JPH07131670A - Television receiver - Google Patents

Abstract

PURPOSE:To prevent such an image that has a tendency to overscan from breaking at the neck part of a CRT by the beam current caused by the AKB (automatic-kine-bias) information. CONSTITUTION:When a level comparing circuit 3 decides that the sawtooth wave acquired by a vertical drive circuit 1 is lower than a prescribed lower limit level A-3, a comparator 4 outputs a high level. Meanwhile a comparator 5 outputs a high level if the sawtooth wave of the circuit 1 reachs a prescribed higher limit level A-2. Then a blanking circuit 2 produces a blanking pulse. A 1st clamping circuit 9 clamps the period sawtooth wave of the pulse acquired by the comparator 5 at a prescribed higher limit voltage level, and a 2nd clamping circuit 10 clamps the period sawtooth wave of the pulse acquired by the comparator 4 at a prescribed lower limit voltage level respectively. These clamped sawtooth waves are led to a deflecting coil L1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television receiver capable of receiving and displaying a television signal such that a video signal exists in a portion of the cathode ray tube (CRT) of the television receiver having a deflection angle or more. It is about.

[0002]

2. Description of the Related Art In recent years, a broadcasting system called high-definition broadcasting has been proposed in order to give a more realistic feeling. This broadcast has 1125 scanning lines and an aspect ratio of 16: 9 on the screen.

On the other hand, in the current NTSC broadcasting, the screen aspect ratio is 4: 3. Therefore, in the current television receiver, the
Cannot display the screen of 6: 9.

Therefore, if an attempt is made to receive a high-definition broadcast and watch a realistic image, the aspect ratio is 16:
A television receiver with 9 screens has become necessary. Therefore, recently, there has been proposed a television receiver as described on page 33 of the monthly issue of Videocom: October issue by AVCC.

By the way, the television receiver having the 16: 9 screen has a function of receiving not only the high-definition broadcast but also the current NTSC broadcast. When receiving the current NTSC broadcast, a display method on a 16: 9 television receiver is as shown in FIG.

That is, in FIG. 4, (a) is a 16: 9 television receiver displaying a 4: 3 image as it is, and (b) is a horizontal image which is stretched to the full and an upper and lower image is cut off. Ha is to stretch the image of the center part horizontally and leave both ends as it is,
On the contrary, the image at the center is left as it is and the images at both ends are stretched to form a fresh image.

By the way, in (b) of FIG. 4, unlike the other screens, the vertical screen portion must be truncated. Particularly, in this case, the overscan amount is 30% in the vertical direction. However, in a normal CRT, when the overscan amount becomes 13 to 15% or more,
There is a problem that the beam current hits the neck portion and the neck portion is broken.

For this reason, conventionally, countermeasures have been taken with a circuit as shown in FIG. That is, in FIG. 2, 1 is a vertical drive circuit, 2 is a blanking circuit, 3 is a level comparison circuit having comparators 4 and 5, 6 is a vertical output circuit, 7 is a vertical output amplifier, and L1 is a vertical deflection coil. .

Further, R1, R2 and R3 are comparators 4 and 5, respectively.
Dividing resistors for supplying a reference voltage to D1, D1 and D2 are diodes, and R4, R5, R6, R7 and R8 are resistors.

Next, the operation will be described. First, a vertical synchronizing signal is input to the vertical drive circuit 1 and a sawtooth wave as shown in A of FIG. 3 is output to the deflection output circuit 6. The sawtooth wave is amplified by the vertical output amplifier 7, and then the deflection coil L
1 to supply the deflection operation.

On the other hand, the sawtooth wave is input to the level comparator 3, and is divided by the dividing resistors R1, R2 and R3 to obtain the reference voltage A-.
2. Create A-3. A-2 is supplied to the comparator 5 to generate the pulse B only when the sawtooth wave is A-2 or more, and A-3 is supplied to the comparator 4 and the sawtooth wave is A-3 or less. The pulse C is generated only when.

A pulse D for blanking the overscan portion is obtained from the pulses B and C, and the blanking circuit 2 adds the pulse for blanking the vertical blanking period to blank the video drive circuit. so,
Prevents damage to the neck of the CRT.

However, in recent television receivers, a function of automatically adjusting the cut-off point (black level of each color) of the output stage based on the information on the amount of current flowing toward the cathode of each color of the CRT, That is, AKB (Auto
Some have a function of "matic-Kine-Bias".

Such an AKB function is described in, for example, Japanese Patent Application Laid-Open No. 60-18087 (H04N9 / 7).
Although it is a known technique as seen in 3), a brief description will be given here. First, FIG. 5 shows a block diagram of an AKB circuit. In FIG. 5, when RGB signals are input,
A reference signal as shown in FIG. 6 is inserted into each signal. (Here, for the sake of explanation, a signal processing circuit for the R signal is shown, but it goes without saying that each signal for GB also has the same signal processing circuit.) This reference signal is generated by the reference signal insertion circuit 11 at the 18th H of the R signal. Is inserted in the line. (The reference signals to the other GB signals may be inserted in the lines before and after the 18th H, or may be inserted in the same line of the 18th H for each field.) Thereafter, via the DC level shift circuit 12. Then, it is blanked by the blanking circuit 2 and output to the CRT 13 by the drive circuit 8. Further, the reference signal extracting circuit 14 extracts the reference signal from the output of the drive circuit 8. Then, the extracted reference signal is controlled so that the DC level is aligned with the reference level.

In such a television receiver with an AKB function, if the blanking pulse obtained by the blanking circuit 2 as described above is used for blanking, the AKB information is also extracted by the blanking pulse. A
There is a problem that it does not fulfill the KB function.

Therefore, in order not to blank only the AKB information portion, a blanking pulse such as F in FIG. 3 is created by the pulse E for extracting the reference signal,
I was working the AKB function.

However, as described above, this AKB information is inserted in the 18th line,
If the overscan is 30%, it is simply considered that there are about 78 overscans in the number of scanning lines in one field. As a result, if there is AKB information, A
A beam current flows due to the information in KB, hits the neck portion of the CRT, and although the neck portion is not destroyed, there arises a problem that the withstand voltage of the CRT is lowered.

[0018]

SUMMARY OF THE INVENTION The present invention is intended to solve the above-mentioned problems, and in an image which is overscanned, destruction by the neck portion of the CRT due to the beam current flowing due to AKB information occurs. The purpose is to prevent.

[0019]

SUMMARY OF THE INVENTION The present invention is a television provided with a deflection circuit which receives a video signal and outputs it to the cathode of a cathode ray tube (CRT) to deflect the beam current of the CRT based on a synchronizing signal from the video signal. In a John receiver, a vertical drive signal that extracts the vertical sync signal from the sync signal and creates and outputs a sawtooth wave for vertical deflection operation, and a predetermined upper limit for the level of the sawtooth wave of the vertical drive circuit And a lower limit level respectively, a pulse is generated when reaching a predetermined upper and lower limit level, and a blanking pulse creation circuit for blanking the video signal period of the period in which the pulse is generated, and a blanking pulse Based on the blanking pulse from the creation circuit, the blanking pulse and the clamp circuit that holds the sawtooth wave at a predetermined reference voltage for a high period A television receiver, which was characterized by Rukoto.

[0020]

According to the present invention, in a television receiver having an AKB function, by blanking a video signal for an overscan and clamping a sawtooth wave flowing to a deflection coil to a predetermined voltage during the blanking period.
Prevent the beam current from flowing to the neck of the CRT due to the KB information.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention. In FIG. 1, those having the same reference numerals as those in FIG. 2 of the prior art have the same functions, and therefore their explanations are omitted.

First, the addition of the present invention in FIG. 1 is a first clamp circuit 9 for clamping the upper limit of the sawtooth wave and a second clamp circuit 10 for clamping the lower limit of the sawtooth wave. The first clamp circuit 9 includes transistors TR1 and TR2, resistors R11 and R12, and a diode D3, and the second clamp circuit 10 includes transistors TR3 and TR4 and resistors R13, R14, and R15.
And a diode D4.

Next, examples of the present invention will be described. The blanking pulse D is created in the same way as in FIG. First, the reference voltage A-2 input to the comparator 5 is applied to the base of the transistor TR1. On the other hand, A-2 'is obtained by the resistor R11, the diode D3, and the resistor R12. This A-2 'is R1 / R2 + R3> R11 / R1
By setting it to 2, it becomes a constant voltage reference voltage that can obtain a voltage equal to the reference voltage A-2.

Then, the blanking pulse B generated from the comparator 5 is supplied to the base of the transistor TR2 through the base resistor R10 and turned on. This on period,
The sawtooth wave A is clamped at A-2 '.

On the other hand, the reference voltage A− input to the comparator 4
3 is added to the base of the transistor TR3, and the resistor R
Reference voltage A by 14 and diode D4 and resistor R15
-3 'is set to a voltage equal to A-3. Then, the blanking pulse C generated from the comparator 4 is supplied to the base of the transistor TR4 via the base resistor R13 and turned on. During this ON period, the sawtooth wave A is A
Clamped to -3 '.

Further, the resistors R16 and R4 are replaced by R4 >> R
By setting to 16, the sawtooth waves A and E during the scanning line period
Make the voltage at the points almost the same.

By operating as described above, the sawtooth wave becomes as shown in G of FIG. 3, and by supplying it to the deflection coil L1, it is synchronized with the blanking pulse D and has a level (A The deflection operation can be performed with a deflection current suitable for −2, A-3).

Therefore, by the blanking pulse, A
Operate with blanking pulse that does not extract KB information,
Instead, by clamping the deflection current up and down, AK
B information is left as it is, the AKB function is operated, and AKB is
The destruction of the neck portion of the CRT of the beam current due to information is prevented.

[0029]

As described above, according to the present invention, it is possible to prevent the destruction of the CRT neck portion by the AKB information without losing the AKB information and keeping the AKB function working.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a conventional technique.

FIG. 3 is a waveform diagram for explaining the operation of the embodiment of the present invention and the prior art.

FIG. 4 is a diagram showing a 4: 3 screen displayed on a television receiver having an aspect ratio of 16: 9.

FIG. 5 is a diagram for explaining the operation of AKB.

FIG. 6 is a diagram showing AKB information.

[Explanation of symbols]

 1 Vertical Drive Circuit 2 Blanking Creation Circuit 3 Level Comparison Circuit 4 Comparator 5 Comparator 6 Vertical Output Circuit 7 Vertical Output Amplifier 9 First Clamp Circuit 10 Second Clamp Circuit L1 Deflection Coil

Claims (1)

[Claims] 1. A television receiver comprising a deflection circuit which receives a video signal and outputs it to the cathode of a cathode ray tube (CRT) to deflect the beam current of the CRT based on the synchronization signal from the video signal. A vertical drive circuit that extracts a vertical synchronization signal from the vertical drive circuit and creates and outputs a sawtooth wave to perform a vertical deflection operation, and a predetermined upper and lower limit level for the sawtooth wave level of the vertical drive circuit, respectively. A blanking pulse generating circuit for generating a pulse when the predetermined upper and lower levels are reached and blanking the video signal period of the period in which the pulse is generated; Based on the blanking pulse, the blanking pulse comprises a clamp circuit for holding the sawtooth wave at a predetermined reference voltage for a high period. Television receiver characterized by.