JP2743412B2 - Color video monitor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color video monitor, and more particularly to a color video monitor having an automatic color temperature correction function.

[Conventional technology]

The color cathode ray tube has a problem that the emission decreases due to aging, and the color temperature deviates from a normal value even if the color temperature (white balance) is correctly adjusted at the time of factory shipment. For this reason, there has been proposed a color video monitor capable of automatically maintaining the color temperature of a display image at a specified value. This color temperature correction circuit adds a reference pulse having a reference level to a signal for driving a color cathode ray tube, detects a cathode current when the color cathode ray tube is driven by the reference pulse, and detects the cathode current as a reference level. This is a configuration for controlling the gain and offset of the color signal so that

In a commercial color video monitor used in a broadcast station or the like, beam scanning can be switched between a normal scan mode and an underscan mode. In the normal scan mode, as shown in FIG. 6A, the effective screen (defined by the frame of the monitor screen) 45 is larger than the effective video signal area 43 (the outer edge thereof is indicated by a broken line 44). Is a large operation mode. The underscan mode is an operation mode in which the effective image signal is smaller in the area 43 than the effective screen 45 as shown in FIG. 6B. The underscan mode is used when it is desired to display all of the effective video signals on the screen for the purpose of checking a signal or the like.

[Problems to be solved by the invention]

By the above-described color temperature correction circuit, the reference pulse is applied to a period that does not affect the effective video signal, for example, a horizontal scanning period or a horizontal blanking period between the vertical blanking period and the effective video signal (where the reference pulse is inserted). It is necessary that the blanking process not be performed during the horizontal blanking period.). In the normal scan mode, this reference pulse is outside the effective screen 45, and no problem occurs. However, in the underscan mode, as can be understood from FIG. 7A and FIG. 7B in which the upper edge thereof is enlarged, the reference pulse Pc represented by the dashed line is the vertical blanking region 46 and the effective video signal region. It appears as a bright line between 43 and 44. As described above, since the reference pulse Pc is seen close to the effective video signal area 43, there is a problem that the effective video signal and the reference pulse Pc are confusing.

Accordingly, an object of the present invention is to provide a color video monitor in which a reference pulse for color temperature correction can be inserted so as to be clearly distinguished from an effective video signal in an underscan mode.

[Means for solving the problem]

According to the present invention, a reference pulse Pc is inserted into a color signal for driving the color cathode ray tube 10, the level of the cathode current of the color cathode ray tube 10 when driven by the reference pulse Pc is compared with the reference level, and the color is output by the comparison output. By controlling at least one of the signal gain and offset, the color video monitor automatically controls the color temperature to be constant, and has a normal pulse width during a normal scan operation and a normal pulse width during an underscan operation. A vertical blanking pulse generating means for generating a vertical blanking pulse PV having a pulse width shorter than the pulse width, and a vertical blanking pulse
Reference pulse generating means for generating a reference pulse Pc after generation of PV, and auxiliary blanking pulse generating means for generating an auxiliary blanking pulse PA between the reference pulse Pc and the effective video signal during an underscan operation, At the time of the underscan operation, a blanking period based on the auxiliary blanking pulse PA is interposed between the reference pulse Pc and the effective video signal.

[Action]

In the underscan mode, the pulse width of the vertical blanking pulse is shorter than in the normal scan mode. The reference pulse Pc is generated after a predetermined sending time from the fall of the vertical blanking pulse. Therefore, in the underscan mode, the position of the reference pulse Pc on the screen is higher and separated from the effective video signal. In addition, in the underscan mode, an auxiliary blanking period is added between the reference pulse Pc and the effective video signal, so that the reference pulse Pc can be easily distinguished from the effective video signal, so that there is no problem in which both are disturbed. .

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the overall configuration of this embodiment,
Reference numeral 1 denotes a color temperature correction circuit. The color temperature correction circuit 1 has a color signal input terminal 2, a color signal output terminal 3, a detection voltage supply terminal 4, a blanking pulse supply terminal 5, and switching signals Pa and Pb output terminals 6 and 7. doing. In the color temperature correction circuit 1, a reference pulse is added to the color signal, the gain and offset of the color signal are controlled in accordance with the level of the detection voltage, and blanking processing is performed on the color signal. You.

The reference pulse from the output terminal 3 of the color temperature correction circuit 1 and the color signal subjected to the blanking process are amplified by the common emitter type transistor 8, and the cathode 11 of the color cathode ray tube 10 is passed through the buffer amplifier constituted by the transistor 9. Supplied to Although not shown for simplicity, the color cathode ray tube 10 has three cathodes, and each cathode has a first cathode.
Circuits similar to those in the figure are connected. The three cathodes
Each is driven by three primary color signals. Therefore, one of the three primary color signals, for example, a red signal, is supplied to the input terminal 2 in FIG.

The detection resistor 12 is connected between the collector of the transistor 9 and the ground. The detection resistor 12 generates a detection voltage corresponding to the cathode current of the color cathode ray tube 10. This detection voltage is fed back to the terminal 4 of the color temperature correction circuit 1.

Constant current sources 13 and 14 are connected between the detection resistor 12 and the terminal 4. The current value of the constant current source 13 is controlled by a DC control voltage from a terminal 15, and its operation / non-operation is controlled by a switching signal Pa from a terminal 6 of the color temperature correction circuit 1. Similarly, the current value of the constant current source 14 is controlled by the DC control voltage from the terminal 16 and the operation / non-operation is controlled by the switching signal Pb from the terminal 7 of the color temperature correction circuit 1. These control voltages are generated by a volume operated by the user, or D / A-converted and superimposed on a digital code signal generated by a user's adjustment operation.

FIG. 2 shows the waveforms of the switching signals Pa and Pb and the detection pulse Pc. The control of the color temperature includes both the control on the highlight side and the control on the low light side. The control on the highlight side is, for example, control for obtaining a white balance when driving the color cathode ray tube 10 with a signal of 1 Vp-p, and by changing the gain of the color signal supplied to the color cathode ray tube 10. Done. The control on the low light side is performed by adjusting the offset level among the three primary color signals to adjust the level of the offset added to the color signal in order to balance around black. As shown in FIG. 2A, the reference pulse Pc includes a portion 41 having a level for controlling the highlight and a portion 42 having a level for controlling the low light.

One switching signal Pa generated from the color temperature correction circuit 1 is, as shown in FIG.
The other switching signal Pb is synchronized with the low light side portion 42 as shown in FIG. 2C. Therefore, the constant current source 13 operates only during the period in which the switching signal Pa is at the high level, and the highlighted portion 41 of the detection voltage having the same waveform as the detection pulse receives the DC shift according to the control voltage from the terminal 15. Terminal 4 of the color temperature correction circuit 1
Supplied to The constant current source 14 operates only during the period when the switching signal Pb is at the high level, and the low light portion 42 of the detection voltage having the same waveform as the detection pulse receives the DC shift according to the control voltage from the terminal 16 to change the color. It is supplied to the terminal 4 of the temperature correction circuit 1.

FIG. 3 shows an example of the color temperature correction circuit 1. An addition circuit 21, a gain control circuit 22, an addition circuit 23, and a blanking circuit 24 are sequentially provided between the input terminal 2 and the output terminal 3. The addition circuit 21 includes a reference pulse generation circuit 25
Is supplied. The gain control circuit 22 is supplied with a control signal from the integration circuit 32.
The offset signal generated by the offset generation circuit 28 is supplied to the addition circuit 23. The blanking circuit 24 is supplied with a blanking pulse from the terminal 5.

Terminal 5 is connected to the output terminal of OR gate 34,
The OR gate 34 is supplied with the vertical blanking pulse PV from the vertical blanking pulse generating circuit 35 and the auxiliary blanking pulse PA from the auxiliary blanking pulse generating circuit 36. The vertical blanking pulse generation circuit 35 is connected to the terminal 37
The vertical blanking pulse PV is formed from the vertical blanking pulse from the vertical blanking pulse. The auxiliary blanking pulse generation circuit 36 forms an auxiliary blanking pulse PA from the vertical blanking pulse PV. The auxiliary blanking pulse PA may be formed from a vertical retrace pulse. Further, a scan mode signal is supplied from a terminal 38 to both the vertical blanking pulse generating circuit 35 and the auxiliary blanking pulse generating circuit 36. By these blanking pulses PV and PA, a blanking circuit 24 performs a blanking process.

The vertical blanking pulse generation circuit 35 and the auxiliary blanking pulse generation circuit 36 are not included in the color temperature correction circuit 1, but are omitted in FIG. 1 for simplicity.

The detection voltage generated by the detection resistor 12 and adjusted in level by the constant current sources 13 and 14 is supplied from the terminal 4 to the input terminal a of the switch circuit 31. One output terminal b of the switch circuit 31
Is supplied to one input terminal of the comparator 26, and is compared with the reference voltage 29 by the comparator 26. The other output terminal c of the switch circuit 31 is supplied to one input terminal of the comparator 27, and is compared with the reference voltage 30 by the comparator 27.
A switching circuit is formed by switching signals Pa and Pb formed at a reference pulse generating circuit 35 and taken out to terminals 6 and 7, respectively.
31 is controlled. That is, during the highlight control period in which the switching signal Pa is at the high level, the input terminal a of the switch circuit 31 is connected to the output terminal b, and the switching signal Pb
Is a high level during a low write control period, the input terminal a of the switch circuit 31 is connected to the output terminal c.

The comparator 26 generates a comparison output according to the difference between the detection voltage in the highlight period and the reference voltage 29, and this comparison output is supplied to the integration circuit 32. The integration circuit 32 is provided to hold a comparison output obtained in a vertical cycle. The output signal of the integration circuit 32 is supplied to the gain control circuit 22 as a control signal. The comparator 27 generates a comparison output according to the difference between the detection voltage during the low light period and the reference voltage 30, and this comparison output is supplied to the integration circuit 33. Integrator circuit
The output signal of 33 is supplied to the offset generation circuit 28 as a control signal. The offset generation circuit 28 generates an offset of a level corresponding to the averaged comparison output from the integration circuit 33.

The above-described color temperature correction circuit 1 adjusts the level of the highlighted portion 41 of the detection voltage having the same waveform as the reference pulse Pc to the reference voltage 29.
The gain of the color signal is controlled so as to be equal to or a constant level difference. Thereby, the white balance can be automatically controlled. Further, the offset of the color signal is controlled such that the level of the low light portion 42 of the detection voltage is equal to the reference voltage 30 or has a constant level difference. Thereby, the balance between the three primary colors near black can be improved.

The reference pulse generating circuit 25 is provided with a vertical blanking pulse PV.
From the reference pulse Pc. When a scan mode signal is supplied from the terminal 38 to the vertical blanking pulse generation circuit 35, the vertical blanking pulse PV has a normal pulse width in the normal scan mode and a normal scan mode in the underscan mode. Has a shorter pulse width than Further, the auxiliary blanking pulse generating circuit 36 generates the auxiliary blanking pulse PA only in the underscan mode.

FIG. 4A shows the vertical blanking pulse PV in the normal scan mode. The reference pulse generation circuit 25
As shown in FIG. 4B, this vertical blanking pulse PV
From the fall of Td, for example, 3 to 5H (H is one horizontal cycle)
The reference pulse Pc is generated at a delayed timing. After the reference pulse Pc, an effective video signal is located.

In the underscan mode, as shown in FIG. 4C, a vertical blanking pulse PV having a shorter pulse width than the normal scan mode is generated. As shown in FIG. 4D, the reference pulse generation circuit 25 generates the reference pulse Pc at a timing delayed by Td from the fall of the vertical blanking pulse PV, as in the normal scan mode. An auxiliary blanking pulse PA is generated between the reference pulse Pc and the effective video signal from the auxiliary blanking pulse generating circuit 36 as shown in FIG. 4E.

The monitor screen in the above-described underscan mode is as shown in FIG. FIG. 5B is an enlarged view of the upper edge portion of FIG. 5A. Since the width of the vertical blanking pulse PV is shortened and the reference pulse Pc is added after that, the display position of the reference pulse Pc is near the upper edge of the effective screen 45 as shown in FIG. Move away from signal area 43. In addition, a blanking region 47 corresponding to the auxiliary blanking pulse is interposed between the reference pulse Pc and the edge 44 of the effective video signal region 43. Therefore, the effective video signal area 43 and the reference pulse Pc can be clearly distinguished.

〔The invention's effect〕

According to the present invention, when the reference pulse for color temperature correction is in the underscan mode, it can be clearly distinguished from the effective video signal, and the problem that the reference pulse is confused with the video signal can be solved. Also in the normal scan mode, it is conceivable that the insertion position of the reference pulse is changed to the same position as in the underscan mode, so that the switching according to the scan mode becomes unnecessary. However, in this case, in the normal scan mode, the reference pulse is located considerably above, and the value of the cathode current corresponding to the reference pulse has a large difference from that in the underscan mode. There is a problem that the beam hits and an unnecessary reflection phenomenon occurs. Therefore, it is effective to change the insertion position of the reference pulse in the underscan mode as in the present invention.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of one embodiment of the present invention,
FIG. 2 is a waveform diagram showing waveforms of a reference pulse and a switch signal. FIG. 3 is a block diagram of an example of a color temperature correction circuit.
FIG. 5 is a timing chart for explaining the operation of the embodiment, FIG. 5 is a schematic diagram used for describing the embodiment, and FIG.
FIG. 7 is a schematic diagram used for explaining an underscan mode, and FIG. 7 is a schematic diagram used for explaining a conventional problem. Explanation of main symbols in the drawings 1: color temperature correction circuit, 2: color signal input terminal, 3: color signal output terminal, 4: detection voltage input terminal, 10: color cathode ray tube, 11: cathode, 12: Detection resistor, 21, 23: Addition circuit, 22: Gain control circuit, 24: Blanking circuit, 28: Offset generation circuit.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-48-69424 (JP, A) JP-A-62-268292 (JP, A) JP-A-61-187487 (JP, A) JP-A-61-187487 251291 (JP, A)

Claims (1)

(57) [Claims] 1. A reference pulse is inserted into a color signal for driving a color cathode ray tube, and a level of a cathode current of the color cathode ray tube when driven by the reference pulse is compared with a reference level. In a color video monitor that automatically controls the color temperature to be constant by controlling at least one of the signal gain and offset, the color video monitor has a normal pulse width during a normal scan operation, and has a normal pulse width during an underscan operation. Vertical blanking pulse generating means for generating a vertical blanking pulse having a pulse width shorter than the pulse width of: a reference pulse generating means for generating a reference pulse after the generation of the vertical blanking pulse; and Auxiliary blanking that generates an auxiliary blanking pulse between the reference pulse and the effective video signal And a down King pulse generating means, at the time of the under-scan operation, a color video monitor, characterized in that so as to interpose the blanking period by the auxiliary blanking pulses between said reference pulse and the effective video signal.