JPH02228179A - Compatible television receiver - Google Patents

Abstract

PURPOSE:To prevent the degradation of picture on the boundary part due to a burning phenomenon of an image receiving tube by adjusting the boundary part between the image part in the center of a screen and the frame picture in the periphery of the screen. CONSTITUTION:A control voltage generating circuit consisting of a Miller circuit to which monostable multivibrators 27 and 28 having prescribed time constants and a capacitor C4 are connected generates a gradually rising/falling control voltage from the leading edge part to the trailing edge part in a blanking period in accordance with a vertical blanking pulse. This voltage is supplied to the contrast control terminal of a video signal amplifying circuit 22, and the contrast of R, G, and B video signals from a converter is adjusted, and the contrast of the boundary part between the image part in the center of the screen and the frame picture in the periphery of the screen, thus preventing a burning phenomenon of the image receiving tube due to picture signals different in aspect ratio. As the result, the degradation of the picture on the boundary part due to the burning phenomenon is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a compatible television receiver that is compatible with the NTSC system, high-definition television system, and the like.

(Prior Art) Currently, NTSC television broadcasting is being carried out in Japan, and large-screen, high-definition, high-definition television broadcasting is about to begin. In this high-definition television broadcasting, M
US E (Multiple Sub-Nyqui
With the development of the standard sampling encoding system, broadcasting via satellite broadcasting has become possible.

Figure 4 shows the video signal of high-definition television broadcasting (MUSE
signal) and current NTSC broadcasting video signal (NTSC signal)
1 is a block diagram showing a conventional compatible television receiver capable of receiving both.

MUS induced in parabolic antenna 1 for satellite broadcast reception
The E signal is input to the BS tuner 2.

The BS tuner 2 selectively receives the MLJSE signal of a predetermined channel and outputs it to the MUSE decoder 3 or down converter 4. MLJSE decoder 3 is MLJSE
The signal is decoded and output to the switching circuit 5. Further, the down converter 4 converts the MUSE signal into an NTSC signal and outputs it to the switching circuit 5. On the other hand, the NTSC signal induced in the antenna 6 is input to the NTSC receiver 7.

The NTSC receiver 7 selectively receives the NTSC signal of a predetermined channel, processes the video, and outputs it to the switching circuit 5 as well as to the switching circuit 5 via the converter 8 .

The switching circuit 5 includes a MUSE decoder 3 and a down converter 4.
, NTSG receiver 7 and converter 8 are selected and output to a monitor device (hereinafter referred to as CRT) 9. Note that, like the down converter 4, the converter 8 performs image processing for displaying the quality television broadcast and the N5TC television broadcast on the common CRT 9.

In other words, the NTSC signal and MLJSE signal are as shown in Fig. 5 (
As shown in FIG. 5(a) and (b), the aspect ratios are different, and the INTSC signal shown in FIG. 5(a) has an aspect ratio of 4:3.
, the MCl5E signal shown in FIG. 5(b) has an aspect ratio of 16:9. Therefore, compression processing is required for video signals having an aspect ratio different from that of the display screen of the CRT 9.

Assume now that the aspect ratio of the CRT 9 is 4:3, which is the same as the aspect ratio of the current NTSC signal.

When receiving an NTSG signal, the switching circuit 5
The NTSC signal from the C receiver'gA device 7 is output to the CRT 9. In this case, the NTSC television image appears over the entire display screen 10.

On the other hand, when receiving the MUSE signal, BS tuner 2
The MUSE signal from is guided to the down converter 4 and applied to the CRT 9 by the switching circuit 5. The down converter 4 compresses the MtJSE signal to the center of the vertical scanning period,
Further, the leading and trailing edges of the vertical scanning period are set to a predetermined image level and output to the switching circuit 5.

FIG. 6 is an explanatory diagram for explaining the high-definition television image displayed on the display screen 10 of the CRT 9 in this case.

As mentioned above, the MUSE signal is compressed in the center of the vertical scanning period, and as shown in FIG.
1 appears. Further, the leading edge and trailing edge of the vertical scanning period are at a predetermined level, and appear as upper and lower peripheral frame images 12 on both surfaces 10.

As a result, the aspect ratio of the high-definition television image 11 appearing on the display screen 10 and the MUSE signal of FIG. 5(b) becomes the same, and a high-definition image without distortion is obtained.

Such a circuit configuration is applicable to the NTSG receiving device 7 and the CRT.
This is a system in which a down converter 4, a switching circuit 5, etc. are added to the current television receiver for receiving NTSC broadcasts, and considering the prevalence of current NTSC television receivers, it will become a system that will not be used in the future. It is expected that

On the other hand, if the CRT 9 has a display screen with the same aspect ratio as the MtJSE signal, the switching circuit 5
A signal from the E-decoder 3 or converter 8 is given to the CRT 9. The converter 8 compresses the video signal output from the NTSC receiver 7 to the center of its horizontal scanning period, sets the leading and trailing edges of the horizontal scanning period to predetermined levels, and supplies the signal to the switching circuit 5.

FIG. 7 is an explanatory diagram for explaining the NTSC television image displayed on the display screen 13 of the CRT 9 in this case.

Since the NTSC video signal is compressed in the center of the horizontal scanning period and the leading and trailing edges of the horizontal scanning period are at a predetermined level, the NTSC broadcast video 14 is displayed in the center of the display screen 13, and the display screen Left and right peripheral frame images 15 of a predetermined level are displayed on the left and right sides of 13. In addition, MLJSE
When the signal is received, the switching circuit 5 provides the signal decoded by the MUSE decoder 3 to the CRT 9. C
A high-quality television image is displayed over the entire area of the display screen 13 of the RT9.

In this way, the video signal is compressed based on the aspect ratio and the image 11.14 is displayed at the center of the display screen.

By displaying frame images 12.15 of a predetermined level around the CRT 9, images with different aspect ratios can be displayed on the common CRT 9. In addition, the upper and lower or left and right peripheral frame images 12
．． 15 is generally set to a black level in consideration of the visibility of images 11 and 14 in the center.

In this way, when displaying images with different aspect ratios, a predetermined black level is displayed continuously for a relatively long time on the top, bottom, left and right sides of the display screen, and a constant beam is placed in the center of the CRT 9. is irradiated, but peripheral areas such as left and right, top and bottom are irradiated for less time. For this reason, CR
At the center of T9, the luminous efficiency of the phosphor deteriorates, and the degree of so-called burn-in increases. When such a burn-in phenomenon occurs, it becomes a problem when using the entire display screen. In particular, changes in brightness due to differences in luminous efficiency at the boundary between the image area at the center of the screen and the peripheral frame image become noticeable, resulting in a problem of extremely deteriorating screen quality.

(Problems to be Solved by the Invention) As described above, in the above-mentioned conventional compatible television receivers, the top and bottom or left and right sides of the screen are fixed at a predetermined black level for a long time, so the CRT burn-in phenomenon occurs. This poses a problem in that it becomes an obstacle when using the entire display screen.

The present invention has been made in view of such problems, and includes:
An object of the present invention is to provide a compatible television receiver that can prevent deterioration of image quality when using the entire display screen by adjusting the contrast of the boundary between the image area at the center of the screen and the surrounding frame image. shall be.

[Structure of the Invention] (Means for Solving the Problems) A compatible television receiver according to the present invention introduces a video signal having an aspect ratio different from that of a display screen,
A converter is provided to enable display of images based on the introduced video signal, and the blanking pulse of the video signal from this converter is input to generate a control voltage that gradually increases and decreases from the leading edge to the trailing edge of the blanking period. and a control voltage from the control voltage generating means to adjust the level of the video signal from the converter before and after the blanking period, and adjust the contrast of the edge of the image displayed on the screen to the periphery of both sides. Contrast 1-adjustment means is provided to reduce the contrast as the distance increases.

(Function) In the present invention, the control voltage generating means
A control voltage that gradually increases or decreases from the leading edge to the trailing edge of the blanking period is applied to the contrast adjusting means. On the other hand, the converter converts a video signal having an aspect ratio different from that of the display screen into a video signal that can be displayed on the display screen, and supplies the video signal to the contrast adjustment means. The contrast adjustment means adjusts the contrast of the video signal from the converter before and after the blanking period based on the output of the control voltage generation means, and adjusts the contrast of the edge of the image displayed on the screen to the periphery of the screen. It can be gradually reduced towards the end. In this way, the contrast at the boundary between the image area at the center of the screen and the frame image area at the periphery of the screen gradually changes, and it is possible to prevent the image quality from deteriorating at the boundary area due to the burn-in phenomenon of the CRT.

(Example) Hereinafter, an example of the present invention will be described in detail based on the drawings. FIG. 1 is a circuit diagram showing an R, G, and B video output circuit of a compatible television receiver according to an embodiment of the present invention.

This embodiment is a system substantially similar to the conventional example shown in FIG.
R (red) on each of the R, G, and B cathodes of a CRT (not shown)
R, G that supplies the signal, G (green) signal and B (blue) signal
, is characterized by the configuration of the B video output circuit. In this embodiment, the aspect ratio of the ORT display screen is 4:
3.

In FIG. 1, an R signal, a G signal, and a B signal are input to video signal input terminals 16, 17, and 18, respectively.

Further, a clamp pulse, a horizontal blanking pulse, and a vertical blanking pulse are input to input terminals 19, 20, and 21, respectively. R, G, and B signals from video input terminals 16, 17, and 18 are connected to clamp capacitors 01 and C2.
, C3, respectively, to the R, G, and 8 input terminals of the video amplification circuit 22. Further, the clamp pulse from the input terminal 19 is input to the clamp input terminal. Input terminal 20.2
1 are connected to the anodes of diodes DI and D2, respectively, and the cathodes of diodes DI and D are connected to the video amplifier circuit 2.
2 and is connected to the blanking input terminal of R1.
is connected to the reference potential point via. In this way, the horizontal and vertical blanking pulses are added and input to the blanking input terminal. Variable resistors VR1 and VR2 are connected in parallel between the voltage terminal 23 and the reference potential point. The sliding end of the variable resistor VR1 is connected to the bright control end of the video amplification circuit 22 via the resistor R2, and the sliding end of the variable resistor VR1 is
The sliding end of R2 is connected to the contrast control end of the video amplification circuit 22 via a resistor R3.

The video amplification circuit 22 is a circuit that performs pedestal clamp processing, brightness control, contrast control, and blanking processing, and has output terminals 24, 25.
26 outputs an R signal, a G signal, and a B signal, respectively. The RoG and B signals of the output terminals 24, 25, and 26 are supplied to R, G, and 8 cathodes of a CRT (not shown). The video amplifying circuit 22 is usually an integrated circuit, such as Toshiba's TA7730P.

In this embodiment, the vertical blanking pulse from the input terminal 21 is also applied to the input end of a monotonically constant multi-biprator (hereinafter referred to as MM) 27. The MM27 becomes a high level (hereinafter referred to as "HII") at the falling edge of the vertical blanking pulse, and becomes a low level (hereinafter referred to as "LII") after a time constant τ1 has elapsed.The output of the MM27 is Input to M2B.

MM28 is “L II” at the falling edge of the input J signal.
It outputs a signal of "H11" after the time constant τ2.

The output terminal of MM28 is connected to the base of transistor Q1. The transistor Q1 constitutes a differential amplifier together with the transistor Q2, and the emitters of the transistors Q1 and C2 are commonly connected and connected to a reference potential point via a current source 1. The load of the differential amplifier is transistor Q3, C
It is composed of a current mirror circuit consisting of 4. That is, the collector of transistor Q1 is connected to transistor Q3,
The base of C4 is connected to the collector of transistor Q3, and the collector of transistor Q2 is connected to the base of transistor Q4.
connected to the collector of The emitters of transistors Q3 and C4 are connected to power supply terminal 29. A constant voltage is applied to the base of the transistor Q2 by a voltage source E,
The collector of the transistor Q2 is connected to the reference potential point via the negative capacitor ff1c4. Also, transistor Q
The collector of No. 2 is connected to the contrast control end of the video amplification circuit 22 via a resistor R4.

Next, a second explanation will be given of the operation of the embodiment configured as described above.
This will be explained with reference to the timing chart shown in the figure and the explanatory diagram shown in FIG. Figure 2(a) shows the video input terminal 16.17.1
8, FIG. 2(b) shows the vertical blanking pulse inputted to the input terminal 21, and FIG. 2(C) shows the output of the MM27. Figure (d
) shows the output of M M 28, FIG. 2(e) shows the collector voltage of transistor Q2, and FIG. 2(f) shows the R, G, B signals output from the output terminal 24.25°26. It shows.

The video amplification circuit 22 has tR and G shown in FIG. 2(a).

B signal is input. The video amplifier circuit 22 clamps the pedestal level to a predetermined value based on the clamp pulse, controls the brightness based on a predetermined DC voltage appearing at the sliding end of the variable resistor vR1, and controls the brightness based on the horizontal and vertical blanking pulses. It is blanked and output to output terminals 24, 25, and 26. Further, the video amplifying circuit 22 adjusts the contrast of the R, G, and B signals based on the signal level input to the contrast control terminal, and outputs the adjusted signals. That is, R, G, [3
The signal contrast is determined by M! of variable resistor VR2. It is controlled by the DC voltage appearing at the ll terminal and the collector voltage of transistor Q2.

Now, the vertical blanking pulse shown in FIG. 2(b) is M
When input to M27, the output of MM27 becomes “HII” at the falling edge of the vertical blanking pulse, and the time constant τ
1 becomes "L 11" (see Figure 2 (C)).Furthermore,
When this output is input to MM28, the output of MM28 becomes ii L n at the falling edge of the output of MM27, and becomes "Ho" after a time constant τ2. The output of MM28 is applied to the base of transistor Q1. M M
When the output of transistor 28 becomes erroneous and the base potential of transistor Q1 becomes higher than the base potential of transistor Q2, transistor Q2 becomes cut-off, and a constant current flows through the collector-emitter path of transistor Q1.

This constant current also flows through the emitter-collector path of the transistor Q3, and a mirror current of approximately the same magnitude flows through the collector of the transistor Q4. This mirror current causes the load capacitance C
4 is charged, and the collector potential of transistor Q2 is 1'
It increases along the i-line (see Figures 2(d) and (e)). On the other hand, when the output of M M 28 becomes L'' and the base potential of transistor Q1 becomes lower than the base potential of transistor Q2, transistor Q1 is cut off and a constant current is applied to the collector-emitter path of transistor Q2. As a result, the charge in the load capacitor 1c4 is discharged, and the collector potential of the transistor Q2 decreases linearly (see FIGS. 2(d) and (e)).

In other words, the collector potential of transistor Q2 starts decreasing after a time constant τ1 from the falling edge of the vertical blanking pulse, and the collector potential of transistor Q2 starts increasing after a time constant (τ1+τ2) from the falling edge of the vertical blanking pulse. do.

This time constant τ1. By setting the value of τ2 appropriately,
As shown in FIG. 2 (l), the collector potential of the transistor Q2 can be made into a triangular wave whose level changes before and after the vertical blanking pulse.

The collector potential of the transistor Q2 is applied to the contrast control terminal via the resistor R4, and
2 adjusts the contrast of input R, G, and B signals. In this way, from the video amplification circuit 22, as shown in FIG. 2(f), R and G signals whose contrast changes before and after the vertical blanking 11 are output.

8 signals are output.

FIG. 3 is an explanatory diagram for explaining an image when a high-definition television image with an aspect ratio of 16:9 is displayed on the display screen 30 with an aspect ratio of 4:3.

As mentioned above, in this case, the high-definition television image 31 is displayed at the vertical center of the display screen 30. Before and after the vertical blanking period of a high-definition television video signal, the contrast changes as shown in FIG. A contrast 1-reduction area 33 is obtained in which the contrast decreases toward the image 32 side. In this way, the upper and lower peripheral frames! By providing the contrast reduction area 33 at the boundary between &32 and the high-quality television image 31, even if burn-in occurs on the CRT, the boundary of the burn-in can be made inconspicuous on the screen. Thereby, even when displaying an image using the entire area of the display screen 30, it is possible to prevent the image quality from deteriorating at the boundary of burn-in.

In this embodiment, the case where the aspect ratio of the display screen of the CRT is 4:3 has been described, but the same configuration may be used even when the aspect ratio of the display screen is 16:9. That is, in this case, a horizontal blanking pulse is given as a trigger signal for MM27 instead of a vertical blanking pulse, and the time constant of MM27.28 is set to τ1. Change τ2 based on the horizontal period. That is, the time constant τ1 may be set to a time slightly shorter than the horizontal scanning period, and the time constant τ2 may be set based on the horizontal retrace period. Further, the capacity of the load capacity ff1c4 may be changed based on the horizontal period. Note that in this embodiment, it is important to adjust the contrast of the boundary portion, and the configuration of the video amplification circuit 22 and the like may be of any type.

[Effects of the Invention] As explained above, according to the present invention, the contrast of the boundary between the image area at the center of the screen and the frame image at the periphery of the screen can be adjusted. This has the effect of preventing deterioration of image quality at the boundary due to the burn-in phenomenon.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an R, G, B111 image output circuit of a compatible television receiver according to an embodiment of the present invention, FIG. 2 is a timing chart for explaining the operation of the embodiment, and FIG. An explanatory diagram for explaining the operation of the embodiment, FIG. 4 is a block diagram showing a conventional compatible television receiver, and FIG.
The figure is an explanatory diagram to explain the difference in aspect ratio between the NTSC signal and the MUSE signal.
FIG. 7 is an explanatory diagram showing an image when a MUSE signal is displayed on a display screen with an aspect ratio of 16:9, and FIG. 7 is an explanatory diagram showing an image when an NTSC signal is displayed on a display screen with an aspect ratio of 16:9. 16-18...Video signal input terminal, 19-21...
Input terminal, 22... Video amplification circuit, 24-26...
Output terminal, 27.28...monostable multivibrator, Q1-Q4...transistor, C4...load capacity,
mo diagram

Claims (1)

[Claims] A converter for introducing a video signal with an aspect ratio different from that of a display screen and displaying an image based on the introduced video signal, and inputting blanking pulses of the video signal from this converter. means for generating a control voltage that gradually increases and decreases from the leading edge to the trailing edge of the blanking period; and using the control voltage from the control voltage generating means, the video signal from the converter is controlled before and after the blanking period. 1. A compatible television receiver comprising: a contrast adjusting means for adjusting the level of the image displayed on the screen and reducing the contrast at the edge of the image displayed on the screen toward the periphery of the screen.