JP2511034B2 - Television receiver - Google Patents

Description

TECHNICAL FIELD The present invention relates to a television receiver mounted on a mobile body.

[Conventional technology]

In an on-vehicle television receiver, the received electric field strength changes due to changes in the surrounding environment accompanying the movement of the vehicle,
When this becomes weak, an image with significantly deteriorated S / N is displayed on the screen.

As a countermeasure against this, a field memory is provided, and when the received electric field strength is high, rewriting is always performed in this field memory. When the received electric field strength becomes weak and the image quality deteriorates, one field video signal is repeatedly read from this field memory. , A television receiver that displays still images has been proposed (Shokai 60-1121).
No. 50).

[Problems to be solved by the invention]

By the way, in the above-mentioned conventional technology, when the received electric field strength becomes weak, the writing operation of the field memory is stopped, and at the same time, the still image signal from this field memory is supplied to the display to perform the still image display. Because of this, there are the following problems.

First, the apparent S / N due to the video being a still image
Deterioration occurs. When the received video signal is stored in the field memory and reproduced as a still image on the screen, the viewer feels that the screen becomes noisey. In the case of a moving image, noise was randomly generated on the screen, so the noise was not noticeable, but when the image is a still image, the noise is also fixed and is noticeable. Therefore, when the received electric field strength is the same when displaying a moving image and when displaying a still image, there is a problem that the evaluation of a still image is poor, and when the still image and the moving image are switched at a certain speed, Feels uncomfortable.

Next, there is a countermeasure when the received electric field strength is in a medium or weak electric field area. When mounted on a moving body, the received electric field naturally changes widely from a strong electric field to a weak electric field. Therefore, in order to make the noise of the still image inconspicuous, it is conceivable to take a large reference electric field intensity to be compared with the received electric field intensity and obtain a still image with a relatively strong received electric field intensity.
There is a problem that a moving image cannot be viewed at all in a medium and weak electric field. As a measure against this, a switch for canceling still images,
Manual setting of the reference electric field strength by the viewer may be the installation of a rum, etc., but any of these measures will bother the viewer.

The object of the present invention is to eliminate such problems and to reduce the S / S
An object of the present invention is to provide a television receiver in which N can be made to be about the same as S / N of a moving image and a moving image can be displayed even in a weak and weak receiving electric field.

[Means for solving problems]

In order to achieve the above object, the present invention compares the received electric field strength with a first reference electric field strength, sets writing start and stop of the field memory according to the comparison result, and sets the received electric field strength. A second weaker than the first reference electric field
The reference electric field strength is compared with the reference electric field strength and the moving image display or the still image display is selected according to the comparison result.

[Action]

When the received electric field strength is stronger than the first and second quasi electric field strengths, the video signal output from the demodulator is supplied to the display to display a moving image, and the contents of the field memory are constantly updated with new video information. Will be updated.

When the received electric field strength is between the first and second reference electric field strengths, the video signal output from the demodulator is supplied to the display and a moving image is displayed, but the updating of the contents of the field memory is stopped. .

When the received electric field strength is weaker than the first and second reference electric field strengths, the video signal stored in the field memory is supplied to the display while the content update of the field memory is stopped, and a still image is displayed. .

By the above-described series of operations, an apparent S / N equivalent to that of a moving image can be obtained even when a still image is displayed, and further, a moving image can be displayed in a weak electric field area as compared with the conventional technique.

〔Example〕

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

1 is a block diagram showing an embodiment of a television receiver according to the present invention, in which 1 is an antenna, 2 is a demodulator, 3
Is an A / D converter, 4 is a field memory, 5 is a D / A converter, 6 is a signal processing circuit, 7 is a display, 8 is an audio reproduction circuit, 9 is a speaker, 10 is a read timing generator, and 11 is write timing generation. , 12 is a signal control circuit, 13 is a comparator, 14 is a reference voltage generator, 15 is a comparator, 16
Is a reference voltage generator, and 17 is a changeover switch.

In the figure, the radio wave received from the antenna 1 is input to the demodulator 2, selected and demodulated, and output as an audio signal and a video signal. The audio signal output from the demodulator 2 is amplified by the audio reproduction circuit 8 and supplied to the speaker 9. The video signal output from the demodulator 2 is input to the A / D converter 3, converted into a quantized digital video signal, and output. This digital video signal is supplied to the field memory 4 on the one hand and to the changeover switch 17 on the other hand. The other input of the changeover switch 17 is the output signal of the field memory 4, and the digital video signal selected by the changeover switch 17 is restored to the original analog video signal by the D / A converter 5 and then processed. The circuit 6 converts the information into luminance information, color information, and synchronization information and supplies the information to the display 7.

The write timing signal and the read timing signal required in the field memory 4 are generated by the read timing generator 10 and the write timing generator 11 using the vertical synchronizing signal and the horizontal synchronizing signal extracted by the signal processing circuit 6. The read timing generator 10 creates a timing for reading data from the field memory 4 from a synchronization signal and sends the timing to the field memory 4. Further, the write timing generator 11 creates a timing for writing data in the field memory 4 from a synchronization signal and sends it to the signal control circuit 12.

In this embodiment, a means for detecting the input electric field strength of the antenna is provided, which includes the gain of the intermediate frequency automatic gain adjustment circuit (hereinafter, IF AGC circuit) used in the demodulator 2. It uses the control voltage. The AGC circuit has a reverse type in which the gain increases as the gain control voltage increases and decreases as the gain control voltage decreases, and a gain decreases as the gain control voltage increases and increases as the gain control voltage decreases. There is a howard type to do, but here we use the howard type.

Therefore, since the gain control voltage of the IF AGC circuit is used as a means for detecting the input electric field strength, the two reference electric field strength generators may be set to voltages corresponding to the gain control voltage of the IF AGC circuit. The voltage V _a of the reference voltage generator 14 is set in the vicinity of 46 dBμ at which the input electric field strength is the allowable limit in screen evaluation. The voltage V _b of the reference voltage generator 16 is provisionally set near 36 dBμ, which is the practical limit of the input electric field strength in screen evaluation.
Then, when a moving image or a still image is output later, fine adjustment is performed so that the apparent S / Ns become equal.

The comparator 15 compares the reference voltage V _b output by the reference voltage generator 16 with the gain control voltage v output by the IF AGC circuit in the demodulator 2. If the gain control voltage v is higher than the reference voltage _Vb , the changeover switch 17 is closed on the A / D converter 3 side to display a moving image. The reference voltage V _b from a reference voltage generator 16 is higher than the gain control voltage v, the selector switch 17 to the image output still images close to the field memory 4 side.

The comparator 13 compares the reference voltage V _a output from the reference voltage generator 14 with
Compare with the gain control voltage v from the IF AGC circuit. If this gain control voltage v is higher than the reference voltage V _a ,
The signal control circuit 12 supplies the output signal of the write timing generator 11 to the write timing input terminal of the field memory 4. If the reference voltage V _a from the reference voltage generator 14 is higher than the gain control voltage v, the signal control circuit 12 prevents the output signal of the write timing generator 11 from being supplied to the field memory 4, Stop the write operation.

Through the series of operations described above, the viewer can watch the moving image even in a place where the received electric field strength is weaker than that of the conventional technology, and the screen displayed as a countermeasure against folding when the received electric field strength is very weak is noisy. You can appreciate a few beautiful still images.

〔The invention's effect〕

As described above, according to the present invention, a moving image can be viewed even when the received electric field strength is weaker than that in the conventional technique, and apparent S / N deterioration when displaying a still image can be suppressed. That is, even if a moving image and a still image are repeated, an excellent effect that the S / N-satisfactory image can be viewed even when the received electric field strength is weak without causing the viewer to feel uncomfortable.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a television receiver according to the present invention. 2 ... Demodulator, 3 ... A / D converter, 4 ... Field memory, 5 ... D / A converter, 7 ... Display, 10 ... Read timing generator, 11 ... Write timing generator, 12 ...... Signal control circuit, 13 …… Comparator, 14 …… Reference voltage generator, 15 …… Comparator, 16 …… Reference voltage generator, 17 …… Change switch.

Claims (1)

(57) [Claims] 1. A field memory that stores a video signal of a desired channel that is demodulated and demodulated by a demodulator, a video signal output from the demodulator, and a still image signal read from the field memory. In a television receiver provided with a changeover switch for selecting and supplying to a display, a first means for judging the electric field strength of the desired channel by a first reference voltage, and a second means lower than the first reference voltage.
Second means for judging the electric field strength of the desired channel by the reference voltage of the second means, and starting and stopping the write operation of the field memory based on the judgment result of the first means. A television receiver configured to control the changeover switch based on a determination result.