JP2982161B2 - 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 regular 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 set 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 the above-described color temperature correction circuit, the color temperature is set to the reference value, but the reference value differs depending on the broadcasting station,
When a large number of color video monitors are used side by side, slight variations in adjustment at the time of shipment from the factory may be found. Therefore, it is necessary for the user to be able to adjust the color temperature of the set value. This adjustment has been made by adjusting the level of the feedback detection voltage. That is, a detection resistor for converting the cathode current of the color cathode ray tube into a voltage is constituted by a volume, and the volume is moved to a place where the user can handle it.

[Problems to be solved by the invention]

Depending on the circuit layout, the position of the internal substrate, and the like, the above-described feedback line of the detection voltage may be extended for a long time. However, some of the cathode current corresponding to the reference pulse has a high frequency component, and when the feedback line of the detection voltage is drawn long by a wire,
Due to the transmission impedance, the feedback amount may be greatly attenuated, or the wire may pick up an interfering signal, so that a stable circuit operation cannot be obtained.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a color video monitor capable of performing a stable color temperature correction operation without having to lay a feedback line of a detection voltage for a long time.

[Means for solving the problem]

The present invention relates to a detection resistor for converting a cathode current into a detection voltage in a color video monitor which automatically controls a color temperature to be constant by inserting a reference pulse into a color signal for driving a color cathode ray tube. And a constant current source connected in parallel with the detection resistor, the current value of which is controlled by a DC control voltage, and comparison means for comparing the detection voltage obtained when the color cathode ray tube is driven with the reference pulse with the reference level. And controlling at least one of the gain and the offset of the color signal by the comparison output by the comparison means to control the color temperature to be constant.

[Action]

Color cathode ray tube 10 to automatically correct color temperature
Is converted into a detection voltage by the detection resistor. A constant current source is connected in parallel with the detection resistor, and the current value of the constant current source is controlled by a DC control voltage to adjust the detection voltage. Therefore, since it is the control voltage supply line that needs to be routed, it is possible to prevent the detection voltage from attenuating and prevent the interference signal from affecting as in the related art.

〔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 passed through the buffer amplifier constituted by the transistor 9 to the cathode 11 of the color cathode-ray tube 10. 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 user-operated volume or obtained by D / A conversion of 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 a DC shift according to the control voltage from the terminal 16, It is supplied to the terminal 4 of the color 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 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
An output signal is supplied to the offset generating 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 has a normal pulse width 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.

In the normal scan mode, the display area of the effective video signal is wider than the effective screen (monitor frame), and in the underscan mode, the display area of the effective video signal is narrower than the effective screen. The underscan mode is required when comparing all of the effective video signals on the monitor screen and checking the signals.

As described above, compared to the normal scan mode,
The reason for shortening the pulse width of the vertical blanking pulse PV in the underscan mode is to separate the insertion position of the reference pulse Pc from the effective video signal. That is, in the underscan mode, the display area of the effective video signal is narrower than the effective screen, so that the vertical blanking period and the reference pulse Pc can be seen at the top of the screen. If the reference pulse Pc is added at the same position as in the normal scan mode, the reference pulse Pc is seen immediately above the area of the effective video signal, and the effective video signal and the reference pulse Pc are confused.

The reference pulse Pc is generated at a timing delayed by a predetermined time, for example, 3 to 5H (H is one horizontal cycle) from the fall of the vertical blanking pulse PV. It is necessary to shorten the pulse width of the ranking pulse PV.

Further, an auxiliary blanking pulse PA is added between the reference pulse Pc moved in the underscan mode and the effective video signal to form a blanking period.
Through these processes, the reference pulse Pc and the effective video signal can be clearly distinguished in the underscan mode.

〔The invention's effect〕

According to the present invention, the set value can be adjusted on the user side by varying the cathode current corresponding to the reference pulse for color temperature correction. Since this adjustment is performed with a DC control voltage, even if the control voltage supply line is routed in a circuit layout, a circuit board position, or the like, the detection voltage is attenuated,
Correction operation is prevented from malfunctioning due to the influence of interference waves,
Color temperature correction operates stably. In addition, the detection voltage can be D / A converted to digitally automatically correct the color temperature.

[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, and FIG. 3 is a block diagram of an example of a color temperature correction circuit. 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: Sense resistor, 13, 14: constant current source.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04N 9/73 H04N 9/16

Claims (1)

(57) [Claims] 1. A color video monitor which automatically controls a color temperature to be constant by inserting a reference pulse into a color signal for driving a color cathode ray tube. A resistance, a constant current source connected in parallel with the detection resistor and having a current value controlled by a DC control voltage, and comparing the detection voltage and a reference level obtained when the color cathode ray tube is driven with a reference pulse. A color video monitor, comprising: comparing means, wherein at least one of a gain and an offset of a color signal is controlled by a comparison output by the comparing means, so that a color temperature is controlled to be constant.