RU16236U1 - DIGITAL FREQUENCY SYNTHESIS WITH FREQUENCY MODULATION - Google Patents

Abstract

A frequency-modulated digital frequency synthesizer contains a reference quartz oscillator, a frequency divider with a fixed division coefficient, a frequency-phase detector, a low-pass filter, a controlled generator, a frequency divider with a variable division coefficient and a pulse-phase modulator, the output of which is connected to the input frequency phase detector, serially connected modulating signal source, controlled attenuator, inverter and integrator, frequency setting device, output to It is connected to the installation input of the frequency divider by a variable division coefficient and the control input of the controlled attenuator, while the second (modulating) input of the controlled generator is connected to the output of the modulating signal source, characterized in that a DC amplifier and an adder are connected in series with it, the output of which is connected with the modulating input of the pulse-phase modulator, while the second input of the adder is connected to the output of the integrator, and the input of the DC amplifier is connected to swing low pass filter.

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 (FM), built on the basis of a pulse-phase-locked loop (IFAP) with a frequency divider with a variable division ratio (DPC) in the feedback circuit, in which a modulating signal is supplied to the second (modulating) ) the input of a controlled generator (see US patent No. 4110707, N 03 C 3/10, 1978). In such a DSC, it is possible to obtain a frequency-modulated signal with an almost unlimited frequency modulation band at the top. Its disadvantage is the lower limit of the range of modulating frequencies due to the feedback in the IFAPH ring.

The modulation of a controlled generator (UG) at its modulating} input is perceived by the IFAPH ring as an external disturbance, which is processed by its negative feedback circuit in the direction of its decreased e1. This response to a modulating disturbance occurs in the pass band of the IFAP ring determined by the low-pass filter (PLL), i.e. only at low frequencies. Therefore, to expand the range of passage of the modulating frequencies towards the lower frequencies, it is necessary to narrow the passband of the IFAPH ring. For this, it is necessary to choose the low-pass filter at the output of the pulse-phase detector more inertial, which leads to a decrease in the speed of the central frequency converter with FM.

Closest to the technical nature of the proposed is a "Digital frequency synthesizer with frequency modulation by AS USSR No. 1252909, H 03 C 3/10, H 03 L 7/18, published. August 23, 1986, adopted as a prototype. In this synthesizer, a two-point method is used to generate a frequency-modulated signal in a wide band of modulating frequencies, when the modulating signal is fed to the modulating input of the UG and simultaneously through a controlled attenuator, inverter and integrator to the modulating input of the phase modulator (more precisely, the pulse-phase mode: curtain) connected between the output of the DPKD and the phase detector (more precisely, the i-pulse-phase detector IFD).

In FIG. 1 shows a block diagram of a prototype device, where 1;

1- controlled generator (UG),

2- frequency divider with variable division ratio (,

3-phase modulator (FM),

4-phase detector (PD),

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I reference generator

8 - source of the modulating signal (IC),

9-controlled attenuator (UA), 10-inverter,

I1 - integrator,

12 - unit for setting the output frequency (BEECH),

In the prototype device, a phase detector 2 is used to isolate the difference between the two compared pulse flows. But the same function is currently performed with a high effect by the frequency-phase dc detector (ChFD), which is a type of pulse-phase detectors and is mainly used as part of the microcircuit digital synthesizer hour goth.

With two-point modulation by this method, the pulses at the output of DPKD5 will be phase-modulated in accordance with the modulating signal from the output of the source of modulating signal 8 to the controlled oscillator 1. Phase modulator 3, switched on after the DPKD2, reverse modulates the phase of the modulated pulses in accordance with the change UG1 frequency from the information (modulating) signal. Therefore, pulses that are no longer modulated in phase arrive at PD4, i.e. as in synchronism mode without modulation. Then, at the output of the PD4 NC, there will be a pulse signal of error from modulation and, therefore, there will be no reaction of the IFAPH ring to a modulating disturbance. At the same time, it is possible in principle to skip the modulating signal in the CSC in a wide frequency band without distortion and maintaining the same speed as in the CSC without modulation, since the choice of the PNF5 is now practically independent of the conditions for passing the given band of modulating frequencies.

However, the introduction of a second modulation point based on a pulse-phase modulator after the DPCD leads to a deterioration in the short-term stability of the carrier frequency of the FMCCH, which is associated with the influence of destillizing factors on the IFM (interference from interference, changes in characteristics under the influence of temperature extremes, etc.). As a result, the phase instability of the pulses at the output of the IFM increases, which leads to a couple of 1-frequency frequency modulation of the output signal of the DSC and non-linear distortions of the modulated signal occur.

The elimination of these disadvantages is achieved by the fact that in a digital frequency synthesizer with frequency modulation, containing a series-connected reference quartz oscillator, a frequency divider with a fixed division coefficient, a frequency-phase detector, a low-pass filter, a controlled generator, a frequency divider with a variable division coefficient and pulse a phase modulator, the output of which is connected to the input of the frequency-phase detector, a series-connected source of a modulating signal, a controlled attenuator, and vertor and integrator, the frequency setting device whose output is connected to the input of the installation dzlitelya variable frequency dividing ratio, and a control input controlled attenuator, the second (modulating) input controlled oscillator connected to the output of the modulating signal source, enter a nd pos / ow /

therefore, the connected DC amplifier and the adder, the output of which is connected to the modulating input of the pulse-phase modulator, while the second input of the adder is connected to the output of the integrator, and the input of the DC amplifier is connected to the output of the low-pass filter.

A significant difference of the proposed DSS with FM is that, using the introduced new nodes combined with the corresponding links with the remaining elements of the synthesizer circuit, automatic compensation of the influence of destabilizing factors on the pulse-phase modulator (IFM) is realized. At the same time, the short-term stability of the carrier oscillation of the DSC increases (the level of spurious frequency modulation decreases) and the nonlinear distortion of the modulated signal is reduced.

In the proposed CSC with FM along the control circuit, phase incursions and phase fluctuations of pulses at the output of the IFM are worked out (reduced), caused by the influence of interference from network pickups, powerful terminal stages of the transmitter, and also due to changes in the modulation characteristics of the IFM and integrator with changing ambient temperature aging elements etc.

Technical solutions with similar features and properties are not known to the applicant, therefore, we can conclude that the proposed technical solution has a significant difference.

Figure 2 shows a block diagram of the proposed device.

A digital frequency synthesizer with frequency modulation contains ps-consequently connected reference crystal oscillator OKG1, a frequency divider with a fixed division coefficient DFKD2, a frequency-phase detector ChFDZ, a low-pass filter LPF4, a controlled oscillator UG5, a frequency divider with a variable division coefficient DPCD6 and a pulse-phase IFM7 modulator, the output of which is connected to the second input of the ChFDZ, series-connected source of the modulating signal ИМ8, controlled attenuator UA9, INV10 inverter and integrator UTP, device Frequency setting unit УУЧ12, the output of which is connected to the installation input ДПКД6 and the control input УА9, series-connected DC amplifier UPT13 and adder CYM14, the output of which is connected to the modulating input of the pulse-phase modulator IFM7, while the second input of the adder is connected to the output of the integrator and the input of the DC amplifier CNT 13 is connected to the output of the low-pass filter LPF4.

A digital frequency synthesizer with frequency modulation operates as follows.

After establishing the synchronism mode in the IFANCH ring, when the modulating voltage is supplied from the IC8 to the modulating input of UG5, its frequency modulation occurs. In this case, the pulses to the output of DPKD6 will be ipOMO phase-adjusted in accordance with the modulation of UG5 with an information signal from IMS8 and will go to signal input IFM7. To compensate for this reaction of the IFAPC ring to the modulating disturbance UG5, the modulating signal from IMS8 is simultaneously fed through UA9, INV10 and the integrator fflTll to the input of the adder SUM14, from the output of which it goes to the modulating

input IFM7. In the pulse-phase modulator IFM7, the phase of the pulses received from the output of DFKD6 is inversely modulated, so that pulses are already generated at the output of IFM7 without phase modulation as in synchronism mode without supplying a modulating signal. These non-modulated ito phase pulses are fed to the ChFDZ input, the second input of which receives reference pulses from the output of DFKD2, which are formed as a result of dividing the reference frequency from OKG1 by the division coefficient R in DFKD2. As a result of the comparison of these pulses in phase, the output of the first ChFDZ does not generate an error signal from modulation and, therefore, the IFAPH ring reaction to the modulating UG5 disturbance is excluded.

However, due to the influence of destabilizing factors in the form of different pickups on the IFM7, as well as the effect of temperature changes on the characteristics of the IFM7, the short-term stability at the output of the DSC is deteriorated (i.e., the parasitic frequency modulation of the IF frequency of the output signal increases) and the nonlinear distortions of the modulated signal increase

Thus, at the output of IFM7, in addition to the useful modulation of cucumber pulses in phase (f information signal contains parasitic phase modulation due to the influence of destabilizing factors.

The pulses from the output of IFM7 with parasitic phase modulation (p are fed to the input of the ChFDZ, the second input of which receives pulses unmanned in phase from the output of the DFKD. In this case, an error signal is generated at the output of the ChFDZ and a voltage corresponding to the phase voltage is generated at the output of the LPF4 from this error signal error - that scares on

DC amplifier UPT13, from the output of which is fed to SUM14. The second input SUM14 from the output of the inverter PfflBlO through the integrator LNT11 receives a modulating voltage proportional. In Result

algebraic addition of these signals at the output of the SMS 14 is formed by the control voltage, which changes according to the law, which is fed to the modulating input IFM7, i.e. an antiphase modulating signal with a bias is received. This prediction in accordance with: with (, -) completely compensates for the modulation of pulses in IFM7, i.e. on the

IFM7 output is (-, -, + 0).

Thus, pulses will be generated at the output of IFM7, which will not have both parasitic modulation (p, and phase modulation (p from the information signal, i.e., both in the synchronism mode and without stray phase: fluctuations.

Proof of the feasibility of the proposed device is that the input nodes are typical. The adder can be made on the basis of operational amplifiers (for example, on a chip 140UD20).

Thus, the use of the proposed digital frequency synthesizer with frequency modulation makes it possible to reduce the influence of the destabilizing factors of the IFM on the short-term stability of the carrier oscillation of the frequency response and to reduce the distortion of the modulated signal.

Claims (1)

A frequency-modulated digital frequency synthesizer contains a reference quartz oscillator, a frequency divider with a fixed division coefficient, a frequency-phase detector, a low-pass filter, a controlled generator, a frequency divider with a variable division coefficient and a pulse-phase modulator, the output of which is connected to the input frequency phase detector, serially connected modulating signal source, controlled attenuator, inverter and integrator, frequency setting device, output to It is connected to the installation input of the frequency divider by a variable division coefficient and the control input of the controlled attenuator, while the second (modulating) input of the controlled generator is connected to the output of the modulating signal source, characterized in that a DC amplifier and an adder are connected in series with it, the output of which is connected with the modulating input of the pulse-phase modulator, while the second input of the adder is connected to the output of the integrator, and the input of the DC amplifier is connected to swing low pass filter.