JPS5915310A - Frequency modulating circuit - Google Patents

Abstract

PURPOSE:To stable the carrier frequency, by correcting the oscillating frequency while no modulated signal is supplied and having a control so that the corrected frequency is maintained as a center frequency even when the modulated signal is supplied. CONSTITUTION:Switches 2 and 9 are turned off and on respectively with a switching signal W. Then the output of a voltage control oscillator 5 is compared with that of a reference oscillator 7 by a phase controller 6. Those compared outputs are connected to the control input terminal of the oscillator 5 through a filter 8 via a buffer part 10. Under such conditions, the oscillating frequency of the oscillator 5 is corrected to the frequency of the oscillator 7. When the switches 2 and 9 are turned on and off respectively with the signal W, a modulated signal S is applied to the control terminal of the oscillator 5. In this case, the output voltage of the filter 8 obtained during correction is held at a capacitor 11 and then applied via the buffer 10. Therefore a carrier frequency is equal to the frequency of a reference signal.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a frequency modulation circuit using a voltage controlled oscillator. 1. Background Art and Problems Related to a Frequency Modulation Circuit That Can Obtain One Frequency Modulated Output Word Having a Frequency I!1. A frequency modulation circuit is generally used in which all modulation signals are supplied to the output terminal of the voltage controlled oscillator and one frequency modulated output word is obtained from the output terminal of the voltage controlled oscillator.Frequency modulation using such a voltage controlled oscillator Although the circuit oscillator has the advantage of being suitable for integrated circuits, the center frequency fluctuates due to changes in the characteristics of the voltage controlled oscillator due to temperature changes, which causes the carrier frequency of the frequency modulated output signal to fluctuate. The drawback is that it cannot be kept stable.

Therefore, in order to stabilize the center frequency of the voltage-controlled excavator and to stabilize the carrier frequency of the frequency modulated output signal, it has been proposed to add an automatic frequency control circuit to the voltage-controlled excavator. Among these automatic frequency control circuits, one that can obtain a relatively high stable IW is a phase-locked loop (phase-locked loop).
There is an application of In a frequency modulation circuit equipped with an automatic frequency control circuit that fully utilizes this phase-locked loop, the output of the voltage control excavator is supplied to the frequency divider, and the divided output obtained by the output of the reference oscillator is different from the output of the reference oscillator. The divided output obtained by being supplied to the frequency divider is supplied to the phase comparator for phase comparison, and the phase comparison output is passed through the low-pass filter and supplied to the control input terminal of the voltage open side 1 oscillator. Then, the oscillation frequency of the voltage controlled oscillator is controlled so that the stable point is when the outputs on both sides are in the same phase.
This stabilizes the center frequency of the voltage controlled oscillator, but as the degree of frequency modulation becomes deeper, the phase difference between the two divided outputs supplied to the phase comparator increases. There is a risk that the phase difference becomes too large and accurate phase comparison cannot be performed.In addition, in order to perform accurate phase comparison, it is necessary to use a frequency divider for the output of the voltage controlled oscillator and a frequency divider for the output of the reference oscillator. Purpose of the Invention In view of these points, the present invention aims to solve the problem of an automatic frequency control circuit added to a voltage controlled oscillator, which is extremely difficult to install and implement. It can be installed without any problem, and moreover, the center frequency of the electric one-voltage control one-shot generator is extremely effectively stabilized by this automatic frequency control circuit, and the frequency modulation has a stable carrier frequency. It is an object of the present invention to provide a frequency modulation circuit capable of obtaining an output signal.

Furthermore, a recording system for a signal including a frequency modulated signal in a magnetic recording/reproducing apparatus that performs helical scan recording on a magnetic tape using two magnetic rad sounds to which such a frequency modulation circuit is applied. The purpose is also to provide. 1. Summary of the Invention A frequency modulation circuit according to the present invention includes a voltage controlled oscillator, a first switch for intermittently supplying a modulation signal to a control input terminal of the voltage controlled oscillator, and an output of the voltage controlled oscillator and a reference. a phase comparator that is supplied with a signal and performs a phase comparison between the two, a filter connected to the output terminal of this phase comparator, and an output of this filter that is intermittently supplied to the 8 control input terminals of the voltage controlled oscillator. and a voltage holding section connected between the second switch and the control input terminal of the voltage controlled oscillator, and one of the first switch and the second switch is connected to the voltage control oscillator. When the first switch is in the non-supply state, the same wave number modulated output signal is derived from the output terminal of the switched voltage-side oscillator. When in the supply state, no modulation signal is supplied to the control input terminal of the voltage-controlled excavator, and at this time, the oscillation frequency of the voltage-controlled oscillator is controlled based on the comparison output from the phase comparator. The frequency is assumed to be the same as that of the reference signal. Further, at this time, the voltage supplied to the control input terminal of the voltage controlled oscillator via the second switch is supplied to the voltage holding section.

When the first switch is in the supply state, the modulation signal is superimposed on the voltage held in the voltage holding section and is supplied to the control input terminal of the voltage controlled oscillator. A modulated output signal is obtained. Therefore, a frequency modulated output signal is obtained intermittently from the frequency modulation circuit according to the present invention, and the center frequency of the voltage controlled oscillator is changed every period in which a frequency modulated output signal is not obtained. is standard 1
If the center frequency is set correctly according to the instructions, the set center frequency is maintained during the period when the frequency modulated output signal is obtained, and the center frequency is stabilized, so it has an extremely stable carrier frequency. 1. Embodiment in which a Frequency Modulated Output Signal is Obtained An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 shows an example of a frequency modulation circuit according to the present invention. In this example, the input terminal / to which the variable NS IN signal S is supplied is connected to the first switch λ and the DC blocking capacitor 3.
is connected to one input terminal of the adder via the adder. , the output end of the adder G is connected to the control input end of the voltage controlled oscillator, and the output end of this voltage controlled oscillator is connected to one input end of the phase comparator B. The output end of the reference oscillator 7 can be connected to the other input end of the phase comparator B. The output terminal of 1 and 16 phase ratio comparison % l= is connected to which input terminal of the filter g, and the output terminal of this filter g is connected to the other input terminal of the adder g via the first switch and buffer section 10. Connected 1, first switch 7 and buffer section 1
0, a capacitor//// which forms the entire voltage holding section is connected. Further, each of the open side ends of the first switch λ and the second switch λ is connected to the control XI i4 element 7.2 to which the switching signal W is supplied, and furthermore, the output terminal of the voltage controlled oscillator Connected to terminal /3.

1 Here, adder G, phase comparator B, reference oscillator 7, filter G, and first switch? , a buffer section 10 and a capacitor // form an automatic frequency control circuit section attached to the left of the voltage controlled oscillator.

In such a configuration, the first switch λ and the second switch are controlled by the switching signal W from the control terminal /2 so that when one is turned on, the other is turned off, and the switching signal 1 is At a predetermined period determined by W, the ON state and the OFF state are alternated. And the first
When the switch λ is turned off and the first switch λ is turned on, the modulation signal S from the input terminal / is not supplied to the input terminal of the voltage controlled oscillator S, and the voltage controlled oscillator at this time The output from the reference oscillator 7 and the reference signal from the reference oscillator 7 are phase-compared by a phase comparator B. The reference signal obtained from this reference oscillator 7 has a frequency equal to the desired carrier frequency of the frequency modulated output signal to be obtained at the output terminal /3.11 The comparison output obtained from the phase comparator 6 is supplied to the filter gK, A DC voltage corresponding to the supplied comparative output is obtained at the cutting edge. This DC voltage is supplied to the control input terminal of the voltage controlled oscillator Shio through the second switch 9, which is turned on at this time, and further through the buffer section 10 and the adder Il. The oscillation frequency of the DC voltage control oscillator left is controlled, and the output of the voltage control oscillator left and the reference oscillator 7 are supplied to the phase comparator B.
It is stabilized in a state where the phase difference between the reference signals from the reference signal becomes zero. That is, the oscillation frequency of the voltage controlled oscillator is made equal to the frequency of the reference signal from the reference oscillator 7.
The DC' expansion pressure that is supplied to the buffer section 10 through ' is also supplied to the capacitor // forming the entire voltage holding section.

Next, when the first switch λ is turned on and the first switch 9 is turned off, the modulation signal S from the input terminal is passed through the first switch λ and three capacitors to one side of the adder G. is supplied to the input end of

The capacitor // holds the DC voltage from the filter g immediately before the first switch 9 is turned off, and the DC voltage held in the capacitor // passes through the buffer section 70 to the other side of the adder g. is supplied to the input end of Therefore,
A modulation signal S superimposed on the DC voltage held in the capacitor // is obtained at the output end of the adder, and this is supplied to the left control input end of the voltage controlled oscillator. As a result, the output of the voltage controlled oscillator S is changed from the previously set reference oscillator 7.
It has a frequency change according to the modulation signal S, centering on a frequency equal to the frequency of the reference 1 word from,
A frequency 'P having a carrier frequency equal to the frequency of the reference signal from the reference oscillator 7, the modulated output signal is output from the output terminal /3
6. Thereafter, there is a period in which the first switch Ω is turned off and the first switch 7 is turned on, and a period in which the first switch Ω is turned on and the second switch 9 is turned off. The periods are repeated alternately, and the operations described above are performed repeatedly. A frequency modulated output signal is intermittently obtained from the output terminal /3 every time the first switch 7 is turned on and the first switch 7 is turned off. At this time, for the voltage controlled oscillator, a frequency setting is performed so that the oscillation frequency is forced to be equal to the frequency of the reference signal of the reference oscillator 7 every period when the frequency a modulation signal is not obtained, and the frequency modulation output is During the period when the signal is obtained, the voltage from the capacitor// is no longer controlling to maintain this set frequency as the center frequency, so the center frequency of the voltage controlled oscillator can be stabilized. As a result, a frequency modulated output signal having an extremely stable carrier frequency can be obtained. This stabilizing operation is performed without being affected by frequency modulation.

Moreover, the automatic frequency control circuit section formed by adder g, phase comparator B, reference oscillator 7, filter g, switch G, buffer section 10, and capacitor// has no difficulty or completeness in its design and implementation. It is said that it can be established without any restrictions. In the above example, the output of the voltage controlled oscillator S and the reference signal from the reference oscillator 7 are directly supplied to the phase comparator B, but the output of the voltage controlled oscillator S A frequency divider may be inserted between the first input terminal of the phase comparator B and the output terminal of the reference oscillator 7 and the other input terminal of the phase comparator B, respectively. . In that case, the relationship between the center frequency of the voltage controlled oscillator, that is, the carrier frequency of the frequency modulated output signal, and the frequency of the reference signal from the reference oscillator 7 is determined according to the frequency division ratio of the frequency divider. The figure shows, as an application example of the frequency modulation circuit according to the present invention, a magnetic recording and reproducing device configured using the frequency modulation circuit according to the present invention, which performs helical scan recording on a magnetic tape using one magnetic head. An example of a recording system for frequency-modulated audio and video signals in a video tape recorder is shown. In this example, the terminal /G to which the first audio word S8 to be recorded is supplied is connected to the input terminal of the pre-emphasis circuit /S, and the output terminal of the pre-emphasis circuit /S is connected to the It is connected to the input terminals of the frequency modulation circuits /B and /7 according to the invention. The first switch in these frequency modulation circuits /B and /7, 2a and 2b1, condensers 3a and 3b, adder t
la and "bt voltage control 1 oscillators 3a and 5b, phase comparators Otsu and 4b, reference oscillators 7a and 7b, filters ga and gb1 second switches 9a and 9b, buffer parts 10a and 10b, and capacitor/ /a and /
/b, the first switch λ, the capacitor 3, the adder G, the voltage controlled oscillator S, the phase comparator, the reference oscillator 7, the filter G, the second switch W, the buffer unit 10 and the capacitor shown in FIG. //D, respectively, correspond to each other. The output terminals of such frequency modulation circuits /B and /7 are connected to one input terminal of each of the mixing circuits 20 and 2/ via bandpass filters /g and /9, respectively.
The output terminal of a video signal processing circuit 22 is connected to the other input terminal of each of the mixing circuits 1 and 2/. The respective output terminals of the mixing circuits 20 and 2/2 are connected to the rotating magnetic head 2S and λB via the recording amplifier 23 and the 2/2 circuit. These rotating magnetic heads 2 (left and right) perform helical scanning on the magnetic tape, alternately forming inclined tracks on the magnetic tape, and record the signals from the mixing circuits 20 and 2/. In this case, signals for /field period are recorded on the seven inclined tracks.

Therefore, the rotating magnetic heads λk and 2B alternately contact the magnetic tape every field period, and perform recording by sequentially forming all inclined tracks.

Also, the first switch in each of the frequency change KI4 circuits /B and /7, 2. The control terminals of the switches a and 2b and the first switches 9a and 9b are connected to a common control terminal 27.
This control terminal 27 is connected to a first switch 2a and a second switch 9b' for each field period.
<The first switch 9a and the first switch 2b'ff are on, and the first switch 9a and the second switch 9b are off, and the first switch 9a and the second switch 9b are off.
A switching word Wf that turns on the first switch 2b' and the first switch 2b' is supplied.

In such a recording system, during the field period when the rotating magnetic head 0 is in contact with the magnetic tape and the rotating magnetic head 0 is not in contact with the magnetic tape, the switching signal Wf from the control terminal 27 and the frequency modulation circuit A are The first switch 62a and the first switch 9b in B and/or are turned on, and the first switch L? The switch 2b and the seventh switch 2b are turned off. As a result, the first switch 64 is connected to the control input terminal of the voltage controlled oscillator 3a of the frequency modulation circuit/B.
The one voice word S8 that has passed through is supplied to the frequency modulation circuit/
A frequency-modulated output signal, that is, a frequency-modulated audio signal SF is obtained at the output end of the audio signal S8. After passing through the band pass filter /g, it is mixed with the video signal Sv from the video signal processing circuit 22 in the mixing circuit 20, and then sent to the rotary magnetic head 2k via the recording amplifier 23.
The recording is performed by the rotating magnetic head 2. During this field period, the frequency modulation circuit/7 does not receive the audio signal Ss from the GREEN 7 abs circuit/shio to the control input terminal of its voltage controlled oscillator 5b, causing the voltage controlled oscillator b to oscillate. Control is performed to make the frequency equal to the frequency of one reference word from the reference oscillator 7b. In this field period, the frequency modulation circuit/7
Although it is not possible to obtain a frequency-modulated audio signal, there is no problem with the side tube because the rotating magnetic head is not in contact with the magnetic tape and is not recording.

On the other hand, during the field period when the rotating magnetic head 23 is in contact with the magnetic tape and the rotating magnetic head 23 is not in contact with the magnetic tape, the switching signal W from the control terminal 27 is
By f, frequency modulation circuit /B and /7 1■/
The switch 'f-2' and the second switch 9b are turned off, and the second switch 9a and the first switch and 2b are turned on. The audio signal Ss that has passed through the reinforcement circuit/left is supplied to the control input terminal of the peeping suppression M1 oscillator 5b through the first switch 2b'i4, and the audio signal Ss that has passed through the reinforcement circuit/left is supplied to the output terminal of the frequency modulation circuit/7. Frequency modulation 1 for Ha No. Ss
−11 force signal, ff1J, etc., frequency-modulated audio signal SF is obtained. After this passes through the bandpass filter /9'z, the video from the video signal processing circuit 2.2 is mixed with the signal Sv in the mixing circuit, 2/, and the recording amplifier 2'l'f)
The information is supplied to the rotating magnetic head 2 through the magnetic head 2, and recording is performed by the rotating magnetic head 2. , and during this field period, the frequency modulation circuit/B is connected to the control input terminal of the left voltage control J oscillator.
The audio signal S8 from k is not supplied, and the voltage controlled oscillator S
Control is performed to make the oscillation frequency of the signal a equal to the frequency of one reference word from the reference oscillator 7a. During this field period, a frequency-modulated audio signal is not obtained from the frequency modulation circuit/B, but at this time, the rotating magnetic head does not contact the magnetic tape for two days and is in the autumn state where it does not record. There is no side pipe problem.

In this way, from the frequency modulation circuits /B and /7, one voice word S is alternately frequency-modulated every field period.
F is obtained, mixed with the video signal and sent to the rotating magnetic head 2k.
and 2, and are recorded on magnetic tape. At this time, the voltage controlled oscillators 5a and 5b in the frequency modulation circuit L'Pr/l and /7 change their oscillation frequencies to the reference oscillator 7a and 7b, followed by a frequency-modulated audio signal S
During the field period when Fe occurs, the DC voltage from capacitors //a and //b maintains the set river wave number as the center frequency, so the frequency obtained from the image frequency modulation circuits /o and /7 The carrier frequency of the modulated audio signal SF becomes extremely stable without fluctuation.

By making the frequencies of the reference signals from the reference oscillators 7a and 7b in the frequency modulation circuits /B and /7 different from each other, the frequency-modulated audio signal recorded by the rotary magnetic head 25 and the rotary magnetic head are The frequency e recorded by Ω4 can be different in total carrier frequency from one sound word modulated by the number of sounds. Since the carrier frequencies of the frequency-modulated audio signals recorded therein are different from each other, it is possible to reduce adjacent trunk crosstalk interference during playback.

Effects of the Invention As described above, in the frequency modulation circuit according to the present invention, the oscillation frequency of the voltage controlled oscillator that performs frequency modulation operation according to the modulation signal is equal to or equal to the reference signal at a predetermined period when no modulation signal is supplied. The center frequency of the voltage controlled oscillator is effectively stabilized by controlling the corrected frequency to be maintained as the center frequency during the period when the modulation signal is supplied. Therefore, a frequency modulated output signal with a very stable carrier frequency is generated. Furthermore, since the automatic frequency control circuit unit that stabilizes the center frequency of such a voltage-controlled oscillator corrects its oscillation frequency in a state where no modulation signal is supplied to the voltage-controlled excavator, it is necessary to use a phase comparator or There is no difficulty in designing each part including the input part and actually incorporating the circuit, and the structure can be easily configured.

[Brief explanation of drawings]

FIG. 1 is a block connection diagram showing an example of a frequency modulation circuit according to the present invention, and FIG. 2 is a block diagram showing an example of a recording system of a video tape recorder configured using the frequency modulation circuit according to the present invention. It is a connection diagram. In the figure, / is an input terminal, 2 is a first switch, G is an adder, S is an electronically limited oscillator, O is a phase comparator, 7 is a quasi-oscillator, 9 is a filter, 9 is a second switch, // is a capacitor that forms the entire voltage holding section, /2 is a control terminal, and /3 is an output terminal.

Claims (1)

[Claims] a voltage-controlled excavator, a first switch for supplying the entire modulation signal to the control input terminal of the voltage-controlled oscillator; a filter connected to the output of the phase comparator; and a second filter for intermittently supplying the output of the filter to the control input of the voltage-controlled excavator.
and a voltage holding section connected between the second switch and the control input terminal of the voltage controlled oscillator, and one of the first switch and the second switch is supplied with a voltage. A frequency modulation circuit configured such that when one of the five voltage controlled oscillators is in the non-supply state, the other is in the non-supply state, and a frequency modulated output signal is derived from the output end of the five voltage controlled oscillators.