FR2713866A1 - Television receiver for PAL and SECAM broadcast signals - Google Patents

Abstract

The receiver includes one or more audio NICAM demodulator circuits which automatically select a B/G sound system, and an I sound system. When the system receives a SECAM broadcast and one demodulator circuit for a SECAM-L system has an amplitude modulator adjusted for audio NICAM. A discrimination circuit determines whether the signal corresponds to the SECAM system. The discrimination circuit generates control signals which match the audio NICAM demodulator to the B/G system. This allows the circuit to function only as a SECAM-L demodulator.

Description

Television receiver capable of receiving signals
broadcast as well in the PAL system
that in the SECAM system
Description of the invention
Field of the invention
The present invention relates to a television receiver capable of receiving television broadcasting signals both in the PAL system and in the SECAM system, this receiver comprising at least one NICAM audio demodulator circuit capable of automatically selecting its B / G system and its sound. system I. This feature can be mainly used for television sets and video recorders incorporating television tuners to receive television broadcast signals.

Prior art
In the past, the NICAM system has never been used as an audio transmission system for broadcasting television signals in the SECAM system. As a result, television receivers capable of receiving television signals in both PAL systems and
SECAM are designed to automatically select an audio demodulation circuit for amplitude modulated audio signals in the SECAM-L system (hereinafter referred to as SECAM-L / AM audio signals) when an appropriate circuit inside the receiver determines that the signals received are television signals in the SECAM system.

 Meanwhile, the start of commercial television broadcasting in the SECAM system with the NICAM audio system, is scheduled for 1994 in FRANCE. The conventional television receivers mentioned above are unable to demodulate audio signals transmitted in the NICAM system.

It is already known that in the NICAM system there are two other systems, the B / G system and the I system, the first being already used for the broadcasting of commercial television in various European countries except the United Kingdom and the second being also already used at
UK. Under these conditions, a type of television receiver on the market, capable of receiving both the PAL system and the SECAM system, is designed to selectively receive the NICAM system with the B / G system or the NICAM system with the I system. , if the receiver detects reception of television signals in the PAL system. There is also another type of television receiver incorporating a demodulation circuit of a German multiplex audio broadcasting system, in addition to the demodulation circuit indicated above for the NICAM system with the B / G system and / or with system I.

 In most of the types of receivers indicated above, the selection of the NICAM system with the B / G system or that of the NICAM system with the I system is carried out by an automatic circuit.

Object to be solved by the invention
In view of the technological orientation indicated above of television receivers, one must arrive at the idea that future television receivers, capable of receiving the SECAM system with the audio system
NICAM, are characterized by the possibility of implementing at the same time a circuit of demodulation of audio signals SECAM-L / AM, this NICAM circuit being able in addition to be selected automatically according to whether it demodulates the system
NICAM with system I, when a discrimination circuit contained in the receiver determines that the television signals received are the SECAM television signals.

However, such television receivers pose the following problem: when the receiver receives television signals from the SECAM system with the NICAM audio system, a NICAM circuit contained in the receiver receives audio signals from the NICAM system with the B / system G using a center frequency of 5.85 MHz, while SECAM-L / AM audio signals have a carrier frequency of 6.5 MHz. As the center frequencies of the NICAM system with the B / G system and with the I system are 5.85 MHz and 6.552 MHz respectively, the center frequency of the NICAM system with the I system is extremely close to the carrier frequency of the SECAM audio signals.
L / AM, which leads to undesirable possibilities of operation in the NICAM demodulation circuit to which both NICAM system audio signals with the B / G system are applied, and SECAM-L / AM audio signals. In particular, it is very possible that this undesirable operation appears as an undesirable operation or a delay of a discrimination circuit contained in the NICAM circuit in order to determine whether the signals applied are those of the NICAM system with the B / G system or those of the NICAM system with system I.

The object of the present invention is to create an improved television receiver comprising a NICAM circuit to which both audio signals are applied
NICAM in the B / G system, and SECAM-L / AM audio signals.

In such a receiver, it is effectively avoided the undesired operation and the delay in determining its discrimination circuit intended to determine whether the audio signals applied are those of the NICAM system with the system.
B / G, or those with the I system.

Movens to solve the object of the invention
The improvement according to the present invention applies to a television receiver characterized by the possibility of receiving television broadcasting signals both in the PAL system and in the system.
SECAM, this receiver further comprising a NICAM circuit provided with a system selection circuit for automatically selecting the B / G system or the system I. To solve the problems indicated above, a television receiver according to the present invention operates in such a way that the operation of the NICAM circuit is automatically fixed to that of the B / G system, and that only a SECAM-L / AM audio signal circuit is implemented in the audio circuits other than those of the NICAM circuit, while the receiver receives television broadcast signals in the SECAM system.

 In such a television receiver, the operation of the NICAM audio circuit is fixed to the B / G system when the television signals thus received are determined to be in the SECAM system. In a receiver provided with a memory for storing tuning information therein, the broadcasting system of each television station, for example PAL or SECAM, can be stored in a corresponding area of the memory. In the receiver provided with such a memory, its NICAM audio circuit is automatically fixed to the B / G system when information is read from the memory indicating that the station selected is a station transmitting SECAM television signals, and when control signal from a system control circuit instructs the receiver to receive only the SECAM television signal.

 In a NICAM audio transmission, only the B / G system is used with a television broadcast in the SECAM system.

Advantage of the invention
As stated above, a television receiver according to the present invention has the advantage that it effectively suppresses unwanted operation and decision delay in a discrimination circuit for determining whether the NICAM system works with the B / G system. or with system I, since the operation of the NICAM circuit is fixed to the B / G system in the event of reception of television signals in the SECAM system.

Drawing
The present invention will be described below in more detail with the aid of an embodiment shown in the attached single figure which illustrates a preferred embodiment according to the present invention.

 In this single figure, only the important parts of a television receiver according to the invention are represented in the form of a block diagram.

Description of the preferred embodiment
In the figure, reference 1 designates an antenna circuit intended to receive television signals transmitted at radio frequency. These television signals received by the antenna circuit 1 are applied to a tuning circuit or tuner circuit 2 for the detection of the video signals and of the sound signals contained in the transmitted signals. This tuner circuit 2 outputs intermediate frequency sound signals (SIF signals) and composite video signals.

The SIF output signals are also applied respectively to a NICAM demodulator circuit 4, to a German-type multiplex audio demodulator circuit 5, to an audio signal demodulator circuit 6 with system frequency modulation I, and to a demodulator circuit. of audio signals 7 with amplitude modulation of system L. Although this is not shown in the figure, the NICAM demodulator circuit 4 is characterized by the possibility of demodulating both the B / G system and the I system, and incorporates for this purpose a selector circuit intended to select one of these two systems according to the result of the determination of the input signals.

 In addition, although the embodiment shown in the figure includes a separate demodulator circuit 6 for the system I frequency modulated audio signals, this circuit 6 can be constructed in the German type multiplex audio demodulator circuit 5 using its circuit and adding certain components such as filters. Although, in the present embodiment, the SIF output signals of the tuner circuit 2 are applied to the amplitude modulation audio signal demodulator 7 of system L, the input of the demodulator 7 can be obtained from the part median of the tuner circuit 2. The audio carrier band can be obtained directly by filtering television signals converted into intermediate frequency with the video and audio carrier, and the audio carrier thus obtained can be applied to the input of the demodulator 7.

The composite video signals output by the tuner circuit 2 are applied to a video processing circuit for other uses such as for example the reproduction of images on a television screen or the recording on a videotape of a hand and the application to a circuit 3 of discrimination
SECAM on the other hand. In the case where the video signals supplied are determined to be SECAM signals by the discrimination circuit 3, this circuit 3 generates and supplies control signals 11 to activate the demodulator circuit 7 of audio signals with amplitude modulation of system L , and control signals 10 for fixing the NICAM demodulator circuit 4 to the B / G system. Since these control signals 10 always fix the system selection to the B / G system in circuit 4, the problems of system selection indicated above in circuit 4 are effectively avoided.

 Simultaneously with the generation and supply of the control signals 10 and 11, control signals 9 are also generated and supplied respectively to the German type multiplex audio signal demodulation circuit 5 and to the modulation signal audio demodulator circuit 6 system frequency I, to inhibit the operation of these circuits 5 and 6, since these circuits 5 and 6 are useless during reception of the SECAM system with the NICAM audio system.

 The embodiment shown in the figure includes a channel memory device 8 for storing information not only on the tuning frequency of each station but also on the broadcasting system of each station, for example SECAM or PAL.

Like the SECAM discrimination circuit 3 indicated above, this channel memory device 8 also generates the same control signals 9, 10, 11 as those described above, so that when the user selects a station transmitting signals television in the SECAM system, the NICAM 4 circuit is always fixed to the B / G system without determining the type of television signals received.

 In addition to the discrimination circuit 3 described above and the channel memory 8 above, a controller 12 is also used to manually generate the control signals 9, 10, 11 above and to supply them to the demodulators. 4, 5, 6 and 7. This controller 12 can be implemented by user selection, for example in the case where the receiver receives television signals from a TV station following a station search. , and where the discrimination circuit 3 does not work properly for any reason.

 Finally, although the control signals 9 of the embodiment described above inhibit the operation of the audio signal demodulator to a German type multiplex 5 and the audio signal demodulator 6 of system frequency modulation I, it will be noted that these control signals 9 can be used to cut the audio signals at each of the output terminals of the demodulators 5 and 6.

Claims (6)

 10) Television receiver capable of receiving television broadcast signals both in the PAL system and in the SECAM system, this receiver comprising at least one NICAM audio demodulator circuit capable of automatically selecting its B / G system and its I system, characterized in that the operation of the NICAM audio demodulator circuit is automatically fixed to the B / G system and its system I, when the receiver receives the television broadcast signals in the SECAM system, and in that only one audio demodulator circuit for system Amplam modulation SECAM-L is implemented among the audio demodulator circuits except for the NICAM audio demodulator circuit.  20) Television receiver according to claim 1, characterized in that this receiver further comprises a discrimination circuit for determining whether the television signals received correspond or not to those of the SECAM system and for generating control signals to fix the circuit NICAM audio demodulator to the B / G system as well as to operate the audio demodulator circuit only for the amplam modulation SECAM-L system among the audio demodulator circuits except for the NICAM demodulator circuit.  30) Television receiver according to claim 1, characterized in that this receiver further comprises a channel memory capable of storing information on the broadcasting system of TV stations, and of generating control signals to fix the audio demodulator circuit NICAM to the B / G system and to operate the audio demodulator circuit only for the amplitude-modulated SECAM-L system among the audio demodulator circuits except for the demodulator circuit NICAM, when selecting a T.V. station in the SECAM system.  40) Television receiver according to claim 1, characterized in that this receiver further comprises a controller for generating control signals intended to manually fix the audio demodulator circuit NICAM to the B / G system and to operate the audio demodulator circuit only for the amplam modulation SECAM-L system among the audio demodulator circuits except for the NICAM demodulator circuit.  50) Television receiver according to claims 1 to 4, characterized in that one of the audio demodulator circuits except for the NICAM demodulator circuit and the audio demodulator circuit for SECAM-L amplitude modulation system, is an audio demodulator with German type multiplex.  60) Television receiver according to claims 1 to 4, characterized in that one of the audio demodulator circuits except for the NICAM demodulator circuit and the audio demodulator circuit for amplam modulation SECAM-L system is an audio demodulator with system frequency modulation I.