RU27441U1 - DEVICE FOR PHASE AUTOMATIC FREQUENCY OF THE FREQUENCY OF THE GENERATOR WITH FREQUENCY MODULATION - Google Patents

Abstract

A frequency-modulation generator phase-locked loop frequency oscillator comprising a phase modulator, a frequency-phase detector, a low-pass filter, a controlled oscillator and a frequency divider for the reduction path, the output of which is connected to the reference input of the frequency-phase detector, and also a series-connected source of the modulating signal and an integrator, the output of which is connected to the second input of the phase modulator, the output of a controlled generator being the output of a device I mean that we introduced a series-connected reference frequency synthesizer and a reference divider, the output of which is connected to the first input of the phase modulator, which contains a series-connected sawtooth voltage generator and a comparator, the second input of which is the second input of the phase modulator, the output of which is the output of the comparator, while the sawtooth voltage generator contains a series connected pulse shaper discharge, a discharge key and an emitter follower, the output of which is connected connected to the second input of the comparison unit, the first input of which is connected to the output of the reference voltage source, the output of the comparison unit is connected to the input of a controlled charge current source, the output of which is connected to the output of the discharge key and one output of the charging capacitor and is the output of a sawtooth generator, in addition, the other terminal of the charging capacitor and the second terminal of the discharge key are connected to the housing.

Description

DEVICE OF PHASE AUTOMATIC FREQUENCY OF THE FREQUENCY OF THE GENERATOR WITH

FREQUENCY MODULATION.

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

A known frequency modulator with a phase-locked loop (PLL) (see patent EP 0403877A1, NOZS 3/09, 1990). The modulator is characterized in that the upper cutoff frequency of the low pass filter (LPF) is less than the lower cutoff frequency of the modulating signal. A summing stage is provided between the low-pass filter and the controlled generator (UG), in which the output signal of the low-pass filter is combined with a modulating signal. In such a device, a frequency modulated (FM) signal can be obtained at the output, however, the range of modulating frequencies will be limited from below due to feedback in the PLL system. In this case, the PLL performance will be low due to a significant decrease in the cut-off frequency of the low-pass filter.

Also noteworthy is a device that implements broadband FM generators covered by a PLL with a narrow bandwidth (see US patent 4074209, NOZS 3/22, 1978). In this device, the modulating frequency band is not limited by the PLL loop parameters, since two-point introduction of the modulating signal is used. However, in this device, along with the low stability of the output FM oscillation parameters, it is not possible to work in the output frequency range, because in the case of frequency overlap, the non-uniformity of the steepness of the controlled generator will lead to inconsistency of the frequency deviation at a constant value of the modulating signal, as well as to the appearance of nonlinear distortions due to the non-identical amplification along the modulation channels when the modulating signal is fed to two points.

2001123900

 : 11111Ш1ШР1И1Ш1ШН

- Н 03 СЗ / 09 Н 04 L27 / 10 with frequency modulation (according to the AS of the USSR No. 1566458A НОЗ СЗ / 09, Н04 L27 / 10,

1990), adopted as a prototype. FIG. 1 shows an enlarged structural diagram of this prototype device, which shows: 1 — reference generator (OG), 2 — phase modulator (FM), 3 — integrator (I), 4 — source of the modulating signal (IC), 5 — frequency -phase detector (ChFD), 6 - low-pass filter, 7 controlled generator (UG), 8 - frequency divider of the drive path (accident). The PLL device contains UG 7 with an accident 8 connected to the input of the PFD 5, to the second input of which through FM 2 is connected OG 1. The output of the PFD 5 is connected to the input of the PLL 6, the output of which is connected to the control input of the UG 7, closing the PLL. The modulating voltage from the IC 4 is supplied to the modulation input of UG 7 and through AND 3 to the control input FM 2.

The device operates as follows.

If the modulating signal from the IC 4 through And 3 is fed only to the input of FM 2, then the phase-modulated output signal of FM 2 and the output signal of the PLL after the accident 8 is converted to PFD 5 into the voltage of the error signal, which is fed through LPF 6 to UG 7. In this case, the low-pass filter 6 in the PLL system attenuates the error signal and reduces the modulation sensitivity at high frequencies. The use of modulation directly of UG 7 when a signal is supplied from IC 4 to its modulation input is characterized by the fact that the PLL system corrects the frequency of the output signal and, therefore, counteracts the modulation. FEGCH 6 in the PLL system attenuates high-frequency signals from the PFD 5, the corrective action of the circuit reduces the modulation sensitivity at low frequencies. Consequently, the use of a single-point PLL-based FM provides a modulation sensitivity with a bandwidth of either high or low frequencies, depending on the modulation application point.

In the case of applying a modulating signal simultaneously to both points, the modulation process is presented as a way of counteracting one phenomenon to another. In this case, a modulation sensitivity with a total transmission characteristic is realized. This characteristic can be gentle in

2

the case of identical amplification on the supply channels of the modulating signal. However, theoretically, the equilibrium condition is valid only for one value of the steepness of the tuning of UG 7 with respect to the modulation input and the transmission coefficient of FM 2. When operating in the range of output frequencies, the modulation system goes out of balance, and additional measures are required to maintain a constant gain ratio over the modulation channels, associated with the attraction of significant hardware costs, which in practice can not always be realized.

The disadvantage of the prototype device is the low stability of steam

meters of output frequency-modulated oscillations. To eliminate these drawbacks, a device containing a phase-modulator, a frequency-phase detector, a low-pass filter, a controlled generator and a frequency divider for the reduction path, the output of which is connected to the reference input of the frequency-phase detector, and also a series-connected modulating signal source and integrator the output of which is connected to the second input of the phase modulator, and the output of the controlled generator is the output of the device; orny synthesizer reference frequency divider and whose output is connected to a first input of the phase modulator, which comprises series-connected sawtooth generator and a comparator, the second input of which is the second input of the phase modulator, the output of which is the output of the comparator. In this case, the sawtooth voltage generator contains a series-connected discharge pulse generator, a discharge key and an emitter follower, the output of which is connected to the second input of the reference unit, the first input of which is connected to the output of the reference voltage source, the output of the comparison unit is connected to the input of the controlled charge current source, the output of which connected to the output of the discharge k; g) cha and one output of the charging capacitor and is the output of the pi3 g-shaped voltage generator. In addition, the other terminal of the charging capacitor and the second terminal of the discharge key are connected to the housing. In FIG. 2 is a structural diagram of the proposed device, de is indicated: 1 - reference frequency synthesizer; 2-phase modulator; 3- integrator; 4- source of the modulating signal; 5- frequency-phase detector; 6- low-pass filter; 7-controlled generator (UG); 8- frequency divider tract reduction; 9- reference divider; 10- discharge pulse shaper; 11-bit key; 12-controlled source of charge current; 13-charge capacitor; 14-emitter repeater; 15- comparison unit; 16- source of reference voltage; 17-comparator; 18 - sawtooth voltage generator. The proposed device contains a series-connected reference frequency synthesizer 1, a reference divider 9, a phase modulator 2 (consisting of a series-connected sawtooth voltage generator 18 and a comparator 17j frequency-phase detector 5, a low-pass filter 6, a controlled oscillator 7, the output of which is the output of the device, and, in addition, connected to the input of the frequency divider of the reduction path 8, the output of which is connected to the reference input of the frequency-phase detector 5. In this case, the output of the source of the modulating signal is 4 3 integrator 3 connections4

nyon with the second input of the comparator 17. Moreover, the sawtooth generator 18 contains a series-connected pulse shaper of discharge 10, a bit key 11 and an emitter follower 14, the output of which is connected to the second input of the comparison unit 15, the first input of which is connected to the output of the reference voltage source, and the output comparison unit 15, the first input of which is connected to the output of the reference voltage source, and the output of the comparison unit 15 is connected to the input of the controlled charge current source 12, the output of which is connected to one and charging terminals of capacitor 13 and output 11-bit key, and is the output of the sawtooth generator. The other terminal of the discharge capacitor 13 and the second terminal of the discharge key are connected to the housing. The second input of the comparator is the second input of the phase modulator 2, the output of which is the output of the comparator 17.

The phase-locked loop frequency generator with frequency modulation operates as follows.

The controlled oscillator 7, the splitter 8 of the reduction path included in the ring, the BFD 5, and the filter 6 form a phase-locked loop of the frequency of the controlled oscillator 7. The PLL circuit monitors the driving action from the reference frequency synthesizer 1, after passing it through the reference divider 9 and a phase modulator 2 to the synchronizing input of the CFD 5. In this case, the output frequency fsbix of the entire device is determined by the following relation

febix ktp fc4 / non (1)

fc4 is the output frequency of the frequency synthesizer 1, NTH is the constant division factor of the cast path divider, Non is the constant division factor of the reference divider.

Thus, at the output of UG 7 it is possible to obtain a discrete set of frequencies with a grid spacing AfBbix Afc4NTn / Non, (2)

g - // ed

AfcH - step of the frequency grid at the output of the reference frequency synthesizer 1.

It should be noted that the comparison frequency on the CFD 5 fcp fc4 / Non varies in the operating frequency range of febix. In the case of equality of the division coefficients, the relation fBbix fc4 is established with the step AfBbix Afc4, and in the case of inequality, a certain transformation of these values is established depending on the value of Nxn / Non.

After the synchronism is established in the PLL ring, the frequency modulation of UG 7 is carried out by applying a modulating signal UM (jQiw) from the source 4 of the modulating signal through an integrator 3 to the control input of the phase modulator 2, which in turn is the second input of the comparator 17. The reference input to the comparator 17 the signal from the sawtooth voltage generator 18 with a constant amplitude A of the saw in the comparison frequency range fcp fc4 / Non (within 0.5 - 2.0 MHz). In the sawtooth voltage generator 18, the output signal is automatically stabilized due to the control circuit of the magnitude of the charge current of the controlled source 12 when the period of the comparison frequency fcp changes. The frequency of the modulating effect is usually in the range of 20-20000 Hz. The modulating effect seems to be a slower process than the process of forming the reference sawtooth voltage. The mechanism of operation of the phase modulator 2 according to the principle of a controlled delay line is illustrated in FIG. 3 using timelines.

At the output of the comparator 17, a rectangular voltage is formed, the front of which is modulated in phase (Fig. 3). In the absence of modulation (FIG. 3a), the front occupies the average temporal (phase) position, indicated by dashed lines on the time line. Changing the modulation signal UM (JQM) in amplitude leads to a change in the phase position by - A (p (Fig. 36) and by + Af (Fig. Sv) relative to the average position. Thus, the phase modulator 2 operates in a controlled line mode beyond

a delay in which the amount of delay and its polarity are controlled according to the UM signal (jftivi).

It can be shown that the frequency deviation at the output of the PLL device from the FM generator is determined by the relation

VSPm) (1 / 27gTi) -Ktp-Kfm-im () am)), (3)

Ф (Пм) is the frequency response of the closed PLL system, Kfm is the 2nd / A transmission coefficient of the FM, UM is the amplitude of the modulating signal, A is the amplitude of the sawtooth voltage, and Ti is the integrator time constant.

From the expression (3) it is seen that the sawtooth voltage generator 18 in the proposed device plays a key role, ensuring the amplitude A (Fig. 3) of the output signal is constant and thereby ensuring the deviation in the operating range of modulating frequencies at different frequencies at the output of UG 7.

The result of modulating the phase of the pulses at the output of the phase modulator 2 is a change in the error signal at the output of the PFD 5, causing a frequency deviation of the output signal of the UG 7 in accordance with the modulation law. In this case, the modulation signal represents an external disturbance for the PLL system. The PLL circuit ensures the stability of the center frequency of UG 7 and does not generate any counteraction signal aimed at eliminating modulation. Consequently, the PLL system behaves as an equivalent low-pass filter with respect to the modulating effect, and at a certain frequency lower than the cutoff frequency Ps 27cFc of the system there is a rise or failure of the frequency modulation characteristic (see Fig. 4). Almost undistorted frequency modulation takes place at frequencies below the cutoff frequency Fc (for example, 30-40 kHz), being limited from below by the integrator time constant at a frequency of 1 / 271Ti (for example, 10-15 Hz).

It should be noted that the high stability of the output parameters

frequency-modulated oscillations occurs with a significant frequency overlap of UG 7. The inherent UG 7 unevenness of the steepness of the control characteristic in the PLL system leads to a slight change in the cutoff frequency of the fie system due to a change in the gain in the circuit. As a result of this, the frequency response mod Ф (Пм) undergoes changes only in the region of the cutoff frequency (see, Fig. 4). This unused portion lies above the highest modulus frequency; its signal is PM max.

Thus, the use of the proposed phase-locked loop frequency generator with frequency modulation can improve the stability of the output FM oscillation parameters with the ability to work in the range of output frequencies while at the same time high speed with a wide frequency range of the modulating signal in combination with simplification of hardware implementation.

A significant difference of the proposed PLL device with FM is a significant simplification of the hardware implementation of this device, because it not only monitors the driving action from the synthesizer, but also introduces the modulating voltage at only one point in the circuit. Frequency modulation of the output oscillations of the UG is carried out using a phase modulator. Since the frequency deviation function is a derivative of the phase deviation function, the modulation signal is preliminarily passed through the integrator, as a result of which the signal acquires frequency modulation at the output of the ultrasonic wave according to the law determined by the shape of the modulating signal. Such a circuit implementation can significantly eliminate the contradictions between the most important characteristics of the PLL device, such as spectral, dynamic and modulation. Patent holder of the Voronezh Research Institute of Communications

c -av / 5 2

8

Claims (1)

A frequency-modulation generator phase-locked loop frequency oscillator comprising a phase modulator, a frequency-phase detector, a low-pass filter, a controlled oscillator and a frequency divider for the reduction path, the output of which is connected to the reference input of the frequency-phase detector, and also a series-connected source of the modulating signal and an integrator, the output of which is connected to the second input of the phase modulator, the output of the controlled generator being the output of a device I mean that we introduced a series-connected reference frequency synthesizer and a reference divider, the output of which is connected to the first input of the phase modulator, which contains a serially connected sawtooth voltage generator and a comparator, the second input of which is the second input of the phase modulator, the output of which is the output of the comparator, while the sawtooth voltage generator contains a series connected pulse shaper discharge, a discharge key and an emitter follower, the output of which is connected connected to the second input of the comparison unit, the first input of which is connected to the output of the reference voltage source, the output of the comparison unit is connected to the input of the controlled charge current source, the output of which is connected to the output of the discharge key and one output of the charging capacitor and is the output of a sawtooth generator, in addition, the other terminal of the charging capacitor and the second terminal of the discharge key are connected to the housing.