RU31080U1 - Frequency Modulated Digital Synthesizer - Google Patents

Description

DIGITAL FREQUENCY SYNTHESIS WITH FREQUENCY MODULATION

The utility model relates to radio engineering and can be used as the exciter of a transmitter with frequency modulation and a local oscillator of the receiver without supplying a modulating signal.

Known digital frequency synthesizer (DSC) with frequency modulation, built on the basis of a pulse-phase-locked loop (IFAPH) with a frequency divider with a variable division ratio (DPDC) in the feedback circuit, in which the modulating signal is fed to the second (modulating) input of the controlled generator (see US patent J o4110707, H 03 With 3/10, 1978). In such a synthesizer, a modulated signal with an almost unlimited bandwidth of modulating frequencies can be obtained from the output. Its disadvantage is the lower limitation of the band of modulating frequencies due to the feedback in the IFAH system. Modulation at the second input of a controlled generator (UG) is perceived by the IFAPH ring as an external disturbance, which is worked out in the feedback circuit in the direction of its decrease. This decrease occurs in the pass band of the IFAPH ring determined by the low-pass filter (PLL), i.e. at low frequencies. Therefore, to expand the modulation band into the low-frequency region, it is necessary to reduce the LPF band and make it more inertial, which leads to a decrease in the speed of the CSC.

The closest in technical essence to the proposed one is a frequency-modulated digital frequency converter (FM), in which to overcome this contradiction and form a modulated signal in a wide frequency band, a combined two-point method is used, when the modulating signal is fed through two channels simultaneously to the modulating UG input and through the integrator at the input of a pulse-phase modulator (IFM) included in the reference path between a frequency divider with a fixed division coefficient (DPCD) and a pulse-phase detector ( FD) (see. AS USSR .№919040, H 03 C 3/10, P 03 L 7/16, 1982).

With two-point modulation by this method using an IFM, the pulses at the reference input of a pulse-phase detector (IPD) should be phase modulated in the same way as pulses after a DPD. Then, there is no pulse error signal from the modulation at the output of the IFD and, therefore, there will be no reaction of the IFAP ring to a modulating disturbance. At the same time, it is possible in principle to skip a modulating signal in a wide frequency band without distortion and maintaining high speed.

However, at present, this possibility is not fully realized, which leads to additional distortions and is explained by the following.

H 03 L 7/18

Turning on the IFM between the reference crystal oscillator and the reference (from the DPCD) input of the synthesizer chip leads to large distortions of the amplitude-frequency modulation characteristic (AFC) and makes it impossible to implement frequency modulation in a wide band modulating; their frequencies are for the following reasons.

It is known (see, for example, V. Manasevich. Frequency synthesizers (Theory and Design), 1979, p. 349) that the most highly stable crystal oscillators are produced at frequencies of 5 and 10 MHz. The deviation of the carrier oscillation received in the connected radio equipment is kHz. Then, for example, if the output frequency of the synthesizer is / cv-SOO MHz and the range of modulating frequencies is kHz, then the frequency deviation at the reference frequency of 10 MHz will be 50 times less (500-10 / 10-10 50) and will be kHz / 50 100 Hz The highest modulation index at the lowest modulation frequency (Hz) l / n 100/10 10, i.e., if you turn on the IFM at the output of the reference 10 MHz crystal oscillator, then its modulation index should be glad.

At the same time, the well-known phase modulators provide a small distortion only with modulation indices not exceeding approximately 0.2 rad (see D. N. Shapiro, A. A. Pain Fundamentals of the Theory of Frequency Synthesis, 1981, p. 228).

Thus, the introduction of two-wavelet modulation by UG and IFM included between the reference quartz oscillator (OKG) and the reference input of the synthesizer chip can lead to unacceptably large distortions of the modulated signal.

The aim of the proposed technical solution is to obtain a uniform frequency response in a wide band of modulating frequencies when tuning the carrier frequency in a wide range.

This goal is achieved in that in a digital frequency synthesizer with frequency modulation, containing a controlled oscillator connected in a ring, a frequency divider with a variable division coefficient, a pulse-phase detector and a low-pass filter, the output of which is connected to the control input of the controlled generator, as well as a fixed frequency divider dividing factor, the output of which is connected to another input of the pulse-phase detector, a frequency setting unit, the output of which is connected to the installation input of the frequency divider from a variable division factor, a modulating signal source whose output is connected to a modulating input of a controlled oscillator and through an integrator to a modulating input of a phase modulator, whose output is connected to an input of a frequency divider with a fixed division coefficient, and a reference crystal oscillator, a reference signal frequency divider is introduced based on a synchronized gecherator whose output is connected to the input of the phase modulator, and the input to the output of the reference crystal oscillator. The output of the controlled generator is the output of the synthesizer.

A significant difference of the proposed technical solution is that with the help of the introduced frequency divider based on a synchronized generator (for example, on a tunnel diode) there is a significant decrease in the modulation index of the phase modulator at the lowest modulating

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frequency and thereby the expansion of the range of modulating frequencies in the low frequency region with small distortions.

Thus, in contrast to the prototype device, the use of which due to the mass production of integrated circuits of DSS, containing DFKD, IFD, DPKD in one block (in one chip) is practically impossible, the proposed DSS device with FM can be used with any integral microchips CSC.

In Fig.1 presents a block diagram of a DSC with FM.

A digital frequency synthesizer with frequency modulation contains UG1, DPKD2, IFDZ and LPF4 connected to the ring, the output of which is connected to the controlled input of UG1, as well as DFKD5, the output of which is connected to another IFDZ input, a frequency setting unit (BEUCH) 6, the output of which is connected to installation input DPKD2, the source of the modulating signal (IC) 7, the output of which is connected to the modulating input UG1 and through the integrator (INT) 8 with the modulating input IFM9, the output of which is connected to the input DFKD5. In this case, the output of the reference quartz oscillator (OCG) 10 through a frequency divider based on a synchronized generator (DC) 11 is connected to another input of IFM9.

A digital frequency synthesizer with frequency modulation operates as follows.

After establishing the synchronism mode in the IFAPCH ring, a modulating signal is supplied from IMS7 to the modulating input of UG1 and through the integrator INT8 to the modulating input of IFM9. In this case, the pulses at the output of DPKD2 will be phase-modulated in accordance with the modulation of the information signal by the IC from IMS7. From the output of D11KD2, phase-modulated short pulses are fed to the first IFDZ input, where they are compared in phase with short reference pulses from the output of DFKD5, phase modulated in the same way as pulses with DPKD2. The reference signal from the output of OKG10 enters through the frequency divider DCH11 to the reference input IFM9, to the modulating input of which from IMS7 through INT8 a modulating signal arrives. As a result, at the output of IFM9, a modulated reference signal is generated with a modulation index n times smaller than if the IFM were immediately after the laser. After dividing this signal in DFKD5 to a given comparison frequency, short, phase-modulated reference pulses are obtained at the output of DFKD5. Since, in the synchronism mode, the IPDZ inputs receive from DFKD2 and DFKD5 identical pulses phase-modulated, then the IPDZ output does not generate an error signal from modulation and there is no reaction to the modulating disturbance UG1 in the IFAPR ring.

In the proposed DSS, the distortion of the modulated signal is completely compensated for using any synthesizer integrated circuits.

The proof of the possibility of implementing the proposed device is that the input frequency divider can be performed in any way, for example, based on a synchronized generator on a tunnel diode. the proposed device is possible with any circuit CSC. widely available types of microformula

Claims (1)

A digital frequency synthesizer with frequency modulation, containing a controlled oscillator connected in a ring, a frequency divider with a variable division coefficient, a pulse-phase detector and a low-pass filter, the output of which is connected to the control input of a controlled generator, as well as a frequency divider with a fixed division coefficient, the output of which connected to another input of the pulse-phase detector, a frequency setting unit, the output of which is connected to the installation input of a frequency divider with a variable division ratio, a modulating signal source, the output of which is connected to a modulating input of a controlled oscillator and through an integrator, to a modulating input of a phase modulator, whose output is connected to an input of a frequency divider with a fixed division coefficient, and a reference crystal oscillator, characterized in that, in order to obtain uniform frequency response in a wide band of modulating frequencies when tuning the carrier frequency in a wide range of frequencies, a frequency divider of the reference signal based on a synchronized generator is introduced into it, output otorrhea connected to the input of the phase modulator, and input - with the output of the reference crystal oscillator, the output of controlled oscillator is an output device.