JPH01135205A - Frequency modulating circuit - Google Patents

Abstract

PURPOSE:To realize an FM processing applicable to both standards of a conventional standard and a high band standard by providing two frequency modulators to give a deviation ratio on a same IC and selecting the output by the external control signal. CONSTITUTION:A first FM processing by a conventional standard is executed by a frequency modulator 1 and a second FM processing by a high band standard is executed by a frequency modulator 2. First, a first control input is given to a terminal 9, the frequency modulator 1 is operated, and in the condition, variable resistances R1 and R2 connected to a terminal 7, an output FM signal is adjusted so as to be an FM carrier frequency and a deviation based on the conventional standard. Next, a second control signal is given to the terminal 9 and the frequency modulator 2 is operated. In the condition, the FM carrier frequency of the output FM signal is adjusted so as to satisfy a high band standard.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to an FM modulation circuit for a video magnetic recording/reproducing device (hereinafter referred to as a VTR), and relates to an FM modulation circuit suitable for semiconductor integrated circuits in 1%.
Related to modulation circuits.

[Conventional technology]

Conventionally, the FM recording method has been used to record luminance signals in home VTRs. That is, a predetermined emphasis is applied to a luminance signal being input as a video signal, and then FM modulated and recorded on a magnetic tape. on the other hand.

During reproduction, the recorded FM signal is amplified by a preamplifier, and then the original luminance signal is obtained by an FM demodulation and de-emphasis circuit. Nowadays, most of the signal processing in home VTRs is made up of conductor integrated circuits (hereinafter referred to as ICs). It is planned.

FIG. 5 shows a 7' diagram of an example of a conventional IC-based F'M 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 15 outputs an FM signal whose oscillation frequency is changed according to the input luminance signal level via the output circuit 6. The signal is output from the IC terminal 8 and is input to a subsequent recording amplifier (not shown). The FM carrier frequency and deviation are adjusted by variable resistors R, , R, connected to the terminal 7. Reference bias circuit 16 supplies bias for F'M modulator 15.

FIG. 6 shows a circuit diagram of a specific example of the FM modulator 15 shown in FIG. This FM modulator receives a video luminance signal input from a terminal 12 via a resistor R, converts it into a current by a pressure-current conversion circuit 31, and converts a current according to the input luminance signal level. Through the mirror circuit 32,
The signal is supplied to the differential transistor Qtsst4 of the oscillation circuit 38 having a multi-viator configuration. In addition, since positive feedback is applied to the transistors Qll and 12, they are turned on alternately.

The transistor Qts * t4 is turned off when the transistor Q1t is on, the transistor Q14 is on, and when the transistor Q12 is on, the transistor Q13 is on, and the transistor Q
14 is turned off, so that the collector of the differential transistor Qts*t4 is turned on and off repeatedly.

It operates to alternately draw the charge charged in the capacitor C■. On the other hand, the collector currents of the transistors Qts and Qt4 are given via a current mirror circuit 32 as a current corresponding to the input level of the video luminance signal. The oscillation frequency f of the oscillation circuit 38 at this time is given by the following equation.

■ However, I is the output current of the current mirror circuit 32.

C is the capacitance value of the capacitor fCtt, and '-voltage (2) is the reference voltage set within the range of 0<V and the power supply voltage.

The FM modulation signal whose oscillation frequency is given by this equation (1) is extracted from the emitters of transistors Qtt and Qtz,
Furthermore, it is taken out via a limiter circuit 33.

FIG. 7 is shown in FIG. FIG. 3 is a diagram showing FM modulator 150 input current versus oscillation frequency characteristics. The FM carrier frequency and deviation are respectively adjusted by external variable resistors R1 and R2 connected to the terminal 7 so that the sync, pre-level, and white 100% level of the normal video luminance signal input meet predetermined standards.

For example, in the case of the VH8 standard, the frequency (fl) of the sink and pre-levels is set to 3.4 MHz, and the frequency (f2) of the white 100-inch level is set to 4.4 MHz.

[Problem that the invention seeks to solve]

As mentioned above, 9. FM modulation processing of video luminance signals during VTR recording is possible. by the way.

Recently, it has been used as a measure to improve the image quality of home VTRs.

As part of efforts to increase the bandwidth of luminance signals, a new standardization called so-called no-band recording is being implemented, which includes shifting the FM modulation carrier frequency of the luminance signal to a higher frequency side and expanding the deviation.

In such a VTR set that supports high band.

At the time of recording, a selection is made as to whether to record according to the conventional standard or to the No. 1 band standard, and the signal processing is changed.

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, F.
Since the M modulation carrier frequency and deviation are set in advance to the conventional standard by the IC internal setting conditions and external variable resistance constant, it is necessary to add FM modulation processing ■C newly adjusted to the high band standard, It is conceivable to use the same IC to switch the external constants, but in the former case, it would be necessary to add a new IC and also make carrier frequency and deviation adjustments, which would increase costs.

In the latter case, the IC internal constants are designed to comply with conventional standards, so the carrier frequency shifts to the higher frequency side and the deviation expands.

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 150 are as follows: the frequency fs of the sink and pre-levels in the high band standard, and the frequency of the white 100% level of 14
Then, the relationship as shown in Fig. 7 is obtained, and the FM modulator 1
5 requires linearity over a wide range of frequencies from ft to 14 at least with respect to changes in input current, but this linear range is already determined within the IC, so it is difficult to achieve a high band. If this is done, there is a problem that linear input current vs. oscillation frequency characteristics cannot be obtained in the high range.

The purpose of the present invention is to solve such problems and provide two FM modulators that comply with the conventional standard and the high band standard on the same IC, so that FM modulation processing for both standards can be performed on the same IC. An object of the present invention is to provide an FM modulation circuit that can be realized in the following manner.

[A great way to solve problems]

The FM modulation circuit of the present invention includes voltage-current conversion means for converting the voltage level of a signal input from a first terminal into a current.

A first current supply means that obtains a first current output using the current from the voltage-current conversion means; an oscillator circuit; and a first M modulator.

1. a second current supply means for obtaining a second current output by the current from the voltage-current conversion means; a second FM modulator including a second oscillation circuit whose FM modulation output is an oscillation frequency determined according to the output current from the second current supply means and the second control input;

a switch circuit that selectively switches and outputs each FM modulation output from the first and second FM modulators;

When the first lid input is applied to the third terminal,
The 10th F'M modulator 1S11 is operated, the second FM modulator is stopped, the switch circuit selects the first F'M modulator output, and the second FM modulator is operated from the third terminal. When a control input is given.

The first FM modulator is stopped, the second FM modulator is operated, and the second FM modulator is activated in the switch circuit.
A control circuit that selects a modulator output.

are 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, during recording, a luminance signal with a predetermined emphasis is input from terminal 12 to IC terminal 7 via resistor R3, and is input to 2M modulators 1 and 2, respectively.

In these 2M modulators 1 and 2, FM signals whose oscillation frequencies are changed according to the luminance signal levels of the two inputs are input to the a and b input points of the switch circuit 4, respectively, and the output of the switch circuit 4 is output to the output circuit 6. It is led to a later stage from the terminal 8 via the terminal 8.

These 2M modulators 1 and 2 have the same configuration as the conventional example shown in FIG. )l, , respectively, the FM carrier frequency,
and deviation adjustments are made. In this case, F.M.
A variable resistor R3 is provided to the modulator 2 via a terminal 10, and this variable resistor R8 allows F to be input independently from the 2M modulator 1.
It is possible to adjust the M carrier frequency. On the other hand, a control circuit 5 having a terminal 9 as a control input point is provided, and provides a control output to the 2M modulator 1.2 and the switch circuit 4.

That is, when the first control input (for example, VCC voltage) is applied from the terminal 9, the 2M modulator 1 is operated, the FM modulator 2 is turned off, and the child circuit 4 outputs "a".
” to select the input.

At this time, the FM modulation output from the FM modulator 1 is taken out to the terminal 8. Further, when a second control input (for example, ground potential) is applied from the terminal 9, the 2M modulator 2 is operated, the FM modulator 1 is turned off, and the switch circuit 4 selects the rbJ input. Make it. At this time, the FM modulation output from the 2M modulator 2 is taken out to the terminal 8.

Here, 1, for example, the first FM modulation processing according to the conventional standard is F
The M modulator 1 causes the 2M modulator 2 to perform second FM modulation processing according to the high band standard. First, apply a first control input to terminal 9.

With the FM modulator 1 in operation, the variable resistors R1 and R connected to the terminal 7 are used to adjust the output FM signal to the FM carrier frequency and deviation based on the conventional standard. , a second control input is applied to terminal 9, and 2
Operate M modulator 2.

In this state, variable resistor R3 connected to terminal 10 causes
Adjustment is made so that the FM carrier frequency of the output FM signal satisfies the high band standard. Here, the key J of F'M carrier frequency is
1 is 1. Normally, the frequency at the time of sync chip level input is set to the specified standard, and on the other hand.

When adjusting the deviation ratio in the high band standard, the deviation ratio between the two standards is known in advance, so the FM variation
Vessel 1. By providing a deviation ratio between these two standards between the input signal and oscillation frequency conversion gains of each of the 2M modulators 2 and 2M modulator 2, adjustments can be made simultaneously during the deviation adjustment 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, FM converter #S 2
The input signal to oscillation frequency conversion gain may be set to 1.5 times the conversion gain of the PM modulator 1.

FIG. 2 shows a specific circuit diagram of the main part of the embodiment.

In the figure, 1 oscillation circuits 22 and 23 correspond to the FM modulators 1 and 1 in FIG. 1, respectively. and 2f, constitute.

The current slurr circuit 24//i transmits a signal obtained by converting the input luminance signal into a current to the oscillation circuits 22 and 23. Here, as a countermeasure for deviation, 1, for example, a current mirror circuit 24
The deviation ratio between the two standards may be given to the emitter area ratio of the transistors Q+aQ and the resistance ratios of the resistors R, .

The control circuit 5 selects the input of the switch circuit 4 in response to the first control input from the terminal 9, and also selects the input of the transistor Q4.
By injecting a current into the resistor R so that the potential of the emitter becomes approximately the base potential of the transistor Q4, the transistor Q4 is turned off and the oscillator circuit 23 stops operating. Conversely, for the second control input from terminal 9, transistor Q3 is turned off and turned off in the same manner.
The i-withdrawal path 22 ceases to operate. Also, transistor Q
Transistor Q a = Q 10 provided between the collector point of 4 and the terminal 10 #Current mirror circuit 24゜ Constant current source 1. Constant voltage source 25. and resistance R,,R
, depending on whether a constant current determined by adjusting the external variable resistor R3 is supplied to the oscillation circuit 23, or whether it is subtracted from the current to the oscillation circuit 23 determined by the current mirror circuit 26. The oscillation frequency of the oscillation circuit 23 is

It is made to be variable independently of the oscillation circuit 22.

FIG. 3 shows an input current versus oscillation frequency characteristic diagram of the F'M modulator constituting this embodiment. In the figure, 1% gonad A corresponds to the conventional standard using FM modulator 1, and characteristic line B corresponds to 2.
This is a case where the M modulator 2 supports the high band standard. As mentioned above, since the FM carrier frequency can be set independently and the deviation ratio is given internally in advance, it is possible to provide the optimum FM modulation operating point for both standards on the same IC.

FIG. 4 is a schematic diagram of the second embodiment of the present 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 2M modulator 2 are provided separately, but as in the second embodiment, each control is commonly controlled. Terminal 13 can be used. 2 on the outside of terminal 13
FM carrier frequency adjustment variable resistor R3 of M modulator 2,
A switch 11 and a diode DI are connected to the control circuit 5. This control circuit 5 has 0 applied to the terminal 13.
The FIVI modulator 2 is operated with a voltage Vx such that ≦Vx≦■l, the FM modulator 1 is cut off, and the FM modulator 1 is operated with a voltage Vx / such that Vl-Vn<vx'.

Turn off the FM modulator 2. KokoteV
1 (V 2- V D to L, Vn/' Iode Q
/, cD forward voltage drop.

At this time, when the switch 11 selects the ground potential, the FM modulator 2 operates and the diode Dl is cut off;9. The FM modulator 2 can be controlled by the variable resistor 3. On the other hand, when the switch 11 selects the negative potential, the FM modulator 2 is cut off. At this time,
However, the control point for the FM modulator 2 by the variable resistor R3 changes.

There is no problem because the FM modulator 2 is not operating.

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

〔Effect of the invention〕

As explained above, the present invention enables two FM modulators in which the F+4 carrier frequency can be adjusted independently and the deviation ratio is given internally as the difference between their respective operating points to be operated at the same -I.
By providing this on the IC and selecting this output using an external control signal, it is possible to implement FMii, 4 processing that complies with both the conventional standard and the high band standard on the same IC. Furthermore, since no special elements or special circuit means are required outside the IC, there is no particular cost increase.

It is most suitable for fields where cost reduction is required, such as home VTRs.

[Brief explanation of the drawing]

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 professional diagram of the second embodiment of the present invention, and Fig. 5 6 is a circuit diagram showing an example of a conventional FM modulation circuit, FIG. 6 is a circuit diagram showing a main part of the conventional example shown in FIG. 5, 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, 22.23.3
8...Oscillation circuit, 24, 26°32...
・Current mirror circuit, 25.37... Constant voltage source, 33... Limit circuit, 34...
Load port M, level shift for 35.36) laljl
L Ctt・Old・Condenbu-Dl e Dll・・
group/diode, ■l*'ll~Its...constant current source, Ql-Ql. 5Qxt~Q2o...transistor, R1~Rs...variable resistor, R4~
R,,I (11, R1, Old...Resistance. Agent Patent Attorney Susumu Uchihara 4th evening 5 Input power figure 7

Claims (1)

[Claims] Voltage-to-current conversion means for converting the voltage level of a signal input from a first terminal into a current; a first FM modulator including a current supply means and a first oscillation circuit whose FM modulation output is an oscillation frequency determined according to the output from the first current supply means; and from the voltage-current conversion means. a second current supply means that obtains a second current output by a current of the second current supply means; a second FM modulator including an oscillation circuit; a switch circuit that selectively switches and outputs each FM modulation output from the first and second FM modulators; and a first control from the third terminal. When an input is applied, the first FM modulator is activated, the second FM modulator is deactivated, and the switch circuit selects the first FM modulator output, and the third FM modulator is activated. When a second control input is applied from a terminal, stopping the first FM modulator;
An FM modulation circuit comprising: a control circuit that operates the second FM modulator and causes the switch circuit to select the output of the second FM modulator; and a control circuit provided on the same semiconductor substrate.