RU2485669C1 - Method to generate coherent modulated signals and device for its realisation - Google Patents

Abstract

FIELD: radio engineering, communications.

SUBSTANCE: method to generate coherent modulated signals consists in the fact that an output signal from a reference generator is sent to microchips: direct digital synthesisers of frequency (DDS) and programmable logical integral circuits (PLIC), at the same time PLIC in software sets all DDS for the specified frequency, amplitude and initial phase, and output oscillations are synchronised from the master DDS.

EFFECT: expansion of functional capabilities.

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Description

The invention relates to the field of radio engineering and can be used in radio communications and radio navigation.

The invention can be most effectively used in the DVOR (VHF Doppler omnidirectional beacon) system for generating coherent modulated signals for measuring the azimuth angle of an aircraft equipped with VOR (VHF omnidirectional beacon) avionics.

To form coherent signals in navigation systems, the phase-filter, phase-compensation and frequency multiplication methods are often used.

The disadvantage of the phase-filter method is the instability of the phase characteristics of the output signal and a narrow range of the operating frequency, because the range of operating frequencies is limited by the passband of bandpass filters, which are selected based on the requirements for the output spectrum of the signal.

The phase compensation method is inherent in suppressing the carrier, as well as the upper or lower lateral frequency, due to the fact that for the formation of a signal in this way, it is necessary to use high-frequency broadband phase shifters.

The disadvantage of high-frequency broadband phase shifters is the instability of the parameters, which in turn leads to instability of the parameters of the output signal of the shaper.

The disadvantages of the shaper, built on the principle of frequency multiplication, are high phase noise and the difficulty of providing high-frequency suppression of harmonic components, which seriously complicates the signal shaper circuit.

The above methods also do not allow changing the signal parameters without hardware intervention.

The objective of the invention is the development of a shaper of coherent modulated signals, which allows without hardware intervention to adjust the initial phase, frequency, amplitude and shape of the modulated signal in order to adapt the radio system to various operating conditions.

The technical result consists in expanding the functionality and in that the applied direct digital frequency synthesizers (DDS) and programmable logic integrated circuit (FPGA) allow synthesizing coherent modulated signals with accuracy typical for digital systems up to the initial phase.

A structure based on direct digital frequency synthesis (DDS) is free from all the inherent disadvantages of these methods. DDS microcircuits are unique in their digital certainty: the signal they generate is synthesized with the accuracy inherent in digital systems. The frequency, amplitude and phase of the signal at any given time are precisely known and controlled.

The frequency resolution of DDS is hundredths or even thousandths of a hertz at an output frequency of the order of tens of megahertz. This resolution is unattainable for other synthesis methods. Another characteristic feature of DDS is the very high speed of switching to another frequency, limited only by the speed of the digital control interface. Moreover, all frequency adjustments occur in DDS without breaking the phase of the output signal. Since the output signal is synthesized in digital form, it is very simple to carry out modulation of various types.

The method of generating coherent modulated signals is that the output signal from the reference generator is supplied to the FPGA and DDS microcircuits, while the FPGA programmatically tunes all DDS to a given frequency up to 400 MHz, amplitude and initial phase, and we obtain output signals at the output of the coherent modulated signal former with the given parameters of frequency, amplitude and phase, while the output oscillations are synchronized from the leading DDS.

The device according to claim 1 includes a reference oscillator and DDS and FPGA circuits, assembled according to a block diagram, where the reference oscillator is connected to an FPGA chip and 4 DDS circuits connected in series with each other, while all DDS circuits are mutually connected to the FPGA chip.

The essence of the invention is that a coherent modulated signal generator using a reference generator (OG) and DDS and FPGA (FPGA) microchips assembled according to the structural diagram shown in Figure 1 allows synthesizing coherent modulated without hardware intervention, unlike similar shapers signals with varying parameters with very high accuracy and tight synchronization (see Figure 2 and 3).

The block diagram of a coherent modulated signal generator shown in Figure 1 consists of:

1. OG (reference generator), designed to clock DDS and FPGA.

2. FPGA (FPGA) provides complete independent control over each DDS chip, as well as receives and transmits commands via the RS-232 or RS-485 interface and controls the parameters of the modulating signal.

3. DDS1 ... DDSN - generate modulated sinusoidal signals in the range of operating frequencies from 0 to 400 MHz, with the ability to control the phase, frequency and amplitude of the signal with high accuracy

Figs. 2 and 3 show synchronized output signals from various DDS synthesizers.

The output signal from the reference generator is supplied to the FPGA and DDS microcircuits. FPGA programmatically tunes all DDS to a given frequency, amplitude and initial phase, as a result of which, at the output of the coherent modulated signal generator, we obtain output signals with specified parameters of frequency, amplitude and phase. The output oscillations are synchronized from the master DDS.

The use of DDS and FPGA chips allowed the coherent modulated signal generator to obtain the following advantages over analogs:

1. Digital control of the frequency and phase of the output signal.

2. Very high resolution in frequency and phase.

3. Extremely fast transition to another frequency (or phase), frequency tuning without phase discontinuity, without outliers associated with the signal establishment time.

4. The architecture based on DDS, due to the very small frequency tuning step, eliminates the need for precise tuning of the reference frequency.

5. The digital interface makes it easy to implement microcontroller control.

Claims (2)

1. The method of generating coherent modulated signals, which consists in the fact that the output signal from the reference generator is supplied to the FPGA and DDS microcircuits, while the FPGA programmatically tunes all DDS to a given frequency up to 400 MHz, amplitude and initial phase, and at the output of the coherent modulated shaper signals we obtain output signals with the given parameters of frequency, amplitude and phase, while the output oscillations are synchronized from the leading DDS. 2. The device for implementing the method according to claim 1, comprising a reference oscillator and DDS and FPGA circuits, assembled according to a structural diagram, where the reference oscillator is connected to an FPGA chip and 4 DDS circuits connected in series with each other, while all DDS circuits are interconnected with FPGA chip.

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