JP3042649B2 - On-screen display circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to CS (communication satellite) and B
Satellite broadcast receiver (tuner) for receiving S (satellite broadcast)
The present invention relates to an on-screen display circuit which makes it easy to see the display when there is no video signal or the like in the on-screen display.

[0002]

2. Description of the Related Art The above-mentioned satellite broadcast receiver requires a user to perform many function selections and adjustments due to the special feature of satellite broadcast reception. Such various function selections and adjustments are generally performed by an on-screen display in order to make the operation easy to understand.However, in order to make the on-screen display easier to see, when there is no video signal, the noise component is attenuated. When a video signal is normally present, the video signal or noise is input to the subsequent on-screen circuit without attenuating. Conventionally, the determination as to whether to attenuate or pass through has been made by detecting a synchronization signal of a video signal.

[0003]

However, in the above-mentioned method which depends only on the detection of the synchronization signal, the normal operation of lowering the original luminance when the signal which is originally noise is mistaken for the synchronization signal is not performed, and the malfunction occurs. The problem of causing a problem was inherent. SUMMARY OF THE INVENTION It is an object of the present invention to provide an on-screen display circuit in which the determination of the presence / absence of a video signal is made more accurate and the on-screen display inherently operates properly.

[0004]

According to the present invention, there is provided a noise voltage detector for detecting a noise voltage mixed in an input video signal or a noise voltage when the video signal is absent, and a synchronizing signal based on the video signal. A synchronous signal detecting section for detecting the presence or absence of the signal, an attenuating circuit to which the video signal is input, and which supplies an on-screen display circuit by passing or attenuating the signal input under the control of the control section, and the synchronous signal detecting section When the synchronization signal is detected and the detection by the noise voltage detection unit is equal to or less than a predetermined value, the attenuating circuit is set to the through state, and when the synchronization signal is not detected by the synchronization signal detection unit or the noise voltage detection unit And a control unit for outputting a control signal for setting the attenuation circuit to a predetermined attenuation when the detection by the control circuit is equal to or more than a predetermined value. It is intended to provide.

[0005]

In addition to the conventional synchronous signal detection, a noise voltage is also detected, and an attenuating circuit provided in the preceding stage of the on-screen display circuit is controlled based on both detection results. Then, when there is no signal, the noise is attenuated, and when there is a video signal whose noise is equal to or less than a certain value, the noise or the video signal is input to the on-screen display circuit at the subsequent stage in a through state.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An on-screen display circuit according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a main part showing an embodiment of an on-screen display circuit according to the present invention, and FIG. 2 is an operation flowchart for explaining FIG.
In FIG. 1, reference numeral 1 denotes a video signal demodulated from a received radio wave;
Denotes a noise voltage detection unit, 3 denotes a synchronization signal detection unit, 4 denotes an attenuation circuit, 5 denotes a control unit, and 6 denotes an on-screen display circuit.

Next, the operation of the present invention will be described.
The ST numbers in parentheses in the following description represent each step in FIG. The noise voltage detector 2 detects a noise voltage level mixed in the video signal 1 or a noise voltage level when the video signal 1 is not present. The latter is particularly significant when noise that is mistaken for a synchronization signal is mixed. The detected voltage level is converted into a digital level and input to the control unit 5. The synchronization signal detection unit 3 has the same function as that of the related art, and determines the presence of a video signal by detecting a synchronization signal from the video signal. The synchronization signal to be detected may be either horizontal synchronization or vertical synchronization. And
H (high level) or L according to the presence or absence of the synchronization signal
(Low level) is output. The damping circuit 4
According to the control of the control unit 5, when the video signal 1 is normally present and the noise component is equal to or less than a certain value, the video signal is passed through without attenuating. If the noise includes a value equal to or larger than the value, the noise is attenuated by a predetermined amount and input to the on-screen display circuit 6. As a result, the brightness of the screen decreases. still,
The amount of attenuation is determined uniformly.

The control unit 5 determines the presence or absence of the video signal 1 from both the signal from the noise voltage detection unit 2 and the signal from the synchronization signal detection unit 3, and controls the attenuation circuit 4 based on the determination result as described above. Control. Specifically, as shown in the drawing, the memory unit has a memory unit and a determination unit, and the memory unit stores a reference value (for example, 2 V) for a noise voltage and a reference for the presence or absence of a synchronization signal. Then, the determination unit determines whether or not the noise voltage from the noise voltage detection unit 2 is equal to or less than a reference value and whether or not there is a synchronization signal. The output mode is H (high level) or L (low level) associated with through or attenuation. The on-screen circuit 6 inserts a predetermined on-screen display signal into the video signal or the noise-only signal from the attenuation circuit 4. In this case, as described above, when the input level is low (at the time of attenuation), the luminance of the background (video or noise) is lower than that of characters displayed on the screen.
As a result, even when there is no signal or when the image has a poor S / N ratio, the displayed characters and the like are easy to see.

The above has described each block individually. Next, the overall operation will be described with reference to the operation flowchart of FIG. When signals are input from the noise voltage detection unit 2 and the synchronization signal detection unit 3, respectively, the control unit 5 causes the determination unit and the memory unit to determine the presence or absence of a synchronization signal and whether the noise voltage is equal to or less than a reference value, respectively (ST1). (ST
2) If "synchronous signal is present" (ST1-YES) and "below reference value" (ST2-YES), a control signal is output to attenuating circuit 4 so that the signal passes through the attenuation circuit 4 without attenuation (ST3). ). On the other hand, in the determination of (ST1),
In the case of “no synchronization signal” (ST1-NO), the control unit 5
The attenuation circuit 4 is attenuated (ST4). In addition, even if there is a synchronization signal (ST1-YES), the attenuation circuit 4 is also attenuated when the noise voltage is higher than the reference value (ST2-NO) (ST4).
This is because the video signal contains noise components in excess of the specified value and the luminance should be reduced. As described above, the on-screen display can be performed by an original operation even when there is a noise component which is erroneously recognized as a synchronization signal when there is no signal.

[0010]

As described above, according to the present invention, in addition to the conventional synchronous signal detection, the level of the noise voltage is also detected, so that the accuracy of discriminating the presence / absence of a video signal and the S / N ratio is improved. be able to. Therefore, the on-screen display can be operated in a proper manner, and the on-screen display plays an important role, which contributes to the improvement of the function of the satellite broadcast receiver.

[Brief description of the drawings]

FIG. 1 is a main block diagram showing an embodiment of an on-screen display circuit according to the present invention.

FIG. 2 is a flowchart for explaining FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Video signal 2 Noise voltage detection part 3 Synchronization signal detection part 4 Attenuation circuit 5 Control part 6 On-screen display circuit

Claims (1)

(57) [Claims] 1. A noise voltage detector for detecting a demodulated video signal and a noise voltage mixed in the video signal or a noise voltage when the video signal is absent. A synchronous signal detecting unit for detecting the presence or absence of a signal, an attenuating circuit to which the video signal is input, and which passes through or attenuates the input signal under the control of the control unit and supplies the signal to an on-screen display circuit; When the synchronization signal is detected by the unit and the detection by the noise voltage detection unit is equal to or less than a predetermined value, the attenuating circuit is set to a through state, and the synchronization signal is not detected by the synchronization signal detection unit, or the noise voltage detection unit An on-screen unit configured to output a control signal for setting the attenuation circuit to a predetermined attenuation when the detection is equal to or more than a predetermined value. Display circuit.