RU10023U1 - DIGITAL FREQUENCY SYNTHESIS WITH FREQUENCY MODULATION - Google Patents

Abstract

A frequency-modulated digital frequency synthesizer comprises a reference oscillator, a frequency divider with a fixed division coefficient, a first frequency-phase detector, a first 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 the first frequency-phase detector, a series-connected source of a modulating signal, a controlled attenuator, an inverter and an integrator, a frequency setting unit, output One of which 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 second frequency-phase detector and a second filter are connected in series low frequencies, the first adder and the second adder, a synchronism indicator and a key, the output of which is connected to the pulse-phase modulating input, in series about the modulator, and the signal input - with the output of the second adder, while the input of the synchronism indicator is connected to the output of the first frequency-phase detector, the second inputs of the first and second adders are connected to the output of the integrator, the first input of the second frequency-phase detector is connected to the output of the second pulse phase modulator, and the second input with the output of the frequency divider with a variable division ratio.

Description

The utility model relates to radio engineering and can be used as a transmitter exciter with frequency modulation.

Known digital frequency synthesis (DSC) with frequency modulation (FM), built on the basis of a pulse-phase-locked loop (IFAP) with a frequency divider with a variable division coefficient (DPC) in the feedback circuit, in which the modulating signal is applied to the second ( modulating) input) of the inventive generator (see US patent No. 4110707, H 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 limitation of the modulating frequency range due to the feedback in the IFAP 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 along the negative feedback circuit in the direction of its decrease. This response to a modulating disturbance occurs in the passband of the IFAP ring determined by the low-pass filter (LPF). To expand the range of passage of the modulating frequencies towards low frequencies, it is necessary to narrow the passband of the IFAPCH ring. For this, it is necessary to choose the phase-to-phase converter 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 JV 1252909, P 03 C 3/10, P 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 supplied to the modulating input of the UG and simultaneously through the controlled attenuator, inverter and integrator to the modulating input of the pulse-phase modulator connected between the output of the DPCD and the pulse -phase detector.

Pa fig. 1 shows a block diagram of a prototype device, where it is indicated:

1- controlled generator (UG),

2 - frequency divider with a variable division ratio (DPKD),

3-pulse-phase modulator (IFM),

4-pulse-phase Yes detector (IFD),

8 - the source of the modulating signal (IC),

9 - refuelable attenuator (UA),

10- inverter

11- integrator

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

In the prototype device, a pulse-phase detector 2 is used to isolate the difference between the two compared pulse flows. This function is currently performed with a high effect by a frequency-phase detector (ChFD), which is a type of pulse-phase detectors and is mainly used in digital microcircuits frequency synthesizer.

With two-point modulation by this method, the pulses at the output of D11KD5 will be phase-modulated in accordance with the modulating signal from the output of the modulating signal source 8 to the controlled generator 1. P1m The pulse-phase modulator 3, switched on after the DPCD2, realizes the modulated phase of the modulated pulses in in accordance with the change in the frequency of UG1 from the information (modulating) signal. Therefore, IFD4 receives pulses that are no longer modulated in phase, as in the synchronism mode without modulation. Then at the output of IFD4 there will be no 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 low-pass filter 5 now practically does not depend on the conditions for the passage of a given band of modulating frequencies.

However, the introduction of a second modulation point based on a pulse-phase modulator in the reference channel leads to a deterioration in the short-term stability of the carrier frequency of the FMFCH, which is associated with the influence of destabilizing 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 spurious frequency modulation of the output signal of the DSC and nonlinear distortion of the modulated signal occurs.

The elimination of these drawbacks is achieved by the fact that in a digital frequency synthesizer with frequency modulation, containing a series-connected onor generator, a frequency divider with a fixed division ratio, a first frequency-phase detector, a first low-pass filter, a controlled generator, a frequency divider with a variable division ratio and a pulse -phase modulator, the output of which is connected to the second input of the first frequency-phase detector, the modulating signal source is connected in series, emy attenuator inverter and integrator, the output frequency setting unit, the output of which is connected to the adjusting input of the frequency divider with a variable division ratio, and a control input controlled attenuator. In this case, the second input of the controlled generator is connected to the output of the modulating signal source.

a second frequency-phase detector, a second low-pass filter, a first adder and a second adder are connected in series, a synchronism indicator and a key are connected in series, the output of which is connected to the modulating input of the pulse-phase modulator, and the signal input to the adder output. The input of the synchronism indicator is connected to the output of the first frequency-phase detector, the second inputs of the first and second adders are connected to the output of the integrator, the first input of the second frequency-phase detector is connected to the output of the pulse-phase modulator, and the second input is connected to the output of the frequency divider with a variable division coefficient .

A significant difference of the proposed CSC with FM is that, with the help of the introduced new nodes combined with the corresponding links with the rest of the synthesizer circuit, automatic compensation is made for the influence of destabilizing factors on the pulse-phase modulator (IPM). At the same time, the short-term stability of the carrier oscillation of the DSC increases (the level of positive frequency modulation decreases) and the nonlinear distortions of the modulated signal are reduced.

In the proposed CSC with FM along the negative feedback 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 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 comprises a reference generator OG1, a frequency divider with a fixed division coefficient DFKD2, a first frequency-phase detector ChFD 3, the first low-pass filter 4, a controlled generator UG5, a frequency divider with a variable division coefficient DPCDb and a pulse-phase modulator IFM7, the output of which is connected to the second input of the first ChFDZ, series-connected source of the modulating signal IC8, controlled attenuator UA9, INVIU inverter and INGI integrator, installation unit frequency BEUCH 12, the output of which is connected to the installation input D11KD6 and the control input UA9, while the second (modulating) input UG5 is connected to the output IC8, connected in series to the second ChFD 13, the second low-pass filter14, the first adder SUM 15 and the second adder SUM 16, connected in series the synchronism indicator IS17 and the key Kl18, the output of which is connected to the modulating input of the FM, and the signal input is connected to the output of the second control system 16. In this case, the input of the synchronism indicator IS17 is connected to the output of the first frequency-phase detector ChFDZ, the inputs of the first control system 15 SUM16 and second INT11 connected to the output of the integrator, the first input of the second PFD 13 is coupled to output IFM7 and "mountain input - yield DPKDb.

A digital frequency synthesizer with frequency modulation operates as follows.

After the sysphonism mode is established in the IFAPH ring, when the modulating voltage is supplied from IMS8 to the modulating input of UG5, its frequency modulation occurs. In this case, the pulses at the output of D11KD6 will be phase-modulated in accordance with the UG5 modulation by an information signal from IMS8 and fed to the IFM7 signal input. To compensate for this reaction of the IFAPC ring to the modulating UG5 disturbance, the modulating signal from IMS8 is simultaneously fed through UA9, INV10 and the INT 11 integrator to the second inputs of the first adder CYM15 and second SUM 16, from the output of which via key Kl18 (unlocked in synchronism mode by signal from the indicator synchronism IS17) is fed to the module input IFM7. In the pulse-phase modulator IFM7, the phase of the pulses received from the output of DPKD6 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 phase-modulated pulses are fed to the first input of the first ChFDZ, the second input of which receives reference pulses from the output of DFKD2, resulting from the division of the reference frequency from OG1 by the division factor R in DFKD2. As a result of these pulses, the phase error at the output of the first ChFDZ does not form an error signal from modulation and, therefore, the response of the IFAPH ring to a modulating disturbance UG5 is excluded.

However, due to the influence of destabilizing factors in the form of different pickups on the IFM7, as well as the influence 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 PM frequency of the output signal increases) and the nonlinear distortions of the modulated signal increase.

Thus, at the output of IFM7, there is a positive phase modulation of fe due to the influence of destabilizing factors.

The pulses from the output of IFM7 with spurious phase modulation of Fe are fed to the first input of the second ChFD13, the second input of which receives phase-modulated pulses from the output of D11KD6. In this case, an error signal is generated at the output of the second ChFD13, and at the output of the second FPF14, a voltage corresponding to a phase error (-Fe + Fm) is generated from this error signal, which is fed to the first input of the first SUM15. Pa the second input of the first SUM15 from the output of the INV10 inverter through the IPT11 integrator receives a modulating voltage proportional to (- srm). As a result of the linear addition of these signals, the output of the first SUM15 produces a signal corresponding only to (- Фе), since fe + fm- Фм - Фе. From the output of the first SUM15, this is the error voltage corresponding to - fe, is fed to the first input of the second SUM16, the second input of which from the output of IPT11 receives a modulating signal, which varies according to the law - fm. As a result of the algebraic addition of these signals, a control voltage is generated at the output of the second SUM16, which changes according to the law (- fm - fe), which is fed to the modulating

input IFM7, i.e. an antiphase modulating signal with a bias is received. This pre-distortion in accordance with (- fm - FE) completely compensates for the modulation of pulses in IFM7, i.e. at the output of IFM7 it turns out - fe - fm

+ F8 + fm 0.

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

In the transient mode, when the synthesizer frequencies are switched by a signal from the BUCH12, when the phase difference at the inputs of the first ChFDZ exceeds a predetermined maximum value, the synchronism indicator IS17 is triggered from the output signal of the first ChFDZ and an inhibit signal is generated at its output, which goes to the control input of the Kl18 key. As a result of this, the Kl18 key is locked and in the IFAPCH ring there is a general adjustment of the synthesizer frequency. Moreover, the speed of the CSC in this case is determined only by the first LPF4, the inertia of which is selected from these conditions, regardless of the band of modulating frequencies.

As soon as the synchronization mode is established in the IFAPC system after switching the frequencies, from the IS17 output to the control input Kl18 a cut-off signal and an auxiliary circuit for the automatic compensation of parasitic phase distortions at the output of IFM7 turn on again, and when the modulating voltage is applied, the IFAPCH ring will be completely compensated for modulating effect according to UG5.

Proof of the feasibility of the proposed device is that the input nodes are typical. The second ChFD13 can be performed in the same way as the first ChFDZ, which is widely used in TSSCh. The key can be made on the basis of the 564KTZ chip. The synchronism indicator is an amplitude detector with a predetermined response threshold, which is also widely used in DSC. Adders 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 weaken the influence of the destabilizing factors of the IFM on the short-term stability of the carrier oscillation of the LCSC and to reduce the distortion of the modulated signal.

Claims (1)

A digital frequency synthesizer with frequency modulation comprises a reference oscillator, a frequency divider with a fixed division coefficient, a first frequency-phase detector, a first 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 the first frequency-phase detector, a series-connected source of a modulating signal, a controlled attenuator, an inverter and an integrator, a frequency setting unit, output One of which 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 second frequency-phase detector and a second filter are connected in series low frequencies, the first adder and the second adder, a synchronism indicator and a key, the output of which is connected to the pulse-phase modulating input, in series about the modulator, and the signal input - with the output of the second adder, while the input of the synchronism indicator is connected to the output of the first frequency-phase detector, the second inputs of the first and second adders are connected to the output of the integrator, the first input of the second frequency-phase detector is connected to the output of the second pulse phase modulator, and the second input with the output of the frequency divider with a variable division ratio.