JP2005204059A - Digital/analog common broadcast receiving device and terrestrial digital television receiving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a broadcast-receiving device which receives and decodes a broadcast signal, the broadcast receiving device being small-sized, and which is low cost. <P>SOLUTION: The broadcast-receiving device has a 1st antenna for digital broadcast reception, a 2nd antenna for analog broadcast reception, a tuning circuit which tunes a signal received by the 1st or 2nd antenna, and a changeover switch, which selectively inputs only the signal that the 1st or 2nd antenna receives to the tuning circuit. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a broadcast receiving apparatus that receives and decodes a broadcast signal, and a terrestrial digital television receiver that receives a terrestrial digital television broadcast signal.

  In recent years, digital television broadcasting has begun to be used in place of conventional analog television broadcasting. Unlike the analog television broadcast, the digital television system is expected to be a next-generation broadcast system because the video / audio does not deteriorate.

  However, in order to perform digital television broadcasting, it is necessary to newly install digital broadcasting equipment at the relay station, so at present, the broadcasting area of digital television broadcasting is narrower than that of analog television broadcasting, limited It has become the only area. For this reason, when viewing digital television broadcasts in a moving body such as an automobile, if the moving body is moving near the boundary of the broadcast area, the reception state and the unreception state are frequently repeated, and the program can be satisfactorily repeated. There was a problem that I could not browse.

As a solution to such a problem, for example, it is considered that the broadcast receiving apparatus described in Patent Document 1 can be used. The broadcast receiving device described in Patent Document 1 combines a receiving device dedicated to analog broadcasting and a receiving device for receiving digital broadcasting, and switches between receiving analog broadcasting and digital broadcasting as appropriate according to the reception state of radio waves. It is. Digital broadcasting and analog broadcasting often perform so-called simultaneous broadcasting, and programs having the same contents as digital broadcasting programs are also broadcast by analog broadcasting. Therefore, when digital broadcasts cannot be received, switching to analog broadcasts (with a wider broadcast area) allows viewers in the mobile body to continue to watch programs with the same content even if digital broadcasts cannot be received. Is possible.
JP-A-5-347736

  However, in the configuration as in Patent Document 1, since two receiving devices are used, the overall size of the device becomes large, and it is not suitable for mounting on a moving body. In addition, the manufacturing cost of the entire device increases.

  In particular, a mobile body often employs a combined diversity system that receives and synthesizes broadcast radio waves from all directions so that digital broadcasts can be received even in a weak electric field. Since the combined diversity method uses a plurality of digital broadcast receiving apparatuses, when combining diversity is used in an apparatus having a configuration as disclosed in Patent Document 1, at least three receiving apparatuses are required. Becomes even larger.

  In view of the above circumstances, an object of the present invention is to provide a small-size and low-cost broadcast receiving apparatus.

  In order to solve the above-described problem, the broadcast receiving apparatus according to claim 1 is received by the first antenna for digital broadcast reception, the second antenna for analog broadcast reception, and the first or second antenna. A tuning circuit that tunes the received signal, and a changeover switch that selectively inputs only the signal received by one of the first and second antennas to the tuning circuit.

  Therefore, according to the present invention, since the same tuning circuit is used for analog broadcast reception and digital broadcast reception, a small-sized and low-cost broadcast receiving apparatus is realized.

  The broadcast receiving apparatus selects which of the signals received by the first and second antennas is input to the tuning circuit based on the reception level of the signals received by the first and second antennas. A switching control means may be included (claim 2). Furthermore, the digital broadcast program received by the first antenna has the same content as the analog broadcast program received by the second antenna.

  With such a configuration, when the digital broadcast program received by the first antenna is disabled, the digital broadcast program is automatically switched to an analog broadcast program that broadcasts the same program. Therefore, even if the digital broadcast program cannot be received, the viewer can continue to watch the program without performing a channel switching operation or the like.

  FIG. 1 is a diagram showing a schematic configuration of a television broadcast receiver according to an embodiment of the present invention.

  In the present embodiment, an OFDM (orthogonal frequency division) system that can efficiently transport a large amount of digital data is adopted during digital television broadcasting.

  In the OFDM system, a digital signal is serial-parallel converted into a plurality of parallel symbols on the transmission side, and further subjected to inverse Fourier transform to obtain a plurality of orthogonal subcarriers of different frequencies, and this is D / A converted OFDM A signal is transmitted. The receiver side performs A / D conversion on the received OFDM signal, obtains parallel symbols by Fourier transformation, and further obtains a decoded digital signal by parallel-serial conversion. Since the subcarriers are orthogonal to each other in the OFDM scheme, the frequency bands of the subcarriers may partially overlap, so that a large amount of data can be transmitted in a limited frequency band.

  On the other hand, in communication including the OFDM system and analog broadcasting, a so-called diversity system is often employed in which signal quality is improved by using a plurality of antennas having different directivities in order to prevent signal attenuation. Diversity systems can be broadly classified into switched diversity systems and composite diversity systems.

  The combining diversity system increases the signal level by combining signals received from a plurality of antennas. However, the arrival times of signals received from a plurality of antennas differ depending on the signal reception path. That is, the signal reflected on the building or the like arrives slightly later than the signal received directly from the transmitter. (Hereafter, the signal that arrives first is called a desired wave, and the signal that arrives late is called a delayed wave.)

  In the OFDM scheme, when a delay wave is combined with a desired wave, the previous symbol overlaps, and the characteristics deteriorate when demodulating the data of each symbol. In order to prevent such deterioration, a signal margin period called a guard interval is added to each subcarrier during signal transmission, for example, as in the configuration of Patent Document 1. The guard interval is a cyclic addition of a part of the waveform of the symbol, and if the delay time of the delay wave is within the guard interval time, the effect of overlapping of its own symbols is inevitable, Demodulation can be performed while avoiding the overlap of the previous symbol. That is, by adding a guard interval, it is possible to prevent deterioration due to delayed waves to some extent and obtain a signal with higher signal quality than when no diversity system is used.

  The receiving apparatus 100 of the present embodiment employs a combining diversity system that combines a master signal received by the master antenna 10a and a slave signal received by the slave antenna 10b when receiving a digital broadcast. The antennas 10a and 10b are antennas having different directivities.

  The receiving apparatus 100 adopts a switching diversity system configured to send the strongest signal among the analog broadcast signals received by the analog antennas 11a to 11d to the tuner unit when receiving the analog broadcast. It is. The analog antennas 11a to 11d are antennas having different directivities.

  First, a digital broadcast reception procedure will be described.

  The signal received by the master antenna 10a is sent to the tuner unit 20a. In the tuner unit 20a, a signal (OFDM signal) in a desired frequency band is extracted by the UHF tuning circuit 21a, and then phase tuning of the OFDM signal is performed by the PLL 70a and the 1st mixer 22a. Next, band filtering by the band filter 23a, down conversion by the 2nd mixer 24a, and the like are sequentially performed to generate an analog signal that can be easily processed by the master OFDM unit 30a. The generated analog signal is sent to the master OFDM unit 30a.

  The master OFDM unit 30a sequentially performs A / D conversion, serial-parallel conversion, and fast Fourier transform on the analog signal sent from the tuner unit 20a to obtain a plurality of symbols.

  On the other hand, the signal received by the slave antenna 10b is sent to the tuner unit 20b. In the tuner unit 20b, a signal (OFDM signal) in a desired frequency band is taken out by the UHF / VHF tuning circuit 21b, and then the phase tuning of the OFDM signal is performed by the PLL 70b and the 1st mixer 22b. Next, band filtering by the band filter 23b and down-conversion by the 2nd mixer 24b are sequentially performed to generate an analog signal that can be easily processed by the slave OFDM unit 30b. The generated analog signal is sent to the slave OFDM unit 30b.

  The slave OFDM unit 30b sequentially performs A / D conversion, serial-parallel conversion, and fast Fourier transform on the analog signal sent from the tuner unit 20b to obtain a plurality of symbols. Then, the plurality of symbols are sent to the master OFDM unit 30a.

  The master OFDM unit 30a combines a plurality of symbols decoded by the master OFDM unit 30a and a plurality of symbols sent from the slave OFDM unit 30b to obtain a symbol with little deterioration. Then, the plurality of symbols are returned to single carrier data. Through the above procedure, video information that is single carrier data is decoded. This video information is an MPEG format data stream. Next, the decoded video information is sent to the MPEG unit 50.

  The MPEG unit 50 converts the video information into a video signal such as an analog video signal and an audio signal, and sends the video signal to the video switch 60.

  Subsequently, an analog broadcast reception procedure will be described.

  Signals received by the analog antennas 11 a to 11 d are sent to the analog signal changeover switch 83. The analog signal changeover switch 83 sends only the signal received by any one of the analog antennas 11a to 11d to the tuner unit 20b. Note that the ATV diver control unit 82 selects which signal from the analog antennas 11a to 11d is sent to the tuner unit 20b. The ATV diver controller 82 switches the antenna connected to the tuner unit 20b when the output level of the ATV demodulator 81 (described later) falls below a predetermined reference value.

  A three-way selector switch 84 is disposed between the analog signal selector switch 83, the slave antenna 10b, and the tuner unit 20b. The three-way selector switch 84 selectively sends either the analog broadcast signal output from the analog signal selector switch 83 or the digital broadcast signal output from the slave antenna 10b to the tuner unit 20b. Note that whether an analog broadcast signal or a digital signal is sent to the tuner unit 20b is selected by a microcomputer (not shown).

  In the tuner unit 20b, a signal of a desired frequency band is taken out by the UHF / VHF tuning circuit 21b, and then phase tuning is performed by the PLL 70b and the 1st mixer 22b. The output of the first mixer 22b is sent to the ATV video filter 25 and the ATV audio filter 26. The ATV video filter 25 and the ATV audio filter 26 perform filtering of the video signal and the audio signal, respectively, and send them to the ATV demodulator 81.

  The ATV demodulator 81 down-converts the ATV video filter 25 and the ATV audio filter 26 to generate a video signal and an audio signal such as an analog video signal. This generated signal is sent to the video switch 60.

  A monitor and a speaker (not shown) are connected to the video switch 60. The video changeover switch outputs either the video signal and audio signal sent from the ATV unit 81 or the video signal and audio signal sent from the MPEG unit 50 to a monitor and a speaker. Can watch moving images. Note that a microcomputer (not shown) selects which of the ATV unit 81 and the MPEG unit 50 outputs the video signal and the audio signal to the monitor and the speaker.

  In the present embodiment, an unillustrated microcomputer selectively selects an analog television broadcast received by the analog antennas 11a to 11d and a digital television broadcast received by the master / slave antennas 11a and 11b in a good reception state. It has come to be watched. The broadcast switching procedure by the microcomputer will be described below. FIG. 2 is a flowchart of a broadcast switching routine executed by the microcomputer. This routine is executed simultaneously with the activation of the receiving apparatus 100. When this routine starts, step S101 is first executed. When the receiving apparatus 100 is activated, a signal received by the slave antenna 10b is sent to the tuner unit 20b.

In step S101, the BER (bit error rate) of the symbols synthesized by the master side OFDM unit 30a is calculated. Here, when the BER exceeds a certain standard (for example, 10 ⁻² ), it is determined that the signal is greatly deteriorated. If the state where the BER exceeds a certain standard continues for a certain time (for example, 3 seconds), the process proceeds to step S102. If it is less than a certain time that the BER is below a certain standard or the BER is above the certain standard, step S101 is continued. That is, step S101 is a step of waiting until a state in which the BER exceeds a certain standard continues for a certain time.

  In step S102, various settings are performed so that the tuner unit 20b can process an analog television broadcast signal. Specifically, the frequency division ratio input to the PLL 70b and the frequency band of the tuning circuit 21b are changed. Further, the three-way selector switch 84 is switched so that the output of the analog signal selector switch 83 is input to the tuner unit 20b. From this time point, the ATV demodulator 81 starts to send a video signal and an audio signal to the video switch 60. From this point onward, the master side OFDM unit processes only a signal obtained from the master antenna 10a via the tuner unit 10a. Next, the process proceeds to step S103.

  In step S103, the channel of the analog television broadcast is selected to be the same channel as the digital television broadcast received before step S102. This channel selection is carried out by referring to a table in which the same series of digital television broadcasts and analog television broadcasts are stored. Next, the process proceeds to step S104.

  In step S104, the microcomputer acquires the AGC (auto gain control) output of the tuner unit 20b and checks the AGC level. The AGC level is an index indicating the electric field strength of the received signal, and the electrolytic strength increases as the AGC level increases. That is, the low AGC level of the tuner unit 20b means that the radio wave received by the analog antenna is weak and therefore contains a lot of noise components. If the AGC level exceeds the predetermined reference value in step S104 (S104: YES), the process proceeds to step S105.

  In step S105, the microcomputer controls the video changeover switch 60 and outputs the output of the ATV demodulator 81 to the monitor and the speaker. Next, the process proceeds to step S106.

  In step S106, the BER of the symbol generated by the master side OFDM unit 30a is calculated. If the state where the BER is below a certain standard continues for a certain time (for example, 3 seconds), the process proceeds to step S107. If it is less than the predetermined time that the BER is above the certain reference or the BER is below the certain reference, step S106 is continued. That is, step S106 is a step of waiting until a state in which the BER is below a certain standard continues for a certain time.

  In step S107, various settings are performed so that the tuner unit 20b can process a digital television broadcast signal. Specifically, the frequency division ratio input to the PLL 70b and the frequency band of the tuning circuit 21b are changed. Further, the three-way selector switch 84 is switched so that the output of the slave antenna 10b is input to the tuner unit 20b. From this point, the slave-side OFDM unit 30b starts to send a video signal and an audio signal to the video switch 60. From this point onward, the master-side OFDM unit 30a performs combining diversity. Next, the process proceeds to step S108.

  In step S108, the microcomputer controls the video changeover switch 60 and outputs the output of the MPEG unit 50 to the monitor and the speaker. Next, the process returns to step S101.

  On the other hand, in step S104, if the AGC level is lower than the predetermined reference value in step S104 (S104: NO), the process proceeds to step S111. In step S111, a receivable analog television broadcast station is searched. Search results are displayed on the monitor. Next, the process proceeds to step S112.

  In step S112, the user of the receiving apparatus 100 operates the receiving apparatus 100 to select a desired broadcast station from the search result of step S111 or to continue to watch digital television broadcasting (that is, digital television). Wait until the strength of the broadcast signal is restored. If the user selects to watch another analog television broadcasting station (S112: YES), the process proceeds to step S113.

  In step S113, the microcomputer tunes the channel to the broadcasting station selected in step S112, then controls the video switch 60, and outputs the output of the ATV demodulator 81 to the monitor and speaker. Next, the process proceeds to step S114.

  In step S114, the channel of the digital television broadcast is selected to be the same series as the digital television broadcast received in step S113. In this way, when the strength of the digital television broadcast signal is restored, the digital television broadcast station that is broadcasting the same program as the analog television broadcast program that has been viewed up to now is switched to. Become. Next, the process proceeds to step S106.

  On the other hand, when the user selects to continue viewing the digital television broadcast in step S112 (S112: NO), the process proceeds to step S121. In step S121, various settings are performed so that the tuner unit 20b can process a digital television broadcast signal. Specifically, the frequency division ratio input to the PLL 70b and the frequency band of the tuning circuit 21b are changed. Further, the three-way selector switch 84 is switched so that the output of the slave antenna 10b is input to the tuner unit 20b. From this point, the slave-side OFDM unit 30b starts to send a video signal and an audio signal to the video switch 60. From this point onward, the master-side OFDM unit 30a performs combining diversity. Next, the process returns to step S101.

  By executing the above routine, when the strength of the digital television broadcast signal is reduced when viewing the digital television broadcast, the channel is automatically switched to an analog television broadcast station that is broadcasting the same program. Next, when the strength of the digital television broadcast signal is restored, the channel is automatically switched to the digital television broadcast station.

It is a figure showing the schematic structure of the television broadcast receiver of embodiment of this invention. 4 is a flowchart of an antenna switching routine according to an embodiment of the present invention.

Explanation of symbols

10a Master antenna 11a, 11b Analog antenna 11c, 11d Analog antenna 10b Slave antenna 20a Master side tuner unit 21a, 21b Tuning circuit 22a, 22b 1st mixer 23a, 23b Band filter 24a, 24b 2nd mixer 25 Video filter for ATV 26 Audio for ATV Filter 20b Slave side tuner unit 30a Master OFDM unit 30b Slave OFDM unit 40 Microcomputer 50 MPEG unit 60 Video switch 70a, 70b PLL
81 ATV unit 82 ATV diver control unit 83 Analog signal changeover switch 84 Three-way changeover switch 100 Digital television broadcast receiver

Claims (11)

A first antenna for receiving digital broadcasts;
A second antenna for analog broadcast reception;
A tuning circuit for tuning a signal received by the first or second antenna;
A changeover switch for selectively inputting only a signal received by one of the first and second antennas to the tuning circuit;
A digital / analog shared broadcast receiving apparatus.   The receiving device selects which of the signals received by the first and second antennas is input to the tuning circuit based on the reception level of the signals received by the first and second antennas. 2. The digital / analog shared broadcast receiving apparatus according to claim 1, further comprising a control unit.   The digital / analog shared broadcast receiving apparatus according to claim 2, wherein the digital broadcast program received by the first antenna includes the same content as the analog broadcast program received by the second antenna. A terrestrial television receiver mounted on a moving body,
The system has at least two systems including an antenna, a tuner, and a digital demodulator, performs video / audio output of digital television broadcast by combining diversity, and one system out of a plurality of systems of the digital television broadcast demodulator includes: A digital television broadcast demodulator configured as a shared tuner in which one tuner is also used for analog television broadcasting;
An analog television broadcast demodulator that demodulates terrestrial analog television broadcast and outputs video and audio;
The signal to be input to the shared tuner is switched between an analog television broadcast signal and a digital television broadcast signal according to the strength of the reception level of the digital television broadcast, and the analog television broadcast signal is sent to the shared tuner unit. Is input by the analog television broadcast demodulator, and when a digital television broadcast signal is input to the shared tuner, the digital television broadcast demodulator Switching control means for controlling the demodulation of the television broadcast;
A terrestrial television receiver. A reception antenna for analog television broadcasting;
The switching control means connects an antenna in the one system to the shared tuner when demodulating the digital television broadcast, and an analog television receiving antenna when demodulating the analog broadcast. Controlling to connect to the shared tuner;
The terrestrial digital television receiver according to claim 4. The reception level of the digital television broadcast is detected in any system other than the one system having the shared tuner in the digital television broadcast demodulation unit;
A terrestrial digital television receiver according to claim 5 or 6.   5. The switching control unit performs switching from reception of the digital television broadcast to reception of analog television broadcast when the reception level falls below a predetermined demodulation limit for a predetermined time. The terrestrial digital television receiver according to any one of claims 6 to 6.   The switching control means performs switching from reception of the analog television broadcast to reception of a digital television broadcast when the reception level exceeds a predetermined demodulation limit for a certain time. The terrestrial digital television receiver according to claim 7.   The switching control means, when receiving the analog television broadcast, controlling to receive an analog television broadcast of the same affiliated station as the affiliated station received in the immediately preceding digital television reception; The terrestrial digital television receiver according to any one of claims 4 to 8, wherein the terrestrial digital television receiver is provided.   The switching control means, when receiving the analog television broadcast, performs control so as to receive the analog television broadcast of the same affiliated station as the affiliated station received in the immediately preceding digital television reception, If it is determined that there is no analog television broadcast of the same affiliated station, further searching for an analog television broadcast of a receivable broadcast station other than the affiliated station and receiving a receivable broadcast; The terrestrial digital television receiver according to any one of claims 4 to 9, wherein   The terrestrial digital television receiver according to any one of claims 4 to 10, wherein the digital demodulator is configured as an OFDM demodulator that performs OFDM demodulation.

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