JPS643257Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an automatic video control circuit for a color television receiver that automatically adjusts the brightness, contrast, coloring (color saturation), etc. of the screen according to the surrounding brightness.

A conventional control circuit of this kind, as shown in Figure 1,
Base bias resistance 2, 3 of control transistor 1
A Cds photoconductive element 4 is connected in parallel to one side 2 of the transistor 1, and the base bias of the transistor 1 is varied by changing the impedance according to the brightness around this element, thereby obtaining bias from the emitter side of this transistor. The video amplifier circuit and chroma amplifier circuit were controlled according to the voltage.

However, in general, the spectral sensitivity characteristics of Cds photoconductive elements deviate greatly from the human visual sensitivity characteristics (curve B in the same figure), as shown by curve A in Figure 4. The drawback was that it was not possible to adjust the screen condition faithfully to the perceived brightness.

Therefore, the present invention proposes an automatic video control circuit that eliminates these drawbacks, and one embodiment shown in FIG. 2 will be described below.

In FIG. 2, 5 is an amorphous silicon optical sensor, and the cathode side of this sensor is an N-channel PN junction type FET 8 along with an impedance reduction resistor 6 and one end of a ripple removal capacitor 7.
The anode side is connected to the gate and the anode side is grounded.
The source of the FET 8 is grounded, the drain is connected to a +12V DC power supply terminal 10 via a load resistor 9, and the drain is connected to a control output terminal 14 via a switch 11, a diode 12, and a resistor 13.
It is connected to the. In addition, this terminal 14 is connected to the slider of a variable resistor 16 for manual adjustment, which is connected together with a resistor 15 between the power supply terminal 10 and the ground point.
It is connected via a resistor 17. The voltage obtained at the output terminal 14 is applied to a gain control terminal of a video amplifier circuit or a chroma amplifier circuit (not shown) of a television receiver.

Each of the above amplifier circuits is of a type in which the gain is controlled by DC voltage, and such circuits are already well known as color TV signal processing ICs, so a detailed explanation will be omitted. Examples include IC manufactured by Sanyo Electric Co., Ltd.: LA7601. In other words, this IC allows the video signal gain and chroma signal gain to be controlled simultaneously by the magnitude of the DC voltage applied to pin 24.
This means that the control output terminal 14 shown in FIG. 2 can be connected to the 24th pin of this IC.

The ripple removal capacitor 7 described above also serves to prevent the optical sensor 5 from being destroyed by unnecessary pulse voltage caused by sparks or the like within the receiver.

FIG. 3 shows a schematic structure of the above-mentioned aluminum phosphor silicon optical sensor 5 used in the previous embodiment. That is, in the figure, 18 is a transparent glass substrate, 19 is a transparent electrode provided thereon, 20, 2
1 and 22 are P-type, I-type (intrinsic), and N-type amorphous silicon layers formed on the electrode in this order, and 23 is aluminum deposited on the N-type silicon layer 22. The electrode 24 is the other aluminum electrode deposited directly on the transparent electrode 19, and 25 and 26 are the respective aluminum electrodes 2.
Metal lead (frame) electrodes are bonded on 3 and 24 with conductive paste, and 27 is a molded body made of epoxy resin. The optical sensor having such a structure generates a voltage of about 0 to 0.6 V between the aluminum electrodes 23 and 24 depending on the intensity of light incident on the lower surface of the glass substrate 18. At this time, one of the lead electrodes 26 becomes an anode (positive side), and the other lead electrode 25 becomes a cathode (negative side). The optical sensor configured in this way has a spectral sensitivity characteristic that peaks in approximately the same wavelength region as the human visibility characteristic (b), as shown by curve c in Fig. 4. ing.

Now, in the embodiment shown in FIG. 2, when the ambient brightness decreases and the intensity of the light incident on the optical sensor 5 becomes weaker, the electromotive force of this optical sensor (negative with respect to the ground point) increases. becomes smaller. Therefore, the forward bias between the gate and source of the FET 8 becomes deep, the drain current increases, and the drain voltage decreases. At this time, if switch 11 is closed, diode 1
2 becomes conductive, and the voltage at the control output terminal 14 decreases in accordance with the decrease in the drain voltage. Conversely, when the surroundings become brighter and the intensity of light incident on the optical sensor 5 increases, the electromotive voltage of this sensor increases, so the drain current decreases and the voltage at the control output terminal 14 increases. Therefore, a DC voltage is obtained at the control output terminal 14, which changes depending on the surrounding brightness and the brightness actually perceived by the eye, and this voltage is applied to the control output terminal 14 as described above.
By applying voltage to an IC or the like, the contrast and color saturation can be adjusted so that they are large when the surroundings are dark and small when the surroundings are bright.

Note that the diode 12 in FIG. 2 turns off when the surrounding brightness becomes very bright and the electromotive voltage of the optical sensor 5 reaches the rated value (approximately 0.6V), thereby causing the control output terminal 14 to The voltage is limited to below the voltage determined by the variable resistor 16 and the resistor 15 for manual adjustment, so that the amount of adjustment does not become larger than necessary. Furthermore, if the switch 11 is opened, the aforementioned contrast etc. can be manually adjusted using the variable resistor 16.

In the above description, the contrast and color saturation are adjusted, but the brightness may also be adjusted by controlling the DC operating level of the video amplifier circuit in accordance with the voltage obtained at the output terminal 14. can.

As explained above, the automatic video control circuit of the present invention detects the ambient brightness using an amorphous silicon optical sensor, and controls contrast and color saturation using a variable DC voltage according to the detected output. As a result, it is possible to almost accurately adjust the optimal image state according to the surrounding brightness that the viewer actually perceives. Further, there is no need to provide a correction circuit for adjusting the control characteristics to human visibility characteristics.

Furthermore, a FET is used as a semiconductor element to create a variable DC voltage in response to the output of the optical sensor, and a switching diode is provided to prevent the variable DC voltage from becoming excessive, making it easy to compare optical sensors. This is preferable because it is possible to perform a sufficient adjustment operation for a relatively low output, and to prevent the brightness from becoming extremely high depending on the surrounding brightness.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a conventional automatic video control circuit, Fig. 2 is a circuit diagram showing an embodiment of the automatic video control circuit of the present invention, and Fig. 3 is a schematic diagram of an amorphous silicon optical sensor used in the present invention. FIG. 4 is a sectional view showing the structure, and is a characteristic diagram showing the spectral sensitivity characteristics of the optical sensor together with the characteristics and visibility characteristics of the Cds photoconductive element. 5...Amorphous silicon optical sensor, 8...
FET, 16...variable resistor for manual adjustment, 14...
Control output terminal.

Claims (1)

[Scope of utility model registration request] In a television receiver that controls at least one of brightness, contrast, and color saturation according to the surrounding brightness, an amorphous silicon photosensor is used as the brightness detection element, and this light The sensor is connected between the control electrode of the FET, whose output electrode is connected to a DC power supply via a load resistor, and a reference potential point, and the output electrode is connected to the output terminal via a switching diode to prevent excessive output. An automatic video control circuit for a color television receiver, characterized in that a variable DC voltage for control is obtained from this output terminal.