RU2568428C2 - Device for detecting frequency-modulated oscillations - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: input (1) and output (2) of the device are connected through a first (C1) and a second (C2) capacitor and an amplitude detector (AD), connection clamps of the first (C1) and second (C2) capacitors are connected through an inductance coil (L1) to the common bus (3) of the circuit, which is connected through a resistor (R1) to the common clamp of the second (C2) capacitor and the input of the amplitude detector (AD).

EFFECT: voltage at the output of the amplitude detector is many times greater than at the input without using amplifiers.

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Description

The invention relates to the field of radio engineering and can be used to build frequency detectors with an extended linearity section and an increased steepness of the detector characteristic.

Known devices for detecting frequency-modulated oscillations described in the sources (see, for example):

1. I.S. Gonorovsky - ″ Radio engineering circuits and signals ″, "Soviet Radio", Moscow, 1963, p. 470-478.

2. B.C. Andreev - “Theory of nonlinear electric circuits”, Moscow: “Communication”, 1972, p. 108.

The closest in technical essence, that is, the prototype, is the device described by B.C. Andreev. On page 108 is a diagram of a prototype (FIG. 1), consisting of elements: a first resistor, a first inductor, a first capacitor, and an amplitude detector. In it, the detector characteristic is formed by the frequency response of a parallel oscillatory circuit.

The disadvantage of the prototype is the small steepness of the detector characteristics due to the small portion of the required linearity of the amplitude-frequency characteristics of the parallel oscillatory circuit at the input of the amplitude detector.

The problem, which is aimed by the claimed device, is to increase the steepness and linearity of the detector characteristics, by including an additional capacitor and resistor and the corresponding construction of the circuit in front of the amplitude detector.

The technical result of the solution of this problem is achieved by the fact that in the device for detecting frequency-modulated oscillations, containing the first capacitor, connected by the first terminal to a common point in parallel connected to the first inductor and the first resistor, which are connected to the common bus of the circuit as well as their other connection of terminals an amplitude detector, the output of which is the output of the device, the input of the device is connected to the second output of the first capacitor, additionally connected in series the second capacitor and the second resistor connected by a free capacitor terminal to the junction point of the first resistor, the first capacitor and the first inductor, and a free resistor terminal to a common bus; the input of the amplitude detector is connected to a common connection point of the second capacitor and the second resistor.

The aim of the invention is to increase the steepness and increase the linear working area of the detector characteristic, which increases the noise immunity of signals with frequency modulation. The goal is achieved by changing the circuit connected in front of the amplitude detector.

Schematic diagram of a device for detecting frequency-modulated oscillations is shown in figure 2.

The essence of the invention lies in the fact that the input (1) and output (2) of the device are connected through the first (C1) and second (C2) capacitors and an amplitude detector (HELL), the clamps of the connection of the first (C1) and second (C2) capacitors through parallel the connected first inductor (L1) and the first resistor (R1) are connected to a common bus line (3) of the circuit, which is connected through a second resistor (R2) to the common terminal of the second capacitor (C2) and the amplitude detector input (AM). Such a circuit scheme provides an increase in the linearity section of the frequency response of the formed circuit during detection and the voltage at its output is many times greater than in the prototype circuit (without the use of amplification devices).

The operator transfer function of the formed chain has the form

where p is the Laplace operator.

The complex transfer function will then be equal to

- мнимая единица.Where $$i=\sqrt{-\mathrm{one}}$$

- imaginary unit.

Selecting the module, we find the amplitude-frequency characteristic

Frequency response at C ₁ = C ₂ = C, R ₁ = R ₂ = R

, а также при частоте $${\omega }_0\text{'}=\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$\sqrt{RC}$}\right.$$

будет равнымat resonant frequency $${\omega }_{}$$$${}_0=\raisebox{1ex}{$\mathrm{one}$}\!\left/ \!\raisebox{-1ex}{$\sqrt{L_{\mathrm{one}}{C}_{\mathrm{one}}}$}\right.$$

as well as at the frequency $${\omega }_0\text{'}\text{'}=\raisebox{1ex}{$\mathrm{one}$}\!\left/ \!\raisebox{-1ex}{$\sqrt{RC}$}\right.$$

will be equal

Therefore, the amplitude of the voltage at the input of the amplitude detector is determined by the value of the Q factor of the circuit (Q) of the formed series circuit L ₁ C ₁ . The greater the resistance values R ₁ and R ₂ will have, the higher the signal level at the output of the circuit.

The ratio of the amplitudes of the voltage at the input of the amplitude detector in the inventive device (for the considered option) is

Thus, when the first and second capacitors, the amplitude detector and the output terminal are connected in series to the device’s input, as well as by connecting the device’s common bus with the leads of the inductance coil and the first resistor connected to the common connection of the terminals of the first and second capacitors, the outputs of the second resistor to the common connection point the second capacitor and the input of the amplitude detector, the steepness of the linearity of the frequency response increases in proportion to the quality factor of the circuit, by input amplitude detector.

Figure 3 presents graphs of the amplitude-frequency characteristics of the circuits connected to the amplitude detector in the prototype (H (f)) and the inventive device (H2C (f)) with correspondingly equal values of the elements.

With a frequency band within the linearity of the frequency response, the slope of the characteristic can be defined as S = ΔU / Δf, where ΔU is the amplitude linearity section and Δf is the frequency linearity section. When the amplitude of the input voltage equal to 1V, and the values of the elements indicated on the curves of figure 3, we will have as a result of calculation:

for prototype

for the claimed device

Therefore, the steepness of the detector characteristics of the claimed device will be greater than in the prototype circuit

The introduction of additional capacitor and resistor provides a positive additional effect - an increase in the linear working section of the characteristics of the device for detecting frequency-modulated oscillations in comparison with the prototype in

.

.

The calculation of the values of the parameters of the elements is based on the solution of the approximation problem for given conditions.

The use of the invention provides an increase in the steepness and an increase in the linearity of the detector characteristic due to the use of additional elements in the circuit to an amplitude detector, which increases the noise immunity of signals with frequency modulation.

The drawing (figure 1) shows a schematic diagram of a device where it is indicated: 1 - input, 2 - output and 3 - common bus device for detecting frequency-modulated oscillations; R1 is the first and R2 is the second resistor, C1 is the first and C2 is the second capacitor, L1 is the first inductor and HELL is an amplitude detector.

The input of the device 1 is the left clamp of the first C1 and second C2 capacitors connected in series, the amplitude detector HELL and the clamp of the output 2 of the device; a common bus 3 with common clamps connected in parallel to the first inductance coil L1 and the first resistor R1 connected to a common switching point of the first C1 and second C2 capacitors, as well as the clamps of the second resistor R2 to the common point of the second capacitor C2 and amplitude detector AM.

Claims (1)

A device for detecting frequency-modulated oscillations, comprising a first capacitor connected by a first terminal to a common point of the first inductance coil and a first resistor connected in parallel, which are connected to the common bus of both the circuit and the amplitude detector by the other terminal connection, the output of which is the output of the device, characterized the fact that the input of the device is connected to the second output of the first capacitor, additionally connected in series are the second capacitor and the second resistor, sub li ne free end of the capacitor to the junction of the first resistor, the first capacitor and the first inductor, and a free terminal of the resistor to a common bus; the input of the amplitude detector is connected to a common connection point of the second capacitor and the second resistor.

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