JPH0638241A - Frequency modulation current generating circuit and frequency modulation method - Google Patents

Abstract

PURPOSE:To suppress the effect in sensitivity dispersion due to dispersion in components of a VCO by implementing frequency modulation based on an original signal and a shift current obtained by a carrier current without temperature dependency decreased by a prescribed reduction rate. CONSTITUTION:A reference current IREF without temperature dependency is fed to a carrier frequency setting current generating circuit 2. An input carrier frequency setting current ICAR from the circuit 2 is inputted to a current 1/N circuit 32 via a switch circuit 31. The current ICAR is branched to 1/N in the circuit 32 and a half shift current IHHS is generated and the current IHHS is outputted to an adder 5. Furthermore, a luminance signal voltage current conversion circuit 4 adjusts a prescribed frequency shift with respect to a luminance signal Y of a video signal to generate a frequency shift setting current IDEV in response to the amplitude of the signal Y and the result is outputted to the adder 5. Thus, the currents ICAR, IHHS, IDEV are added by the adder 5 and the sum is outputted to an FM modulation circuit 6, and frequency modulation to a luminance signal deviated by 1/2fH is implemented by the current sum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency modulation current generating circuit and a frequency modulation method used in a recording system such as a video tape recorder.

[0002]

2. Description of the Related Art Conventionally, in a video tape recorder, a video signal is separated into a luminance signal Y and a color difference signal C at the time of recording to improve the S / N in a high frequency band for the luminance signal Y of both signals. Therefore, frequency modulation (hereinafter referred to as FM (Freguency Modulation)) is performed by applying emphasis, and the luminance signal Y after FM modulation is recorded on the magnetic tape. FIG. 6 shows an example of a signal recording pattern in the SP mode of the 8 mm video tape recorder. As shown in FIG. 6, the luminance signal Y is recorded on a predetermined track TR of the magnetic tape TP.

The luminance signal Y thus recorded on the magnetic tape TP is reproduced by the reproducing head. At this time, as shown in FIG. 7, the luminance signal Y is adjacent to the track to be reproduced on which the luminance signal Y is recorded. There is a high possibility that the crosstalk components CT from the tracks overlap and so-called beat interference is received. Therefore, in the conventional video tape recorder, F
An FM modulation current generation circuit including an M modulation circuit is provided, and FIG.
As shown in (a), in order to spectrally interleave the luminance signal Y during recording, so-called interleaving, the horizontal sync frequency f _H (15.734 kHz in the NTSC system) is (1/2) f _H (half) (H) is applied (hereinafter referred to as “half H shift”), and the crosstalk component is removed by using the comb filter FLT shown in FIG. c)
A luminance signal Y having no beat interference is obtained as shown in FIG.

FIG. 9 is a block diagram showing a configuration example of a conventional FM modulation current generating circuit in a recording system of a video tape recorder. In FIG. 9, 1 is a reference current generation circuit,
2 is a carrier frequency setting current generation circuit, 3 is a half H shift current generation circuit, 4 is a luminance signal voltage current conversion circuit, 5
Is an adder, and 6 is an FM modulation circuit.

In such a configuration, the temperature-independent reference current I _REF generated by the reference current generating circuit 1 which is a current source whose current value can be selected by an external external resistor.
Is the carrier frequency setting current generation circuit 2 and half H
It is supplied to the shift current generating circuit 3. The carrier frequency setting current generation circuit 2 receives the reference current I _REF and generates a carrier frequency setting current I _CAR whose frequency is adjusted so as to absorb the element variation of the FM modulation circuit 6, and outputs it to the adder 5. . The half H shift current generation circuit 3 receives the reference current I _REF and receives the half H shift current I at a timing corresponding to the switching pulse SW of a predetermined cycle.
_HHS is generated and output to the adder 5. Further, the brightness signal voltage / current conversion circuit 4 adjusts a predetermined frequency deviation amount with respect to the brightness signal Y of the video signal separated by the Y / C separation circuit (not shown), and adjusts it according to the amplitude of the input brightness signal Y. The frequency deviation amount setting current I _DEV is generated and output to the adder 5.

In the adder 5, the input carrier frequency setting current I _CAR , the half H shift current I _HHS and the frequency deviation setting current I _DEV are merged and output to the FM modulation circuit 6. In the FM modulation circuit 6, the input merged current I
Predetermined FM modulation is performed based on (I _CAR + I _HHS + I _DEV ), and a luminance signal Y FM-modulated and offset by 1/2 f _H is recorded on a magnetic tape by a recording head (not shown).

[0007]

In the above conventional circuit, the half H shift current I _HHS generated by the half H shift current generating circuit 3 depends on the temperature generated by the reference current generating circuit 1 as an external current source. Non-reference current I
_Since it is generated based on _REF , it has no temperature dependence. However, the reference current I _REF is equal to VC of the FM modulation circuit 6.
Since it is not adjusted so as to absorb the element variation of O (Voltage Control Oscillator), the half H shift current I _HHS is affected by the sensitivity variation due to the element variation of the VCO as shown in FIG. as a result,
1 / 2f is greater possibility that the absolute value is shifted in _H, in this way 1 / 2f absolute value of _H the current for generating the offset is shifted, disposed reproducing system crosstalk components from adjacent tracks occurring during reproduction Comb-shaped filter FL
Since it cannot be removed due to T, it is not possible to obtain a highly accurate image without beat interference.

The present invention has been made in view of the above circumstances, and an object thereof is to suppress the influence of sensitivity variations due to VCO element variations and to generate a highly accurate offset current and a frequency modulation current generation circuit thereof. It is to provide a frequency modulation method using current.

[0009]

To achieve the above object, in a frequency modulation current generating circuit of the present invention, a carrier current generating circuit for generating a carrier current having no temperature dependence, and a carrier from this carrier current generating circuit. A shift current generation circuit that generates a shift current by reducing the current by a predetermined reduction amount, and frequency modulation is performed based on the carrier current from the carrier current generation circuit, the shift current from the shift current generation circuit, and the original signal component. And a frequency modulation circuit.

In the frequency modulation current generating circuit of the present invention, a carrier current generating circuit for generating a carrier current having no temperature dependence, and the carrier current from this carrier current generating circuit are reduced by a predetermined reduction amount to obtain a video signal component. Half H to add offset of 1/2 of horizontal sync frequency to
A shift current generating circuit that generates a shift current and a frequency modulation circuit that performs frequency modulation based on a carrier current from the carrier current generating circuit, a half H shift current from the shift current generating circuit, and a video signal component are provided. did.

In the frequency modulation method of the present invention, frequency modulation is performed based on the carrier current having no temperature dependence, the shift current obtained by reducing the carrier current by a predetermined reduction amount, and the original signal component.

[0012]

According to the frequency modulation current generating circuit of the present invention, the carrier current generating circuit generates a carrier current having no temperature dependency, and the carrier current is output to the shift current generating circuit and the frequency modulating circuit. The shift current generation circuit generates a shift current by reducing the input carrier current by a predetermined reduction amount, and the shift current is output to the frequency modulation circuit. In the frequency modulation circuit, based on the input carrier current, shift current and original signal component,
Frequency modulation is performed on the original signal that is deviated by a predetermined amount.

According to the frequency modulation current generating circuit of the present invention, the carrier current generating circuit generates a carrier current having no temperature dependence, and the carrier current is output to the half H shift current generating circuit and the frequency modulating circuit. The half H shift current generation circuit generates a half H shift current for adding an offset of 1/2 of the horizontal synchronizing frequency to the video signal component obtained by reducing the input carrier current by a predetermined reduction amount. The shift current is output to the frequency modulation circuit. In the frequency modulation circuit, frequency modulation is performed on the video signal deviated by 1/2 f _H based on the input carrier current, half H shift current and video signal component.

According to the frequency modulation method of the present invention, based on the carrier current having no temperature dependence, the shift current obtained by reducing the carrier current by a predetermined reduction amount, and the original signal component,
Frequency modulation is performed on the original signal that is deviated by a predetermined amount.

[0015]

1 is a block diagram showing an embodiment of a frequency modulation current generating circuit according to the present invention, showing a conventional example.
The same components as those are denoted by the same reference numerals. Ie 1
Is a reference current generation circuit, 2 is a carrier frequency setting current generation circuit, 3a is a half H shift current generation circuit, 4 is a luminance signal voltage / current conversion circuit, 5 is an adder, and 6 is an FM modulation circuit.

The reference current generating circuit 1 is a current source whose current value can be selected by an external external resistor, generates a reference current I _REF having no temperature dependence, and generates a carrier frequency setting current generating circuit 2 and a half H shift current. Output to the generation circuit 3a.

FIG. 2 is a circuit diagram showing a concrete configuration example of the reference current generating circuit 1. This reference current generating circuit 1 is
Band gap regulator V ₁₀₁ , npn type transistors Q _{101 to} Q ₁₁₀ , pnp type transistors P _{101 to} P
₁₀₆ and resistance elements R _{101 to} R _114, and an external variable resistance element Rx.

The output of the bandgap regulator V ₁₀₁ is divided by the resistance elements R ₁₀₁ and R ₁₀₂ and supplied to the base of the transistor Q ₁₀₆ , and at the same time, the resistance element R _103.
Is supplied to the collector of the transistor Q _{101 and} the base of the transistor Q ₁₀₃ .

Transistors Q _101, Q _102, Q ₁₀₄ and Q
The base of ₁₀₅ is connected in series, and each transistor Q _101,
The emitters of Q _102, Q ₁₀₄ and Q ₁₀₅ are resistive elements R _104,
R _105, R _106, are connected respectively to R _107, the resistance elements _{R 104, R 105, R 106} , R 107 is connected to the resistor element R ₁₀₂ and R _114. The collector of transistor Q ₁₀₂ is connected to its base and to the emitter of transistor Q ₁₀₃ . The collector of the transistor Q ₁₀₄ is connected to the emitter of the transistor Q ₁₀₆ , and the collector of the transistor Q ₁₀₅ is connected to the emitter of the transistor Q ₁₀₇ . These transistors Q _101,
Q _102, Q _104, Q ₁₀₅ and resistance elements R _104, R _105, R _106,
R ₁₀₇ constitutes a so-called constant current circuit.

The collector of the transistor Q ₁₀₃ forms a current mirror circuit via resistance elements R _{108 and} R _109.
It is connected to the emitters of np type transistors P _{101 and} P ₁₀₂ , and is also connected to the emitters of multi-emitter pnp type transistors P _{103 and} P _{104 which also} form a current mirror circuit via resistance elements R _{110 and} R ₁₁₁ . The bases of the transistors P ₁₀₁ and P ₁₀₂ are connected to each other, and the base and collector of the transistor P ₁₀₁ are connected.
The midpoint of the connection between the collector and the base of the transistor P ₁₀₁ is connected to the collector of the transistor Q ₁₀₆ , and the collector of the transistor P ₁₀₂ is connected to the collector of the transistor Q _{107 and} the base of the transistor Q ₁₀₈ .

Similarly, the bases of the multi-emitter pnp transistors P ₁₀₃ and P ₁₀₄ are connected to each other, and the base and collector of the transistor P ₁₀₄ are connected to each other. The collector of the transistor P ₁₀₃ is connected to the emitter of the multi-emitter pnp type transistor P ₁₀₅ , and the midpoint of the collector and the base of the transistor P ₁₀₄ is connected to the emitter of the multi-emitter pnp type transistor P ₁₀₆ . The transistors P ₁₀₅ and P _{106 form a} current mirror circuit, the bases of both are connected, and the base and collector of the transistor P ₁₀₅ are connected.

The emitters of the transistors Q ₁₀₆ and Q ₁₀₇ are connected to each other, and the transistors Q ₁₀₆ and Q _{107 form} a differential amplifier. The base of the transistor Q ₁₀₇ is connected to the external resistor Rx via the resistance elements R _{112 and} R ₁₁₃ . Further, the output of the differential amplifier, that is, the collector of the transistor Q ₁₀₇ is connected to the base of the transistor Q ₁₀₈ as described above. The emitter of the transistor Q ₁₀₈ is connected to the connection midpoint between the resistance elements R ₁₁₂ and R _113, and the collector is connected to the connection midpoint between the base and collector of the transistor P ₁₀₅ .

Further, the collector of the multi-emitter pnp type transistor P ₁₀₆ which constitutes the current mirror circuit is connected to the base of the npn type transistor Q ₁₁₀ which also constitutes the current mirror circuit and the collector of the multi emitter npn type transistor Q ₁₀₉ , The emitter of the transistor Q ₁₀₉ is connected to the resistance element R ₁₁₄ , and the base is connected to the emitter of the transistor Q ₁₁₀ .

In the reference voltage generating circuit 1 having such a configuration, the current I _R adjusted by the external resistor Rx and amplified by the differential amplifier composed of the transistors Q ₁₀₆ and Q ₁₀₇ is supplied to the transistor Q ₁₀₈ . The current is mirrored through the collector through a current mirror circuit composed of a multi-emitter pnp-type transistor and appears as a temperature-independent reference current I _{REF in} the collector of the multi-emitter pnp-type transistor P ₁₀₆ . This transistor P
_The reference current I _REF that appears in the collector of ₁₀₆ is output through the base of a transistor Q ₁₀₉ that forms a current mirror circuit, for example.

The carrier frequency setting current generating circuit 2 receives the reference current I _REF from the reference current generating circuit 1 and generates a carrier frequency setting current I _CAR whose frequency is adjusted so as to absorb the element variation of the FM modulation circuit 6. , And outputs the carrier frequency setting current I _CAR to the half H shift current generating circuit 3 a and the adder 5.

FIG. 3 is a circuit diagram showing a concrete configuration example of the carrier frequency setting current generating circuit 2. The carrier frequency setting current generating circuit 2 includes a variable voltage source V ₂₀₁ , constant voltage sources V _{202 and} V ₂₀₃ , and npn transistors Q _{201 to} Q _201.
215, multi-emitter pnp type transistor P ₂₀₁ ~P
₂₀₄ and resistance elements R _{201 to} R ₂₁₈ .

The output of the variable voltage source V ₂₀₁ is the transistor Q.
Supplied to the base of ₂₀₁ . The collector of the transistor Q _{201 is} the collector of the transistors Q _202, Q _203, Q _{204 and} Q ₂₀₅ , the base of the transistor Q ₂₀₂ via the resistance element R ₂₀₃ , and the current mirror circuit via the resistance elements R ₂₁₀ and R _211. Are connected to the emitters of the multi-emitter pnp type transistors P _{201 and} P ₂₀₂ , respectively.

The emitter of the transistor Q ₂₀₁ is connected to the collector of the transistor Q ₂₁₀ , and is connected to the emitter of the transistor Q ₂₀₂ via the resistor elements R _{201 and} R ₂₀₁ for attenuation. The connection midpoint between the resistance elements R ₂₀₁ and R ₂₀₁ is connected to the base of the transistor Q ₂₀₅ ,
The midpoint of connection between the emitter of the transistor Q ₂₀₂ and the resistance element R ₂₀₂ is connected to the collector of the transistor Q ₂₁₁ .

Base of transistor Q ₂₀₂ and resistance element R
Connection point between ₂₀₃ is connected to the base of the transistor Q ₂₀₃ through a resistor R _204, resistor to a connection point between the base and the resistor R ₂₀₄ of the transistor Q ₂₀₃ is element R ₂₀₅
And R ₂₁₄ are connected in series. Transistor Q
The emitter of ₂₀₃ is connected in parallel via a resistance element R _206, R ₂₀₇ for impedance adjustment to a transistor Q _204.
Of the transistor Q _{212 and} the collector of the transistor Q ₂₁₂ .

The emitter of the transistor Q ₂₀₄ is connected to the collector of the transistor Q _{206 and} the base of the transistor Q ₂₀₈ via the resistance element R ₂₀₈ . The base of the transistor Q ₂₀₆ is connected to the collector, and the emitter is connected to the emitter of the transistor Q _{207 and} the collector of the transistor Q ₂₁₃ , respectively. The emitter of the transistor Q ₂₀₅ is connected to the collector of the transistor Q _{207 and} the base of the transistor Q ₂₀₉ via the resistance element R ₂₀₉ . The base of the transistor Q ₂₀₇ is connected to the collector, the base of the transistor Q ₂₁₃ is connected to the positive potential side of the constant voltage source V ₂₀₂ , and the emitter is connected to the constant voltage source V ₂₀₂ via the resistance element R _216.
And the negative potential side of V ₂₀₃ . The emitters of the transistors Q ₂₀₈ and Q ₂₀₉ are connected to each other, and the midpoint of the connection is connected to the collector of the transistor Q ₂₁₄ .

Multi-emitter pnp type transistor P
The bases of ₂₀₁ and P ₂₀₂ are connected to each other, and the base and collector of the transistor P ₂₀₂ are connected. The collector of the transistor P ₂₀₁ is a multi-emitter p
It is connected to the emitter of the np type transistor P ₂₀₃ , and the midpoint of the connection between the collector and the base of the transistor P ₂₀₂ is connected to the emitter of the multi-emitter pnp type transistor P ₂₀₄ . The multi-emitter pnp type transistors P ₂₀₃ and P ₂₀₄ form a current mirror circuit, the bases of which are connected to each other, and the transistor P
Base and collector of ₂₀₃ is connected, the connection point is connected to the collector of the transistor Q _209. Also,
The collector of the transistor P ₂₀₄ is connected to the collector of the transistor Q ₂₁₅ and serves as the output of the carrier frequency setting current generating circuit, and the latter half H
It is connected to the input end of the shift current generating circuit 3a.

Further, each transistor Q _210, Q _211, Q _212,
The bases of Q ₂₁₄ and Q ₂₁₅ are connected in series to the positive potential side of the constant voltage source V ₂₀₃ , and the transistors Q ₂₁₀ and Q ₂₁₅ are connected in series.
The emitters of _211, Q _212, Q ₂₁₄ and Q ₂₁₅ are constant voltage sources V ₂₀₂ and V via resistive elements R _{212 to} R ₂₁₈ , respectively.
It is connected to the negative potential side of ₂₀₃ . The transistors Q _{210 to} Q ₂₁₅ and the resistance elements R _{212 to} R _{218 form} a so-called constant current circuit, and the reference current I generated by the reference current generation circuit 1 described above does not depend on temperature.
_REF is configured to be supplied to the base of the transistor Q ₂₁₄ .

[0033] In the carrier frequency setting current generating circuit 2 having such a configuration, the above-mentioned transistors Q ₂₀₄ to Q
_The so-called Gilbert amplifier G _{m including a} two-stage differential amplifier is constituted by ₂₀₉ , and the Gilbert amplifier G _m
The current that has undergone the prescribed amplification action at is the Gilbert amplifier G
The output of _m , that is, the collector of the transistor Q ₂₀₉ , is folded back by the current mirror circuit formed by the multi-emitter pnp type transistor, and the collector of the multi-emitter pnp type transistor P ₂₀₄ absorbs the element variation of the FM modulation circuit 6. Thus, the carrier frequency setting current I _CAR whose frequency has been adjusted appears and is output to the half H shift current generating circuit 3 a and the adder 5. The adjustment for absorbing the VCO element variation of the FM modulation circuit 6 is performed by observing the output of the FM modulation circuit 6 with, for example, a frequency synthesizer while adjusting the adjustment terminal CARCON.
Done through T.

The half H shift current generating circuit 3a is opened / closed in response to the input of the switching pulse SWP to control the output of the input carrier frequency setting current I _CAR , and the carrier input via the switch circuit 31. The frequency setting current I _CAR is shunted to 1 / N and half H
It has a current 1 / N circuit 32 which generates a shift current I _HHS, and outputs a half-H-shift current I _HHS generated in the adder 5.

FIG. 4 shows a half H shift current generating circuit 3a.
3 is a circuit diagram showing a specific configuration example of FIG. This half H shift current generating circuit 3a is composed of an npn type transistor Q _301.
To Q ₃₀₅ , pnp transistors P _{301 to} P _310, and resistance elements R _{301 to} R ₃₁₈ .

The carrier frequency setting current I _CAR output from the carrier frequency setting current generating circuit 2 is supplied to the base of the transistor Q ₃₀₁ . The emitter of the transistor Q ₃₀₁ is grounded via the resistance element R _302, and the collector is connected to the collector of the transistor P ₃₀₃ . The base of the transistor Q ₃₀₂ is connected to the base of the transistor Q ₃₀₄ , the collector is connected to the collector of the transistor P ₃₀₄ , and the emitter is connected to the ground line GND via the resistance element R ₃₀₂ . Also, the transistor Q
_{The 302} base and collector are connected.

The power supply voltage V _CC is _supplied to the transistor P which constitutes a current mirror circuit via the resistance elements R _{303 and} R _304.
Transistor P that forms a current mirror circuit through the emitters of _{301 and} P ₃₀₂ , through the resistor element R ₃₀₅ and through the resistor element R _{307 and} R ₃₀₈ at the emitter of the transistor P ₃₀₅
They are connected to the emitters of _{307 and} P ₃₀₈ , respectively, and to the collector of the transistor Q ₃₀₅ .

The bases of the transistors P ₃₀₁ and P ₃₀₂ are connected to each other, and the base and collector of the transistor P ₃₀₂ are connected. The collector of the transistor P ₃₀₁ is connected to the emitter of the transistor P ₃₀₃ , and the midpoint of the connection between the collector and the base of the transistor P ₃₀₂ is connected to the emitter of the transistor P ₃₀₄ . A current mirror circuit is constituted by these transistors P ₃₀₃ and P ₃₀₄ , the bases of both are connected, the base and collector of the transistor P ₃₀₃ are connected, and the midpoint of the connection is connected to the collector of the transistor Q ₃₀₁ as described above. ing.

The collector of the transistor P ₃₀₅ is connected to the emitter of the transistor P ₃₀₆ via the resistance element R _306, and the predetermined signal SWPV for switching is supplied to the base. The collector of the transistor P ₃₀₆ is the ground line G
It is connected to ND and the base has switching pulse SWP.
Is supplied. That is, the transistor P ₃₀₆ functions as the switch circuit 31.

The bases of the transistors P ₃₀₇ and P ₃₀₈ are connected to each other, and the base and collector of the transistor P ₃₀₇ are connected. The midpoint of the connection between the collector and the base of the transistor P ₃₀₇ is connected to the emitter of the transistor P ₃₀₉ , and the collector of the transistor P ₃₀₈ is connected to the emitter of the transistor P ₃₁₀ . The transistors P ₃₀₉ and P _{310 form a} current mirror circuit, the bases of both are connected, the base and collector of the transistor P ₃₁₀ are connected, and the midpoint of the connection is connected to the collector of the transistor Q ₃₀₃ . The collector of the transistor P ₃₀₉ is connected to the output terminal of the half H shift current generating circuit 3a.

The base of the transistor Q ₃₀₃ is connected to the connection midpoint between the collector of the transistor P ₃₀₅ and the resistance element R ₃₀₆ , the emitter is connected to the emitter of the transistor Q ₃₀₅ , and the connection midpoint between them is the collector of the transistor Q ₃₀₄ . It is connected to the. The emitter of the transistor Q ₃₀₄ is connected to the ground line GND via the resistance elements R _{309 to} R ₃₁₈ connected in series. These resistance elements R
_The total resistance value of _{309 to} R ₃₁₈ is set to, for example, about 500 kΩ, and the carrier frequency setting current I _CAR input by the resistance elements R _{309 to} R ₃₁₈ is _shunted to 1 / N. That is, the resistance elements R _{309 to} R ₃₁₈ make the current 1 / N.
The circuit 32 is configured. Also, the transistor Q ₃₀₅
A predetermined signal VG is supplied to the base of the.

[0042] In the half H shift current generating circuit 3a having such a configuration, when the carrier frequency setting current I _CAR outputted from the carrier frequency setting current generating circuit 2 is input to the base of the transistor Q _301, the transistor Q ₃₀₁ The current that appeared in the collector of the transistor P ₃₀₁
Is folded by the current mirror circuit of the first stage consisting to P ₃₀₄ are appeared on the collector of the transistor P _304. This current is supplied to the base of the transistor Q ₃₀₄ via the base of the transistor Q ₃₀₂ . As a result, the input current I _CAR is shunted to 1 / N of the input value by the current 1 / N circuit 32 including the resistance elements R _{309 to} R _318, and appears at the collector of the transistor Q ₃₀₄ and further at the collector of the transistor Q _303. , This current is applied to transistors P _{307 to} P ₃₀₇
It is folded back by the current mirror circuit of the next stage consisting of ₃₁₀ , appears at the collector of the transistor P ₃₀₉ , and is output as the output current I _HHS of the circuit. The output of the half H shift current I _HHS is output timing by turning on and off the transistor Q ₃₀₃ in accordance with the input state of the switching pulse SWP to the base of the transistor P ₃₀₆ that forms the switch circuit 31. Is controlled.

The luminance signal voltage / current conversion circuit 4 adjusts a predetermined frequency deviation amount with respect to the luminance signal Y of the video signal separated by the Y / C separation circuit (not shown), and adjusts it according to the amplitude of the input luminance signal Y. The frequency deviation amount setting current I _DEV is generated and output to the adder 5.

The adder 5 merges the input carrier frequency setting current I _CAR , the half H shift current I _HHS, and the frequency deviation amount setting current I _DEV, and merges the combined current I (I _CAR
+ I _HHS + I _DEV ) is output to the FM modulation circuit 6.

The FM modulation circuit 6 receives the input combined current I
Based on (I _CAR + I _HHS + I _DEV ), frequency modulation is performed on the luminance signal deviated by 1 / 2f _H , and the modulation current Y _FM obtained as a result of the modulation is output to a limiter (not shown).

FIG. 5 is a circuit diagram showing a concrete configuration example of the FM modulation circuit 6. The FM modulation circuit 6 includes constant voltage sources V _{601 to} V ₆₀₃ and npn type transistors Q _{601 to} Q _613.
And resistor elements R _{601 to} R ₆₀₆ .

The drive current I (I _CAR + I _HSS + I _DEV ) output from the adder 5 is supplied to the base of the transistor Q ₆₀₁ and the collector of the transistor Q ₆₀₂ . The emitter of the transistor Q ₆₀₁ is connected to the bases of the transistors Q ₆₀₂ and Q ₆₀₆ , and the collector is connected to the collector of the transistor Q ₆₀₃ , the collector and base of the transistor Q ₆₀₇ , and the collectors of the transistors Q ₆₀₈ and Q ₆₁₁ , respectively. The base of the transistor Q ₆₀₂ is connected to the base of the transistor Q ₆₀₆ , and the emitter is connected to the resistance elements R ₆₀₂ and R ₆₀₆ via the resistance element R ₆₀₁ .

The emitter of the transistor Q ₆₀₃ is connected to the collector of the transistor Q ₆₀₄ , and is connected to the emitter of the transistor Q ₆₀₇ via the resistance element R ₆₀₃ .
The emitter of the transistor Q ₆₀₄ is connected to the collector of the transistor Q ₆₀₅ , and is connected to the emitter of the transistor Q ₆₀₉ via the capacitor C ₆₀₁ . The base of the transistor Q ₆₀₄ is connected to the emitter of the transistor Q ₆₁₁ . The emitter of the transistor Q ₆₀₅ is connected to the emitter of the transistor Q ₆₁₀ , the connection midpoint between them is connected to the collector of the transistor Q ₆₀₆ , and the base is connected to the positive potential side of the constant voltage source V ₆₀₁ . The emitter of the transistor Q ₆₀₆ is connected to the resistance element R ₆₀₂ .

The emitter of the transistor Q _{608 is connected to} the collector of the transistor Q ₆₀₉ , the base of the transistor Q ₆₁₁ and the resistance element R ₆₀₄ at the midpoint of connection between the emitter of the transistor Q ₆₀₇ and the resistance element R ₆₀₃ .
The positive potential side of the constant voltage source V ₆₀₂ is connected to the bases of the transistors Q ₆₀₃ and Q ₆₀₈ , and the positive potential side of the constant voltage source V ₆₀₃ is connected to the base of the transistor Q ₆₀₉ .

The midpoint of connection between the emitter of the transistor Q _{611 and} the base of the transistor Q ₆₀₄ is the transistor Q _612.
Connected to the collector. Also, the transistor Q
The collector and the base of ₆₁₂ are connected, the emitter is connected to the base of the transistor Q ₆₁₀ via the resistance element R _605, and the connection midpoint between them is connected to the collector of the transistor Q ₆₁₃ . The emitter of the transistor Q ₆₁₂ is connected to the output terminal of the circuit. The emitter of the transistor Q ₆₁₃ is connected to the resistance element R ₆₀₆ , and the base is connected to the positive potential side of the constant voltage source V ₆₀₄ .

In the FM modulation circuit 6 whose main constituent element is the VCO including the capacitor C ₆₀₁ , frequency modulation is carried out based on the input current I to the transistors Q ₆₀₁ and Q ₆₀₂ , and half of the horizontal synchronizing frequency f _H is obtained. The luminance signal Y _FM that has been subjected to the frequency shift action of is output from the emitter to the transistor Q ₆₁₂ . The oscillation frequency f of the VCO in this FM modulation circuit 6 is expressed by the following equation. f = I ₀ / 4V ₀ C ₆₀₁ Actually, 5 to 1 of the capacitor C ₆₀₁ as the internal capacitance
A capacity variation of about 0% cannot be avoided. Therefore, even if I ₀ and V ₀ do not vary, the VCO oscillation frequency f also varies by about 5 to 10%. However, the half H shift current I _HHS included in the drive current is based on the carrier frequency setting current I _CAR adjusted so as to absorb the element variation of the VCO while observing the output Y _FM of the FM modulation circuit 6. Since it is generated, it is not affected by the element variation of the VCO. As a result, the shift amount of the output luminance signal Y _FM of the FM modulation circuit 6 does not change and a stable output can be obtained.

Next, the operation of the above configuration will be described. The reference current I _REF , which is a current source whose current value can be selected by an external external resistor and is not dependent on temperature, is supplied to the carrier frequency setting current generating circuit 2.

In the carrier frequency setting current generating circuit 2,
Upon receiving the reference current I _REF , the carrier frequency setting current I _CAR whose frequency is adjusted so as to absorb the VCO element variation of the FM modulation circuit 6 is generated and output to the half H shift current generation circuit 3 a and the adder 5. It

In the half H shift current generating circuit 3a, the input carrier frequency setting current I _CAR is input to the current 1 / N circuit 32 via the switch circuit 31 which opens and closes in response to the switching pulse SW of a predetermined cycle. In the current 1 / N circuit 32, the carrier frequency setting current I _CAR is shunted to 1 / N, the half H shift current I _HHS is generated, the half H shift current I _HHS is outputted to the adder 5.
The half H shift current I _HHS generated by the half H shift current generation circuit 3a is based on the temperature-independent reference current I _REF generated by the reference current generation circuit 1 and is based on the VCO of the FM modulation circuit 6. Since it is generated based on the carrier frequency setting current I _CAR generated by adjusting the frequency so as to absorb the element variation, it has no temperature dependence and is also affected by the sensitivity variation due to the VCO element variation. There is no. That is, 1 /
VCO of FM modulation circuit 6 with no deviation in absolute value of 2f _H
Is output as a highly accurate half H shift current I _HHS corresponding to the sensitivity variation.

Further, in the luminance signal voltage / current conversion circuit 4,
A predetermined frequency shift amount is adjusted with respect to the luminance signal Y of the video signal separated by the Y / C separation circuit (not shown),
Frequency deviation amount setting current I according to the amplitude of the input luminance signal Y
_DEV is generated and output to the adder 5.

In the adder 5, the input carrier frequency setting current I _CAR , the half H shift current I _HHS and the frequency deviation setting current I _DEV are merged, and the merged current I (I
_CAR + I _HHS + I _DEV ) is output to the FM modulation circuit 6.

In the FM modulation circuit 6, the input merged current I
Based on (I _CAR + I _HHS + I _DEV ), frequency modulation is performed on the luminance signal deviated by ½ f _H, and the modulated luminance signal Y _FM obtained as a result of the modulation is output to a limiter (not shown) or the like. As a result, the luminance signal Y that has been FM-modulated and offset by 1/2 f _H is recorded on the magnetic tape by a recording head (not shown).

In this case, as described above, the half H shift current I _HHS does not have a deviation in the absolute value of 1 / 2f _H and FM.
Since the current is a highly accurate current corresponding to the variation in the sensitivity of the VCO of the modulation circuit 6, the crosstalk component from the adjacent track generated at the time of reproduction is reliably removed by the comb filter arranged in the reproduction system.

As described above, according to this embodiment,
V of FM modulation circuit 6 with no deviation in the absolute value of 1 / 2f _H
It is possible to obtain a highly accurate half H shift current I _HHS corresponding to the CO sensitivity variation, and as a result, the crosstalk component from the adjacent track generated during reproduction is
The comb-shaped filter arranged in the reproduction system ensures that the comb-shaped filter is removed, so that a highly accurate image without beat interference can be obtained.

The circuit configurations of the reference current generating circuit 1, the carrier frequency setting current generating circuit 2, the half H shift current generating circuit 3a and the FM modulating circuit 6 shown in this embodiment are shown in FIGS. It goes without saying that it is not limited to circuits.

[0061]

As described above, according to the present invention,
The influence of sensitivity variation due to VCO element variation can be suppressed, a highly accurate offset current can be generated, and a crosstalk component from an adjacent track generated at the time of reproduction can be reliably removed by a comb filter arranged in the reproduction system. You can obtain highly accurate images without beat interference.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a frequency modulation current generation circuit according to the present invention.

FIG. 2 is a circuit diagram showing a configuration example of a reference current generation circuit according to the present invention.

FIG. 3 is a circuit diagram showing a specific configuration example of a carrier frequency setting current generation circuit according to the present invention.

FIG. 4 is a circuit diagram showing a specific configuration example of a half H shift current generation circuit according to the present invention.

FIG. 5 is a circuit diagram showing a specific configuration example of an FM modulation circuit according to the present invention.

FIG. 6 is a diagram showing an example of a signal recording pattern in an SP mode of an 8 mm video tape recorder.

FIG. 7 is an explanatory diagram of a crosstalk component from a track adjacent to a track on which a luminance signal is recorded and which should be reproduced.

FIG. 8 is a diagram for explaining a basic recording / reproducing operation of a luminance signal in the video tape recorder.

FIG. 9 is a block diagram showing a configuration example of a conventional FM modulation current generation circuit in a recording system of a video tape recorder.

FIG. 10 is a graph showing an oscillation frequency characteristic with respect to a drive current of a VCO in the FM modulation circuit.

[Explanation of symbols]

 1 ... Reference current generation circuit 2 ... Carrier frequency setting current generation circuit 3a ... Half H shift current generation circuit 4 ... Luminance signal voltage / current conversion circuit 5 ... Adder 6 ... FM modulation circuit

Claims (3)

[Claims] 1. A carrier current generation circuit for generating a carrier current having no temperature dependence, and a shift current generation circuit for generating a shift current by reducing the carrier current from the carrier current generation circuit by a predetermined decrease amount. A frequency modulation current generation circuit comprising: a frequency modulation circuit that performs frequency modulation based on a carrier current from the carrier current generation circuit, a shift current from the shift current generation circuit, and an original signal component. 2. A carrier current generating circuit for generating a carrier current having no temperature dependence, and a carrier current from the carrier current generating circuit is reduced by a predetermined reduction amount, so that a horizontal synchronizing frequency of 1 is added to a video signal component.
A shift current generating circuit for generating a half H shift current for adding an offset of / 2, and a frequency based on a carrier current from the carrier current generating circuit, a half H shift current from the shift current generating circuit, and a video signal component. A frequency modulation current generation circuit, comprising: a frequency modulation circuit that performs modulation. 3. A frequency modulation method characterized by performing frequency modulation based on a carrier current having no temperature dependence, a shift current obtained by reducing the carrier current by a predetermined reduction amount, and an original signal component.