JPH0951486A - On-vehicle television receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To block a disturbed reception image/sound output by forcibly resetting RAMs when an electric field strength of a received signal is decreased more than a prescribed value. SOLUTION: When a control section 10 detects it that an electric field strength of an MPEG signal received by an MPEG signal reception section 1 is less than a prescribed value, the control section 1 forcibly resets a 1st RAM 3a ancillary to an MPEG demultiplexer 3, a 2nd RAM 4a ancillary to an MPEG video decoder 4, and a 3rd RAM 5a ancillary to an MPEG audio decoder in the order of the 3rd, 2nd and 1st RAMs or the 3rd and 2nd RAMs simultaneously and then the 1st RAM. Since various data stored in the 1st to 3rd RAMs are cleared, even when the electric field strength of the MPEG signal is rapidly very weak, the data at that time are properly cleared from the 1st to 3rd RAMs and display of a disturbed image on an image display section or a sound output of hard of hearing by an audio reproduction section is not caused.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an in-vehicle television device, and more particularly, to preventing a display image from being significantly disturbed when the electric field strength of the television signal is drastically lowered at the time of receiving an MPEG television signal. The present invention relates to a vehicle-mounted television device provided with means.

[0002]

2. Description of the Related Art Recently, MPEG2 (Moving Pic)
Television broadcasting using compressed digital image data and compressed digital audio data according to the ture Experts Group 2) system has started overseas.

Here, FIG. 3 is a block diagram showing an example of a television apparatus capable of receiving a television broadcast signal according to the MPEG2 system.

In FIG. 3, 31 is a signal receiving section, 31a.
Is a receiving antenna, 32 is a digital modulation decoder, 32a
Is a memory attached to the digital modulation decoder 32, 33 is an MPEG demultiplexer, 33a is a first memory attached to the MPEG demultiplexer 33, 34 is an MPEG video decoder, 34a is a second memory attached to the MPEG video decoder 34, and 35 is An MPEG audio decoder, 35a is a third memory attached to the MPEG audio decoder 35, 36 is a first digital-analog converter (D / A), and 37 is a second digital-analog converter (D).
/ A), 38 is an image display unit, 39 is an audio reproducing unit,
Reference numeral 40 is a control unit.

The input of the signal receiving unit 31 is connected to the receiving antenna 31a, and the output is connected to the input of the digital modulation decoder 32. MPEG demultiplexer 3
3, the input is connected to the output of the digital modulation decoder 32, and the output is connected to the respective inputs of the MPEG video decoder 34 and the MPEG audio decoder 35. Digital-
The input of the analog converter 36 is connected to the output of the MPEG video decoder 34, and the output is connected to the input of the image display unit 38. The input of the digital-analog converter 37 is connected to the output of the MPEG audio decoder 35, and the output is connected to the input of the audio reproducing unit 39. Also,
The controller 40 is connected to the signal receiver 31 and the MPEG demultiplexer 33, respectively.

Here, FIG. 4 shows such MPEG2.
In the television broadcasting signal according to the system, MPEG2
It is explanatory drawing which shows an example of the hierarchical structure of the compressed digital image data by a format.

As shown in FIG. 4, the compressed digital image data includes a sequence layer and a GOP (Group of Picture).
It has a three-layer structure of a layer and a picture layer. In the sequence layer, many sequences are continuously formed, and each sequence is provided with a sequence header (HD) at the beginning and then a plurality of GOPs.
Are consecutively provided, and finally, a sequence end code is provided, and these constitute one sequence. In addition, the GOP layer starts with a GOP header (H
D) is provided, followed by a plurality of three pictures I, P, B, preferably 15 pictures I ₃ , B ₁ , B.
₂ , P ₆ , B ₄ , B ₅ , P ₉ , B ₇ , B ₈ , P ₁₂ ,
B ₁₀ , B ₁₁ , P ₁₅ , B ₁₃ , and B ₁₄ are provided, and these constitute 1 GOP. Further, the picture layer is provided with a picture header (HD) at the beginning,
After that, coded data is provided, and these form one picture. In this case, I,
In each of the P and B pictures, the I picture is an intra-frame coded image and can be independently decoded by itself, and the P picture is an inter-frame predictive coded image and the latest Past I picture and P
The B picture is a picture that is predictively coded on the basis of a picture, and is a picture peculiar to MPEG. It has been interframe predictive coded.

The three types of 15 pictures of I, P and B are B ₁ , B ₂ , I ₃ , B ₄ , B ₅ , P ₆ , B ₇ , B.
_{8, P 9, B 10,} B 11, intended to be supplied in the order of _{P 12, B 13, B 14} , P 15, if the MPEG decoding is carried out, but I ₃ picture is MPEG decoded by themselves , P ₆ picture is MPEG decoded by using MPEG decoded I ₃ picture, and P ₉ picture is MP decoded.
MPEG decoding is performed using the EG-decoded P ₆ picture, and P ₁₂ picture is MPEG-decoded P ₉ picture.
MPEG decoded using pictures, P ₁₅ picture is MPE using MPEG decoded P ₁₂ pictures
G-decoded. Further, the B ₁ picture and the B ₂ picture are both MPEG-decoded using the MPEG-decoded I ₃ picture and the MPEG-decoded P ₁₅ picture in the immediately preceding GOP, and the B ₄ picture and the B ₄ picture
_{All 5} pictures are MPEG-decoded I ₃
MPE using picture and decoded P ₆ picture
Is G decoded, in the same manner, B ₇ pictures, B ₈
Pictures, B ₁₀ pictures, B ₁₁ pictures, B ₁₃ pictures, and B ₁₄ pictures are also MPEG decoded.

The television apparatus shown in FIG. 3 generally operates as follows.

When a television broadcasting signal according to the MPEG2 system is received by the signal receiving unit 31 via the receiving antenna 31a, the digital modulation decoder 32 digitally modulates and decodes the television broadcasting signal received by the signal receiving unit 31, Play back compressed digital image data and compressed digital audio data. Next, the MPEG demultiplexer 33 separates the reproduced compressed digital image data and compressed digital audio data, and supplies the compressed digital image data to the MPEG video decoder 34 and the compressed digital audio data to the MPEG audio decoder 35, respectively. Subsequently, the MPEG video decoder 34 MPEG-decodes the supplied compressed digital image data in the manner described in the explanatory diagram of FIG. 4, and decodes the decoded video data as a first digital-image.
Meanwhile, the MPEG audio decoder 35 supplies the compressed digital audio data, which is also supplied to the MPEG audio decoder 35, to the analog converter 36 in a manner similar to that described in the explanatory diagram of FIG. The decoded audio data is supplied to the second digital-analog converter 37. At this time, the first digital-analog converter 36 performs digital-analog conversion on the decoded video data and supplies it to the image display section 38 to display the required image on the image display section 38, and also to perform the second digital-analog conversion. Analog converter 3
Reference numeral 7 digital-analog converts the decoded audio data and supplies it to the audio reproducing section 39, and the audio reproducing section 39 reproduces the required audio output in synchronization with the image display.

[0011]

When a television broadcast signal complying with the MPEG2 system is received by a vehicle-mounted television device, the television broadcast signal complying with the MPEG2 system is a digital broadcast signal, and therefore the digital modulation decoder 3
The digital modulation decoding of the television broadcast signal in 2 is performed by the memory 3 attached to the digital modulation decoder 32.
Decoding using 2a is performed, and M is used for demultiplexing the compressed digital video data and the compressed digital audio data in the MPEG demultiplexer 33.
First memory 33 attached to PEG demultiplexer 33
demultiplexing using a is performed, and MPE
For decoding the compressed digital video data in the G video decoder 34, decoding using the second memory 34a attached to the MPEG video decoder 34 is performed, and MP decoding is performed.
Decoding of the compressed digital audio data in the EG audio decoder 35 is performed using the third memory 35a attached to the MPEG audio decoder 35.

In this way, the in-vehicle television apparatus transmits the television broadcast signal according to the MPEG2 system to the MPEG2 system.
From the reception of the television broadcast signal complying with the system by the signal reception unit 31 to the display of an image corresponding to the television broadcast signal on the image display unit 38, and the audio reproduction of the sound corresponding to the television broadcast signal. There is a time delay before being reproduced by the section 39, and both the image displayed on the image display section 38 and the sound reproduced by the audio reproducing section 39 correspond to the transmitted television broadcast signal. The image and sound are not displayed and reproduced in real time.

In general, a vehicle-mounted broadcast signal receiving device such as a vehicle-mounted television device has a vehicle entering a tunnel or a large broadcast signal regardless of whether the source of the broadcast signal is a broadcasting satellite or a terrestrial broadcasting station. When traveling near an obstacle, a weak reception electric field strength state in which the required C / N (carrier to noise ratio) is far below the received broadcast signal may occur. .

By the way, in a known vehicle-mounted television device which receives a television broadcast signal according to the MPEG2 system, when the weak reception electric field strength state is reached, the display of the image being displayed on the image display section 38 is only interrupted. Instead, the MPEG video decoder 34 uses a specific picture (I
When the received electric field strength state suddenly becomes weak while decoding (picture), a disturbed image is displayed on the image display unit 38, and the MPEG audio decoder 35 also receives the received electric field strength state. When the sound becomes suddenly weak, there is a problem that an uncomfortable sound is output from the audio reproducing unit 39.

In addition, in a known vehicle-mounted television device that receives a television broadcast signal according to the MPEG2 system, when the reception state of the broadcast signal leaves the weak electric field strength state and is restored to the normal reception electric field strength state. , Number 100
Except when the broadcast signal is cut off for a short period up to about ms, the previously received data is stored in the second memory 34a attached to the MPEG video decoder 34 or the third memory 35a attached to the MPEG audio decoder 35. Since it is stored, when the MPEG video decoder 34 decodes the newly supplied P picture using the already stored I picture or P picture, the new I picture is decoded for a while. Until then, there is a problem in that a distorted image is still displayed on the image display unit 38 and an uncomfortable sound is output from the audio reproducing unit 39.

The present invention solves the above problems,
An object of the present invention is to provide an in-vehicle television device which prevents occurrence of disturbance in a display image and output sound when the received electric field strength largely changes during reception of a television broadcast signal according to the MPEG2 system. It is in.

[0017]

To achieve the above object, the present invention provides an MPEG signal receiving section, an MPEG demultiplexer with a first RAM, an MPEG video decoder with a second RAM, and a third RAM. Attached MPEG audio decoder, video signal playback unit,
In a vehicle-mounted television device including an audio signal reproducing unit and a control unit for controlling the entire device, first to third reset switches are connected to the first to third RAMs, respectively, and the control unit is configured to control the MPEG signal. When it is detected that the electric field strength of the MPEG reception signal received by the receiving unit is lower than a predetermined value, the first to third reset switches are operated in time sequence to force the first to third RAMs in order. A means for resetting is provided.

[0018]

According to the above-mentioned means, when the control section detects that the electric field strength of the MPEG reception signal received by the MPEG signal reception section is lower than the predetermined value, the first RAM and the MPEG video attached to the MPEG demultiplexer. The second RAM attached to the decoder and the third RAM attached to the MPEG audio decoder are the third RAM, the second RAM, and the first RAM.
Forcibly reset in the order of RAM, or the third
Since the RAM and the second RAM are simultaneously reset and the first RAM is forcibly reset to clear various data stored in the first RAM to the third RAM, the electric field strength state of the MPEG reception signal is sharply increased. Even when the electric field strength becomes weak, the data when the electric field strength becomes weak is appropriately cleared from the first RAM to the third RAM, so that a distorted image is displayed on the image display unit or an uncomfortable voice is displayed on the audio reproducing unit. Is not output, and when the electric field strength of the MPEG reception signal recovers from the weak state to the normal state, the first RAM to the third RA
MPEG demultiplexing, MPEG video decoding and MPEG based on new data stored in M
Since the audio decoding is performed, the distorted image is not displayed on the image display unit and the uncomfortable sound is not output on the audio reproducing unit for a while.

[0019]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a vehicle-mounted television device capable of receiving a television broadcast signal according to the MPEG2 system of the present invention, and FIG.
FIG. 8 is an operation explanatory diagram showing an example of a forced reset order of the first to third RAMs in the embodiment shown in FIG.

In FIG. 1, 1 is a signal receiving unit (MPEG
(Signal receiver) 1a is a receiving antenna, 2 is a digital modulation decoder, 2a is a RAM (memory) attached to the digital modulation decoder 32, 3 is an MPEG demultiplexer, 3
a is a RAM (first memory) attached to the MPEG demultiplexer 3, 4 is an MPEG video decoder, 4a is an MP
RAM (second memory) attached to the EG video decoder 4, 5 is an MPEG audio decoder, 5a is MPE
RAM (third memory) attached to the G audio decoder 5, 6 is a first digital-analog converter (D / A),
7 is a second digital-analog converter (D / A), 8 is an image display unit, 9 is an audio reproducing unit, 10 is a control unit, 11
Is a reset switch of the first memory 3a (first reset switch), 12 is a reset switch of the second memory 4a (second reset switch), and 13 is a reset switch of the third memory 5a (third reset switch).

The input of the signal receiving unit 1 is connected to the receiving antenna 1a, and the output is connected to the input of the digital modulation decoder 2. The MPEG demultiplexer 3 has an input as an output of the digital modulation decoder 2 and an output as MPEG.
It is connected to each input of the video decoder 4 and the MPEG audio decoder 5. The input of the first digital-analog converter 6 is the output of the MPEG video decoder 4,
The outputs are connected to the inputs of the image display unit 8, respectively. Second
The input of the digital-analog converter 7 is connected to the output of the MPEG audio decoder 5, and the output is connected to the input of the audio reproducing unit 9. The controller 10 is also connected to the signal receiver 1 and the MPEG demultiplexer 3, respectively. The first reset switch 11 includes the first memory 3a.
Is connected to the control unit 10, and the control unit 10 forcibly resets the first memory 3a. The second reset switch 12 is connected to the second memory 4a and the control unit 10, and the control unit 10 forcibly resets the second memory 4a. The third reset switch 13 is connected to the third memory 5a and the control unit 10, and the control unit 10 controls the third memory 5a.
Forcibly reset a.

The on-vehicle television set according to this embodiment having the above-described structure operates as follows.

When a television broadcast signal according to the MPEG2 system is received by the signal receiving unit 1 via the receiving antenna 1a, the control unit 10 always detects the received electric field strength of the broadcast signal and reproduces the received broadcast signal. It is determined whether or not the normal (medium) received electric field strength has been reached.

In this case, it is said that the electric field strength of the broadcast signal received by the control unit 10 has reached a medium level without any cause of failure that attenuates the television broadcast signal received by the in-vehicle television device. Once a decision is made,
The control unit 10 sets the vehicle-mounted television device to the broadcast signal receiving operation in the normal mode without operating the first reset switch 11, the second reset switch 12, and the third reset switch 13. When the vehicle-mounted television device is set to the normal mode, the digital modulation decoder 2 digitally modulates and decodes the television broadcast signal received by the signal receiving unit 1, and reproduces compressed digital image data and compressed digital audio data. Next, the MPEG demultiplexer 3 separates the reproduced compressed digital image data from the compressed digital audio data, and supplies the compressed digital image data to the MPEG video decoder 4 and the compressed digital audio data to the MPEG audio decoder 5. Then, the MPEG video decoder 4
MPEG-decodes the supplied compressed digital image data, supplies the decoded video data to the first digital-analog converter 6, and the MPEG audio decoder 5 similarly compresses the compressed digital image data supplied to the MPEG audio decoder 5. The audio data is MPEG-decoded and the decoded audio data is supplied to the second digital-analog converter 7. Further, the first digital-analog converter 6 digital-analog converts the decoded digital image data and supplies it to the image display unit 8, and the image display unit 8 supplies the supplied analog image data to the NTS.
After being converted into image data according to the C system, the image data is supplied to a display (not shown) to display an image corresponding to the received broadcast signal. In addition, the second digital-analog converter 7
Supplies the decoded digital audio data to an analog-to-analog converter and supplies it to the audio reproducing unit 9. The audio reproducing unit 9 amplifies the supplied analog audio signal and then supplies the amplified analog audio signal to a speaker (not shown) or the like. Then, an audio signal corresponding to the received broadcast signal is emitted.

On the other hand, because the car has entered a tunnel or the like or is under the influence of a large radio wave obstacle, a cause of an obstacle that attenuates the received television broadcast signal occurs, and the broadcast signal received by the control unit 10 is generated. When it is determined that the electric field strength of (1) does not reach the middle level (weak reception electric field strength state), the control unit 10 causes the first reset switch 11, the second reset switch 12, and the third reset switch 13 to operate. Are operated in the order as described below, and the on-vehicle television device is switched to the setting of the broadcast signal receiving operation in the emergency mode. When the vehicle-mounted television device is switched to the emergency mode setting, as shown in FIG. 2, first, the third memory 5a is operated by the operation of the third reset switch 13 within (1/30) seconds from the switching time point. Is forcibly reset, audio mute is performed by a mute circuit (not shown), and at the same time, all audio data stored in the third memory 5a is cleared. At the same time, the B-picture memory (not shown) in the second memory 4a is forcibly reset by the operation of the second reset switch 12, and the second memory 4a
All B pictures stored in are cleared. Next, the P picture memory (not shown) in the second memory 4a is forcibly reset by the operation of the second reset switch 12 within (1/30) to (3/30) seconds from the switching time point. Stored in the second memory 4a.
All pictures are cleared. Then, during (3/30) to (15/30) seconds from the time of switching, the I in the second memory 4a is operated by the operation of the second reset switch 12.
The picture memory (not shown) is forcibly reset, and all the I pictures stored in the second memory 4a are cleared. After that, from the time of switching (15/30)
During 1 to 1 second, the first memory 3a is forcibly reset by the operation of the first reset switch 11, and the compressed digital video data and the compressed digital audio data stored in the first memory 3a are all cleared.

As described above, when the on-vehicle television set is switched to the emergency mode setting, the digital audio data stored in the third memory 5a is immediately cleared and then stored in the first memory 3a. Since the compressed digital audio data that has been recorded is also cleared, the uncomfortable sound is not output from the audio reproducing unit 9, and the digital video data stored in the second memory 4a is a B picture, a P picture, an I picture. The images are cleared in the order of pictures, and then the compressed digital video data stored in the first memory 3a is also cleared, so that the disordered image is not displayed on the image display unit 8.

Further, since the car exits the tunnel or the like and the influence of a large radio wave obstruction is eliminated, the cause of obstruction that attenuates the received television broadcast signal is eliminated,
When the control unit 10 determines that the electric field strength of the received broadcast signal has reached a medium level (returned to the normal electric field strength), the control unit 10 causes the first reset switch 11 and the second reset switch. The operation of the switch 12 and the third reset switch 13 is released, and the in-vehicle television device is set back to the normal mode broadcast signal receiving operation. in this case,
In the vehicle-mounted television device, the broadcast signal receiving operation when set to the normal mode as described above is performed.
The decoding of the compressed digital video data in the PEG video decoder 4 and the decoding of the compressed digital audio data in the MPEG audio decoder 5 are both an I picture or a P picture obtained from a broadcast signal received in a state where the electric field strength is restored to normal. Is used for decoding, so even if it is only temporary,
The disordered image is not displayed on the image display unit 8, and a normal image is displayed. The audio reproducing unit 9 does not output an uncomfortable sound but outputs a normal sound.

As described above, according to the present embodiment, even if the received electric field strength of the broadcast signal is suddenly reduced for some reason, a distorted image is displayed on the image display unit 8 or audio reproduction is performed. The unpleasant sound is not output from the unit 9, and even when the reception electric field strength of the broadcast signal is reduced to the original state, the image display unit 8 displays a distorted image or audio. It is possible to display a normal image and to output a normal sound without causing the reproducing unit 9 to output an uncomfortable sound.

In the above embodiment, when the second memory 4a is forcibly reset by the second reset switch 12, first the B picture memory, then the P picture memory, and finally the The I-picture memory is forcibly reset.
The compulsory reset order of the memory 4a is not limited to this order, and the B picture memory, the P picture memory, and the I picture memory in the second memory 4a are forcibly reset simultaneously by the second reset switch 12. You may do it.

In addition, B, P, I in the third memory 5a
When the memory for each picture is forcibly reset at the same time, the reset timing may be the same as the forcible reset of the third memory 5a. After the forcible reset of the third memory 5a, the first memory 3a is forcibly reset. Before a general reset.

[0032]

As described in detail above, according to the present invention, when the control unit 10 detects that the electric field strength of the MPEG reception signal received by the MPEG signal reception unit 1 is lower than a predetermined value. , MPEG demultiplexer 3
RAM3a attached to the, MPEG video decoder 4
The second RAM 4a attached to the MPEG audio decoder 5, or the third RAM 5a attached to the MPEG audio decoder 5, are forcibly reset in the order of the third RAM 5a, the second RAM 5a, and the first RAM 5a, or the third RAM 5a and the second RAM 4a are simultaneously and then the first RAM 3a is attached. Since it is forcibly reset to clear various data stored in the first to third RAMs 3a to 5a,
Even if the electric field strength state of the MPEG received signal suddenly becomes weak, the data when the electric field strength state becomes weak becomes the first RA.
Since it is appropriately cleared from the M to third RAMs 3a to 5a, the distorted image is not displayed on the image display unit 8 and the audio reproducing unit 9 does not output uncomfortable sound. When the electric field strength recovers from the weak state to the normal state, MPEG demultiplexing, MPEG video decoding, and MPEG audio decoding are performed based on new data stored in the first RAM to the third RAM 3a to 5a. During this period, it is possible to display a normal image and output a normal sound without displaying a distorted image on the image display unit 8 or outputting an uncomfortable sound on the audio reproducing unit 9. There is.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a vehicle-mounted television device capable of receiving a television broadcast signal according to the MPEG2 system of the present invention.

2 is an operation explanatory view showing an example of a reset order of the first to third memories in the embodiment shown in FIG. 1. FIG.

FIG. 3 is a block diagram showing an example of a television device capable of receiving a television broadcast signal according to a known MPEG2 system.

FIG. 4 is an explanatory diagram showing an example of a hierarchical structure of compressed digital image data in the MPEG2 format in a television broadcast signal according to the MPEG2 system.

[Explanation of symbols]

1 signal receiving section (MPEG signal receiving section) 1a receiving antenna 2 digital modulation decoder 2a RAM (memory) attached to digital modulation decoder 32 3 MPEG demultiplexer 3a RAM attached to MPEG demultiplexer 3
(First memory) 4 MPEG video decoder 4a RAM attached to MPEG video decoder 4 (second memory) 5 MPEG audio decoder 5a RAM attached to MPEG audio decoder 5
(3rd memory) 6 1st digital-analog converter (D / A) 7 2nd digital-analog converter (D / A) 8 Image display part 9 Audio reproduction part 10 Control part 11 Reset switch of the 1st memory 3a (First reset switch) 12 Reset switch of second memory 4a (second reset switch) 13 Reset switch of third memory 5a (third reset switch)

Claims (3)

[Claims] 1. An MPEG signal receiving unit, an MPEG demultiplexer having a first RAM, an MPEG video decoder having a second RAM, an MPEG audio decoder having a third RAM, an image display unit, and an audio reproducing unit. A vehicle-mounted television device including a control unit that controls the entire device,
First to third reset switch is connected to each of
The control unit controls the MPE received by the MPEG signal receiving unit.
When it is detected that the electric field strength of the G reception signal is lower than a predetermined value, the first to third reset switches are operated in time sequence to forcibly reset the first to third RAM in order. In-vehicle television device. 2. The forced reset order of the first to third RAMs is first in the third RAM and then in the first RAM.
The vehicle-mounted television device according to claim 1, wherein is the last one. 3. The second RAM is a B picture memory,
It is composed of three memories of P picture memory and I picture memory, a reset switch is connected to each of the three memories, and the control unit controls the electric field strength of the MPEG reception signal received by the MPEG signal reception unit. When it is detected that the value is lower than the predetermined value, the reset switch connected to the B picture memory is first operated, the reset switch connected to the P picture memory is operated next, and finally the reset switch connected to the I picture memory is operated. The vehicle-mounted television device according to claim 1, wherein a switch is operated to forcibly reset the three memories in time sequence.