JPH0527281B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an FM modulation circuit for a video magnetic recording/reproducing device (hereinafter referred to as a VTR), and particularly to an FM modulation circuit suitable for a semiconductor integrated circuit.

[Conventional technology]

Conventionally, home VTRs have used the FM recording method to record luminance signals. That is, a predetermined emphasis is applied to the luminance signal being input as a video signal, and then FM modulated and recorded on a magnetic tape. on the other hand,
During playback, the recorded FM signal is amplified by the preamplifier, and then the original luminance signal is obtained by the FM demodulation and de-emphasis circuit. Nowadays, home use
The majority of VTR signal processing is made up of semiconductor integrated circuits (hereinafter referred to as ICs).
As sets become smaller, lighter, and more multifunctional, they are becoming more highly integrated.

FIG. 5 shows a block diagram of an example of a conventional IC-based FM modulation processing circuit for luminance signals. In the figure, during recording, a luminance signal with a predetermined emphasis is input from the IC terminal 7, and the FM modulator 1
5 changes the oscillation frequency according to the input luminance signal level, and outputs the FM signal from the IC terminal 8 via the output circuit 6, and a recording amplifier (not shown) at the subsequent stage.
is being input. Switchable resistor connected to terminal 7
The FM carrier frequency and deviation are adjusted by R ₁ and R ₂ . Reference bias circuit 16
provides bias for the FM modulator 15.

FIG. 6 shows a circuit diagram of a specific example of the FM modulator 15 shown in FIG. In this FM modulator, a video luminance signal inputted from a terminal 12 is inputted via a resistor R ₂ , is converted into a current by a voltage-current conversion circuit 31 , and a current corresponding to the input luminance signal level is sent to a current mirror circuit 32 . through the differential transistor of the oscillation circuit 38 with a multivibrator configuration.
Supply to Q _13,14 . Also, since positive feedback is applied to the transistors Q _{11 and 12} , they are alternately turned on and off, and when the transistor Q ₁₁ is on, the transistor _{Q 13 is} also off, and the transistor Q ₁₄ is on. When transistor Q ₁₂ is on, transistor Q ₁₃ is on, transistor
Since _Q14 is turned off, the collectors of the differential transistors Q13 _{and Q14} alternately operate to draw the charges charged in the capacitor _C11 . On the other hand, the collector currents of the transistors Q ₁₃ and Q ₁₄ are given via a current mirror circuit 32 as a current according to the video luminance signal level. The oscillation frequency of the oscillation circuit 38 at this time is given by the following equation.

=/4CV...(1) However, is the output current of the current mirror circuit 32, C is the capacitance value of the capacitor _C11 , and voltage V is the reference voltage set in the range of 0<V<power supply voltage.

The FM modulation signal whose oscillation frequency is given by equation (1) is taken out from the emitters of the transistors Q ₁₁ and Q ₁₂ and further taken out via the limiter circuit 33.

FIG. 7 is an input current versus oscillation frequency characteristic diagram of the FM modulator 15 shown in FIG. The FM carrier frequency and deviation are adjusted by external variable resistors R ₁ and R ₂ connected to terminal 7, respectively, so that the sync chip level of the normal video brightness signal input and the white 100% level meet the specified standards. . For example, in the case of the VHS standard, the sync chip level frequency ( ₁ ) is set to 3.4MHz, and the white 100% level frequency ( ₂ ) is set to 4.4MHz.

[Problem that the invention seeks to solve]

As mentioned above, the conventional circuit constituted by the IC shown in FIGS. 5 and 6 can perform FM modulation processing of the video luminance signal during VTR recording. By the way, as a measure to improve the image quality of home VTRs, recently, as part of efforts to increase the band of the luminance signal, so-called high-band conversion has been adopted, in which the FM modulation carrier frequency of the luminance signal is shifted to the higher frequency side and the deviation is expanded. New standardization, including standardization, is being undertaken. In such a high-band compatible VTR set, during recording, the signal processing is changed by selecting whether to record according to the conventional standard or the high-band standard.

Here, in the FM modulation processing circuit for the luminance signal,
In the case of the conventional example, in order to comply with the high band standard, the FM modulation carrier frequency and deviation are set in advance to the conventional standard by the internal setting conditions of the IC and the external variable resistance constant. Standard-tuned FM modulation processing IC
It is possible to add a new IC or to switch external constants using the same IC.
Adding an IC and adjusting the carrier frequency and deviation are also required, increasing costs. In the latter case, the IC internal constants are designed to comply with conventional standards, so the shift of the carrier frequency to the higher frequency side and the expansion of the deviation are
For example, the variable resistance constant connected to the terminal 7 may be switched, but a switching means must be provided outside the IC. In this case, the input current vs. oscillation frequency characteristics of the FM modulator 15 are sync chip level frequency ₃ in the high band standard, white
If the 100% level frequency is ₄ , the relationship as shown in Figure 7 will be obtained, and the characteristics of the FM modulator 15 are such that the frequency changes from at least frequency ₁ to changes in the input current.
Linearity is required over a wide range up to ₄ , but this linear range is already determined within the IC, so when supporting high bands, linear input current vs. oscillation frequency characteristics in the high range are required. There is a problem that it becomes impossible to obtain.

The purpose of the present invention is to solve such problems and to develop two
An object of the present invention is to provide an FM modulation circuit that can implement FM modulation processing of both standards on the same IC by providing an FM modulator on the same IC.

[A great way to solve problems]

The FM modulation circuit of the present invention has a voltage that converts the voltage level of a signal input from the first terminal into a current.
a current converting means; a first current supplying means for inputting the current from the voltage-current converting means to obtain a current output according to the first gain; and a carrier determined according to the output of the first current supplying means. a first FM modulator including a first oscillation circuit that produces an FM modulated output having an oscillation frequency and a deviation ratio; and a first FM modulator that receives the current from the voltage-current conversion means and outputs a current according to a second gain. and a carrier oscillation frequency that is determined according to the output of the second current supply means and a carrier oscillation frequency that is further adjusted according to the control voltage from the second terminal. a second FM modulator including a second oscillation circuit that outputs a modulated output; a switch circuit that selectively switches and outputs each modulated output from the first and second FM modulators; and a third terminal. When a first control input is given, the first FM modulator is operated and the second FM modulator is operated.
The FM modulator is stopped and the switch circuit selects the output of the first FM modulator, and when the second control input is applied from the third terminal, the first FM modulator is switched on. A control circuit for stopping the second FM modulator and causing the switch circuit to select the output of the second FM modulator is provided on the same semiconductor integrated circuit board.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 shows a block diagram of one embodiment of the invention. In the figure, when recording, a resistor is connected to terminal 12.
A luminance signal with a predetermined emphasis is input to the IC terminal 7 via _R2 , and is input to the FM modulators 1 and 2, respectively. In these FM modulators 1 and 2, the FM signal whose oscillation frequency is changed according to the input luminance signal level is sent to the switch circuit 4.
The output of the switch circuit 4 is led to the subsequent stage from the terminal 8 via the output circuit 6.

These FM modulators 1 _{and 2} have the same configuration as the conventional example shown in FIG. adjustments will be made. In this case, a variable resistor R ₃ is provided to the FM modulator 2 via a terminal 10 so that the FM carrier frequency can be adjusted independently of the FM modulator 1 by means of the variable resistor R ₃ . On the other hand, a control circuit 5 with terminal 9 as a control input point is provided, and the FM modulator 1,
A control output is provided to the switch circuit 2 and the switch circuit 4.

That is, the first control input (for example,
Vcc voltage) is applied, the FM modulator 1 is operated, the FM modulator 2 is cut off, and the switch circuit 4 selects the "a" input.
At this time, the FM modulation output from the FM modulator 1 is taken out to the terminal 8. Also, when the second control input (for example, ground potential) is applied from terminal 9, the FM
The modulator 2 is operated to cut off the FM modulator 1, and the switch circuit 4 selects the "b" input. At this time, the FM modulation output from the FM modulator 2 is taken out to the terminal 8.

Here, for example, the first FM modulation process according to the conventional standard is performed by the FM modulator 1, and the second FM modulation process according to the high band standard is performed by the FM modulator 2. First, with the first control input applied to terminal 9 and the FM modulator 1 operating, variable resistors R ₁ and R ₂ connected to terminal 7 change the output FM signal to the FM carrier frequency based on the conventional standard. , and deviation. Next, a second control input is applied to the terminal 9 to operate the FM modulator 2. In this state, the variable resistor connected to terminal 10
R ₃ adjusts the FM carrier frequency of the output FM signal to meet the high band standard. FM here
The carrier frequency is normally adjusted so that the frequency at the time of sync chip level input conforms to a predetermined standard.On the other hand, when adjusting the deviation in the high band standard, since the deviation ratio between the two standards is known in advance, the FM modulator 1 By providing a deviation ratio between these two standards between the input signal and oscillation frequency conversion gain of each of the FM modulator 2 and the input signal of the FM modulator 2, the deviation adjustment can be performed simultaneously when adjusting the deviation of the conventional standard. For example, if the ratio between the deviation of the high band standard and the deviation of the conventional standard is 1.5,
The input signal to oscillation frequency conversion gain of FM modulator 2 is
It may be set to 1.5 times the conversion gain of the FM modulator 1.

FIG. 2 shows a specific circuit diagram of the main part of the embodiment.
In the figure, the oscillation circuits 22 and 23 each have a first
It constitutes FM modulators 1 and 2 in the figure. The current mirror circuit 24 transmits a signal obtained by converting the input luminance signal into a current to the oscillation circuits 22 and 23. To cope with the deviation, for example, if the emitter area ratio of the transistors Q ₁ and Q ₂ and the resistance ratio of the resistors R ₅ and R ₆ constituting the current mirror circuit 24 are given the deviation ratio between the two standards. good.

The control circuit 5 selects the input of the switch circuit 4 in response to the first control input from the terminal 9, and supplies a current to the resistor _R6 so that the emitter potential of the transistor _Q4 approximately becomes the base potential of the transistor _Q4 . Due to the injection, the transistor _Q4 is cut off, and the oscillation circuit 23 becomes inoperable. vice versa,
In response to a second control input from terminal 9, transistor _Q3 is similarly cut off, and oscillation circuit 22 becomes inoperable. Also, transistor
Transistors _Q5 to _Q10 provided between the collector point of _Q4 and the terminal 10, current mirror circuit 24, constant current source _I1 , constant voltage source 25, and resistor _R7 ,
A differential circuit consisting of _R8 allows external variable resistance
A constant current determined by adjusting R ₃ is supplied to the oscillation circuit 23, or a current mirror circuit 2
The oscillation frequency of the oscillation circuit 23 can be varied independently of the oscillation circuit 22 by subtracting it from the current to the oscillation circuit 23 determined by 6.

FIG. 3 shows an input current versus oscillation frequency characteristic diagram of the FM modulator constituting this embodiment. In the figure, characteristic line A
Characteristic line B shows the case where the FM modulator 1 complies with the conventional standard, and characteristic line B shows the case where the FM modulator 2 complies with the high band standard. As mentioned above, since the FM carrier frequency can be set independently and the deviation difference is given internally in advance, it is possible to provide the optimal FM modulation operating point for both standards on the same IC.

FIG. 4 is a block diagram of a second embodiment of the invention. In the first embodiment, the control input terminal 9 of the control circuit 5 and the FM carrier frequency adjustment terminal 10 for the FM modulator 2 are provided separately, but as in the second embodiment, each control is commonly controlled. This can be done using the terminal 13. Connect FM modulator 2 externally to terminal 13.
A switch 11 and a diode D ₁ are connected to the variable resistor R ₃ for adjusting the FM carrier frequency and the control circuit 5. This control circuit ₅ operates the _FM modulator ₂ with _a voltage _V
The FM modulator 1 is operated with a voltage V _{X '} , and the FM modulator 2 is cut off. Here V ₁
<V ₂ −V _D and V _D is the forward voltage drop of diode D1.

At this time, if switch 11 selects the ground potential,
When the FM modulator 2 operates, the diode _D1 is cut off, and the FM modulator 2 can be controlled by the variable resistor _R3 . On the other hand, when the switch 11 selects the potential _V2 , the FM modulator 2 is cut off. At this time, due to variable resistance _R3
Although the control point for FM modulator 2 changes, the FM
There is no problem because modulator 2 is not operating.

In this way, in this embodiment, by sharing the IC terminals, it is possible to reduce the number of pins by one.

〔Effect of the invention〕

As explained above, in the present invention, the FM carrier frequency can be adjusted independently, and the deviation ratio is internally given in advance as the difference between the two operating points.
By installing an FM modulator on the same IC and selecting its output using an external control signal, it is possible to comply with both conventional standards and high-band standards on the same IC.
FM modulation processing can be realized. Moreover, for that purpose
Since no special elements or special circuit means are required outside the IC, there is no particular increase in costs, making it ideal for fields such as home VCRs where low costs are required.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention;
Fig. 2 is a circuit diagram showing the main parts of this embodiment, Fig. 3 is a characteristic diagram of the FM modulation circuit of this embodiment, Fig. 4 is a block diagram of the second embodiment of the present invention, and Fig. 5 is a diagram showing the characteristics of the FM modulation circuit of this embodiment. Traditional
A circuit diagram showing an example of an FM modulation circuit.
FIG. 7 is a circuit diagram showing the main parts of the conventional example, and FIG. 7 is a characteristic diagram of the conventional FM modulation circuit. 1, 2, 15... FM modulator, 3, 16... Reference bias circuit, 4, 11... Switch circuit, 5... Control circuit, 6... Output circuit, 7 to 10, 12, 13... Terminal, 21, 31... Voltage -Current conversion circuit, 22,2
3, 38... Oscillator circuit, 24, 26, 32... Current mirror circuit, 25, 37... Constant voltage source, 33... Limiter circuit, 34... Load circuit, 35, 36... Level shift circuit, C ₁₁ ... Capacitor, D ₁ , _D11 ...Diode, _I1 , _I11 to _I13 ...Constant current source, _Q1 to _Q10 ,
Q ₁₁ ~ Q ₂₀ ... transistor, R ₁ ~ _{R 3} ... variable resistor,
_R4 to _R8 , _R11 , _R12 ...Resistance.

Claims (1)

[Claims] 1. Voltage-current converting means for converting a voltage level input from a first terminal into a current; and a current output according to a first gain by inputting the current from the voltage-current converting means. and a first oscillation circuit that produces an FM modulation output having a carrier oscillation frequency and a deviation ratio determined according to the output of the first current supply means. and a second current supply means that inputs the current from the voltage-current conversion means and obtains a current output according to the second gain, and a carrier oscillation frequency and a frequency determined according to the output of the second current supply means. a second FM modulator including a second oscillator circuit that produces an FM modulated output having a carrier oscillation frequency adjusted in accordance with the deviation ratio and a control voltage from a second terminal; a switch circuit that selectively switches and outputs each modulation output from the FM modulator; and a switch circuit that operates the first FM modulator and operates the second FM modulator when a first control input is applied from a third terminal. When the FM modulator is stopped and the switch circuit selects the output of the first FM modulator, and the second control input is applied from the third terminal, the first
stops the FM modulator, operates the second FM modulator, and instructs the switch circuit to operate the second FM modulator.
An FMF modulation circuit characterized in that a control circuit for selecting an output of an FM modulator is provided on the same semiconductor substrate.