JPH0628417B2 - Multi-channel TV receiver - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-system television receiver that receives a plurality of systems of television signals.

2. Description of the Related Art In recent years, the introduction of multi-system television receivers has become popular especially in the Middle East, and the audio intermediate frequency (SIF) detection circuit has become complicated. For example, in the NTSC system, the audio intermediate frequency is 4.5 MHz, and in the PAL system and SECAM system,
There are 5.5MHz, 6.0MHz and 6.5MHz, and it is necessary to detect four types of SIF signals in order to receive all of them.

Hereinafter, an example of the SIF circuit of the conventional multi-system television receiver will be described with reference to the block diagram. FIG. 2 shows the configuration of a conventional SIF circuit. In Figure 2, 1 is 5.5MHz, 2 is 4.5MHz, 11 is 6.5MH
z and 12 are filters that respectively pass 6.0 MHz. Reference numerals 4, 14 are limiter amplifiers, and 5 is an SIF signal discrimination circuit. 6 and 15 are detectors and 7 is S of 5.5 MHz
A phase shifter for detecting the IF signal, 8 is 4.5MHz, 1
Reference numeral 6 is a phase shifter for detecting a 6.5 MHz SIF signal and 17 is a 6.0 MHz SIF signal. Reference numerals 3, 9, 10, 13, and 18 are switches.

The operation of the SIF circuit configured as above will be described. Input filters 1, 2, 11, from video detection signal
Only the SIF signal is taken out by 12 and added to the limiter amplifiers 4 and 14 to output the SIF signal having a constant amplitude.

This SIF signal is FM-detected by the detectors 6 and 15 to become an audio signal, which is added to the circuit in the subsequent stage. 5.5M
Regarding the SIF signals of Hz and 4.5 MHz, the discrimination circuit 5 automatically discriminates the SIF signal using the output of the limiter amplifier 4 to control the switches 3 and 9. The switches 10, 13 and 18 are manually controlled.

However, in the above configuration, the detectors 6 and 15 have two
In addition, the number of phase shifters to be adjusted is four, which is complicated.

An example of solving this is shown in FIG. In FIG. 3, 2
Reference numeral 1 is a switch for selecting which input filter the video detection signal is added to. Reference numerals 1, 2, 11 and 12 are filters for each SIF signal as in FIG. 2, 22 is a mixer, 2
3 is a switch, 24 is a 1 MHz oscillator, 25 is a 0.5 MHz oscillator, 26 is a limiter amplifier, 27 is a 5.5 MHz detector, and 28 is a 5.5 MHz detection phaser.

The operation in the case of this configuration will be described. The SIF signal that has passed one of the input filters is generated by the oscillator 24 or 2
When it is mixed with the output signal of No. 5 and inputted to the limiter amplifier 26, it is always converted into a 5.5 MHz SIF signal, and the detector need only be a 5.5 MHz detector. 4.5MHz S
When the IF signal is applied to the mixer 22, 1 MHz of the oscillator 24
The z signal is added to the mixer 22, and the added 5.5 MHz signal is input to the limiter amplifier 26.

Problems to be Solved by the Invention However, in the above-mentioned configuration, since the output of the limiter amplifier is always 5.5 MHz, it is impossible to automatically distinguish between 4.5 MHz and 5.5 MHz as performed by the judgment circuit 5 in FIG. is there.

In view of the above problems, the present invention provides a multi-channel television receiver that requires only one detector and one phaser and is capable of automatic discrimination.

Means for Solving the Problems In the present invention, a limiter amplifier is provided in the preceding stage for converting SIF signals of different frequencies into SIF signals of a single frequency, and the output signal of the limiter amplifier is mixed with the SIF signal discriminating circuit. It is configured to input to the detector and S in the discrimination circuit.
The IF signal is automatically discriminated.

Effect According to the present invention, the above-described configuration can realize a multi-system television receiver for which only one detector and one phaser are required and the SIF signal can be automatically discriminated.

Embodiment One embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 31, 32, 33, 34,
Reference numeral 35 is a switch, and reference numerals 1, 2, 11, 12 are input filters for the respective SIF frequencies, which are the same as those shown in FIGS.
Reference numeral 36 is a limiter amplifier, and 37 is an SIF signal discrimination circuit. Also, mixer 22, 1MHz oscillator 24, 0.5MHz
Oscillator 25, limiter amplifier 26, 5.5MHz detector 2
The phase shifter 28 for 7 and 5.5 MHz detection is the same as in FIG.

The operation of the SIF circuit configured as above will be described. First, the video detection signal passes through the SIF input filter corresponding to the signal, and only the SIF signal is applied to the limiter amplifier 3.
6 is input.

To the mixer 22, the output of the limiter amplifier 36 and the oscillator 24
Or 25 outputs are input and 5.5MHz SIF is output
Only the signal is detected and detected as an audio signal in the detection circuit in the subsequent stage. The output of the limiter amplifier 36 is also applied to the discrimination circuit 37 to discriminate between 4.5 MHz and 5.5 MHz, and the switch 32 and the switch 35 are controlled.

As described above, according to the present embodiment, the limiter amplifier 36
Even if the detection circuit has only one unit,
It is possible to automatically distinguish between 4.5MHz and 5.5MHz.

In the above embodiment, the discriminating circuit 37 is for discriminating between 4.5 MHz and 5.5 MHz, but conversely, a discriminating circuit for discriminating between 6.0 MHz and 6.5 MHz may be used.

EFFECTS OF THE INVENTION As described above, according to the present invention, since the limiter amplifier is provided in the preceding stage of the mixer, the SIF signal can be automatically discriminated even in the converter system having one detector.

[Brief description of drawings]

FIG. 1 is a block diagram of a multi-system television receiver according to an embodiment of the present invention, and FIGS. 2 and 3 are block diagrams of a conventional multi-system television receiver. 1, 2, 11, 12 ... Input filter, 22 ... Mixer, 24, 25 ... Oscillator, 36 ... Limiter amplifier,
37 ... Discrimination circuit.

Claims (1)

[Claims] 1. An input filter corresponding to audio intermediate frequency signals of a plurality of types of television signals respectively, the input filters being connected in common as a set of two and divided into a plurality of sets, and the plurality of sets of input filters. Switching means for selectively switching the group of input filters, and second switching means provided for each group of input filters for switching the connection of the input filters of the group switched and selected by the first switching means. A first limiter amplifier connected to the plurality of sets of input filters via the second switching means and receiving an audio intermediate frequency signal; and a mixer to which an output of the first limiter amplifier is supplied, An output signal from the mixer, which comprises a discrimination circuit, a plurality of oscillators connected to the mixer through a third switching means, a second limiter amplifier, a detector and a phaser. A detection circuit for detecting and outputting an audio signal, the frequency of the audio intermediate frequency signal output from the first limiter amplifier is determined by the determination circuit, and the second and third switching means are determined by the determination signal. Switching control is performed, and the first
From the mixer to which the output of the limiter amplifier and the oscillator output are input, a single frequency audio intermediate frequency signal is output, and the detection circuit detects the single frequency audio frequency signal. A multi-system television receiver characterized by.