JP2844781B2 - RF modulator - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an RF modulator that frequency-division multiplexes an audio signal and a video signal and transmits the signal using a main carrier signal, and is particularly suitable for UHFTV (television). Related to compact RF modulators.

[Summary of the Invention]

The RF modulator according to the present invention includes an FM modulator to which an audio signal is supplied, an FM-modulated output and a video signal to be supplied.
An AM modulator for modulating, an audio sub-carrier signal oscillator, and a main carrier signal oscillator.
It is characterized in that it is made up of CO and the whole is made up of a one-chip IC for miniaturization.

[Conventional technology]

2. Description of the Related Art Conventionally, an FM modulator using a PLL (Phase Locked Loop) has been known as described in, for example, JP-A-1-129614.

That is, in the block diagram showing an example of the conventional FM modulator using the PLL shown in FIG. 3, 1 indicates a PLL circuit as a whole, 2a indicates a reference oscillator, and 2b indicates a frequency obtained by dividing the oscillation output of the reference oscillator 1. a reference frequency divider for outputting a reference frequency f _r.
3 is a VCO (voltage controlled oscillator), a phase comparator 5 with a reference frequency f _r and the output of the reference divider 2b, which is divided by the variable frequency divider 4 of the VCO3 division ratio oscillator output N The comparison output is supplied to the VCO 3 via the charge pump 6 and the LPF (low-pass filter) 7 to control the frequency and phase of the VCO 3. Reference numeral 8 denotes a lock detector, 9 denotes a transmitting unit, and 10 denotes an output terminal from which an FM modulated signal is output. Here, MC indicates a microphone for inputting a modulation signal.

In the above configuration, the reference frequency of the reference frequency divider 2b is
If f _r , the divided output frequency of the variable frequency divider 4 is f _v , and the oscillation frequency of the VCO 3 is f ₀ , By changing N, the oscillation frequency of VCO3
f ₀ (= N · f _r ) can be controlled.

For example, by changing the N in the range of 800 to 900 the reference frequency f _r as 100 KHz, the oscillation frequency f ₀ between 80 to 90 MHz 1
It can be varied at a channel spacing frequency of 00 KHz.

[Problems to be solved by the invention]

However, the above-mentioned FM modulator modulates only an audio signal, and cannot be immediately applied as an RF modulator in which an audio signal and a video signal are frequency-division multiplexed and transmitted using a main carrier signal.
(Integrated circuit) has not been proposed.

Accordingly, it is an object of the present invention to provide an RF modulator with the above disadvantages improved.

[Means for solving the problem]

The RF modulator of the present invention, an FM modulator to which an audio signal is supplied, and an FM modulated output and a video signal of the FM modulator are respectively supplied, and a main carrier signal is formed by the FM modulated output and the video signal. An AM modulator that performs AM modulation, an audio subcarrier signal oscillator that supplies an audio subcarrier signal to the FM modulator, and a main carrier signal oscillator that supplies a main carrier signal to the AM modulator, a reference oscillator, A phase comparator, a VCO, and a variable frequency divider, wherein the output of the reference oscillator and a frequency-divided output obtained by dividing the output of the VCO by the variable frequency divider are phase-compared by the phase comparator; A first PLL that controls the VCO by means of
Circuit, another phase comparator, a VCO, and a variable frequency divider, and the divided output of the reference oscillator of the first PLL circuit and the output of the another VCO are divided by another variable frequency divider. A second phase comparator compares the output with another output and controls the another VCO using the phase comparison output.
Wherein the VCO of the first PLL circuit is used as the main carrier signal oscillator and the second PLL circuit is used.
Another VCO of the L circuit is used as the audio subcarrier signal oscillator, and the FM modulator, the AM modulator, the first PLL circuit, and the second
Is constituted by a one-chip IC.

[Action]

According to the RF modulator of the present invention, the main carrier signal is AM-modulated by the FM modulated output obtained by FM-modulating the audio sub-carrier signal with the audio signal and the video signal, and the frequency-division multiplexed AM-modulated output is converted to the first AM modulated output. By varying the frequency division ratio of the variable frequency divider of the PLL circuit, a desired channel frequency signal can be obtained, and the frequency division ratio of another variable frequency divider of the second PLL circuit can be varied to produce the audio subcarrier signal. The frequency can be changed. In addition, FM modulator, AM modulator,
Since the PLL circuit and the second PLL circuit are constituted by a one-chip IC, downsizing can be achieved and the frequencies of the main carrier signal and the audio sub-carrier signal can be stabilized against a temperature change.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a basic configuration of an RF modulator according to the present invention. Reference numeral 14 denotes a one-chip IC (integrated circuit) as a whole. Reference numeral 15 denotes a first PLL circuit having a reference frequency _fr
A reference oscillator 16 for generating a reference frequency signal, a VCO (voltage controlled oscillator) 17, a variable frequency divider 18 having a frequency division ratio N, and a phase comparator 19, and the oscillation output of the VCO 17 is controlled by the variable frequency divider 18. to divide the the reference frequency f _r and the output of the reference oscillator 16 is compared by a phase comparator 19, controls the frequency and phase of VCO17 the comparison output is supplied to the VCO17 via the LPF (low pass filter) 20 To be configured. P ₁ denotes an input terminal for a video signal (V) is supplied, P ₂ denotes an input terminal to which the audio signal (A) is supplied. 21 amplifier connected to the input terminal P _1, 22 denotes an FM modulator, FM modulator 22 second PLL circuit including an audio signal input terminal P ₂ and (A) as an audio subcarrier signal oscillator 23 to frequency f _s
Are supplied. Reference numeral 24 denotes a mixer that mixes the video signal (V) amplified by the amplifier 21 with an FM-modulated output of the FM modulator 22. The output of the mixer 24 is supplied to one input of an AM modulator 25. Wherein the other input of the AM modulator 25, a main carrier signal of a frequency f ₀ from the VCO17 of the first PLL circuit 15 is supplied, a main carrier signal is AM-modulated by the object to be FM modulated output and the video signal, supplying a AM modulated output (TV signal) S _TV to an output terminal P _3. 16a is the terminal P ₄ and the terminal
It is external Crystal of connected reference oscillator 16 between the P _5. P ₆ is a channel frequency setting terminal.
Control voltage V _c1 of P ₆ is converted into a predetermined digital value by, for example, A / D converter 18a, for varying the frequency division ratio N ₁ of the variable frequency divider 18 in response to this digital value. The second PLL circuit 23 includes:
The first PLL circuit 15 includes a phase comparator 26, a VCO (voltage controlled oscillator) 27, and a variable frequency divider 28, which are different from the first PLL circuit 15.
The output of the reference oscillator 16 is frequency-divided by a fixed frequency divider 29 having a frequency division ratio M and the phase is compared by another phase comparator 26. This phase comparison output is passed through another LPE (low-pass filter) 30 to another The frequency f _s of the audio subcarrier signal supplied to the VCO 27
Is configured to be controlled. P ₇ is the frequency setting terminal of the audio sub-carrier signal, the control voltage V _c2 of the terminals P ₇ is converted into a predetermined digital value by 3 State switch 28a for example, minutes of the variable frequency divider 28 in accordance with the digital value Circumference ratio N ₂
Control. Incidentally, P ₈ is a terminal for grounding the one-chip IC 14, P ₉ denotes a power supply terminal.

In the above configuration, the input terminals P ₁ to a video signal (V)
When the audio signal (A) is supplied to the input terminal P ₂ , the video signal (V) is amplified by the amplifier 21 (white clipping may be performed if necessary) and supplied to the mixer 24.

On the other hand, the audio signal (A) is supplied to the FM modulator 22, an audio subcarrier signal having a frequency f _s, for example, 6MHz and FM modulation, supplying a FM modulated output to the mixer 24. The output of the mixer 24 is supplied to the AM modulator 25, and the VCO 17 of the first PLL circuit 15
A main carrier signal of a frequency f ₀ supplied from the AM-modulated by the object to be FM modulated output and the video signal, and outputs to the output terminal P _3. In this case, the frequency f ₀ of the AM-modulated output S _TV is varied according to each channel frequency of 30 to 39 channels in the UHF TV band (544 MHz to 616 MHz) in Europe, for example. N ₁ is changed. As an example, if the reference number of wavenumber f _r of the reference oscillator 16 to 8 MHz, the time of locking of the PLL circuit 15, Therefore, if N is varied between 68 and 77, a desired channel frequency can be set in 8 MHz steps.

Another VCO27 audio subcarrier signal frequency f _s of the second PLL circuit 23, the frequency division ratio of the reference frequency f _r 8 MHz fixed frequency divider 29 of reference oscillator 16 M, another variable divider Divide ratio of 28
Assuming N ₂ , when the second PLL circuit 23 is locked Since the can change the f _s by varying the N.
For example, if a 8MHz the f _r, the M 16, and a variable between N ₂ and 11, 12, 13, f _s is 5.5 MHz, (West Germany PAL system), 6.0
It can be changed between MHz (UK PAL system) and 6.5MHz (France SECAM system). Further, according to the present invention, the FM
Since the modulator 22, the audio sub-carrier signal oscillator 23, the AM modulator 25, the first PLL circuit 15 and the second PLL circuit 23 are constituted by a one-chip IC 14, miniaturization can be achieved, and the main carrier signal is converted to the frequency f _0. the及音voice subcarrier signal frequency f _s can be stabilized against temperature changes.

Next, a description will be given of a block diagram showing an embodiment of the present invention shown in FIG. 2 in which the present invention is applied to a VTR (Video Tape Recorder).

In FIG. 2, 31 is a TV antenna, 32 is a distributor, and a TV signal of the distributor 32 is supplied to one input of a TV tuner 33 and one input of a mixer 34, respectively. The other input of the mixer 34, 1 connected to the output terminal P ₃ of the chip IC14 and AM modulator 25
Supplies the AM-modulated output S _TV from the
It is supplied to the output terminal 35. The other configuration is the same as that of the circuit of FIG. 1, and a detailed description thereof will be omitted.

In the above configuration, 1 supplies the input terminal P ₁ to the video signal of the chip IC 14 (V), and supplies the audio signal (A) to the input terminal P _2, a variable frequency divider of the first PLL circuit 15 18 by setting the frequency division ratio N ₁ of example to 68, RF output terminal 35
The, the AM modulated output S _TV to obtain the frequency f ₀ of the AM modulated main carrier signal by the object to be FM modulated output and the video signal is at 544MHz, VTR by sending to the TV receiver (not shown)
Can be monitored. Further, the TV signal from the TV antenna 31 is received by the TV tuner 33 via the distributor 32, and the monitor signal is output to the RF output terminal 35 via the mixer. In the embodiment shown in FIG. 2, the same operation and effect as those of the RF modulator shown in FIG. 1 can be expected.

〔The invention's effect〕

As is apparent from the above description, according to the present invention, the main carrier signal is AM-modulated by the FM modulated output obtained by FM-modulating the audio sub-carrier signal with the audio signal and the video signal, and the frequency-division multiplexed AM By modulating the frequency division ratio of the first PLL circuit, the modulation output can be obtained as a desired channel frequency signal, and the frequency division ratio of another variable frequency divider of the second PLL circuit can be varied to change the audio subcarrier. There is an advantage that the frequency of the signal can be changed.

In addition, since the FM modulator, the audio subcarrier signal oscillator, the AM modulator, and the first PLL circuit are formed by a one-chip IC, the size can be reduced, and at the same time, the main carrier signal and the audio subcarrier signal can be reduced. Has the advantage that the frequency of the above can be stabilized against a temperature change.

Furthermore, since the reference oscillator is shared by the first and second PLL circuits, there is an advantage that the configuration can be simplified.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of an RF modulator of the present invention, FIG. 2 is a block diagram showing an embodiment of the present invention,
FIG. 3 is a block diagram showing an example of a conventional FM modulator using a PLL. 14 One-chip IC 15 First PLL circuit 16 Reference oscillator 17 VCO (voltage-controlled oscillator) 18 Variable frequency divider 19 Phase comparator 20 LPF (Low-pass filter) 21 ... Amplifier 22 ... FM modulator 23 ... Second PLL circuit (voice subcarrier signal oscillator) 24 ... Mixer 25 ... AM modulator 26 ... Phase comparator 27 ... VCO 28 ... Variable component Frequency divider 29 ... Fixed frequency divider 30 ... LPF 31 ... TV antenna 32 ... Distributor 34 ... Mixer 35 ... RF output terminal

Claims (2)

(57) [Claims] An FM modulator to which an audio signal is supplied;
An FM modulator to which an FM-modulated output and a video signal of the FM modulator are respectively supplied and AM-modulating a main carrier signal with the FM-modulated output and the video signal, and an audio subcarrier signal to the FM modulator An audio subcarrier signal oscillator,
A main carrier signal oscillator for supplying the main carrier signal to an AM modulator, a reference oscillator, a phase comparator, a VCO and a variable frequency divider, and the output of the reference oscillator and the output of the VCO are controlled by the variable frequency divider. The phase of the divided output is compared with the phase of the divided output by the phase comparator.
A first PLL circuit configured to control a frequency divider, another phase comparator, a VCO, and a variable frequency divider. The divided output of the reference oscillator of the first PLL circuit and the output of the another VCO are A second PLL circuit configured to compare the phase of the output divided by another variable frequency divider with the another phase comparator and control the another VCO with the phase comparison output,
Using the VCO of the first PLL circuit as the main carrier signal oscillator and another VCO of the second PLL circuit as the audio subcarrier signal oscillator;
Modulator, 1st PLL circuit and 2nd PLL circuit are one chip IC
An RF modulator comprising: 2. An FM modulator to which an audio signal is supplied;
An FM modulator to which an FM-modulated output and a video signal of the FM modulator are respectively supplied and AM-modulating a main carrier signal with the FM-modulated output and the video signal, and an audio subcarrier signal to the FM modulator An audio subcarrier signal oscillator,
A main carrier signal oscillator for supplying the main carrier signal to an AM modulator, a reference oscillator, a phase comparator, a VCO and a variable frequency divider, and the output of the reference oscillator and the output of the VCO are controlled by the variable frequency divider. The phase of the divided output is compared with the phase of the divided output by the phase comparator.
A first PLL circuit for controlling the output of the first PLL circuit and the divided output of the reference oscillator of the first PLL circuit and the another VCO output. The phase of the output divided by the variable frequency divider is compared with the phase of the output by the another phase comparator.
A second PLL circuit for controlling a VCO; and a switch for changing a frequency division ratio of the another variable frequency divider in accordance with a frequency of a predetermined audio subcarrier signal.
A circuit using the VCO as the main carrier signal oscillator and another VCO of the second PLL circuit as the audio subcarrier signal oscillator, wherein the switch varies the audio subcarrier frequency. RF modulator.