JPH02137591A - Color video monitor - Google Patents

Abstract

PURPOSE:To make it unnecessary to draw around the feedback line of a detected current, and to stabilize the operation of a circuit by controlling the level of a cathode current by a DC control signal. CONSTITUTION:A color temperature correction circuit 1 adds a reference pulse to a chrominance signal, and controls the gain and the offset of the chrominance signal according to the level of detected voltage, and simultaneously, executes blanking processing for the chrominance signal. The chrominance signal from the output terminal 3 of the circuit 1 is supplied to the cathode 11 of a color cathode ray tube 10 through transistors 8, 9. The detected voltage corresponding to the cathode current of the tube 10 is generated at a detection resistor 12, and is fed back to the terminal 4 of the circuit 1. Constant-current sources 13, 14 are controlled in their current values by DC voltage from the terminals 15, 16, and simultaneously, are controlled in their operation/non-operation by switching signals Pa, Pb from the terminals 6, 7. Thus, the attenuation of the detected voltage or the influence of a disturbing wave are removed, and the operation of the circuit is stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to color video monitors, particularly those having automatic color temperature correction.

[Summary of the invention]

In this invention, a reference pulse is inserted into a color signal that drives a color cathode ray tube, and the level of cathode current of the color cathode ray tube when driven by the reference pulse is compared with the reference level.
In a color video monitor that automatically controls the color temperature to a constant level by controlling at least one of the gain and offset of the color signal using the comparison output, by controlling the level of the cathode current using the DC control signal, There is no need to route the detection voltage feedback line, and the circuit operation becomes stable.

[Conventional technology]

Color cathode ray tubes suffer from a decrease in emissions due to aging, and even if the color temperature (white balance) is adjusted correctly at the time of shipment from the factory, the color temperature may deviate from the normal value. For this reason, color video monitors have been proposed that are capable of automatically maintaining the color temperature of a displayed image at a set value. This color temperature correction circuit adds a reference pulse having a reference level to the signal generator that drives the color cathode ray tube.
The configuration is such that the cathode current when the color cathode ray tube is driven with this reference pulse is detected, and the gain and offset of the color signal are controlled so that the cathode current is at the reference level.

In the color temperature correction circuit described above, the color temperature is set to a standard value, but if the standard value differs depending on the broadcasting station or if many color video monitors are used side by side, the color temperature may be slightly different from the factory adjustment. You may notice some variation. 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 detected voltage that is fed back.

In other words, the detection resistor for converting the cathode current of the color cathode ray tube into voltage was configured with a volume, and this volume was moved to a location where the user could handle it.

[Problem to be solved by the invention]

Depending on the layout of the circuit, the position of the internal board, etc., there may be cases where the feedback line for the above-mentioned detection voltage is routed long. However, the cathode current that corresponds to the reference pulse has high frequency components, and if the detection voltage feedback line is routed for a long time using a wire, the amount of feedback may be greatly attenuated due to its transmission impedance, or the wire may cause interference signals. There was a problem that stable circuit operation could not be obtained.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a color video monitor that does not require a long detection voltage feedback line and can perform stable color temperature correction operations.

[Means to solve the problem]

This invention inserts a reference pulse Pc into the color signal that drives the color cathode ray tube 10, compares the level of the cathode current of the color cathode ray tube 10 when driven by the reference pulse PC with the reference level, and uses the comparison output as a color signal. In a color video monitor that automatically controls color temperature to a constant level by controlling at least one of signal gain and offset, the cathode current level is controlled by a DC control signal.

[Effect]

Color cathode ray tube 10 to automatically correct color temperature
The cathode current of is converted into a detection voltage by a detection resistor. A constant current source is connected in parallel with this 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 only the control voltage supply line that needs to be routed, it is possible to prevent the detection voltage from attenuating or being affected by interference signals as in the conventional case.

〔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.
indicates the 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 an output terminal 6.7 for switching signals Pa and Pb. are 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 according to the level of the detection voltage, and blanking processing is performed on the color signal. Ru.

The reference pulse and the blanked color signal from the output terminal 3 of the color temperature correction circuit 1 are amplified by a common emitter transistor 8 and sent to the cathode 11 of the color cathode ray tube 10 via a buffer amplifier constituted by a transistor 9.
supplied to The color cathode ray tube 10 has three cathodes, although omitted for simplicity, and a circuit similar to that shown in FIG. 1 is connected to each cathode. The three cathodes are driven by three primary color signals, respectively. Therefore, one of the three primary color signals, such as a red signal, is supplied to the input terminal 2 in FIG.

A detection resistor 12 is connected between the collector of transistor 9 and ground. This detection resistor 12 includes a color cathode ray tube lO
A detection voltage corresponding to the cathode current is generated. This detected voltage is applied to terminal 4 of color temperature correction circuit 1.
will be given feedback.

Constant current sources 13 and 14 are connected between the detection resistor 12 and the terminal 4.
is connected. 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 its 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 a user or obtained by D/A converting a digital code signal generated by a user's adjustment operation.

Fig. 2 shows switching signals Pa, Pb and detection pulse P.
The waveform of c is shown. Color temperature control consists of both highlight side control and lowlight side control. The highlight side is controlled by the color cathode ray tube 1 using the IVp-p signal, for example.
This is control for achieving white balance when driving the color cathode ray tube 10, and is performed by varying the gain of the color signal supplied to the color cathode ray tube 10. Control on the low light side is performed by adjusting the level of the offset added to the color signal by adjusting the offset levels among the three primary color signals in order to maintain balance near black.

As shown in FIG. 2A, the reference pulse Pc consists of a portion 41 having a level for controlling the highlight side and a portion 42 having a level for controlling the low light side.

As shown in FIG. 2B, one switching signal Pa generated from the color temperature correction circuit 1 is transmitted to
1, and 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 receives the switching signal P
The highlighted part 41 of the detection voltage having the same waveform as the detection pulse receives a DC shift according to the control voltage from the terminal 15 and is applied to the terminal 4 of the color temperature correction circuit 1. Supplied. The constant current source 14 operates only during the period when the switching signal Pb is at a 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. The signal 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. As shown in FIG. Input terminal 2
An addition circuit 21, a gain control circuit 22, an addition circuit 23, and a blanking circuit 24 are sequentially provided between the output terminal 3 and the output terminal 3. The addition circuit 21 is supplied with a reference pulse Pc from a reference pulse generation circuit 25. A control signal from an integrating circuit 32 is supplied to the gain control circuit 22 . The adder circuit 23 is supplied with an offset signal generated by an offset generation circuit 28 .

The blanking circuit 24 is supplied with a blanking pulse from the terminal 5 .

The terminal 5 is connected to the output terminal of the OR gate 34, and the OR gate 34 receives the vertical blanking pulse PV from the vertical blanking pulse generation circuit 35 and the auxiliary blanking pulse from the auxiliary blanking pulse generation circuit 36. PA is supplied. The vertical blanking pulse generation circuit 35 forms a vertical blanking pulse PV from the vertical retrace pulse from the terminal 37. 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 blanking pulse. Further, a scan mode signal is supplied from a terminal 38 to both the vertical blanking pulse generation circuit 35 and the auxiliary blanking pulse generation circuit 36. Blanking processing is performed by the blanking circuit 24 using these blanking pulses PV and PA.

The vertical blanking pulse generation circuit 35 and the auxiliary blanking pulse generation circuit 36 have the following components in the color temperature correction circuit 1:
Although not included, it is omitted in FIG. 1 for simplicity.

A detection voltage generated by the detection resistor 12 and whose level is adjusted 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 of the switch circuit 31 is supplied to one input terminal of a comparator 2=10-6, and is compared with a reference voltage 29 by a comparator 26. The other output terminal C of the switch circuit 31 is supplied to one input terminal of the comparator 27 and compared with the reference voltage 30 by the comparator 27 . The switch circuit 31 is controlled by switching signals Pa and pb formed by the reference pulse generation circuit 35 and taken out to terminals 6 and 7, respectively. In other words, the switching signal Pa
In the highlight control period when Pb is at a high level, the input terminal a of the switch circuit 31 is connected to the output terminal, and during the low light control period when the switching signal Pb is at a high level, the input terminal a of the switch circuit 31 is connected to the output terminal. Connected to C.

The comparator 26 generates a comparison output according to the difference between the detection voltage during the highlight period and the reference voltage 29, and this comparison output is supplied to the integration circuit 32. Integrating circuit 32 is provided to hold comparison outputs obtained in vertical cycles. The output signal of the integrating circuit 32 is transmitted to the gain control circuit 2.
2 as a control signal. The comparator 27 is
A comparison output is generated 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 integrating circuit 33. The output signal of the integrating circuit 33 is supplied to the offset generating circuit 28 as a control signal. The offset generation circuit 28 generates an offset of a level according to the averaged comparison output from the integration circuit 33.

The color temperature correction circuit 1 described above controls the gain of the color signal so that the level of the highlighted portion 4 of the detection voltage having the same waveform as the reference pulse Pc is equal to the reference voltage 29 or has a constant level difference. This allows the white balance to be automatically controlled.

Further, the offset of the color signal is controlled so 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. As a result, the balance of the three primary colors near black can be improved.

The reference pulse generation circuit 25 generates a vertical blanking pulse P.
A reference pulse Pc is formed from V. By supplying the scan mode signal from the terminal 38 to the vertical blanking pulse generation circuit 35, the vertical blanking pulse PV is
In normal scan mode, the normal pulse width is
The underscan mode has a shorter pulse width than the normal scan mode. Further, the auxiliary blanking pulse generation 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 (image frame of the monitor), and in the underscan mode, the display area of the effective video signal is narrower than the effective screen. Underscan mode is required when checking the signal by comparing all of the valid video signals on the monitor screen.

As described above, the reason why the pulse width of the vertical blanking pulse PV in the underscan mode is made shorter than that in the normal scan 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 the vertical blanking period and the reference pulse Pc are visible 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 will be visible just above the area of the effective video signal, making it difficult to confuse the effective video signal and the reference pulse Pc.

The reference pulse Pc is generated at a timing delayed by a predetermined period of time, for example, 3 to 5H (H is one horizontal period) from the fall of the vertical blanking pulse P■, so the reference pulse Pc
To move the position of the vertical blanking pulse P■
It is necessary to shorten the pulse width.

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

〔Effect of the invention〕

In this invention, the cathode current corresponding to the reference pulse for color temperature correction is varied, and the set value can be adjusted by the user. Since this adjustment is performed using a DC control voltage, even if the control voltage supply line is routed depending on the circuit layout, the position of the circuit board, etc., the detection voltage may attenuate or the correction operation may malfunction due to the influence of interference waves. is prevented, and color temperature correction operates stably. It is also possible to digitally correct the color temperature automatically by D/A converting the detected voltage.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an 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. 4: Detection voltage input terminal, 10: Color cathode ray tube, 11: Cathode, 12: Detection resistor, 13.14: Constant current source.

Claims (1)

[Claims] A reference pulse is inserted into a color signal that drives a color cathode ray tube, and the level of the cathode current of the color cathode ray tube when driven by the reference pulse is compared with the reference level, and the comparison output is In a color video monitor that automatically controls the color temperature to a constant level by controlling at least one of the gain and offset of the color signal, the level of the cathode current is controlled by a DC control signal. Features a color video monitor.