JPH031784A - Audio fm modulation circuit - Google Patents

Abstract

PURPOSE:To avoid deterioration in modulation characteristic and to avoid both channel of modulation characteristics from being deviated by applying frequency conversion to a prescribed frequency by means of the heterodyne system using a multiplier when the audio signal is FM-modulated based on a color subcarrier frequency. CONSTITUTION:The circuit is provided with 1st and 2nd FM modulation circuits 30, 40 FM-modulating an audio signal based on the color subcarrier frequency, 1st and 2nd local oscillators 50, 60 converting the FM modulation signal being the output of the circuits 30, 40 into a prescribed frequency by the heterodyne system and 1st and 2nd multipliers 21, 22. Then a color subcarrier signal with a comparatively high frequency is used for the reference signal of the FM modulation circuits 30, 40 and the FM modulation signal with the same frequency is obtained and converted into a prescribed frequency by the heterodyne system. Thus, the deterioration in the modulation characteristic due to the leakage of the reference signal in the 1st and 2nd FM modulation circuits is avoided and the modulation characteristic of the 1st and 2nd FM modulation circuits is arranged.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to, for example, audio F
This relates to an M modulation circuit.

[Conventional technology]

FIG. 2 is a block diagram showing a conventional audio FM modulation circuit for HiFi VTR. In the figure, 1 is an input terminal into which a color subcarrier signal having a predetermined color subcarrier frequency is input, 2 is an input terminal into which a left channel audio signal is input, and 3 is an input terminal into which a right channel audio signal is input manually. An input terminal, 4 is an output terminal to which the left channel F~1 modulation signal is output, 5 is an output terminal to which the right channel FM modulation signal is output, 6 is a frequency divider for dividing the color subcarrier signal. , 30 is a voltage controlled oscillator (hereinafter referred to as vCO)
) 71 frequency divider 81 phase comparator 9 and adder 10
a first FM modulation circuit consisting of a VCOII 40, a frequency divider 129, a second FM modulation circuit consisting of a phase comparator 13 and an adder 14;
This is an FM modulation circuit.

In operation, the color subcarrier signal input to input terminal 1 is frequency-divided by frequency divider 6 to a frequency of several 1,00 Hz.
These become the reference frequency signals before and after. The first and second FM modulation circuits 30 and 40 convert the left and right channel audio signals inputted to the input terminals 'r-2 and 3 into FM signals, respectively, using the reference frequency signal from the frequency divider 6 as a reference. Modulate. That is, v
The oscillation outputs of CO7 and CO11 are divided by frequency dividers 8 and 12,
The phase comparator 9.13 compares the reference frequency signal from the frequency divider 6 with the phase I+. The comparison result is the H1 comparator 9.
．． After high-frequency components are removed through a low-pass filter in 13, the adder 10.14 adds the signal to left and right channel audio signals, and supplies the result to control inputs of vCOs 7 and 11, respectively. The oscillation frequency of the vCOs 7 and 11 changes according to the audio signal, thereby performing FM modulation. vCO
The fundamental frequency and phase of the oscillation outputs 7 and 11 are kept stable through phase comparison in phase comparators 9 and 13. Different division ratios of frequency division W8.12 are used,
This allows the FM of the left and right channels of the desired frequency, respectively.
I am getting a modulated signal.

[Problem to be solved by the invention]

The conventional single audio FM converter circuit for HiFi VTRs is configured as described above, and because phase comparison is performed at a reference frequency of around several hundred Hz, there is a problem of deterioration of modulation characteristics due to leakage of the reference frequency signal. Ta.

Also, the left channel and right channel have different vC frequencies.
Because O is used, there is also the problem that the modulation characteristics of both channels are not the same.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an audio FM modulation circuit in which the modulation characteristics do not deteriorate and the modulation characteristics of both channels do not deviate.

[Means to solve the problem]

The audio FM modulation circuit according to the present invention receives a color subcarrier signal and a first channel audio signal, and converts the first channel audio signal into an FM signal using the color subcarrier frequency as a reference.
a first FM modulation circuit that modulates and provides a first channel FM modulated signal, receives the color subcarrier signal and the second channel audio signal, and FM modulates the second channel audio signal using the color subcarrier frequency as a reference; a second FM modulation circuit that provides a channel FM modulation signal, and a first frequency that receives a color subcarrier signal, is synchronized with the color subcarrier signal, and divides the color subcarrier frequency by a first frequency division ratio. a first local oscillator that provides a first fundamental signal having a first frequency, and a second local oscillator that receives a color subcarrier signal, is synchronized with the color subcarrier signal, and divides the color subcarrier frequency by a second frequency division ratio. the second with the frequency
a second local oscillator that receives the first channel FM modulated signal and the first reference signal, and multiplies them to derive a first channel FM modulated signal of a desired frequency. multiplier receives the second channel FM modulation signal and the second reference signal, multiplies them to obtain a second signal of the desired frequency.
and a second multiplier for deriving a channel FM modulation signal.

[Effect]

First in this invention. The second FM modulation circuit converts the audio signal into FM based on the color subcarrier frequency.
M modulates. At this time, since the color subcarrier frequency is relatively high, there is no fear of reference signal leakage.

Also number 1. Since the frequency of the FM variable one week signal is converted to the required frequency by the hetero gain method using the second multiplier, the first. The FM modulation signals from the second modulation circuit may be of the same frequency.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of an audio FMM conversion circuit 71M according to the present invention. In the figure, 1 is an input terminal to which a color subcarrier signal having a predetermined color subcarrier frequency is manually input, 2 is an input terminal to which a left channel audio signal is manually input, and 3 is an input terminal to which a right channel audio signal is manually input. terminals; 4 is an output terminal to which the left channel FM modulation signal is output; 5 is an output terminal to which the right channel FM modulation signal is output; 6 is a frequency divider for dividing the color subcarrier signal; 30 is a frequency divider for dividing the color subcarrier signal; A first FM modulation circuit consisting of a VCO 7, a phase comparator 9 and an adder 10, 40 is a VC
OI 1. A second FM modulation circuit comprising a phase comparator 13 and an adder 14; 50 a first local oscillation circuit comprising a VCOI 5, a frequency divider 16 and a phase comparator 17; 60 a VCOI 8. A second local oscillation circuit consisting of a frequency divider 19 and a phase comparator 20, 21 a first multiplier for deriving a left channel FM modulation signal of a desired frequency, and 22 a right channel FM modulation signal of a desired frequency. A second multiplier for deriving the signal.

In operation, 1st. The second FM modulation circuit 30°40 uses the color subcarrier frequency of the color subcarrier signal inputted to the input terminal 1 as a reference, and the second FM modulation circuit 30.
The left and right channel audio signals input to the FM
Modulate. That is, the oscillation outputs of the VCOs 9 and 11 are output from the phase comparators 9 and 13 to match the color subcarrier signal.
be compared.

The comparison result is passed through the low-pass filters in the phase comparators 9 and 13 to remove high frequency components, and then the adder 10.
14, it is added with the left and right channel audio signals, and the VCO
1j is applied to control inputs 7 and 11, respectively. VCO7
, il changes according to the point signal, thereby performing FM modulation. The fundamental frequency and phase of the oscillation outputs of the VCOs 7 and 11 are kept stable through the phase I'l+ comparison in the phase comparators 9 and 11. VCO7,
The fundamental oscillation frequencies of 11 are the same, so that the modulation characteristics of the left and right channels are the same. In addition, the color subcarrier signal is used as a reference signal and the phase comparator 9.13
Since the color subcarrier signal has a relatively high frequency, there is no leakage of the reference signal, and therefore the modulation characteristics do not deteriorate.

1st. The second local oscillator circuit 50.60 synchronizes with the color subcarrier signal and changes the color subcarrier frequency to the first. A first frequency having a first frequency and a second frequency divided by a second frequency division ratio. A second reference signal is generated. That is, the phase comparators 17 and 20 divide the color subcarrier signal inputted to the input terminal 1 into a frequency-divided signal using the frequency divider 6, and
COL5.

The phase of the oscillation output of 18 is compared with a signal obtained by dividing the frequency of the oscillation output by frequency dividers 16 and 1.9. The comparison result is the phase comparator 17.2
After the high frequency components are removed through a low-pass filter within 0.0, the signals are applied to the control inputs of VCOIs 5 and 1.8, respectively. By phase comparison using phase comparison 2W17.20,
The phases of the oscillation outputs of VCOIs 5 and 18 are aligned with the color subcarrier signal, and the oscillation frequency is the first frequency determined by the division ratio of the frequency divider 616 in the case of VCOI 5, and the first frequency determined by the division ratio of the frequency divider 616 in the case of VCOI 8. The second frequency is determined by the frequency division ratio of the frequency converters 6 and 19. ■C015,
The oscillation output of 18 is the 1st. The first signal is used as the second base signal. They are respectively sent to second multipliers 21 and 22.

1st. The second multiplier 21.22 is connected to the first multiplier 21.22. The FPvl modulation signal output from the second FM variable circuit 30.40 is the first FM modulated signal. The first oscillator output from the second local oscillation circuit 50. FM modulation signals of the left and right channels each having a desired frequency are outputted to output terminals 4 and 5. In this way, the first. After the second FM modulation circuits 30 and 40 convert the left and right channel FM modulation signals of the same relatively high frequency into p7, they are converted to respective required frequencies by the heterodyne method.

It goes without saying that the circuit shown in FIG. 1 may be implemented using a semiconductor integrated circuit.

〔Effect of the invention〕

As explained above, according to the present invention, the first
．． The second FM conversion circuit and the first FM conversion circuit convert the output FM conversion 1 signal into the required frequency using the heterodyne method. a second local oscillator and a first local oscillator; A color subcarrier signal having a relatively high frequency is used as a reference signal for the first and second FM modulation circuits, and a color subcarrier signal having a relatively high frequency is used as a reference signal for the first and second FM modulation circuits. Since the FM modulation signal of the same frequency is obtained from the second FM modulation circuit and converted to the required frequency by the heterodyne method, the first and second FM
The deterioration of the Variable 11.1 characteristics due to reference signal leakage in the M modulation circuit is eliminated, and the 1.1. This has the effect that the modulation characteristics of the second FM modulation circuit can be made the same.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of an audio FM modulation circuit according to the present invention, and FIG. 2 is a block diagram showing a conventional audio FM modulation circuit. In the figure, 21 is a first multiplier, 22 is a second multiplier, 30 is a first FM modulation circuit, 40 is a second FM modulation circuit, 50 is a first local oscillation circuit, and 60 is a second This is a local oscillation circuit. Note that the same reference numerals in each figure indicate the same or corresponding parts. Diagram

Claims (1)

[Claims] (1) a first FM modulation circuit that receives a color subcarrier signal and a first channel audio signal, performs FM modulation on the first channel audio signal using the color subcarrier frequency as a reference, and provides a first channel FM modulated signal; a second FM modulation circuit that receives the color subcarrier signal and the second channel audio signal, performs FM modulation on the second channel audio signal using the color subcarrier frequency as a reference, and provides a second channel FM modulated signal; receives a subcarrier signal, synchronizes with the color subcarrier signal and sets the color subcarrier frequency to the first
a first local oscillator for providing a first reference signal having a first frequency divided by a frequency division ratio; Second
a second local oscillator that provides a second reference signal having a second frequency divided by a frequency division ratio; and a second local oscillator that receives the first channel FM modulation signal and the first reference signal and multiplies them the first channel F of the required frequency.
a first multiplier for deriving an M modulation signal; a first multiplier for receiving the second channel FM modulation signal and the second reference signal;
and a second multiplier for deriving the M modulated signal.
Modulation circuit.