RU2114498C1 - Method and device for frequency modulation - Google Patents

Abstract

FIELD: radio engineering; transmitting devices. SUBSTANCE: high-stability frequency standard 1 functions to regulate frequency of variable-frequency oscillators 2₁ and 2₂ by means of PLL rings incorporating respective phase detectors 3₁ and 3₂ and low-frequency filters 4₁ and 4₂. Frequency of first variable-frequency oscillator 4₁ is varied obeying modulating signal law S(t), that of second oscillator, obeying inverting signal law S(t). Signal picked off first oscillator 4₁ is multiplied n times in multiplier 6₁ and that taken off second oscillator 4₂ is multiplied (n-1) times in multiplier 6₂. Signals taken off multipliers 6₁ and 6₂ are supplied to mixer 7 and then differential signal is discriminated by band filter 8. EFFECT: enlarged frequency variation range ensuring improved frequency stability. 2 cl, 2 dwg

Description

 The invention relates to radio engineering and may find application in transmitting devices.

 A known method of frequency modulation (Dixon R.K. Broadband systems. -M.: Communication, 1979, p.111, Fig. 4.22a), based on changing the frequency of the tunable generator according to the law of the modulating signal and tuning the frequency of the tunable generator using the control voltage formed by quartz discriminator.

 The disadvantage of this method is the impossibility of changing the frequency over a wide range and the limited stabilization range determined by the frequency range of the available quartz discriminators.

 The closest in technical essence to the proposed one is the method of frequency modulation (Dikson R.K. Broadband systems. -M .: Communication, 1979, p. 111), based on a change in the law of the modulating signal of the frequency of the tunable generator, which is tuned using the control voltage formed using a stable reference generator.

 In FIG. 2 shows a block diagram of a device that implements this method, where it is indicated: 1 - stable reference generator; 2 - phase detector; 3 - low pass filter; 4 - tunable generator; 5 - high-pass filter.

 The device comprises a stable reference oscillator 1, a phase detector 2, an LPF 3, a tunable generator 4, one output of which is the output of the device, and the other connected to the second input of the phase detector 2, connected in series.

 The input of the device is the input of the HPF 5, the output of which is connected to the input of the tunable generator 4.

 The device operates as follows.

 The information modulating signal through the high-pass filter 5 gets to the input of the tunable generator 4, which changes its frequency according to the law of the modulating signal. The tunable oscillator 4 is stabilized using a PLL, consisting of a phase detector 2 and a low-pass filter 3, with a stable reference signal generated by the reference generator 1.

 The disadvantage of the prototype is the inability to create a stable frequency that can be changed over a wide range, especially in the case of using tunable crystal oscillators having a low noise level.

 To eliminate this drawback, in the method based on the law of the modulating signal of the frequency of the tunable generator, which is tuned using a stable reference oscillator, the frequency of the additional tunable generator stabilized by the same reference oscillator is changed according to the law of an out-of-phase (inverse) modulating signal, multiplied by n and ( n-1) times the frequency of the primary and secondary tunable generators, with the subsequent separation of the difference frequency signal.

 The first multiplier connected to the output of the first tunable generator is introduced into the device containing the reference oscillator, the first phase detector, the first low-pass filter, the first tunable generator, the output of which is connected to the second input of the first phase detector, and the high-pass filter connected to the input of the first tunable generator generator, connected in series with a second phase detector, a second low-pass filter, a second tunable generator, the second output of which is connected to the second input of the phase detector, second multiplier, a mixer, a bandpass filter, and an inverter connected between the output of the HPF and the input of the second tunable oscillator output of the first multiplier is connected to the second input of the mixer, a second input of the phase detector is coupled to the reference oscillator output.

 The proposed method is as follows.

 Change the frequency of the first tunable generator according to the law of the modulating signal. This frequency is stabilized by a control signal generated using a stable reference non-tunable generator. The frequency of the second tunable oscillator stabilized by the same reference oscillator is changed according to the law of the inverse (antiphase) modulating signal. The frequency of the first tunable generator is multiplied by n times, and the frequency of the second by (n-1) times, after which the difference frequency signal is extracted.

 The proposed method can be implemented in the device shown in figure 1, where it is indicated: 1 - stable reference generator; 2 - phase detector; 3 - low pass filter; 4 - tunable generator; 5 - high-pass filter; 6 - frequency multiplier; 7 - mixer; 8 - band-pass filter; 9 - inverter.

The device contains a stable reference generator 1, the output of which is connected to the inputs of the first and second phase detectors 2 ₁ and 2 ₂ , the outputs of which are connected through the corresponding low-pass filters 3 ₁ and 3 ₂ to the first and second tunable generators 4 ₁ and 4 ₂ . The outputs of these generators 4 ₁ and 4 ₂ through the corresponding frequency multipliers 6 ₁ and 6 _{2 are} connected to the inputs of the mixer 7. The output of the mixer 7 is connected to the input of the bandpass filter 8, the output of which is the output of the device. The second outputs of tunable generators 4 ₁ and 4 _{2 are} connected to the second inputs of the corresponding phase detectors 2 ₁ and 2 ₂ , and the inputs are connected to the output of the HPF 5, and the input of the generator 4 _{1 is} directly connected to the HPF 5, and the input of the generator 4 ₂ through the inverter 9 .

 The device operates as follows.

The information modulating signal S (t) through the HPF 5 is fed to the first tunable generator 4 ₁ , which changes its frequency according to the law S (t). At the same time, S (t) through the HPF 5 and inverter 9 is fed to the input of the second tunable generator 4 ₂ . Moreover, in the generator 4 ₂ frequency modulation is carried out according to the law of inverse (antiphase) S (t). The frequency stabilization of blocks 4 ₁ and 4 _{2 is} carried out by the reference oscillator 1 using the corresponding PLL containing a phase detector 2 and an LPF 3. The signal from the output of the generator 4 ₁ goes to the multiplier 6 ₁ , where the frequency of the multiplier signal is n times, and from the generator output 4 _{2 the} signal goes to the multiplier 6 ₂ , where its frequency is multiplied by (n-1) times (n is an integer). From the outputs of the multipliers 6 ₁ and 6 _{2, the} signals are supplied to the mixer 7, and then the difference signal is allocated by a band-pass filter 8.

The prototype device provides a signal with a frequency modulation of the form
U (t) = U _o cos [ω _o t + Δω (t) + Δω _ns (t) + φ _o ], (1)
Where
U ₀ is the oscillation amplitude;
ω _o is the carrier frequency;
φ _o - the initial phase of the oscillation;
Δω _ns (t) is an alternating random deviation of the frequency of the tunable generator, due to the instability of the stabilizing reference generator;
Δω (t) = K • S (t),
Where
K is the proportionality coefficient connecting the change in frequency with the modulating voltage S (t).

В (2) и (3) учтена стабилизация блоков 4₁ и 4₂ общим стабильным генератором 1. После умножения сигнала (2), сформированного в блоке 4₁ в n раз (n - целое число) в умножителе 6₁, на его выходе имеем
U_1n(t) = U $\genfrac{}{}{0ex}{}{\text{*}}{\text{o}}$ cos[nω_ot+nΔω(t)+nφ_o+nΔω_нс(t)] (4)
Аналогично, после умножения колебания (3) в (n-1) раз в блоке 4₂ на его выходе имеем

После выделения сигнала разностной частоты в смесителе 7 с полосовым фильтром 8 на выходе устройства получаем
U_вых(t) = U $\genfrac{}{}{0ex}{}{\text{**}}{\text{o}}$ cos[ω_ot+(2n-1)Δωt+Δω_нс(t)+φ_o] (6)
Из выражения (6) видно, что предлагаемый способ частотной модуляции обеспечивает изменение частоты генератора в более широких пределах, чем прототип, при той же нестабильности частоты, определяемой стабильным опорным генератором.In the proposed device, taking into account the modulation of the first tunable generator 4 ₁ according to the law S (t) and the modulation of the second tunable generator 4 ₂ according to the law inverse S (t) at the output of blocks 4 ₁ and 4 ₂ we have, respectively

In (2) and (3), stabilization of blocks 4 ₁ and 4 _{2 by a} common stable generator 1 was taken into account. After multiplying the signal (2) generated in block 4 _{1 by} n times (n is an integer) in the multiplier 6 ₁ , at its output we have
U _1n (t) = U $\genfrac{}{}{0ex}{}{\text{*}}{\text{o}}$ cos [nω _o t + nΔω (t) + nφ _o + nΔω _ns (t)] (4)
Similarly, after multiplying the oscillations (3) by (n-1) times in block 4 _2, at its output we have

After extracting the differential frequency signal in the mixer 7 with a bandpass filter 8 at the output of the device, we obtain
U _o (t) = U $\genfrac{}{}{0ex}{}{\text{**}}{\text{o}}$ cos [ω _o t + (2n-1) Δωt + Δω _ns (t) + φ _o ] (6)
From the expression (6) it can be seen that the proposed method of frequency modulation provides a change in the frequency of the generator over a wider range than the prototype, with the same frequency instability determined by a stable reference generator.

The frequency range in the proposed device is greater than in the prototype, n times, where n is the frequency multiplier in blocks 6 ₁ and 6 ₂ .

Claims (2)

 1. A frequency modulation method based on a change in the law of a modulating signal of the frequency of a tunable generator synchronized by a stable reference generator, characterized in that the frequency of an additional tunable generator stabilized by the same reference generator is changed according to the law of an inverse modulating signal, the frequency of the main and (n-1) times the frequency of the additional tunable generators, and then the difference frequency signal is isolated.  2. A frequency modulation device comprising a stable reference oscillator, a first phase detector, a first low-pass filter (LPF), a first tunable generator, the input of which is connected to the output of a high-pass filter (HPF) and the output to the second input of the first phase detector, characterized in that the first frequency multiplier is introduced n times, the input of which is connected to the output of the first tunable generator, the second phase detector, the second low-pass filter, the second tunable generator are connected in series a torus, a second frequency multiplier (n-1) times, a mixer, the second input of which is connected to the output of the first multiplier, a bandpass filter, and an inverter connected between the output of the HPF and the input of the second tunable generator, the second output of which is connected to the second input of the second phase a detector connected to the output of a stable reference generator by its input.

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