RF modulator

Abstract: An RF modulator comprising an FM modulator (22) supplied with an audio signal, an AM modulator (24) supplied with the FM audio output and a video signal, an oscillator (32) for generating a sound subcarrier signal, and an oscillator (7) for generating a main carrier signal. Each of the oscillators (32, 17) consists of a VCO with a PLL circuit, and the entire components are composed of a single IC chip so as to be formed into a compact miniature structure. A modified RF modulator includes a PLL circuit (15) for varying the oscillation frequency of a VCO (17) by a variable frequency divider (18), and a modulation circuit supplied with a modulating signal and the oscillation output of the VCO (17). The division ratio (integer) of the variable frequency divider (18) is continuously varied, and the reference frequency of a reference oscillator (16) is set to be less than a predetermined channel interval frequency, thereby reducing the frequency error in the modulated signal output.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an RF (radio frequency) modulator for transmission of an audio signal and a video signal through frequency-division multiplexing, and more particularly to a modulation circuit and a PLL (phase-locked loop) circuit relative thereto in a compact miniature RF modulator adapted for use in VHF-UHF television. 2. Description of the Prior Art There is known a conventional example of an RF converter as disclosed in U.S. Patent US-A-4,654,607. First the operation of such exemplary converter will be described below with reference to Fig. 1 which shows the circuit configuration thereof. The above modulator comprises bipolar transistors. A video signal e V' is supplied to both bases of transistors Q5 and Q6 of a differential amplifier 6, and the output thereof is supplied as a signal current to a common emitter junction of paired differential transistors Q1 and Q2 which constitute a double balanced modulator. Meanwhile a frequency-modulated (FM) audio signal e A is supplied to both bases of transistors Q7 and Q8 constituting a differential amplifier 7, and the output thereof is supplied as a signal current from a collector of the transistor Q7 to a common emitter 3 4 junction of paired differential transistors Q3 and Q4 constituting a double balanced modulator. Signals of modulation frequencies fc, fc are supplied respectively to the bases of paired differential amplifier transistors 4, 5 of such double balanced modulators and are amplitude-modulated by the video signal e V' and the FM audio signal. The outputs of the paired differential transistors 4 and 5 are combined with each other and, after being amplified by a buffer amplifier 3, the combined output is taken out as an AM carrier signal from an output terminal 2. For frequency modulation of an audio signal, it is generally customary to employ a voltage controlled oscillator (VCO) . In the VHF band, an oscillator with an SAW resonator is used for generating the carrier signals fc, fc which are to be modulated by the video signal e V' and the FM audio signal e A . Meanwhile in the UHF band, it is usual to use an LC oscillator with a coaxial resonant circuit consisting of a variable capacitor. The modulator for use in a VHF video tape recorder (VTR) is so designed as to be switchable merely to two channels due to the employment of a SAW resonator. Meanwhile the UHF RF modulator is designed to be adjustable to a selected channel with control of a variable capacitor due to employment of a coaxial resonant circuit. Each of such two types is operated manually. Although the RF converter mentioned above is adoptable for transmission of an audio signal and a video signal through frequency-division multiplexing, no contrivance is proposed with regard to realization of an IC (integrated circuit) configuration. Digital tuners incorporating PLL circuits have been used in television signal receivers. US-A-4 816 781 describes an FM modulator incorporating a PLL for generating a modulated audio carrier in the head end of a video distribution system. Before output, the frequency-modulated audio signal is added to a modulated video carrier, the carrier signal being produced by a reference oscillator. The PLL in the frequency modulator includes a fixed frequency divider dividing the frequency of the carrier signal produced by the reference oscillator, the frequency-divided signal is phase compared with the output of a VCO which receives as an input the sum of the phase error signal (filtered and integrated) and the audio signal. The output from the VCO is frequency-converted and output as the modulated audio carrier. The article "VHF/UHF modulator IC" by J. Fenk, from IEEE Transactions on Consumer Electronics CE-30 (1984) Aug., No.3, (New York), pages 312-318, describes an RF modulator incorporating an audio signal FM modulator, an audio signal AM modulator and a balanced mixer operating on the modulated audio signal and on a video signal, all provided in an integrated circuit together with an oscillator. The main carrier frequency may be set by connecting particular external components to the IC. The article "Modular aufgebaute RF-Oszillatoren im GHz-Bereich mit quarzgenauer Frequenzstabilität" by Bernhard et al., from Mikrowellen magazin, Vol. 8, No. 5, 1982, describes an RF modulator, including a PLL, for frequency modulating input signals onto a carrier at microwave frequencies (6-9GHz). This modulator is built by assembling together modules made from discrete components, namely a microwave oscillator module including a resonant cavity, and a synchronisation module. OBJECTS AND SUMMARY OF THE INVENTION In an attempt to eliminate the drawbacks mentioned, the present invention has been accomplished to provide an improved RF modulator free from the above disadvantages as well as to provide a novel PLL (phase-locked loop) circuit capable of minimizing the frequency error in the modulated signal output of the modulator. A first object of the present invention is to generate a high frequency carrier, which is to be modulated by an audio signal and a video signal, from an oscillator with a PLL circuit in an RF modulator. A second object of the present invention is to generate a carrier to be modulated by an audio signal from an oscillator with a PLL circuit, and also to generate a carrier to be modulated by a video signal and a frequency-modulated signal from an oscillator with a PLL circuit. And a third object of the present invention is to provide a PLL circuit employed for an oscillator which generates a carrier to be modulated by an audio signal and a video signal. The present invention provides an RF modulator as defined in claim 1. According to the present invention, both the oscillator for generating a sound subcarrier signal and the oscillator for generating a main carrier signal each consist of a VCO with a PLL circuit, and the entire components are composed of a single IC chip so as to be structurally miniaturized. The division ratio of the variable frequency divider takes a selectable integer value, and the reference frequency of the reference oscillator is set to be smaller than a predetermined channel interval frequency, thereby reducing the frequency error in the modulated signal output. The above and other features of the present invention will become apparent from the following description which will be given with reference to the illustrative accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a circuit configuration of a conventional AM modulator; Fig. 2 shows an RF modulator for amplitude-modulating, by a video signal and an FM audio signal, a carrier outputted from an oscillator with a PLL circuit; Fig. 3 shows the RF modulator of Fig. 2 employed in a video tape recorder; Fig. 4 shows an embodiment of the invention for generating, from an oscillator with a PLL circuit, a carrier to be frequency-modulated by an audio signal; Fig. 5 shows an embodiment of the invention where the RF modulator of Fig. 4 is used in a video tape recorder; Fig. 6 shows an exemplary modulator employing the PLL circuit of the invention; and Fig. 7 shows a frequency spectrum of a carrier obtained from the modulator of Fig. 6. DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter a first circuit will be described with reference to the accompanying drawings. Fig. 2 is a block diagram showing a fundamental constitution of an RF modulator useful for understending the present invention, in which reference numeral 14 denotes a chip of integrated circuit (IC) as a whole. This diagram represents an example where an oscillator with a PLL circuit is employed for generating a carrier which is to be amplitude-modulated by a video signal and a frequency-modulated audio signal. Denoted by 15 is a PLL circuit which comprises a reference oscillator 16 for generating a reference frequency signal of a reference frequency f r , a VCO (voltage-controlled oscillator) 17, a variable frequency divider 18 of a division ratio N, and a phase comparator 19. The oscillation output of the VCO 17 is divided by the variable frequency divider 18 and then is compared with the reference frequency f r of the reference oscillator 16 by the phase comparator 19. The comparison output obtained therefrom is supplied to the VCO 17 via an LPF (low pass filter) 20, thereby controlling the frequency and the phase of the VCO 17. There are also shown an input terminal Pl supplied with a video signal (V); an input terminal P2 supplied with an audio signal (A); an amplifier 21 connected to the input terminal Pl; an FM modulator 22 which receives the audio signal (A) from the input terminal P2 and also a sound subcarrier signal of a frequency f s from a sound subcarrier signal oscillator 23; and an AM modulator 24 for amplitude-modulating the video signal (V) amplified by the amplifier 21 and the frequency-modulated output of the FM modulator 22. A main carrier signal of a frequency f 0 is supplied from the VCO 17 of the PLL circuit 15 to the other input terminal of the AM modulator 24, and the amplitude-modulated output (television signal) S TV is supplied to an output terminal P3. Also shown are an external crystal 16a connected between terminals P4 and P5 for the reference oscillator 16; an external capacitor 20a connected to a terminal P6 for the LPF 20; and an external parallel resonant circuit 23a connected to a terminal P7 for the sound subcarrier signal oscillator 23. The resonance frequency of the circuit 23a is selectively set to, e.g., 4.5 MHz. There are further shown a ground terminal P8 of the IC chip 14 and a terminal P9 through which a control voltage of a potentiometer 18a is applied to an A-D (analog-to-digital) converter 18b when necessary to change the division ratio N of the variable frequency divider 18. Denoted by P10 is a power supply terminal. In the above constitution, when the video signal (V) and the audio signal (A) are supplied to the input terminals P1 and P2 respectively, the video signal (V) is amplified by the amplifier 21 (with white clip when necessary) and then is supplied to the AM modulator 24. Meanwhile the audio signal (A) is supplied to the FM modulator 22 where the sound subcarrier signal having a frequency f s of 4.5 MHz for example is thereby frequency-modulated, and then the modulated output is supplied to the AM modulator 24. The output of the AM modulator 24 is fed for amplitude-modulating the main carrier signal of a frequency f 0 supplied from the VCO 17 of the PLL circuit 15, and thus the amplitude-modulated signal is obtained from the output terminal P3. In this case, the division ratio N of the variable frequency divider 18 is varied for changing the frequency f 0 of the modulated output S TV in accordance with each channel frequency of, for example, channels 13 to 64 in the UHF television band (470-630 MHz). In an example where the reference frequency f r of the reference oscillator 16 is 1 MHz, the frequency division ratio N becomes f 0 /f r when the PLL circuit 15 is locked, so that if the ratio N is changed between 470 and 630, it is possible to set the main carrier frequency f 0 to a desired channel frequency at a step of 1 MHz. As in the present invention, all of the above-described FM modulator 22, sound subcarrier signal oscillator 23, AM modulator 24 and PLL circuit 15 are composed of a single IC chip 14 to be consequently formed into a miniature structure, and the frequency f 0 of the main carrier signal can be stabilized despite occurrence of any temperature fluctuation. Referring now to a block diagram of Fig. 3, a description will be given on a second circuit where the above RF modulator is applied to a VTR (video tape recorder). In Fig. 3, there are included a television antenna 25 and a distributor 26. A television signal from the distributor 26 is supplied to a television tuner 27 and one input terminal of a mixer 28. The other input terminal of the mixer 28 is connected to an output terminal P3 of an IC chip 14 and is thereby supplied with an AM output S TV from an AM modulator 24. And the output of the mixer 28 is supplied to an RF output terminal 29. Since the other circuit configuration is the same as that shown in Fig. 1, a detailed description thereof is omitted here. In the above constitution, a video signal (V) and an audio signal (A) are supplied respectively to the input terminals Pl and P2 of the single IC chip 14, and the division ratio N of a variable frequency divider 18 in the PLL circuit 15 is set to 630 for example. Then a modulated main carrier signal having a frequency f 0 of 630 MHz is obtained as an AM output S TV from an RF output terminal 29, so that a playback output of the VTR can be monitored by feeding such AM output S TV to an unshown television receiver. In this case also, satisfactory function and effect can be expected as in the aforementioned RF modulator of Fig. 2. The sound subcarrier signal oscillator 23 may be formed of another PLL circuit. In such a case, an external parallel resonant circuit 23a and a terminal P7 can be dispensed with. As is obvious from the above description, where the main carrier signal is amplitude-modulated by the video signal and the FM output obtained through frequency modulation of the sound subcarrier signal by the audio signal, the AM output processed through frequency-division multiplexing can be obtained with facility as a signal of a desired channel frequency by varying the frequency division ratio of the PLL circuit. Furthermore, there is attainable another advantage that, since all of the above-described FM modulator, sound subcarrier signal oscillator, AM modulator and PLL circuit are composed of a single IC chip, the structure can be miniaturized and the frequency of the main carrier signal can be stabilized despite occurrence of any temperature fluctuation. Hereinafter an embodiment of the present invention will be described with reference to Fig. 4. In this embodiment, a carrier to be frequency-modulated by an AM audio signal is generated from an oscillator with a PLL circuit. And another carrier to be modulated by such FM audio signal and a video signal is generated from another oscillator with a PLL circuit. Now a detailed description will be given below with regard to this first embodiment. Fig. 4 is a block diagram showing a fundamental constitution of an RF modulator according to the present invention, in which reference numeral 14 denotes a chip of integrated circuit as a whole. Denoted by 15 is a first PLL circuit which comprises a reference oscillator 16 for generating a reference frequency signal of a reference frequency f r , a VCO (voltage-controlled oscillator)17, a variable frequency divider 18 of a division ratio N, and a phase comparator 19. The oscillation output of the VCO 17 is divided by the variable frequency divider 18 and then is compared with the reference frequency f r of the reference oscillator 16 by the phase comparator 19. The comparison output obtained therefrom is supplied to the VCO 17 via an LPF (low pass filter) 20, thereby controlling the frequency and the phase of the VCO 17. There are also shown an input terminal P1 supplied with a video signal (V); an input terminal P2 supplied with an audio signal (A); an amplifier 21 connected to the input terminal P1; an FM modulator 22 which receives the audio signal (A) from the input terminal P2 and also a sound subcarrier signal of a frequency f s from a second PLL circuit 30; and an AM modulator 24 for amplitude-modulating the video signal (V) amplified by the amplifier 21 and the frequency-modulated output of the FM modulator 22. A main carrier signal of a frequency f 0 is supplied from the VCO 17 of the first PLL circuit 15 to the other input terminal of the AM modulator 24, and the amplitude-modulated output (television signal) S TV is supplied to an output terminal P3. Also shown are an external crystal 16a connected between terminals P4 and P5 for the reference oscillator 16, and a channel frequency setting terminal P6. A control voltage V cl at the terminal P6 is converted to a predetermined digital value by an A-D (analog-to-digital) converter 18b, and the division ratio N1 of the variable frequency divider 18 is varied in accordance with the digital value thus obtained. The second PLL circuit 30 comprises a phase comparator 31, a VCO 32 and a variable frequency divider 33 which are different from those included in the aforementioned first PLL circuit 15. The output of the reference oscillator 16 in the first PLL circuit 15 is frequency-divided by a fixed frequency divider 34 of a division ratio M, and the output thereof is phase-compared by the phase comparator 31. The comparison output thus obtained is then supplied via an LPF (low pass filter) 35 to the VCO 32, thereby controlling the frequency f s of the sound subcarrier signal. Denoted by P7 is a terminal for setting the frequency of the sound subcarrier signal. A control voltage V c2 at the terminal P7 is converted to a predetermined digital value by a three-state switch 36, and the division ratio N2 of the variable frequency divider 33 is controlled in accordance with such digital value. There are further shown a terminal P8 for grounding the IC chip 14, and a power supply terminal P9. In the above constitution, when the video signal (V) and the audio signal (A) are supplied to the input terminals P1 and P2 respectively, the video signal (V) is amplified by the amplifier 21 (with white clip when necessary) and then is supplied to the AM modulator 24. Meanwhile the audio signal (A) is supplied to the FM modulator 22 where the sound subcarrier signal having a frequency f s of 6 MHz for example is thereby frequency-modulated, and then the modulated output is supplied to the AM modulator 24. The main carrier signal of a frequency f 0 supplied from the VCO 17 of the first PLL circuit 15 is amplitude-modulated and then is fed to the output terminal P3. In this case, the division ratio N1 of the variable frequency divider 18 is varied for changing the frequency f 0 of the modulated output S TV in accordance with each channel frequency of, for example, channels 30 to 39 in the UHF television band (544-616 MHz) adopted in Europe. In an example where the reference frequency f r of the reference oscillator 16 is 8 MHz, the frequency division ratio N1 becomes f 0 /f r when the first PLL circuit 15 is locked, so that if the ratio N1 is changed between 68 and 77, it is possible to set the main carrier frequency f 0 to a desired channel frequency at a step of 8 MHz. With regard to the reference frequency f r (8 MHz) of the reference oscillator 16, the division ratio M of the fixed frequency divider 34 and the division ratio N2 of the variable frequency divider 33, there exists a relationship of f s /N2 = f r /M when the second PLL circuit 30 is locked. Consequently, it becomes possible to change, by varying the division ratio N, the sound subcarrier signal frequency f s of the VCO 32 in the second PLL circuit 30. In an exemplary case where the division ratio N2 is varied among 11, 12 and 13 with the frequency f r set to 8 MHz and the division ratio M to 16, the frequency f s can be changed among 5.5 MHz (PAL system in West Germany), 6.0 MHz (PAL system in U.K.) and 6.5 MHz (SECAM system in France). Furthermore, the present invention is so contrived that all of the above-described FM modulator 22, sound subcarrier oscillator 23, AM modulator 24, first PLL circuit 15 and second PLL circuit 30 are composed of a single IC chip 14, whereby a miniature structure is achievable and both the main carrier signal frequency f 0 and the sound subcarrier signal frequency f s can be maintained stable despite occurrence of any temperature fluctuation. Referring now to Fig. 5 which is a block diagram of a second embodiment, a description will be given on an example where the present invention is applied to a video tape recorder. In Fig. 5, there are included a television antenna 25 and a distributor 26. A television signal from the distributor 26 is supplied to a television tuner 27 and one input terminal of a mixer 28. The other input terminal of the mixer 28 is connected to an output terminal P3 of an IC chip 14 and is thereby supplied with an AM output S TV from an AM modulator 24. And the output of the mixer 28 is supplied to an RF output terminal 29. Since the other circuit configuration is the same as that shown in Fig. 4, a detailed description thereof is omitted here. In the above constitution, a video signal (V) and an audio signal (A) are supplied respectively to the input terminals P1 and P2 of the single IC chip 14, and the division ratio N of a variable frequency divider 18 in the PLL circuit 15 is set to 68 for example. Then a modulated main carrier signal having a frequency of f 0 of 544 MHz is obtained as an AM output S TV from an RF output terminal 29, so that a playback output of the VTR can be monitored by feeding such AM output S TV to an unshown television receiver. The television signal obtained from the antenna 25 is fed via the distributor 26 to the television tuner 27 while being fed as a monitor signal via the mixer 28 to the RF output terminal 29. In this second embodiment of Fig. 5 also, satisfactory function and effect can be expected as in the aforementioned RF modulator shown in Fig. 4. As is obvious from the above description, according to the second embodiment where the main carrier signal is amplitude-modulated by the video signal and the FM output obtained through frequency modulation of the sound subcarrier signal by the audio signal, the AM output processed through frequency-division multiplexing can be obtained with facility as a signal of a desired channel frequency by varying the frequency division ratio of the first PLL circuit, and also the frequency of the sound subcarrier signal can be changed by varying the division ratio of the frequency divider in the second PLL circuit. Furthermore, there is attainable another advantage that, since all of the above-described FM modulator, sound subcarrier signal oscillator, AM modulator, first PLL circuit and second PLL circuit are composed of a single IC chip, the structure can be miniaturized and the frequencies of both the main carrier signal and the sound subcarrier signal can be stabilized despite occurrence of any temperature fluctuation. In addition, due to common use of the reference oscillator for the first and second PLL circuits, the circuit configuration can be further simplified. Hereinafter a third embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 6 is a block diagram showing a fundamental constitution of a modulator with a PLL, in which reference numeral 15 denotes the PLL circuit as a whole. There are included a reference oscillator 16 for generating a reference frequency signal of a reference frequency f r , and a VCO (voltage-controlled oscillator) 17 having an oscillation frequency f 0 . The oscillation output of the VCO 17 is frequency-divided by a variable frequency divider 18 of a division ratio N (integer) and then is compared with the reference frequency f r of the reference oscillator 16. The comparison output thus obtained is supplied to the VCO 17 via an LPF (low pass filter) 20, thereby controlling the frequency and the phase of the VCO 17. The oscillation output of the VCO 17 is supplied to one input terminal of an AM modulator 24, and a modulating signal fed to an input terminal IN is supplied to the other input terminal of the AM modulator 24. Denoted by OUT is an output terminal from which a modulated output is obtained. In the constitution mentioned, the following operation is performed. When the PLL circuit 15 is locked, the oscillation frequency f 0 of the VCO 17 becomes N . f r (where N is an integer as will be described later). Therefore the channel frequency of the AM modulator 24 is varied, by continuously changing the division ratio N, at a step of a predetermined channel interval frequency f ch in an allocated band for UHF television channels adopted in Europe for example. In the aforementioned European UHF television channels, the channel frequency is varied within a range from channel No. 30 (543.25 MHz) to channel No. 39 (615.25 MHz) at a step of 7.99 MHz less than the channel interval frequency f ch (= 8 MHz), and the desired oscillation output of the VCO 17 is amplitude-modulated in the known manner by the modulating signal so that the modulated signal for a television receiver can be obtained from the output terminal OUT of the AM modulator 24. In an exemplary case where the reference frequency f r of the reference oscillator 16 is set to 7.99 MHz or 7.985 MHz less than the channel interval frequency f ch (8 MHz), the frequency error f E (kHz) in the modulated signal can be reduced in comparison with another case of setting the reference frequency f r to 8 MHz, as shown in Table 1 below. Frequency Errors to Reference Frequencies Channel No. f 0 (MHz) N (Integer) f E1 (kHz) (f r = 8 MHz) f E2 (kHz) (f r = 7.99 MHz) f E3 (kHz) (f r = 7.985 MHz) 30 543.25 68 +750 +70 -270 31 551.25 69 +750 +70 -285 32 559.25 70 +750 +50 -300 33 567.25 71 +750 +40 -315 34 575.25 72 +750 +30 -330 35 583.25 73 +750 +20 -345 36 591.25 74 +750 +10 -360 37 599.25 75 +750 0 -375 38 607.25 76 +750 -10 -390 39 615.25 77 +750 -20 -405 As is apparent from the frequency errors f E1 - f E3 given in Table 1 with respect to the individual reference frequencies, the frequency error in the modulated signal can be reduced by setting the reference frequency f r to a value less than the channel interval frequency f ch (= 8 MHz). Fig. 7 shows an exemplary frequency error spectrum in the present invention, representing the frequency error f E2 caused with respect to each channel when the reference frequency f r is set to 7.99 MHz. Denoted by U L is a UHF broadcasting frequency band for lower channels. It is possible to further reduce the frequency error f E2 or f E3 by an AFT (automatic fine tuning) function of an unshown television receiver connected to the output terminal OUT of the AM modulator 24.

Claims: A VHF-UHF RF modulator comprising: an FM modulator (22) supplied with an audio signal; an AM modulator (24) supplied with a video signal and the modulated output of said FM modulator (22), said AM modulator being adapted to be capable of generating a modulated output at any of a plurality of different channel frequencies which approximate to respective target channel frequencies, said target channel frequencies being spaced apart by a predetermined frequency interval, f ch ; a sound subcarrier signal oscillator (23/32) for supplying a sound subcarrier signal to said FM modulator (22); a main carrier signal oscillator for supplying a VHF-UHF RF main carrier signal to said AM modulator (24); and a PLL (phase-locked-loop) circuit (15) having a reference oscillator (16/16a) outputting a reference signal at a fixed reference frequency f r , a phase comparator (19), a voltage-controlled oscillator (17) and a variable frequency divider (18), in which the output of said voltage-controlled oscillator (17) is frequency-divided by said variable frequency divider (18) and then is phase-compared, by the phase comparator (19), with the reference signal output by the reference oscillator (16/16a) and the comparison output thus obtained is fed to said voltage-controlled oscillator (17) via a low pass filter (20) to thereby control said voltage-controlled oscillator (17); wherein said voltage-controlled oscillator (17) of said first PLL circuit constitutes the main carrier signal oscillator generating a main carrier frequency f o = N. f r , the division ratio N of the variable frequency divider (18) is set at a selected one of a plurality of integer values by a digital signal input to the variable frequency divider as a control input whereby to select a channel frequency for the modulated output of the AM modulator, and the reference frequency, f r , of the reference signal satisfies 7.985 8 f ch ≤ f r ≤ 7.99 8 f ch ; wherein there is further provided a second PLL (phase-locked-loop) circuit (30) having a second phase comparator (31), a second voltage-controlled oscillator (32) and a second variable frequency divider (33), in which the output of said second voltage-controlled oscillator (32) is frequency-divided by said second variable frequency divider (33) and phase-compared, by the phase comparator (31), with a second reference signal, said second reference signal being the reference signal of fixed reference frequency f r from the reference oscillator (16/16a) of the first PLL frequency-divided by a predetermined factor (M), and the comparison output thus obtained is fed to said second voltage-controlled oscillator (32) to thereby control the same; and wherein the second voltage-controlled oscillator (32), of said second PLL circuit, constitutes the sound subcarrier signal oscillator, and all of said FM modulator (22), AM modulator (24), and first and second PLLs are composed of a single IC chip. A VHF-UHF RF modulator according to claim 1, wherein the second PLL further comprises: a fixed frequency divider (34) implementing the frequency division of the reference signal from the first PLL by said predetermined factor (M) to produce said second reference signal; and a three-state switch (36) the state of which determines the division ratio applied by the second variable frequency divider (33), whereby to enable the sound subcarrier signal to be generated at a selected one of three different frequencies. A VHF-UHF RF modulator according to claim 1, wherein the predetermined frequency interval between the target channel frequencies is 8 MHz the frequency of the reference signal output by the reference oscillator (16/16a) is less than 8 MHz; the division ratio of the variable frequency divider (18) in said first PLL circuit (15) is set to 75; the oscillation frequency f 0 of the voltage-controlled oscillator in the first PLL circuit (15) is set to 599.25 MHz; and the division ratio of the second variable frequency divider (33), of the second PLL circuit (30), is set to 11. A VHF-UHF RF modulator according to any previous claim, wherein the predetermined frequency interval between the target channel frequencies is 8 MHz and the frequency of the reference signal output by the reference oscillator (16/16a) is 7.99 MHz. A VHF-UHF RF modulator according to any previous claim, wherein the predetermined frequency interval between the target channel frequencies is 8 MHz and the frequency of the reference signal output by the reference oscillator (16/16a) is 7.985 MHz.

Inventors: HIGUCHI HIROSHI, ISHIKAWA FUMIO, ISHIKAWA NOBUYUKI, NARAHARA HISAAKI, TANABE SHINICHI, HIGUCHI, HIROSHI, ISHIKAWA, FUMIO, ISHIKAWA, NOBUYUKI, NARAHARA, HISAAKI, TANABE, SHINICHI
Applicants: SONY CORP, SONY CORPORATION
Application year: 1990
Main classification: H04N5
IPC codes: H03C5, H04N5