JPH03218184A - Multiple sound detecting circuit - Google Patents

Abstract

PURPOSE:To prevent a QPSK signal from being inputted to a sound detecting circuit by deciding whether a sound intermediate frequency signal from a picture detecting circuit is the 2nd frequency band signal or not and selecting the output of a sound intermediate frequency converter. CONSTITUTION:The multiple sound detecting circuit is provided with the picture detecting circuit 4 capable of detecting a picture intermediate frequency signal, band pass filters(BPFs) 7, 9 for passing only the 1st frequency band signal out of the sound intermediate frequency signal outputted from the circuit 4 by detecting an RF signal, a sound intermediate frequency converter 10 for converting the output signal of the BPF 7 or 9 into the 2nd frequency band signal, the 2nd BPF 13 for using the 2nd frequency band as a passing band, a switch 23 for selectively applying the sound intermediate frequency signal to the 2nd BPF 13, a sound detecting circuit 14 for detecting the output of the BPF 13 and outputting a sound signal, and a control means 24 for discriminating the DC level of a detected output and controlling the switch. Thereby, a sound signal prevented from the interference of a QPSK signal can be outputted even at the time of receiving NICAM system television broadcasting.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a multi-audio detection circuit, and in particular, the present invention relates to a multi-audio detection circuit that automatically determines the broadcasting system and detects input RF signals without user operation.
The present invention relates to a multi-audio detection circuit that receives signals.

(Prior Art) Conventionally, multi-system television receivers that can receive television broadcasts from different broadcast systems have been developed. Various standards have been established for broadcasting systems. For example, due to differences in color broadcasting systems,
It is classified into PAL system, SECAM system and NTSC system, and due to the difference in carrier frequency and video signal, B/G system,
It is classified into 1 method, D/K method, etc. Furthermore, as shown in Table 1 below, the audio intermediate frequency of the B/G method is 5.
．． 5MHZ, and the audio intermediate frequency of the ■ method is 6.0M.
Hz, and the audio intermediate frequency of the D/K system is 6.5 MHz.
It is z.

Many of the multi-system television receivers in Table 1 are equipped with a multi-audio detection circuit that automatically discriminates each broadcast system and obtains audio output. FIG. 2 is a block diagram showing a television receiver incorporating such a conventional multi-audio detection circuit.

The RF signals of the B/G system, 1 system, and [)/K system induced in the antenna 1 are input to the tuner 2 . The tuner 2 applies a video intermediate frequency signal obtained from a video signal of a predetermined channel of the input RF signal to a video bandpass filter (hereinafter referred to as
A video intermediate frequency amplification and detection circuit (referred to as PSE) 3 is connected to the video intermediate frequency amplification and detection circuit (
(hereinafter referred to as a PIF detection circuit) 4. The PIF detection circuit 4 amplifies and detects the video intermediate frequency signal, and outputs the video signal and the audio intermediate frequency signal (hereinafter referred to as the SIF signal) at 14.The video signal is output to the output terminal 5, and the SIF
The signal is applied to buffer 6. The SIF signal output of the buffer 6 is connected to a resistor R1 and a band pass filter (hereinafter referred to as BP).
)7, resistor R2 and BPF8 or resistor R3
and an audio intermediate frequency converter (hereinafter referred to as
10 (referred to as SrFl inverter). In addition, B
The passband of PF7.8.9 is 5.5MHz. 6.
0MHz, 6.5MHz.

The SIF converter 10 has a mixer 11, and the mixer 11 mixes the oscillation output from the oscillator 12 with an oscillation frequency of 0.5 MHz and the input signal, thereby outputting a component with a frequency of 6 MHz. . In other words, the SIF-1 inverter 10 supports B/G system with an audio intermediate frequency of 5.5 MHZ and D/K system with an audio intermediate frequency of 6.5 MHZ.
By mixing the IF signal and the oscillation output with a frequency of 0.5 MHz, a 6 MHz component is output and J
The SIF signals of one system with an audio intermediate frequency of 6 M l-{ z are output as they are without being mixed.

The frequency output from the SIF converter 10 is 6MHZ
The B/G, t, D/K system SIF signal is sent to the SIF detection circuit 1 via the BPF 13 with a passband of 6 MHz.
given to 4. The SIF detection circuit 14 detects an input signal at a detection frequency of 6 MHz using a 6 MHz resonator 15 and outputs an audio signal to an output terminal 16. In this way, B/G. I. By detecting the audio intermediate frequency of the D/K system at a common 6MHz, it is possible to receive television broadcasts of either system.

Note that the channel selection operation is performed by a key manual device 17. The key human power device 17 includes a brisset/normal key 1
8, a position key 19, a search key 20, etc. are provided, and signals based on the operations of these keys are given to the channel selection microcomputer 21. For example, when the search key 20 is operated, the tuning microcomputer 21 sequentially changes the tuning frequency of the tuner 2 to perform search tuning. The signal presence detection circuit 22 detects whether the video signal is a signal presence or not and outputs a detection signal to the channel selection microcomputer 21, and the channel selection microcomputer 21
When selecting a search station, the search operation is stopped by the detection signal.

By the way, in England and other countries, N[CAM broadcasting, which is audio multiplex broadcasting, is being carried out. In this NI CAM broadcast, in addition to normal audio broadcasting in which the audio signal is FM modulated, stereo broadcasting is performed in which the audio signal is PCM modulated. Note that the audio signal of the stereo broadcast is a QPSK signal. The carrier wave frequencies of the audio signals of NICAM broadcasting are shown in Table 2 below.

(The circuit shown in Figure 2 of Table 2 cannot demodulate QPSK audio signals, but it can demodulate the normal audio of NJCAM television broadcasting. It is currently being used in the UK. In this case, the carrier frequency of normal audio is 6.0M}{2, which is the same as the audio carrier frequency of PAL-1. Therefore, this normal voice is applied to the Sll~'' converter 10 via the BPF 8, and is further applied to the SIF detection circuit 14 via the BPF 13 for detection.

However, since the carrier frequency band of the QPSK signal in the UK-NICAM system is 6.552±0.4MHz, the Q
The PSK signal component passes through the BPF 9 and is given to the SIF converter 10. This QPSK signal component is SI
F converter 1o / - SIF of Maru M Pa
It is superimposed on the signal and becomes a noise component.

In addition, the number of poems received by the Scandinavian N I CAM system is 5.
．． The QPSK signal of 850±0.4MHz passes through BPF8, and the normal audio signal that passes through BPF7.
5M} is applied to the S1 converter 10 together with the Iz component and becomes a noise component.

In any NICAM method, the SIF detection circuit 1
Since the normal audio signal on which the QPSK signal is superimposed on the SIF detection circuit 14 is input, the detection output of the SIF detection circuit 14 is extremely degraded.

(Problem to be Solved by the Invention) In this way, in the conventional multi-audio detection circuit described above, all SIF signals of different frequencies = a common S[F
Since it is applied to the converter for frequency conversion, Nr
When receiving a CAM-based normal audio signal, the QPSK signal is given to the SIF-1 inverter, resulting in a problem in that the normal audio is interfered with by the QPSK signal.

The present invention has been made in view of such problems, and includes:
Even when receiving NICAM television broadcasts,
It is an object of the present invention to provide a multi-audio detection circuit capable of outputting an audio signal that is not affected by QPSK signal interference.

[Configuration 1 of the Invention (Means for Solving the Problems) A multi-audio detection circuit according to the present invention is capable of detecting a video intermediate frequency signal obtained from input RF signals of a first method group and a second method group. a video detection circuit, and a first band pass that allows only signals in a first frequency band to pass through the audio intermediate frequency signal that the video detection circuit detects and outputs the RF signal of the first or second method group. a filter, an audio intermediate frequency inverter that converts the audio intermediate frequency signal that has passed through the first band pass filter into a signal in a second frequency band, and a second band whose pass band is the second frequency band. a pass filter; a switch for selectively applying the audio intermediate frequency signal from the video detection circuit and the audio intermediate frequency converter to the second band pass filter; It is equipped with an audio detection circuit that detects and outputs an audio signal, and a control means that determines the DC level of the detection output of the audio detection circuit and controls the switch.

(Function) In the present invention, the first bandpass filter passes the signal in the first frequency band among the audio intermediate frequency signals of the first and second system groups. This first frequency band signal is frequency-converted into a second frequency band signal by an a-voice intermediate frequency converter. The switch selectively applies the a-voice intermediate frequency signal from the reflection detection circuit and the audio intermediate frequency converter to the second bandpass filter. In other words, the audio intermediate frequency signal in the first frequency band is converted to a signal in the second frequency band and is applied to the second band pass filter, or the audio intermediate frequency signal in the entire band is directly converted to the signal in the second frequency band. given to the pass filter. The control means controls the switch to first apply the output of the video detection circuit to the audio detection circuit for detection, and determines the DC level of the detection output. This determines whether the audio intermediate frequency signal from the video detection circuit is a signal in the second frequency band. Only when the signal is not in the second frequency band, the switch is changed to select the output of the audio intermediate frequency converter. For example, in the NICAM system, a normal audio signal and a QPSK audio signal have different frequency bands; one is in the first frequency band and the other is in the second frequency band.
frequency band. By controlling the switch based on the DC level of the audio detection output, only normal audio is provided to the audio detection circuit.

(Example) Hereinafter, an example of the present invention will be described in detail based on the drawings. FIG. 1 is a block diagram showing a television receiver incorporating a multi-audio detection circuit according to an embodiment of the present invention. In FIG. 1, the same components as in FIG. 2 are given the same reference numerals.

Tuner 2 has PAL8/G,I induced in antenna 1.
, D/K system and NICAM system R[signal are input. The tuner 2 is controlled by a tuning microcomputer 24 (not shown) and outputs a video intermediate frequency signal obtained from a video signal of a predetermined signal of the input RF signal to the PIF detection circuit 4 via the PSF 3. The PIF detection circuit 4 amplifies and detects the video intermediate frequency signal, and outputs the video signal and SI
I am getting an F signal. The video signal is output to an output terminal 5, and the SIF signal is supplied to a buffer 6.

The SIF signal output of the buffer 76 is connected to the resistor R5 and B PF.
7 or also via resistor R6 and BPF9.
It is also applied to terminal b of the audio selector switch 23 via a resistor R4.

Note that the passbands of BPF7 and BPF9 are respectively 5.5MHz.
It is 6.5MHz.

The S[Fl inverter 10 is on the right side of the mixer 11.

The mixer 11 has a frequency of 5.5 MHz via the BPF 7.
When a component with a frequency of 6 MHz is input, a component with a frequency of 6 MHz is output by adding the oscillation output with an oscillation frequency of 0.5 MHz from the oscillator 12 and the input signal, and the component with a frequency of 6.5 MHz is output via the BPF 9. When the z component is input manually, the frequency becomes 6MH by subtracting the oscillation output and the input signal.
Outputs the Z component. The output of the [SiF] inverter 10 is output to the terminal a of the switch 23.

The SIF signal from the common end C of the switch 23 is the BPF
13, the band is limited to the 6MHz band signal and the SIF
The signal is applied to the detection circuit 14. The SIF detection circuit 14 detects the input signal at a detection frequency of 6 MHz using the resonator 15 and outputs the audio signal to the output terminal 16. Also, S.I.
The DC component of the audio signal from the F detection circuit 14 is transferred to the buffer 12.
5 to the channel selection microcomputer 24. Note that the signal presence detection circuit 22 detects whether or not a video signal is included in the detection output of the PIF detection circuit 4, and this detection W
g is input to the channel selection microcomputer 22.

On the other hand, the channel selection operation is performed by operating the preset/normal key 18, position key 19, search key 20, etc. provided on the key-powered device 11. A signal based on each key operation is given to the tuning microcomputer 24, and the tuning microcomputer 24 controls the tuner 2 based on this signal to perform tuning. That is, when the position key 19 is operated, the channel selection microcomputer 24 increases or decreases the selected channel of the tuner 2 based on this operation. Further, when the position key 19 is operated to switch channels, the channel selection microcomputer 24 first causes the switch 23 to select terminal b. Then, the tuning microcomputer 24 determines whether the frequency of the SIF signal given to the SIF detection circuit 14 is 6M}-12 from the DC level of the detection output of the SIF detection circuit 14, and determines whether the frequency of the SIF signal is 6M}-12. When the SIF signal is 6Ml-IZ, the switch 23 is made to select terminal b, and when the frequency of the SIF signal is not 6 MHz, the switch 23 is switched to select terminal a. Note that the tuning microcomputer 24 compares the detected output DC level with a predetermined threshold value and selects S
It is designed to judge the input of the IF detection circuit 14,
Scandinavian-NICAM 6MHz QPSK signal is SI
Even when input to the F detection circuit 14, the 6MHz SI
It can be determined that the F signal is not input,
The switch 23 can be switched to terminal a.

Further, when the search key 20 is operated and the preset search mode is designated, the channel selection microcomputer 24 causes the terminal b of the switch 23 to be selected during the search. After the presence of a signal is detected by the signal detection circuit 22,
The switch 23 is switched by determining the DC level of the detection output.

Next, the operation of the multi-audio detection circuit configured as described above will be explained.

It is now assumed that the position key 19 of the input device 17 is operated to select a channel. The tuning microcomputer 24 causes the tuner 2 to select a station depending on the operation of the position key 19, and causes the switch 23 to select terminal b. The IF signal from tuner 2 is given to PIF detection circuit 4 via PSF 3. PIF circuit 4 outputs the video signal to terminal 5
and the right signal detection circuit 22, and outputs the SIF signal via the buffer 6. Since the switch 23 selects the terminal b, the SIF signal passes only through the B P F 13 and is applied to the SIF detection circuit 14 . 6MHz
The SIF signal is detected by the SIF detection circuit 14 and output.

Here, if the PIF detection circuit 4 outputs an SIF signal of PAL-1 system or UK-NICAM system with a frequency of 6 MHz, the channel selection microcomputer 24 selects the SIF signal.
It is determined that the DC level of the detection output of the detection circuit 24 is higher than a predetermined threshold value, and the switch 23 is not switched. Therefore, in this case, the QPSK signal of the UK-NICAM system having a frequency of 6.552 MHz is not input to the SrF detection circuit 14.

On the other hand, it is assumed that the PIF detection circuit 4 outputs an SIF signal of the PAL-B/G system having a frequency of 5.5 MHz, the Nordic-NICAM system, or the PALD/K system having a frequency of 6.5 MHz.

In this case, only the QPSK signal of the Scandinavian NI CAM system passes through the BPF 13 and is sent to the SIF detection circuit 1.
Detected at 4. Since the DC level of the detection output of the QPSK signal of the Scandinavian NICAM method is lower than the predetermined threshold,
The channel selection microcomputer 24 switches the switch 23 to select pane a. As a result, PAL-B/G system and Scandinavian-N
The normal audio SIF signal of the ICAM system is BPF7.
6 MH
The signal is frequency-converted to Z, and is applied to the SIF detection circuit 14 via the BPF 13 for detection. Also, PAL-D/K
The SIF signal of the system is given to the SIF converter 10 via the BPF 9, frequency-converted to 6 MHz, and the SIF signal of the B P
The signal is applied to the SIF detection circuit 14 via F13 and detected.

The 5.850 MHz QPSK signal of the Scandinavian NICAM system does not pass through any BPF7.9 and is sent to the SIF
There is no manual input to the detection circuit 14.

When the preset search mode is designated, the tuning microcomputer 24 first selects the terminal b of the switch 23 and causes the tuner 2 to search and select a channel. During the search, the switch 23 is fixed to terminal b.

When the signal detection circuit 22 determines that the detected output of the PIF detection circuit 4 is a signal, the channel selection microcomputer 2
4 determines the DC level of the detection output of the SIF detection circuit 14. Thereafter, the channel selection microcomputer 24 switches the switch 23 in the same manner as when the position key 19 is operated.

As described above, in this embodiment, the channel selection microcomputer 24 determines the DC level of the detection output of the 6 MHz component and controls the switch 23, and when receiving UK-NICAM television broadcasting, the terminal of the switch 23 is By selecting b, the 6.552M}lz QPSK signal is prevented from being input to the S[F detection circuit 14, and the Scandinavian-
When receiving a NICAM television signal, by selecting terminal a of switch 23, 5.850M
This prevents the Hz QPSK signal from being input to the SIF detection circuit 14. As a result, the SIF detection circuit 14
The detected output is not degraded by the QPSK signal, and good audio output can be obtained.

[Effects of the Invention] As explained above, according to the present invention, it is possible to prevent the QPSK signal which becomes an interference component of the audio detection output from being input to the audio detection circuit, and it is possible to output a good audio output. It has the effect of being able to.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a television receiver incorporating a multi-audio detection circuit according to an embodiment of the present invention, and FIG.
The figure is a block diagram showing a divisional receiver incorporating a conventional multi-audio detection circuit. 4... PIF detection circuit, 7.9.13... BPF, 10... SIFT] inverter, 14... SIF detection circuit, 24... Tuning microcomputer.

Claims (1)

[Scope of Claims] A video detection circuit capable of detecting a video intermediate frequency signal obtained from input RF signals of a first method group and a second method group; a first band-pass filter that passes only a signal in a first frequency band among the audio intermediate frequency signals detected and outputted from the group of RF signals; an audio intermediate frequency converter that converts the signal into a signal in a second frequency band; a second bandpass filter whose passband is the second frequency band; and an audio intermediate frequency signal from the video detection circuit and the audio intermediate frequency converter. a switch that selectively applies the signal to the second band-pass filter; an audio detection circuit that detects the audio intermediate frequency signal that has passed through the second band-pass filter and outputs an audio signal; A multi-audio detection circuit comprising: control means for determining the DC level of the output and controlling the switch.