a device that converts the magnitude of the deviation of the frequency-modulated signal into instantaneous power values. The supporting contour does not have any design or circuit features. The threshold device can be a voltage comparator with a small hysteresis of the characteristics and high speed in the integrated design, the industry produces a wide range of such products.

The device operates as follows. PFM oscillations are fed to the limiter amplifier, where possible fluctuations in the signal amplitude are eliminated, and the signal itself is normalized by level, which is necessary for the threshold device to work correctly. Further, the PFM oscillations are applied to the reference circuit and to the circuit with a variable transmission coefficient. Depending on the deviation of the signal arriving at the reference circuit, the voltage on the circuit, and hence the instantaneous power, will change. In FIG. 2 shows the resonance curve of the reference contour. At a certain value of the deviation, the voltage across the circuit will become less than the value of the response level of the threshold device shown by a horizontal line in FIG. 2. In this case, the threshold device detects a mode with low instantaneous power and provides a control signal to the circuit with a variable transmission coefficient, aimed at reducing the transmission coefficient. As a result, at the output of the device, the amplitude of the PFM oscillations will be much smaller each time its deviation exceeds a certain value, which can be adjusted by changing the threshold level of the threshold device (arrow in Fig. 2). When the response level changes, the bandwidth of the device changes. As a result, we obtain a rectangular frequency response limited by the frequencies f _min and f _max shown in FIG. 2. The high squareness coefficient of the obtained frequency response is determined by the speed of the circuit with a variable transmission coefficient and a threshold device. High attenuation beyond the passband can be obtained by selecting circuit parameters with a variable transmission coefficient or by increasing the amount of these circuits.

Claims (2)

1. A method of generating an amplitude-frequency characteristic with a high squareness factor of the paths of frequency-modulated signals with pulse modulation, characterized in that the amplitude of the frequency-pulse-modulated oscillations is normalized first, then the deviation of the frequency-pulse-modulated oscillations is converted to instantaneous values signal amplitude, wherein the tracking is performed instantaneous signal amplitude so that the amplitude decreases below a predetermined threshold U ₀ provide a control signal to decrease the gain, and if the return value of the instantaneous signal amplitude at the limits above the set threshold U ₀ control signal is removed. 2. A device for generating an amplitude-frequency characteristic with a high coefficient of rectangularity of the paths of frequency-modulated signals with pulse modulation, including a threshold device and at least one circuit with a variable transmission coefficient and ensuring the implementation of the method according to claim 1, characterized in that it contains an amplifier-limiter and a reference circuit, while the input of the device is connected to an amplifier-limiter, and the output of an amplifier-limiter is connected to a circuit with a variable transmission coefficient and to op a circuit connected to a threshold device, which, in turn, is connected via a control circuit to a circuit with a variable transmission coefficient.

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