JPH074020B2 - Color temperature automatic adjustment circuit - Google Patents

Description

The present invention relates to a color temperature automatic adjustment circuit (Auto White Balance circuit) used in a color television receiver or the like.

[Outline of Invention]

According to the present invention, in a color temperature automatic adjusting circuit used for a color television receiver or the like, a clamp circuit is provided, the cathode current detection signal is clamped by the clamp circuit during a vertical blanking period, and the signal is supplied through the clamp circuit. The difference voltage between the cathode current detection signal and the reference voltage in the reference pulse section immediately after the vertical blanking period is obtained by the comparator, and the color temperature is automatically adjusted by canceling the leak current by controlling the level of the primary color signal. It was done like this.

[Conventional technology]

As a conventional color temperature automatic adjusting circuit, there is one disclosed in Japanese Patent Application No. 60-27420, which is proposed by the present applicant. This color temperature automatic adjustment circuit inserts a reference pulse in a predetermined horizontal period of a vertical blanking period of a video signal, detects a cathode current flowing corresponding to the reference pulse, and detects the cathode current at a timing when the reference pulse is inserted. The detection signal of the cathode current and the reference voltage are compared in a comparator to obtain an error signal, and the level of the primary color signal is controlled based on this error signal to adjust the white balance.

However, this color temperature automatic adjustment circuit controls the cathode current on the assumption that the cathode current all flows in the color picture tube to illuminate the fluorescent surface and that the cathode current and the brightness of the fluorescent surface are in a proportional relationship. Therefore, when a leak current is generated between the heater cathode of the picture tube, between the cathode and the cathode, or dust on the substrate, and the proportional relationship between the cathode current and the luminance is no longer established, the white balance shifts. It occurs.

Therefore, in order to prevent the deviation of the white balance due to the leak current, it is necessary to accurately detect the cathode current from which the leak current is subtracted. For example, a leak cancel circuit shown in FIG. 3 has been proposed.

A cathode current is supplied from the terminal 40, and a cathode current detection signal corresponding to the resistor 41 is supplied to one input terminal of the comparator 42 and one input terminal of the comparator 46. The comparator 42 is controlled so that the output is generated only in the vertical blanking period, and the detection signal of the cathode current flowing in the vertical blanking period, that is, the leak current is equal to the voltage level of the reference voltage source 43 in the comparator 42. Comparison is made and an error signal corresponding to the leak current is generated. This error signal is held in the capacitor 44 and the reference voltage source 45
And the reference voltage is controlled based on the error signal. Further, the comparator 46 is controlled so that the output is generated only in the reference pulse period, and the detection signal of the cathode current including the leak current component generated corresponding to the level of the reference pulse is detected by the comparator 46. It is compared with the voltage level of the reference voltage source 45 which is changed according to the leak current. In the comparator 46, an error voltage with respect to a predetermined reference voltage is generated in a form in which the leak current component is offset, and this error voltage is held in the capacitor 47 and taken out from the output terminal 48.

[Problems to be solved by the invention]

However, in the conventional leak cancel circuit, the capacitor 44 for detecting the leak current is required, and there is a problem that the number of pins must be increased to form an IC and the cost increases.

Therefore, it is an object of the present invention to accurately detect a cathode current proportional to the brightness of a color picture tube in a form of canceling the leakage current with a simple circuit configuration, and preventing deviation of white balance due to the leakage current. It is to provide an automatic color temperature adjustment circuit.

[Means for solving problems]

The present invention provides a clamp circuit 25, 28, 29, 30 which is supplied with a cathode current detection signal of a color picture tube and clamps the detection signal in the vertical blanking period, and an output signal of the clamp circuit 25, 28, 29, 30. An automatic color temperature adjusting circuit characterized by comprising comparators 31 and 34 for comparing the level of the reference signal and the reference voltage of, and a circuit for controlling the level of the primary color signal by the outputs of the comparators 31 and 34. is there.

[Action]

A clamp circuit composed of a capacitor 25, a switch circuit 28, a diode 29 and a reference voltage source 30 has a connection point between the collector of the transistor 6 through which the cathode current flows and the resistor 24, and switch circuits 26 and 27 for sampling the reference pulse.
It is provided between and. The switch circuit 28 forming the clamp circuit is turned on in the vertical blanking period, and the sampling switch circuit is provided in the section of the reference pulse inserted in one horizontal period immediately after the vertical blanking period.
26 and 27 are turned on respectively. The detection signal of the cathode current proportional to the luminance in which the leakage current is offset is supplied to the comparators 31 and 34 via the capacitor 25 which constitutes the clamp circuit, and the error signals generated in the comparators 31 and 34, respectively. The gain control amplifier 3 and the level shift circuit 4 are controlled based on the above, and the level of the primary color signal is adjusted.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the structure of a color television receiver to which the present invention is applied. A matrix circuit is designated by 1 in FIG.

The composite color video signal is separated into a brightness signal Y and a color signal C in a brightness / color separation circuit (not shown), and the brightness signal Y is transmitted from the terminal 13 through the amplifier to the matrix circuit 1.
Is supplied to. Further, the color signal C is converted into a red color difference signal RY and a blue color difference signal BY by passing through a color demodulation circuit (not shown), and the red color difference signal RY is supplied from the terminal 14 to the matrix circuit 1. At the same time, the blue color difference signal BY is supplied from the terminal 15 to the matrix circuit 1.

In the matrix circuit 1, the luminance signal Y and the color difference signal R
-Y, BY matrix processing is performed for red, green,
The blue three primary color signals R, G, B are output. The red primary color signal R is supplied to the adder 2R, the green primary color signal G is supplied to the adder 2G, and the blue primary color signal B is supplied to the adder 2B.

The red primary color signal R output from the adder 2R is supplied via the gain control amplifier 3 and the level shift circuit 4 to the base of the NPN transistor 5 that constitutes the video output circuit, and the emitter is grounded. It is supplied to the collector of the NPN transistor 12 for ranking.

The video output circuit is composed of an NPN type transistor 5 and a PNP type transistor 6, the emitter of the transistor 5 is grounded via a resistor 22, and the collector of the transistor 5 is connected to a power supply terminal 20 via a resistor 21. With
It is connected to the base of the transistor 6. The emitter of the transistor 6 is connected to the red cathode K _R of the color picture tube 7, and the collector is grounded via the resistor 24.

Although not shown, the green primary color signal G output from the adder 2G and the blue primary color signal B output from the adder 2B are supplied to a circuit configured similarly to the above red signal system. In the color picture tube 7 in the drawing, K _G and K _B are cathodes for green and blue.

A connection point between the collector of the transistor 6 and the resistor 24 is connected to one end of a capacitor 25 which constitutes a clamp circuit. The other end of the capacitor 25 is connected to one input terminal of a comparator 31 via a sampling switch circuit 26, and the other end of the capacitor 25 is connected to one input terminal of a comparator 34 via a sampling switch circuit 27. Connected to the input terminal. Also,
The other end of the capacitor 25 is connected via a switch circuit 28 to the cathode of a diode 29 whose anode is connected to the reference voltage source 30. The capacitor 25, the switch circuit 28, the diode 29 and the reference voltage source 30 constitute a clamp circuit. Each of the switch circuits 26, 27, 28 described above is configured to turn on when a high level control signal is supplied, for example.

The reference voltage source 32 is connected to the other input terminal of the comparator 31, the output terminal of the comparator 31 is grounded via the holding capacitor 33, and the output terminal of the comparator 31 is connected to the level shift circuit 4 Connected to the control terminal of.

A reference voltage source 35 is connected to the other input terminal of the comparator 34, the output terminal of the comparator 34 is grounded via a hold capacitor 36, and the output terminal of the comparator 34 is connected to the gain control amplifier 3 Connected to the control terminal of.

The horizontal and vertical deflection coils 23 of the color picture tube 7 are supplied with a deflection signal from a horizontal deflection circuit (not shown) from a terminal 17 and a deflection signal from a vertical deflection circuit (not shown) from a terminal 19. To be done. Further, the horizontal synchronizing signal is supplied from the terminal 16 to each of the pulse forming circuit 8, the blanking pulse generating circuit 10 and the gate pulse generating circuit 11. The vertical synchronizing signal is supplied from the terminal 18 to the pulse forming circuit 8, the blanking pulse generating circuit 10 and the gate pulse generating circuit 11, respectively.

The pulse forming circuit 8 is a circuit for forming a reference pulse for white balance adjustment. In the pulse forming circuit 8, the first half of one horizontal period is at a level of, for example, 601RE, and the latter half is at a level of 15 to 20 IRE. A level reference pulse is formed. The beam current at the white level is adjusted at the level of the first half of the reference pulse, and the beam current at the black level is adjusted at the level of the latter half of the reference pulse.

The output of the pulse forming circuit 8 is added through the inserting circuit 9 to the adder 2
R, 2G, 2B are supplied to the primary color signals as shown in FIG. 2A.
The reference pulse is inserted in a predetermined horizontal period immediately after the R, G, B vertical blanking periods. (B in FIG. 2 indicates a blanking pulse.) The blanking pulse generation circuit 10 is a pulse generation circuit for generating a horizontal blanking pulse and a vertical blanking pulse as shown in FIG. The output of the pulse generation circuit 10 is supplied to the base of the transistor 12 for video blanking, and is also supplied to the switch circuit 28 of the clamp circuit as a control signal.

In the section where the blanking pulse is at the high level, the transistor 12 is turned on, the base of the transistor 5 forming the video output circuit is grounded, the video blanking is applied, and the horizontal and vertical blanking lines are generated. It is so arranged that it does not appear on the screen of the color picture tube 7.

As shown in FIGS. 2C and 2D, the gate pulse generating circuit 11 has a high level pulse in the first half P ₁ of the section in which the reference pulse is inserted and the second half P of the section in which the reference pulse is inserted. _{At 2} , high-level pulses are generated. The signal shown in FIG. 2C is supplied to the switch circuit 27 for sampling as a control signal, and
The signal shown in FIG. D is supplied to the switch circuit 26 as a control signal.

The operation of the embodiment of the present invention will be described below. In the vertical blanking period, the output of the blanking pulse generation circuit 10 is set to the high level, the transistor 12 is turned on, and the switch circuit 28 of the clamp circuit is turned on. When the transistor 12 is turned on, the transistor 5 of the video output circuit is turned off and the video blanking state is set.

When the switch circuit 28 is turned on, the connection point between the capacitor 25 and the switch circuits 26 and 27 becomes the clamp voltage. At this time, if a leak current is generated between the cathode of the color picture tube 7 and the ground, a detection voltage corresponding to the leak current is generated at the connection point between the collector of the transistor 6 and the resistor 24.

When the vertical blanking period ends, the output of the blanking pulse generation circuit 10 is set to low level and the transistor
When 12 is turned off, the switch circuit 28 of the clamp circuit is turned off. When the transistor 12 is turned off, the red primary color signal R from the level shift circuit 4 passes through the transistors 5 and 6 and the cathode K _{R of the} color picture tube 7
Is supplied to.

Reference pulse in one horizontal period immediately after the vertical blanking period
P ₁ and P ₂ are inserted, and the cathode current I _K corresponding to the level of the first half P _{1 and} the level of the second half P ₂ of the reference pulse section
Flows, and a detection voltage corresponding to the cathode current I _{K including} a leak current is generated at the connection point between the collector of the transistor 6 and the resistor 24.

Therefore, at the connection point between the capacitor 25 and the switch circuits 26 and 27, the detection voltage corresponding to the leak current is canceled out, and the cathode current detection signal in the form in which the clamp voltage is added is generated.

By the signal shown in FIG. 2C from the gate pulse circuit 11,
The switch circuit 27 is turned on in the first half P ₁ of the reference pulse section, the detection signal of the cathode current corresponding to the level of P ₁ is supplied to the comparator 34, and the comparator 34 compares it with a reference voltage that is a predetermined voltage. To be done.

The error signal obtained at the output side of the comparator 34 is held by the holding capacitor 36 and supplied to the control terminal of the gain control amplifier 3. In the gain control amplifier 3, the gain is controlled and the red primary color signal R is controlled to have a predetermined level in consideration of white balance.

Further, the switch circuit 26 is turned on in the latter half P ₂ of the reference pulse section by the signal shown in FIG. 2D from the gate pulse circuit 11, and the detection signal of the cathode current corresponding to the level of P ₂ is supplied to the comparator 31. Then, the comparator 31 compares it with a reference voltage which is a predetermined voltage.

The error signal obtained at the output side of the comparator 31 is held by the holding capacitor 33 and supplied to the control terminal of the level shift circuit 4. In the level shift circuit 4, the direct current level is controlled and the red primary color signal R is controlled so as to be a predetermined level in consideration of white balance.

Although not shown, the control of the cathode current as described above is similarly performed for the green signal system and the blue signal system.

〔The invention's effect〕

In the present invention, the clamp circuit is provided, the cathode current detection signal is clamped by the clamp circuit in the vertical blanking period, and the sampling switch circuit is turned on in the section in which the reference pulse is inserted immediately after the vertical blanking period. , The detection signal of the cathode current proportional to the luminance of the leak current is offset through the capacitor that constitutes the clamp circuit is supplied to the comparator, and the level of the primary color signal is changed based on the error signal generated in the comparator. Controlled.

Therefore, according to the present invention, the cathode current proportional to the luminance of the color picture tube can be accurately detected, and the deviation of the white balance due to the leak current can be prevented. Further, since the leak current can be canceled by a simple circuit, it is possible to make an IC without increasing the circuit configuration, which is advantageous in making an IC.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a waveform diagram of each part used for explaining the operation of an embodiment of the present invention, and FIG.
The figure is a block diagram of a conventional leak current cancel circuit. Description of main symbols in the drawings 1: Matrix circuit, 2R, 2G, 2B: Adder, 3: Gain control amplifier, 4: Level shift circuit, 7: Color picture tube,
8: Pulse forming circuit, 9: Inserting circuit, 10: Blanking pulse generating circuit, 11: Gate pulse generating circuit, 24: Resistor for detecting cathode current, 25: Capacitor for clamping, 26, 27, 2
8: Switch circuit, 29: Diode, 30, 32, 35: Reference voltage source, 31, 34: Comparator, 33, 36: Hold capacitors.

Claims (1)

[Claims] 1. In horizontal and vertical blanking periods,
A switching means that operates by a blanking pulse so as to cut off the video signal supplied to the color image pickup tube, and a reference signal whose white level and black level are defined as reference levels are inserted immediately after the vertical blanking period. Insertion means for detecting the cathode current of the color image pickup tube in the vertical blanking period and generating a detection signal of the cathode current, and the detection signal of the cathode current is supplied to the detection signal. And a comparator that is supplied with the output signal of the clamp means, detects the white level and the black level of the reference signal, and compares the detection level with the reference voltage. And the white level and black level of the primary color signal are controlled by the output of the comparator. Color temperature automatic adjusting circuit is characterized in that a control means.