JP3353864B2 - Television receiver with shading correction signal generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television receiver provided with a shading correction signal generator for generating a shading correction signal.

[0002]

2. Description of the Related Art In a projection television, picture tubes (C) of three colors R (red), G (green) and B (blue) are used.
RT) to project a beam of three colors toward the screen, and combine them on the screen to form an image.

In this case, since the distance between the picture tube and the screen is different between the central portion and the peripheral portion of the screen, a so-called shading phenomenon in which the luminance decreases as the position approaches the peripheral portion of the screen occurs. The degree of this shading differs depending on the positional relationship between the three picture tubes and the screen, the size of the screen, and the like.

Conventionally, a shading correction circuit as shown in FIG. 4 has been provided in order to remove unevenness in brightness of a screen due to shading. The shading correction circuit is provided for each of the R, G, and B video signals. Hereinafter, the red (R) video signal will be described.

[0005] Video signal voltage R _IN is a comparison amplifier (Comparative amplifier) 1, is compared with the reference voltage V _S corresponding to the black level V _I of the screen, only the signal component exceeds the reference voltage V _S is to the multiplier 2 Is entered. The multiplier 2 modulates the input video signal voltage R _IN with a correction wave signal such as a sawtooth wave or a parabolic wave signal, and corrects the correction voltage V _C.
Is calculated.

[0006] In this case, the correction voltage V _C is linearly changed, and is set to be larger the higher the brightness.
The reason for this is that if a correction is simply made with a fixed correction voltage, a bright screen is properly corrected but a dark screen is overcorrected. Therefore, in order to perform appropriate correction from a bright screen to a dark screen, the correction amount is changed linearly according to the brightness of the screen, that is, the luminance level.

The thus obtained correction voltage V _C
And the adder 3, by adding to the video signal voltage RIN, image signal voltage R _OUT as shown is obtained.
The same correction operation as described above is performed for the green (G) and blue (B) video signals.

[0008]

However, in the above-described conventional method, since the correction voltage is obtained by modulating the video signal voltage with the correction waveform in the multiplier 2, the S / N ratio is low in a dark scene. This caused the ratio to deteriorate, which was a problem.

Accordingly, the present invention has an object to solve the above-mentioned problems by providing an inexpensive device for generating a shading correction signal which does not cause deterioration of the S / N ratio.

[0010]

In order to solve the above-mentioned problems, a television receiver provided with a shading correction signal generator according to the present invention comprises: an input terminal for inputting a parabola signal; A television receiver comprising a shading correction signal generator having an input terminal for inputting an ABL voltage, an inverting amplifier for inverting the ABL voltage of the television receiver, and a multiplier for outputting a shading correction signal. A multiplier of the shading correction signal generator, a modulator for modulating the parabolic wave signal with an output signal from the inverting amplifier, and an output unit for adding an output signal from the modulator to a video signal. A configuration is provided.

[0011]

The voltage that increases linearly from the cutoff to the highlight by inverting the ABL voltage of the television receiver, which linearly decreases from the cutoff (minimum luminance) to the highlight (maximum luminance) with the inverting amplifier. Is generated, and the parabolic wave signal is modulated by the voltage (output signal) generated by the inverting amplifier by the modulating means to obtain a shading correction signal that changes linearly with the luminance level of the video signal. Then, a corrected video signal can be obtained by adding the shading correction signal, which is an output signal from the modulating means, to the video signal.

As a result, a shading signal that changes linearly according to the luminance level of the video signal is obtained.
As in a conventional shading correction circuit using a shading correction signal obtained by modulating a video signal with a correction waveform, the deterioration of the S / N ratio of the video signal does not occur.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a television receiver provided with a shading correction signal generator according to the present invention will be described below with reference to the drawings. The same components as those in the prior art will be described by assigning the same numbers for easy understanding.

CRT (Cathode R) as a picture tube
A television receiver provided with an “Ay Tube” irradiates an electron beam obtained by supplying a video signal voltage to a cathode onto a phosphor screen to form an image. The unevenness in luminance of the formed image is appropriately corrected by the shading correction signal generating device to obtain a uniform image quality. The shading correction signal generator has a configuration in which a parabolic wave signal is generated by modulating it with an inverted ABL voltage, and will be described below with reference to FIGS.

The shading correction signal generator linked to the ABL voltage shown in FIG. 1 has input terminals T1 to T4, an output terminal T5, a multiplier M corresponding to a multiplier, and a resistor R.
1 to R9, capacitors C1 and C2, and transistor T
r1 and Tr2, and a Zener diode D.

A horizontal parabolic wave signal and a vertical parabolic wave signal having a shading correction waveform signal are input to input terminals T1 and T2, respectively. The reason for using the parabolic wave signal is as follows.

The distance that the electron beam reaches the screen of the flat screen changes parabolically in both the horizontal and vertical directions from the center to the periphery of the screen. Therefore, even if the luminance is constant, shading occurs in each of the horizontal direction and the vertical direction. Therefore, each of the horizontal and vertical shadings is corrected with the horizontal and vertical parabolic wave signals, respectively.

The image signal of the spot of the electron beam projected on the screen is corrected by a composite wave of a horizontal parabolic wave signal and a vertical parabolic wave signal according to the coordinates of the spot. In addition, each frequency of a horizontal parabolic wave signal and a vertical parabolic wave signal is equal to the horizontal scanning frequency and the vertical scanning frequency, respectively.

The input terminals T1 and T2 are respectively connected to a resistor R
1, and one end of the coupling capacitor C1 via R2. The other end of the coupling capacitor C1 is connected to one input terminal a of the multiplier M via a resistor R3, and is grounded via a resistor R4.

Thus, a composite wave signal of the horizontal parabola wave signal and the vertical parabola wave signal is inputted to one input terminal a of the multiplier M.

The input terminal T3 has a transistor Tr1,
The power supply voltage VCC (for example, +12 V) of Tr2 is input.

The ABL voltage is input to the input terminal T4. The ABL voltage is AB (not shown).
The output voltage of the L circuit (automatic luminance limiting circuit) is used. As is well known, the ABL circuit detects a current (referred to as an ABL current) proportional to a cathode current of a picture tube (CRT), and feeds it back to a cathode voltage to cut off a cathode current (C / O). ) Point, that is, the point with the lowest luminance, and the highlight (H / L) point of the cathode current, that is, the point with the maximum luminance, are automatically controlled.

The ABL voltage changes linearly as shown by a straight line L1 in FIG. 2, and becomes maximum at cutoff (C / O) and minimum at highlight (H / L). .

The input terminal T4 is connected to the base of the transistor Tr1 via a smoothing circuit composed of a resistor R5 and a capacitor C2 and a constant voltage limiting zener diode D. The emitter of the transistor Tr1 is connected to the power input terminal T3 via the resistor R6. The collector is grounded via a resistor R7.

With such a connection, the transistor Tr
1 functions as an inverting amplifier. That is, a voltage as shown by a straight line L2 in FIG. 3 appears between the collector and the ground (the resistor R7). As can be seen from the straight line L2, the output voltage of the transistor Tr1 increases linearly from the cutoff and becomes a constant value when the ABL circuit operates and the luminance of the highlight is held at the limit value.

Returning to FIG. 1, the transistor Tr2 is a transistor for impedance conversion, the emitter of which is grounded via a resistor R8 and the other input terminal of the multiplier M via a resistor R9. b. This collector is connected to the power input terminal T3. By this connection, the terminal b of the multiplier M is
A voltage as shown by 2 is input.

Returning to FIG. 1, the multiplier M modulates a composite wave signal of the horizontal parabolic wave signal and the vertical parabolic wave signal input to the input terminal a with the inverted ABL voltage input to the input terminal b. The obtained waveform signal is output from the output terminal c as a shading correction signal.

The output terminal c of the multiplier M is connected to the output terminal T5. Therefore, a shading correction signal is obtained from the output terminal T5. This shading correction signal is added to each of the R, G, B video signals to generate a shading corrected video signal.

[0029]

As described above, the voltage changes linearly with the inverting amplifier of the shading correction signal generator, becomes maximum at the time of cutoff (C / O), and highlights (H / L).
Invert the ABL voltage, which is sometimes minimized,
By modulating the parabolic wave signal with the inverted ABL voltage (output signal), a shading correction signal that changes linearly according to the luminance level of the video signal is generated, and this correction signal is added to each of the R, G, and B video signals. This makes it possible to obtain a corrected video signal which does not cause deterioration of the S / N ratio on the cutoff side in a dark scene as in the case where a conventional R, G, B video signal is modulated with a parabolic wave signal. it can.

Further, since the number of parts is small, the manufacturing cost can be reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a configuration of an embodiment of a television receiver provided with a shading correction signal generation device linked to an ABL voltage according to the present invention.

FIG. 2 is an explanatory diagram showing an ABL voltage.

FIG. 3 is an explanatory diagram showing an output voltage of a transistor Tr1 in FIG.

FIG. 4 is an explanatory diagram showing a conventional shading correction circuit.

[Explanation of symbols]

 C1, C2 Capacitor D Zener diode M Multiplier R1 to R9 Resistor T1 to T4 Input terminal T5 Output terminal Tr1, Tr2 Transistor

────────────────────────────────────────────────── (5) References JP-A-5-191678 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04N 5/14-5/217 H04N 5 / 68

Claims (1)

(57) [Claims] (1) An input terminal for inputting a parabolic wave signal, Input terminal for inputting ABL voltage of the television receiver
When, Reversal increase for reversing the ABL voltage of the television receiver
Breadth and And a multiplier for outputting a shading correction signal.
Television receiver equipped with an edging correction signal generator
An image machine, A multiplier of the shading correction signal generator,
The parabolic wave signal is converted by the output signal from the inverting amplifier.
Modulating means for modulating, To add the output signal from the modulating means to the video signal
Characterized in that said shading comprises:
A television receiver provided with a correction signal generator.