JPH06217339A - Television receiver - Google Patents

Abstract

PURPOSE:To eliminate an undesired picture blanking time when power is applied again just after power is interrupted. CONSTITUTION:In the television receiver in which an automatic white balance circuit 1 makes white balance constant with a feedback quantity of a cathode current of a CRT 3, an OFF time from power interruption till power recovery is detected. Then a microcomputer 5 controls so that a release time of a picture blanking of the automatic white balance circuit 1 is quickened in response to the off time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television receiver having an automatic white balance function.

[0002]

2. Description of the Related Art An output video signal of an auto white balance circuit is supplied to a CRT via a CRT drive circuit,
This drives the CRT. The cathode current amount of the CRT is fed back to the auto white balance circuit, and the auto white balance circuit changes the output level of the video signal so as to keep the white balance constant.

By the way, when the heater of the CRT is not warmed up, the cathode current does not flow, so the feedback loop of the auto white balance circuit does not work and a normal image cannot be obtained. Therefore, conventionally, as shown in FIG. 6, the auto white balance circuit is controlled so that image blanking is performed for a certain time T (for example, 10 seconds) after the power is turned on.

[0004]

However, according to the above-mentioned conventional structure, even when the power is turned off immediately after the power is turned off, such as when the power is turned off by mistake, the constant time T is maintained. Only the image blanking is always applied. In such a case, the heater of the CRT is warmed up and the auto white balance circuit operates normally immediately after the power is turned on, so that it is not necessary to perform the image blanking for a certain time.

Therefore, according to the present invention, when the power is turned off and again when the power is turned on, the picture blanking period immediately after the power is turned on can be released as early as possible to eliminate unnecessary picture blanking time. It is an object to provide a John receiver.

[0006]

A television receiver according to the present invention for achieving the above object detects a cathode current of a CRT, feeds back the detected amount to an auto white balance circuit, and outputs the detected amount to this feedback amount. Accordingly, the automatic white balance circuit changes the signal output level to control the white balance to be constant, and immediately after the power is turned on, the feedback control of the automatic white balance circuit is stopped to perform the image blanking. In the above, the off-time from the power-off to the power-on again is detected, and if the off-time is short, the image blanking cancellation time is controlled to be shortened according to the short time. .

[0007]

When the power is turned off, the temperature of the CRT gradually decreases with time. However, the shorter the off time from when the power is turned off to when the power is turned on again, the shorter the CRT heater temperature is. Proper image is displayed even if it is released early in proportion to the off time.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 3 show a first embodiment of the present invention. FIG. 1 shows a partial circuit block diagram of a television receiver. In FIG. 1, R, G, and B video signals are supplied to an auto white balance circuit 1, and the auto white balance circuit 1 adjusts the signal level of the video signal as described below and outputs it. The output video signal of the auto white balance circuit 1 is supplied to the CRT 3 via the CRT drive circuit 2, and the CRT 3 is driven by this video signal.

The cathode current detection circuit 4 detects the cathode current of the CRT 3 and feeds back the detected amount to the auto white balance circuit 1. The automatic white balance circuit 1 changes the signal output level according to this feedback amount and controls so as to keep the white balance constant. When the image blanking control signal from the microcomputer 5 is input, the automatic white balance circuit 1 is configured to forcibly output the image blanking signal without performing white balance control.

The microcomputer 5 is supplied with a detection signal indicating the on / off state of the power switch SW. The microcomputer 5 has a first counter and a second counter built therein, and executes the flowchart shown in FIG. 2 according to whether the power switch SW is turned on or off.

The operation of the above configuration will be described below. When the power switch SW is turned off while the power switch SW is on, the power of each circuit is turned off except for a part of the microcomputer 5 and the like. As shown in FIG. 2, the microcomputer 5 is set to the first state when the power switch SW is turned off.
When the counter is started and the power switch SW is turned on again, the count-up of the first counter is stopped. That is, the first counter counts the off time from power off to power on and holds this count value A.

When the power switch SW is turned on, the microcomputer 5 starts the second counter this time and outputs an image blanking control signal to the auto white balance circuit to perform image blanking. When the count value B of the second counter matches the count value A of the first counter, the output of the image blanking control signal is terminated and the image blanking is canceled. That is, when the power switch SW is turned off, the temperature of the heater of the CRT 3 gradually decreases with time as shown in FIG. 3, but the shorter the off time is, the higher the temperature of the heater of the CRT 3 is. Proper image is projected even if released quickly in proportion. However, the maximum count value of the first counter is determined in advance and set so as not to count up any more.

Further, by making the clock frequencies of the first counter and the second counter different according to the external temperature, the temperature characteristic of the heater of the CRT 3, and the like, the correspondence between the off time and the image blanking time is made more appropriate. be able to.

4 and 5 show a second embodiment of the present invention. FIG. 4 shows a partial circuit block diagram of the television receiver. The second embodiment has a memory 6, and this memory 6 has a power switch S as shown in FIG.
Data of time (image blanking time) characteristics required for the automatic white balance circuit 1 to properly operate when W is turned on again after being turned off is stored. The microcomputer 5 counts the off time from when the power switch SW is turned off until it is turned on, and obtains the image blanking time corresponding to the off time from the memory 6. Then, the image blanking control signal is output to the auto white balance circuit 1 for the image blanking time. Since other configurations are the same as those of the first embodiment, the same reference numerals are given to the drawings and the description thereof will be omitted.

According to the second embodiment, since the image blanking time is set according to the temperature characteristic of each CRT 3,
Fine control according to each CRT 3 is possible.

[0016]

As described above, the first to fourth aspects of the invention are described.
According to the invention of claim 1, in a television receiver having an auto white balance circuit, an off time from when the power is turned off to when the power is turned on again is detected, and if the off time is short, the off time is determined according to the shortness. Since the image blanking release time is configured to be shortened, it is possible to eliminate unnecessary image blanking time. Then, in order to eliminate unnecessary image blanking time, it is possible only by changing software without adding hardware.

According to claim 3, the external temperature, the CRT
It is possible to set an appropriate image blanking time in consideration of the temperature characteristic of the heater, and according to the fourth aspect, it is possible to perform finer control according to each CRT.

[Brief description of drawings]

FIG. 1 is a partial circuit block diagram of a television receiver (first embodiment).

FIG. 2 is a flowchart (first embodiment).

FIG. 3 is a temperature drop characteristic diagram of a CRT heater (first embodiment).

FIG. 4 is a partial circuit block diagram of a television receiver (second embodiment).

FIG. 5 is a characteristic diagram of a time required for the automatic white balance circuit to properly operate when the power is turned off and then turned on again (second embodiment).

FIG. 6 is a time chart during image blanking (conventional example).

[Explanation of symbols]

 1 ... Auto white balance circuit 3 ... CRT 6 ... Memory

Claims (4)

[Claims] 1. A cathode current of a CRT is detected, the detected amount is fed back to an automatic white balance circuit, and the automatic white balance circuit changes a signal output level according to the feedback amount to control white balance to a constant value. In addition, immediately after the power is turned on, the feedback control of the auto white balance circuit is stopped and the image blanking is performed.In the television receiver, the off time from the power off to the power on again is detected and this off time is detected. When the time is short, the television receiver is controlled so that the cancellation time of the image blanking is shortened according to the short time. 2. A first counter for counting an off time from turning off the power supply to turning on the power supply again, and a second counter for starting counting after turning on the power supply. A count value of the second counter. 2. The television receiver according to claim 1, wherein the image blanking is canceled at a time when the count value matches the count value of the first counter. 3. The clock frequency of the first counter is different from that of the second counter.
The television receiver described in. 4. The time blanking data required for the automatic white balance circuit to operate properly when the power source is turned off and then turned on again is stored in a memory, and the data in the memory is used to release the image blanking time. The television receiver according to claim 1, wherein: