SU1515363A2 - Fm digital frequency synthesizer - Google Patents

Abstract

The invention relates to radio engineering and can be used as a driver of a frequency modulated transmitter. The purpose of the invention is to increase the purity of the output spectrum. To achieve the goal, a high-pass filter 14, 15, a key 16 and a synchronization sensor 17 are inserted into the device. In order to obtain a good interference suppression with a frequency of comparison and its harmonics, the cut-off frequency of the low-pass filter 5 is usually chosen more than an order of magnitude lower than the frequency of comparison. The cut-off frequency of the filter 14 is chosen so as to pass from the output of the phase detector 4 interference, starting with the frequency of comparison and above. The device automatically removes all inaccuracies in the compensation of the modulating signal at the output of the phase modulator 3 with a wide band of modulating frequencies with technological variation and aging of the elements. In addition, interference with the reference frequency and its harmonics, both in the modulation mode and without modulation, is significantly attenuated. 1 il.

Description

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The invention relates to radio engineering and can be used as a driver of a frequency modulated transmitter.

The aim of the invention is to increase the frequency of the output spectrum.

The drawing shows an electrical structural diagram of a digital frequency synthesizer with frequency modulation.

A frequency modulated digital frequency synthesizer contains a controlled oscillator 1, a frequency divider 2 with a variable division factor (DCCD), a phase modulator 3, a phase detector (PD) 4, a low-pass filter 5 (LPF), a divider 6 frequency c fixed division factor (DFCD), reference generator 7, modulating signal source 8, controlled attenuator 9, inverter 10, integrator 11, frequency setting unit 12, analog adder 13, high-pass filter 14 (HPF), amplifier 15, key 16 and sensor 17 synchronism.

A frequency modulated digital synthesizer works as follows.

In synchronism mode without applying modulating voltage from source 8, the signal from the output of controlled oscillator 1 is accessed at the input of DCD 2, where it is divided by frequency by the division factor N, specified from unit 12. From the output of DPKD 2, the signal in the form of short pulses with frequency is fed to the first input of the phase modulator 3 and through it to the input of the PD 4, to the other input of which the reference pulses from the reference generator 7 through DFCD 6. Control its voltage through the low-pass filter 5 is fed to the first control input of the controlled generator 1 and adjusts it in frequency and phase to the reference generator 7.

The phase locked loop rejects changes in the frequency of the controlled oscillator 1, starting with the NIZKO and ending with the cutoff frequency of the low-pass filter 5. Above the cut-off frequency, the fast drifts of the frequency of the controlled oscillator 1 are not processed.

In order to obtain good interference suppression with a frequency of comparison and its harmonics, the cutoff frequency of the low-pass filter 5 is usually

is selected by more than an order of magnitude lower frequency comparison. The cutoff frequency of the HPF 14 is chosen so as to pass from the output of the PD 4 interference, starting with the frequency of the comparison and in the type. These high-frequency components of the voltage from the output of the PD 4 pass through the HPF 14 and the amplifier 15 to the key 16. The second input of the key 16 from the output of the synchronization sensor 17 receives a signal that allows only in the synchronization mode the signal from the output of the amplifier 15 to the output of the key 16 In a transient mode, a stop signal is generated at the output of the synchronization sensor 17 and the key 16 is closed. From the output of the key 16, the interference voltage with a comparison frequency and its harmonics is fed to the second input of the analog adder 13, the first input of which, in the absence of modulation, receives a constant bias voltage from the output of the controlled attenuator 9. The output signal of the analog adder 13 through the inverter 10 and the integrator 11 is fed to the control input of the phase modulator 3 and modulates the phase of the pulses from the output of the PDKD 2 so that at the output of the PD 4 the interference voltage with the reference frequency and its harmonics decreases.

When applying modulating voltage from source 8 to the second input of controlled generator 1, the pulses at the first input of phase modulator 3 will also be phase modulated in accordance with the law of frequency modulation. At the same time, the modulating voltage from the output of source 8 through a controlled attenuator 9, analog adder 13, inverter 10 and integrator 11 is fed to the control input of phase modulator 3 in antiphase and compensates for the modulation of the phase of pulses fed to the signal input of phase modulator 3. As a result, the phase-unmodulated pulses arrive at the second input of the PD 4, as well as into the mode without modulation supply. The accuracy of compensation is determined by the correct selection of the level and phase of the reverse modulation at the control input of the phase modulator 3. The change of the gain of the controlled attenuator 9 is carried out simultaneously. With the change of the division ratio of the PDKD 2 using the code from the block

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12 installations. With the help of the integrator 11, amplitude-frequencies are generated per the characteristic of the bias signal at the control input of the phase modulator 3, inverse to its modulation characteristic.

With inaccurate compensation at the output of the phase modulator 3, the pulses can be modulated by the high-frequency components of the modulating voltage, which will pass to the output of the PD 4. The same high-frequency components in the negative feedback circuit through the HPF 14, amplifier 15, key 16, analog adder 13, the inverter 10 and the integrator 11 are fed to the control input of the phase modulator 3 and compensate for the residual products of incomplete compensation.

Thus, interference with the frequency of comparison and interference from incomplete compensation of the high-frequency components of the modulating voltage are fulfilled. As a result of this compensation, the phase locked loop system becomes open-modulated and the modulation distortion caused by the closed-loop response is greatly attenuated.

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In a digital frequency modulated frequency synthesizer, all inaccuracies in the compensation of the modulating signal at the output of the phase modulator 3 are automatically removed with a wide range of modulating frequencies with technological variation and aging of the elements. In addition, interference with the comparison frequency and its harmonics both in the modulation mode and without modulation is significantly reduced.

Claims (1)

Invention Formula Digital frequency synthesizer with frequency modulation, according to author. No. 1252909 characterized in that, in order to increase the purity of the output signal spectrum, a series-connected high-pass filter, an amplifier and a key, as well as a synchronization sensor are introduced, and the output of the controlled attenuator is connected to the input of the inverter via a newly entered analog adder, second input which is connected to the key output, the control input of which is connected to the output of the synchronization sensor, the input of which is combined with the input of the high-pass filter and connected to the output of the phase detector. Compiled by Y. Kovalev Editor A. Lezhgshna Tehred A. Kravchuk Corrector t. Paliy Order 6294/56 Circulation 884 VNIIPN State Committee for Inventions and Discoveries at the State Committee on Science and Technology of the USSR 113U35, Moscow, Zh-35, 4/5 Raushsk nab. Subscription