RU2449462C1 - Synthesizer of frequency-modulated signals - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: synthesizer of frequency-modulated signals comprises a phase detector, a low pass filter, a controlled generator, a divider with an alternating division ratio (DADR), a reference generator, a divider with a fixed division ratio (DFDR), an information source, M (M>1) generators of sine and cosine components of manipulation frequencies, M scale amplifiers for sine outputs and M scale amplifiers for cosine outputs, the first and second switchboards, a controlled phase inverter, the first and second multipliers, a control unit, a summator, a quadrature signal shaper.

EFFECT: higher efficiency of digital information transfer, removal of limitation for transferred information.

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Description

The proposed device relates to radio communications and can be used in radio receivers and radio transmitting devices designed for the formation of frequency-modulated radio signals.

To transmit and receive signals, frequency modulation of harmonic oscillations of the carrier frequency is used.

The frequency modulation of the harmonic oscillator is described, for example, in information sources [1], [3], [7], but has a significant drawback - low frequency stability or out-of-band components.

Most often, synthesizers based on phase-locked loop (PLL) are used to generate harmonic oscillations, the main requirements for which are to generate a given carrier frequency or local oscillator frequency with high stability of the output oscillation. Such a possibility is considered in the literature, for example [1], [2], [3], [8].

A typical functional diagram of the synthesizer is given in [4] in Fig. 1.15. p.33.

However, all known technical solutions do not provide the transmission of digital signals with a large number of identical symbols, for example, units.

For clarification, we consider a special case. If an FM signal is transmitted with a deviation of the output frequency of 5 kHz and a transmission speed of 8 kbit (bit duration 0.125 Moscow time), then for one bit the phase advance relative to the carrier wave will be φ ₁ = 2π · 0.125 × 5 or φ ₁ = 2π · 0.625. When transmitting in a row N identical characters, φ _N = 2π 0.625 × N. At the output of the phase modulator, the phase should change less by a factor of division of the DPKD times, i.e. k times and make φ _NFD = 27π · 0.625 × (N / k). It was shown in [1] (p.250) that the maximum value of phase deviation in an analog phase modulator is ± 2π / 3, and in the same book (p.272) the maximum value of phase deviation in a digital phase modulator is ± π. Similar results are given in many other sources.

Thus, for the considered example, the number of identical symbols should not exceed for the case under consideration N _MAX = k / 1.25. If we consider the transmission of characters in various combinations, then the restriction will be even more stringent. Therefore, the existing frequency modulators impose a restriction on the transmitted information, which is not permissible.

The closest in technical essence to the proposed one is the FM synthesizer of harmonic oscillations, given in [5], Ch. 1, Fig. 1.8, adopted as a prototype.

The functional diagram of the prototype device is presented in figure 1, where it is indicated:

1 - source of information;

4 - phase detector (PD);

5 - low-pass filter (low-pass filter);

6 - controlled generator (UG);

7 - reference generator (OG);

8 - frequency divider with a fixed division ratio (DPCD);

9 - frequency divider with a variable division ratio (DPKD);

19 - integrator;

20 - phase modulator (FM).

The prototype device contains a serially connected information source 1, integrator 19, FM 20, FD 4, low-pass filter 5 and UG 6, the output of which is the output of the device and through DPKD 9 is connected to the second input of FD 4. In addition, the output of exhaust gas 7 through DFKD 8 connected to the second input of FM 20.

The device operates as follows.

The reference generator 7 generates a reference high-frequency oscillation, the frequency of which is divided by a fixed number in DFKD 8. From the output of the divider 8, the high-frequency voltage is supplied to the second input of the phase modulator 20, the first input of which is supplied with a low frequency voltage from the information source 1, passed through the integrator 19. The output voltage of the phase modulator 20 is supplied to the first input of the phase detector 4, which generates a voltage proportional to the phase difference between the high-frequency voltages at the first and second the inputs of the PD 4, and the high-frequency voltage from the output of FM 20 is supplied to the first input, and the high-frequency voltage from the output of the controlled generator 6 passed through the divider with a variable division coefficient 9 is supplied to the second input. The output voltage of the phase detector 4 is integrated in the low-pass filter 5 and fed to the input of the controlled generator 6 and changes its frequency so that the phase of the high-frequency oscillation at the second input of the phase detector 4 is equal to the phase at the first input of the phase detector 4. For this reason, the output voltage UG 6 will have a phase equal to the phase of high-frequency oscillations at the first input of PD 4, increased by the division coefficient of DPKD 9 k times. In other words, the frequency of harmonic oscillations at the output of UG 6 will be k times greater than the oscillation frequency at the first input of phase detector 4, and the phase deviation of the high-frequency oscillation will be k times greater than the phase deviation at the first input of phase detector 4.

However, phase modulators have a limited maximum phase deviation, which limits the number of consecutive characters to N _MAX ; more precisely, any combination of characters in which the number of zeros and ones differs by N _MAX will be distorted. Thus, the prototype synthesizer is inefficient when transmitting a digital signal.

The objective of the proposed technical solution is to increase the efficiency of digital information transmission, i.e. removal of restrictions on the transmitted information.

To solve the problem, a frequency-modulated signal synthesizer containing a series-connected phase detector (PD), a low-pass filter, a controlled oscillator and a frequency divider with a variable division ratio (DPD), the output of which is connected to the second input of the PD, and the output of the controlled generator is with the output of the synthesizer, a reference oscillator and a frequency divider with a fixed division coefficient (DPCD), as well as an information source, according to the invention, are introduced in series M (M> 1) gene sine and cosine components of the manipulation frequencies, the sine and cosine outputs of which are connected through the corresponding M scale amplifiers for sine outputs and M scale amplifiers for cosine outputs to the corresponding inputs of the first and second switches, the control inputs of which are connected to the first output of the control unit, the second output of which connected to the control input of the controlled phase inverter, the output of which is connected to the second input of the adder, the output of which is connected to the first input of the PD, when In this case, the DFCA output is connected to the input of the quadrature signal driver, the sine output of which is connected to the first input of the first multiplier, and the cosine output is connected to the first input of the second multiplier, the output of which is connected to the input of the controlled phase inverter, the output of the first multiplier is connected to the first input of the adder, in addition , the outputs of the first and second switches are connected to the second inputs of the first and second multipliers, respectively, the output of the information source is connected to the input of the control unit.

Functional diagram of the proposed device is shown in figure 2, where indicated:

1 - source of information;

2 - control unit;

3 - shaper quadrature signal;

4 - phase detector (PD);

5 - low-pass filter (low-pass filter);

6 - controlled generator (UG);

7 - reference generator (OG);

8 - frequency divider with a fixed division ratio (DPCD);

9 - frequency divider with a variable division ratio (DPKD);

10, 11 - the first and second multipliers;

12 - controlled phase inverter;

13, 14 - the first and second switches;

15 ₁ , 15 ₂ , ... 15 _M - large-scale amplifiers of harmonic oscillations of the sine channels of the FM generators;

16 ₁ , 16 ₂ , ... 16 _M - large-scale amplifiers of harmonic oscillations of the cosine channels of FM generators;

17 ₁ , 17 ₂ , ... 17 _M - generators of the sine and cosine components of the frequencies of manipulation;

18 - adder.

At present, harmonic generators are widely used, which simultaneously generate the sine and cosine components. For example, in the description [9] of Analog devices AD6620 digital receiver, there is a functional diagram in which there is a complex NCO (Numerically Controlled Oscillator - Digitally Generated Generator), which has two outputs: sine and cosine.

The quadrature channel shaper (a generator with two sine and cosine outputs) has several implementation options, for example, [10], p. 147, fig. 5.18; p. 151, fig. 5.21; [11], p. 72 fig. 3.13, fig. 3.14 and others.

The proposed device contains a reference oscillator 7 connected through DFKD 8 with a quadrature signal shaper 3, the sinus output of which is connected to the first input of the first multiplier 10, the cosine output of the quadrature signal shaper 3 is connected to the first input of the second multiplier 11, while the second inputs of the multipliers 10 and 11 connected to the outputs of the first 13 and second 14 switches, respectively. The output of the first multiplier 10 is connected to the first input of the adder 18, and the output of the second multiplier 11 through a controlled phase inverter 12 is connected to the second input of the adder 18, the output of which is connected to the first input of the phase detector 4, the output of which is through a serial chain from the low-pass filter 5, UG 6 and DPKD 9 is connected to the second input of the PD 4, and the output of the controlled generator 6 is the output of the frequency synthesizer.

The information source 1 is connected to the input of the control unit 2, the first output of which is connected to the control inputs of the switches 13 and 14, and the second output of the control unit 2 is connected to the control input of the phase inverter 12. In addition, the sine and cosine outputs M of the sine and cosine frequency generators manipulations 17 through the corresponding scale amplifiers 15 ₁ , 15 ₂ , ... 15 _M for sine outputs and scale amplifiers 16 ₁ , 16 ₂ , ... 16 _M for cosine outputs are connected to the corresponding inputs of the first 13 and second 14 switches.

Before considering the operation of the proposed device, we consider the principle of the formation of multi-frequency telegraphy (MCT). Consider the simplest case of 4-position frequency telegraphy, i.e. there are four informational positions 0, 1, 2 and 3. Let 0 correspond to a frequency deviation of -2ΔF, let 1 correspond to a frequency deviation of -ΔF, let 2 correspond to a frequency deviation of ΔF, let 3 correspond to a frequency deviation of 2ΔF.

Similarly, you can imagine work with an arbitrary number of positions. Note once again that the deviation of the synthesizer output signal will be larger by a factor of k, i.e. -2kΔF, -kΔF, kΔF, 2kΔF.

Suppose you want to transfer position 3, i.e. establish a deviation of 2ΔF. In accordance with the above, harmonic signals sin (2πf ₀ t) and sin (2π2ΔFt) will act on the inputs of the first multiplier 10, and harmonic signals cos (2πf ₀ t) and cos (2π2ΔFt) will act on the inputs of the second multiplier 11. The voltage u (t) at the output of the adder 18 can be written as

u (t) = sin (2π2ΔFt) sin (2πf ₀ t) ± cos (2π2ΔFt) cos (2πf ₀ t)

or in accordance with the formula for the cosine of the sum of two angles

u (t) = - cos (2π (f ₀ ± 2ΔF) t).

Thus, the frequency at the first input of the phase detector 4 changes, which will lead to a change in the output frequency of the synthesizer by 2ΔF, and the phase by 2ΔFt. With this approach, the phase grows linearly with time and, in principle, there is no limit to its growth in magnitude. Consequently, the restriction on the transmitted information by the number of identical symbols transmitted in a row is removed.

Consider the operation of the proposed device as a whole.

The proposed device operates as follows. The generators of the sine and cosine components of the manipulation frequencies 17 ₁ , 17 ₂ , ... 17 _M generate harmonic oscillations at the frequencies ΔF ₁ , ΔF ₂ , ... ΔF _M , and each generator generates sinusoidal and cosine components of the harmonic oscillation with the corresponding frequency. Sinusoidal components from the generators 17 ₁ , 17 ₂ , ... 17 _{M are} connected to the inputs of scale amplifiers of harmonic oscillations 15 ₁ , 15 ₂ , ... 15 _M (they provide the conversion of phase modulation to frequency - multiplication by 1 / F _i ). The cosine components from the generators 17 ₁ , 17 ₂ , ... 17 _{M are} connected to the inputs of large-scale harmonic oscillation amplifiers 16 ₁ , 16 ₂ , ... 16 _M (they provide the conversion of phase modulation to frequency - multiplication by 1 / ΔF _i , i takes values from 1 to M). The output voltages of scale amplifiers of sinusoidal harmonic oscillations 15 ₁ , 15 ₂ , ... 15 _M are applied to the inputs of the first switch 13, to the control input of which a command is sent from the control unit 2, this command connects to the output of the switch 13 and, therefore, to the input of the first multiplier 10 one of the M sinusoidal harmonic components. The number (from 0 to M) of the harmonic component is determined by the control unit 2 according to digital information from source 1.

The output voltages of scale amplifiers of cosine harmonic oscillations 16 ₁ , 16 ₂ , ... 16 _M are applied to the inputs of the second switch 14, to the control input of which a command is sent from the control unit 2, this command connects to the output of the switch 14 and, therefore, to the input of the second multiplier 11 through a controlled phase 12 inverter, one of the M cosine harmonic components. The number (from 0 to M) of the harmonic component is determined by control unit 2 from digital information from source 1, phase switching in a controlled inverter of phase 12 is also carried out by command of control unit 2 depending on the sign of the frequency deviation. A sinusoidal voltage from the output of the shaper 3 is supplied to another input of the first multiplier 10, and a cosine voltage from the other output of the shaper 3 is fed to another input of the second multiplier 11. The output voltages of the multipliers 10 and 11 are summed by an adder 18, the output of which is supplied to the first input of the phase detector 4. The second input of the phase detector 4 is supplied with voltage from the output of the controlled generator UG 6 through a divider with a variable division coefficient 9, the phase difference between harmonic oscillations at the first and second inputs f call detector 4 is an error signal, which is output from the phase detector 4 through a low-pass filter 5 to the control input of the controlled oscillator 6 and tunes the generator 6 in frequency so that its phase divided in a divider with a variable division coefficient 9 becomes equal to the phase harmonic oscillation at the first input of the phase detector 4. Thus, the output frequency of the harmonic oscillation of the controlled oscillator 6 is shifted in frequency by the value of kΔF _i , and the phase changes by 2πΔF _i t. When the sign changes in the controlled inverter of phase 12, the output frequency of harmonic oscillations of the controlled generator 6 is shifted in frequency by an amount - kΔF _i , and the phase changes by -2πΔF _i t. Note that the number of positions with M generators is 2M due to a change in sign.

The control unit can be performed, for example, according to the scheme shown in figure 3, where D1 is a shift register; D2 - counter; D3.2, D3.3 - controlled inverters; D4 - decoder.

The control unit operates as follows. Data in sequential form is loaded into the shift register D1, the counter on D2 after the arrival of three clock pulses gives an enable signal to the shift register, according to which the latter gives the previously recorded information to the output in parallel form. Elements D3.2 and D3.3 are used as controlled inverters. The decoder on element D4 converts the binary combination into a positional code, which is a set of signals for controlling the polarity and switching on the generators. Element D3.1 is used as an inverter. The counter D2 with the element D3 operates in the mode of division into three.

The control unit, implemented according to the scheme in figure 3, can be performed on chips from Texas Instruments: element D1 - SN74hc595; D2 - SN74alsl61; D3 - SN74als86; D4 - SN74als139.

Information sources

1. The generation of oscillations and the formation of radio signals. Ed. V.N. Kuleshov and N.N. Udaltsova. - M .: Publishing house MPEI. 2008 .-- 416 pp., Ill.

2. Radio transmitting devices. Shakhgildyan V.V., Kozyrev V.B., Lyakhovkin A.A. et al. Ed. V.V.Shahgildyan. - 2nd ed., Revised. and add. - M .: Radio and communications, 1990. - 432 p.: Ill.

3. Radio transmitting devices. Shakhgildyan V.V., Kozyrev V.B., Lyakhovkin A.A. et al. Ed. V.V. Shahgildyan. - 3rd ed., Revised. and add. - M .: Radio and communications, 2003 .-- 560 p.: Ill.

4. Manassevich V. Frequency synthesizers (Theory and design): Per. from English / Ed. Galina. M .: Communication, 1979.- 384 p. silt.

5. Tikhomirov N.M., Romanov S.K., Lenshin A.V. Generation of FM signals in synthesizers with automatic tuning. - M .: Radio and communications, 2004 .-- 210 p .: ill.

6. Phase synchronization systems / Akimov VN, Belyustina LN, Belykh VN and etc.; Ed. V.V. Shahgildyan, L.N. Belustoy - M .: Radio and communications, 1982 - 288 p., Ill.

7. Gonorovsky I.S. Radio circuits and signals. - M .: "Soviet Radio". 1971. - 672 p.

8. Kapranov M.V. Elements of the theory of phase synchronization systems. - M.: Publishing House MPEI, 2006. - 208 p.

9. ANALOG DEVICES 65 MSPS Digital Receive Signal Processor. AD6620.

10. Dixon P.K. Broadband systems. Per. with eng. / Ed. V.I. Zhuravleva. - M.: Communication, 1979. - 304 p., Ill.

11. The theory of signal transmission in railway transport. Gorelov G.V. Fomin A.F. et al. M .: Transport, 2001 .-- 415 p.

Claims (1)

A frequency-modulated signal synthesizer comprising a phase detector (PD) connected in series, a low-pass filter, a controlled oscillator and a variable divisor frequency divider (DPCD), the output of which is connected to the second input of the PD, and the output of the controlled generator is the output of the synthesizer, connected in series reference generator and frequency divider with a fixed division coefficient (DPCD), as well as an information source, characterized in that M (M> 1) sine and cosine generators are introduced manipulation frequencies whose sinus and cosine outputs are connected through the corresponding M scale amplifiers for sinus outputs and M scale amplifiers for cosine outputs to the corresponding inputs of the first and second switches, whose control inputs are connected to the first output of the control unit, the second output of which is connected to the control input controlled phase inverter, the output of which is connected to the second input of the adder, the output of which is connected to the first input of the PD, while the output of the DPCD is connected to the input a quadrature signal shaper whose sinus output is connected to the first input of the first multiplier, and the cosine output is to the first input of the second multiplier, the output of which is connected to the input of the controlled phase inverter, the output of the first multiplier is connected to the first input of the adder, in addition, the outputs of the first and second switches connected to the second inputs of the first and second multipliers, respectively, the output of the information source is connected to the input of the control unit.

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