JP2514014B2 - L-SECAM system TV signal audio detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention converts an L-SECAM system television signal into an intermediate frequency by the upper heterodyne system in any of VHF low band, VHF high band and UHF band. The present invention relates to a sound detection device for an L-SECAM system television signal in a receiver.

(Prior Art) The television broadcast band of the L-SECAM system is within the PAL (B / G) system television broadcast band except for the channel A having the lowest frequency. Therefore, the reception range of the electronically tuned tuner of the receiver is widened, and the L-SECAM system and PAL (B / B
There is a system that can receive both G) systems.

FIG. 2 shows a block circuit diagram of a main part of the conventional receiver described above.

In FIG. 2, television signals of the L-SECAM system and the PAL (B / G) system are given to the tuner 1 via an RF circuit (not shown). The tuner 1 converts all signals in the VHF low band, the VHF high band and the UHF band into an intermediate frequency by the upper heterodyne method.

Here, in the L-SECAM system VHF low band television signal, the frequency of the audio carrier is set to be lower than that of the video carrier, but other L-SECAM system GF high band, UHF band and PAL (B / B In the television signal of each band of the G) system, the frequency of the audio carrier is set higher than that of the video carrier. Then, frequency conversion is performed so that the band of the intermediate frequency of the image carrier output from the tuner 1 and the band of the intermediate frequency of the color subcarrier match each other.

Then, for a television signal other than the V-HF low band of the L-SECAM system, the intermediate frequency fp of the video carrier is set to 38.9 MHz and the intermediate frequency fc of the color subcarrier is set to 34.
If the frequency is converted to 47MHz, the intermediate frequency fs of the audio carrier is 3
It is output to 2.4MHz and the lower side. However, the L-SECAM system VHF low-band television signal is shown in FIG. 3 (b).
As described above, if the intermediate frequency fp 'of the video carrier is frequency-converted to 34.47 MHz and the intermediate frequency fc' of the color subcarrier is frequency converted to 38.9 MHz, the intermediate frequency fs' of the audio carrier is output to 40.97 MHz.

The intermediate frequency output from the tuner 1 is the first and second intermediate frequencies.
Is given to the intermediate frequency amplifier circuits 2 and 3. Then, the output appropriately amplified by the first intermediate frequency amplifier circuit 2 is given to the video intermediate frequency filter 4. The video intermediate frequency filter 4 has a frequency band for passing the intermediate frequency shown in FIG. 3 (a) of the television signal other than the L-SECAM VHF low band, and the output of the video intermediate frequency filter 4 is a video. The L-SECAM system and PAL provided to the detection circuit 5
Both (B / G) type video detection outputs are output to the output terminal 6. Also, a part of the output of the video intermediate frequency filter 4 is given from the video detection circuit 5 to the PAL audio detection circuit 7,
The (B / G) type voice detection output is output to the output terminal 8.

The output, which is appropriately amplified by the second intermediate frequency amplifier circuit 3, is applied to the SECAM audio intermediate frequency filter 9. The SECAM audio intermediate frequency filter 9 is provided with a switching terminal 10, and a switching voltage is applied when the VHF low band of the L-SECAM system is selected. Depending on the presence or absence of this switching voltage, the passage center frequency is switched as shown by the solid line and the broken line in FIG. That is, when the switching voltage is applied, as shown by the broken line in FIG. 4, L-SE is set with 40.97 MHz as the pass center frequency.
Intermediate frequency fs' of CAM type VHF low band voice carrier
Is extracted and the switching voltage is not given, as shown by the solid line in FIG.
The intermediate frequency fs of the audio carrier other than the VHF low band of the method is extracted.

Further, the output of the SECAM audio intermediate frequency filter 9 is given to the mixing / amplifying circuit 11. The local oscillation signal from the local oscillation circuit 12 is given to the mixed amplification circuit 11. The local oscillator circuit 12 is provided with a control terminal 13 and is supplied with a control voltage when selecting the VHF low band of the L-SECAM system. The local oscillator circuit 12 oscillates when this control voltage is applied, and does not oscillate unless the control voltage is applied. Then, when the control voltage is applied to the control terminal 13 and the local oscillation signal is applied to the mixing / amplifying circuit 11, the intermediate frequency fs' of the L-SECAM type VHF low band audio carrier is the intermediate frequency of the other band audio carrier. The frequency is converted to the fs frequency and is given to the SECAM voice detection circuit 14. If the control voltage is not applied to the control terminal 13, the mixing amplifier circuit 11 acts as an amplifier to appropriately amplify the intermediate frequency fs of the sound carrier of the other band, and the SECAM
It is given to the voice detection circuit 14.

The SECAM audio detection circuit 14 includes a tank circuit 15 including a Q damping resistor R, a resonance capacitor C, and a resonance variable coil L connected in parallel. The SECAM audio detection circuit 14 detects and outputs an audio signal by a pseudo-synchronous detection method, and outputs an L-SECAM audio signal. The detection output is output to the output terminal 16. And this tank circuit 15
The resonance frequency of 32.4MHz by adjusting the resonance variable coil L
Adjusted to.

Since the PAL (B / G) type audio signal is superimposed on the audio carrier by frequency modulation and the L-SECAM type audio signal is superimposed on the audio carrier by amplitude modulation, the audio detection output path is set as described above. It cannot be made common and is detected and output by separate paths.

(Problems to be Solved by the Invention) As described above, the VHF low-band voice detection output of the L-SECAM system has a smaller output level than the voice detection outputs of other bands because the frequency is converted by the mixing / amplifying circuit 11. As it becomes distorted, the audio S / N ratio and audio sensitivity tend to deteriorate. In addition, the relative level with respect to the video detection output becomes too small, and audio buzz is likely to occur. Further, there is a problem that the circuit configuration is complicated.

The object of the present invention is to solve the above-mentioned problems of the conventional sound detection device for L-SECAM system television signals, and the output level of the VHF low-band sound detection output does not decrease, and moreover, Simple circuit configuration L
-To provide a sound detection device for SECAM television signals.

(Means for Solving the Problems) In order to achieve such an object, an audio detection device for an L-SECAM system television signal according to the present invention mixes an L-SECAM system television signal with an upper oscillation wave to obtain a VHF signal. The band of the intermediate frequency of the video carrier and the color subcarrier of the low band, the VHF high band and the UHF band are matched and output.
A tuner that outputs the intermediate frequencies of the VHF low-band audio carrier and the intermediate frequencies of the VHF high-band and UHF band audio carriers differently, and a pass center frequency of the VHF low-band audio carrier intermediate frequency and the VHF An audio intermediate frequency filter that is switched to the intermediate frequency of the audio carrier of the high band and the UHF band, and a resonance frequency is switched to the intermediate frequency of the audio carrier of the VHF low band and the intermediate frequency of the audio carrier of the VHF high band and UHF band. And a voice detection circuit that detects and outputs a voice signal by a pseudo-synchronous detection method including a tank circuit.

(Operation) The resonance frequency of the tank circuit included in the audio detection circuit for detecting and outputting the audio signal by the pseudo-synchronous detection method is L-SECAM.
The VHF low-band audio carrier intermediate frequency of the system is switched to the intermediate frequency of the audio carrier of other bands, so that the conventional mixed amplifier circuit is used.
No frequency conversion of the intermediate frequency of the VHF low-band voice carrier is required, and the output level of the VHF low-band voice detection output does not become small and is not distorted.

(Example) Hereinafter, an example of the present invention will be described with reference to FIG.
FIG. 1 shows the essential part of an embodiment of a receiver capable of receiving both the L-SECAM system and the PAL (B / G) system by using the sound detection device for the L-SECAM system television signal of the present invention. It is a partial block circuit diagram. In FIG. 1, the same block circuits in FIG. 2 are designated by the same reference numerals and duplicate description will be omitted.

1 is different from FIG. 2 in that the mixing amplifier circuit 11 and the local oscillator circuit 12 of FIG. 2 are omitted, and the output of the SECAM audio intermediate frequency filter 9 is directly applied to the SECAM audio detection circuit 14. The configuration is such that the resonance frequency of the tank circuit 17 included in the SECAM voice detection circuit 14 can be switched.

The tank circuit 17 has a structure in which a resonance variable capacitor C1 and a switching diode D are connected in parallel to a Q damping resistor R, a resonance capacitor C, and a resonance variable coil L.
And a series connection body of the coupling capacitor C2 is connected in parallel. The anode of the switching diode D is connected to the tank circuit resonance switching terminal 18 via the resistor R1, and the cathode is grounded via the resistor R2.

In such a configuration, when the VHF low band of the L-SECAM system is selected, the resonance switching voltage is not applied to the tank circuit resonance switching terminal 18, the switching diode D is non-conductive, and the tank circuit 17 is resonance variable with the resonance capacitor C. The resonance frequency is determined by the coil L, and the resonance variable coil L is adjusted to 40.97 MHz. And L-SECA
When the other band of the M method is selected, a resonance switching voltage is given to the switching diode D to conduct, and the tank circuit 17 resonates by the resonance capacitor C, the resonance variable coil L, the resonance variable capacitor C1 and the coupling capacitor C2. The frequency is fixed, and the resonance variable capacitor C1 is adjusted to 32.4MH.
adjusted to z.

Therefore, the intermediate frequencies of the L-SECAM type VHF low band and other bands of the audio carrier selectively output from the SECAM audio intermediate frequency filter 9 are both directly.
The SECAM voice detection circuit 14 performs voice detection using a pseudo-synchronous detection method.

In the above embodiment, the L-SECAM system television signal voice detection apparatus of the present invention is used.
Although both the system and the PAL (B / G) system can be received, it goes without saying that the system may be used in a receiver capable of receiving only the L-SECAM system.

(Effects of the Invention) As described above, according to the sound detection device for the L-SECAM system television signal of the present invention, the intermediate frequency of the sound carrier, which is obtained by frequency-converting the L-SECAM system television signal by the tuner, Since the voice detection is performed by the pseudo-synchronous detection method without further frequency conversion for detection, the output level of the detection output does not become small and is not distorted, and the voice S / N ratio and voice sensitivity are excellent.
In addition, no sound buzz is generated. The circuit configuration is simple, the device can be easily downsized, and the device can be manufactured at low cost. Furthermore, the conventional local oscillation circuit required for further frequency conversion for voice detection of the intermediate frequency output after being frequency-converted by the tuner is unnecessary, and spurious interference due to this local oscillation signal does not occur. It has an excellent effect.

[Brief description of drawings]

FIG. 1 shows the essential part of an embodiment of a receiver capable of receiving both the L-SECAM system and the PAL (B / G) system by using the sound detection device for the L-SECAM system television signal of the present invention. FIG. 2 is a block circuit diagram of a part, and FIG. 2 shows an L-SECAM system using a conventional L-SECAM type television signal voice detection device.
FIG. 3 is a block circuit diagram of a main part of an example of a receiver that is capable of receiving both the PAL (B / G) system and the PAL (B / G) system, and FIG. 3 is a diagram showing an intermediate frequency spectrum output from a tuner, FIG. 4 is a diagram showing frequency characteristics of the SECAM voice detection circuit. 1: Tuner, 9: SECAM audio intermediate frequency filter, 14: SECAM audio detection circuit, 17: Tank circuit, 18: Tank circuit resonance switching terminal.

Claims (1)

(57) [Claims] Claim: What is claimed is: 1. A L-SECAM television signal is mixed with an upper oscillation wave to produce VHF low band, VHF high band and UH.
The intermediate frequencies of the F-band image carrier and the color sub-carrier are matched and output, and the frequencies of the intermediate frequency of the VHF low-band audio carrier and the intermediate frequencies of the VHF high-band and UHF-band audio carriers are different. A tuner for outputting the sound, an intermediate frequency filter of which the passing center frequency is switched between the intermediate frequency of the VHF low band audio carrier and the intermediate frequency of the VHF high band and UHF band audio carrier, and the resonance frequency of the VHF low band. An audio detection circuit for detecting and outputting an audio signal by a pseudo-synchronous detection method, which includes a tank circuit that is switched between the intermediate frequency of the audio carrier and the intermediate frequency of the audio carrier of the VHF high band and the UHF band. Characteristic L-SECAM
Audio detection system for television signals.