JP3020586B2 - Image display device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a picture tube driving circuit used for a video circuit such as a character graphic display, a television, and a monitor.

[Prior art] Conventionally, the white balance of a color picture receiver adjusted at the time of shipment from a factory is affected by the aging of the color picture tube such as the emission of the cathode and the drift of the circuit, so that the white balance is changed by a long use. There was a problem that it was easy. An automatic white balance adjustment circuit for compensating for such a change in white balance is described in, for example, Japanese Patent Application Laid-Open No. 60-18087.

FIG. 4 is a block diagram showing the above-mentioned conventional automatic white balance adjustment circuit.

In FIG. 4, video output circuits 12R, 12G and 12B
Collector resistance 2 as shown in video output circuit 12B respectively
It has the same circuit configuration as the circuit composed of 6 and the transistor 24. Cathode current detection circuits 9R, 9G and 9B
Are each composed of a transistor 28 and a resistor as shown in the cathode detection circuit 9B.

In FIG. 4, the R (red), G (green), and B (blue) primary color signals input to the input terminals 1R, 1G, and 1B respectively pass through signal synthesizing circuits 8R, 8G, and 8B for drive adjustment. Are amplified by the variable gain amplifier circuits 10R, 10G, and 10B, and are level-shifted by the level correction circuits 11R, 11G, and 11B for cutoff adjustment. The video output circuits 12R, 12B, and 12B amplify the driving tube to a driveable amplitude, and the cathode current detection circuits 9R, 9G, and 9B
Are supplied to the cathode terminals 7R, 7G, 7B of the picture tube 6 for image display.

The automatic white balance adjustment operation performed at that time will be described below. Signal generation circuit 2 for automatic white balance adjustment
Are two types of reference signals for white balance adjustment, that is, cutoff adjustment and drive adjustment, output from the horizontal and vertical blanking pulses input to the input terminals 3H and 3V, respectively, via the reference signal line 4. And a gate pulse output through the gate signal line 5 are generated.
These generated signals are used as signal synthesizing circuits 8R and 8R, respectively.
G, 8B and the sampling circuits 13R, 13G, 13B. B
Focusing on the primary color signal system, a detection voltage proportional to the cathode current from the cathode 7b flowing into the emitter of the transistor 28 in the cathode current detection circuit 9B is input to the sampling circuit 13B via the cathode current detection signal line 30B. . A gate pulse is supplied to the sampling circuit 13B via the gate signal line 5, and the operation of the operational amplifier 16B for cut-off adjustment and the operational amplifier 17B for drive adjustment produce a negative feedback operation. The control voltage is held on the hold capacitors 14B and 15B. Note that R
And the primary color signal circuits of G have the same circuit configuration as B, and operate in the same manner as B.

Here, by sharing the reference voltage sources 17 and 18 with the R, G, and B primary color signal circuits, the ratio of the cathode current of each primary color is controlled to a constant value, and the white balance is stabilized.

[Problem to be Solved by the Invention] In the conventional example shown in FIG.
Since R, 11G, and 11B are located before the video output circuits 12R, 12G, and 12B, respectively, the signal dynamic range after these video output circuits must be set widely in consideration of the level correction amount. It is necessary to increase the power supply voltage to be added. In addition, in order to ensure the resolution required for the receiver, it is necessary to suppress a decrease in the cutoff frequency of the output circuit, which is determined by the output capacitance including the collector resistance 26 in the video output circuit and the floating capacitance of the wiring. , Collector resistance 26
Cannot be set to a high value.

Further, since the cathode current detection circuits 9R, 9G, and 9B are interposed between the video output circuit and the picture tube, the output capacitance increases due to the influence of parasitic capacitance and the like. Therefore, it is necessary to lower the value of the collector resistor 26 in order to secure a desired frequency band.

Therefore, when the terminal 27 of the power supply voltage is kept constant, the current flowing through the collector resistor 26 increases, so that the power consumption of the video output circuit increases. In particular, it has been difficult to realize automatic white balance adjustment for a high-definition display or the like that requires wideband characteristics.

An object of the present invention is to provide an image display device capable of performing automatic white balance adjustment while suppressing power consumption of a video output circuit.

[Means for Solving the Invention] To achieve the above object, an image display device according to the present invention provides a video output circuit for amplifying a video signal, a beam current for detecting a beam current corresponding to the luminance of each primary color. A detection circuit is connected, a level correction circuit for correcting the DC level of the video signal is connected to the beam current detection circuit, and the level correction circuit is connected to a cathode of a picture tube.

In addition, a video output circuit for amplifying the video signal is connected to a level correction circuit for correcting the DC level of the video signal, the level correction circuit including means for detecting a beam current corresponding to the luminance of each primary color. May be connected.

Further, a level correction circuit for correcting the DC level of the video signal is connected to a video output circuit for amplifying the video signal, the level correction circuit is connected to a cathode of a picture tube, and a beam current is supplied to an anode of the picture tube. A configuration in which a beam current detection circuit to be detected may be connected.

[Operation] In each of the above technical means, each component has the following functions.

The video output circuit amplifies the video signal to an amplitude required for driving the picture tube. The level correction circuit corrects the DC level of the video signal so that a white balance can be secured. Here, the power consumption of the video output circuit can be reduced by providing the level correction circuit after the video output circuit as described in the above technical means. The beam current detection circuit has a function of detecting a beam current corresponding to the luminance of each primary color.

Hereinafter, an embodiment of a picture tube driving circuit according to the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a picture tube driving circuit according to an embodiment of the present invention. In FIG. 1, 31 is an input signal source, 12 is a video output circuit, 11 is a level correction circuit, 9 is a beam current detection circuit, and 6 is a picture tube. In FIG. 1, a picture tube driving circuit 911 including a level correction circuit 11 and a beam current detection circuit 9 arranged at a subsequent stage is provided at a subsequent stage of the video output circuit 12. By using the configuration shown in FIG. 1, the power consumption of the video output circuit 12 can be suppressed. FIG. 2 shows a specific circuit configuration of the block diagram of one embodiment of the present invention shown in FIG. In FIG. 2, a level correction circuit 110 controlled by a signal transmitted from a control line 20R is inserted between the video output circuit 12 and the picture tube 6, thereby reducing the power consumption of the video output circuit. Have been. The video output circuit 12 is a transistor
The band is broadened by the cascode configuration by 24 and 241, the emitter peaking by the capacitor 252, and the parallel peaking by the coil 261. Reference numeral 25 denotes a resistor for setting the gain of the common-emitter amplifier circuit including the transistor 24, and reference numeral 251 denotes a resistor for setting the characteristics of the emitter peaking. 27 is a power supply voltage terminal of the video output circuit. 242
Is the transistor 241 that constitutes the common base amplifier circuit.
Is a terminal for applying a bias voltage to the base. The level shift amount of the level correction circuit 110 is controlled by a signal transmitted from the control line 20R. The beam current detection circuit guides the cathode current flowing through the emitter of the transistor 28 to the collector side, converts the current into a voltage by the detection resistor 29, and outputs the converted signal to the signal line 30R. At this time, the cathode current includes not only the beam current but also a leakage current from another electrode of the picture tube 6. Therefore, in order to detect the beam current, the detected beam current is made sufficiently larger than the above-mentioned leakage current, or the leakage current is canceled by means described later. The diode 282 and the resistor 284 protect the transistor 28 during the discharge of the picture tube 6. Also, by adjusting the value of the resistor 284,
Gamma correction can also be performed.

In the circuit of FIG. 2, when the resistance 291 is zero Ω, the deterioration of the frequency characteristic of the driving circuit is caused by the floating capacitance 293 of the signal line 30R connected via the stray capacitance 71R of the picture tube and the parasitic capacitance 281 of the transistor 28. It is caused by the parasitic capacitance of the diode 292.

Therefore, in the present invention, the value of the resistor 291 shown in FIG. 2 is set to be sufficiently larger than the value of the resistor 26, or the parallel impedance of the stray capacitance 293 and the parasitic capacitance of the diode 292 at the frequency at which the characteristic deterioration is problematic. It is set to be much larger than that. This allows transistor 28
The above-mentioned adverse effect of the stray capacitance 293 acting via the parasitic capacitance 281 can be eliminated. Also, in FIG.
Has a function of bypassing the video signal in order to compensate for the lack of the driving capability of the picture tube at a high frequency of the transistor 28. Due to this bypass effect, the Miller effect due to the amplifying operation of the transistor 28 is also eliminated. The diode or zener diode 292 functions to protect the control circuit connected via the signal line 30R, to improve the beam current detection sensitivity by increasing the value of the resistor 29, and to reduce the collector voltage of the transistor 28. It has the effect of suppressing saturation due to the rise. In FIG. 4, a sampling circuit 13R is connected to a stage preceding the comparison circuit 16R to form a control circuit. However, normally, a sampling circuit follows the connection of the comparison circuits 16R and 17R to form a control circuit. FIG. 3 shows an embodiment which is effective even when the driving voltage amplitude and the beam current at the time of driving are increased in accordance with the large screen and high brightness of the picture tube. When the driving voltage or the current at the time of driving increases, the voltage between the emitter and the collector of the transistor 28 decreases and saturates, and there is a possibility that a trouble such as an intermittent driving operation of the picture tube or a detecting operation of the beam current occurs. is there. Therefore, in FIG. 3, the clamp operation of the diodes 285 and 286 prevents the base-collector voltage of the transistor 28 from being deeply biased in the forward direction. Here, the types of the diodes 285 and 286 can be arbitrarily selected as long as they satisfy the absolute rating conditions such as reverse withstand voltage.For example, a Schottky barrier diode or the like can be used in consideration of high-speed performance. The types may be different. For example, the saturation prevention effect can be improved by a Baker-clamp configuration using the diode 285 made of silicon and the diode 285 made of germanium.

Next, a picture tube driving circuit is provided at the subsequent stage of the video output circuit, and the structure of the picture tube driving circuit is shown in FIG. . By using the configuration shown in FIG. 5, the power consumption of the video output circuit 12 can be suppressed and the beam current detection circuit 9 can have a wider band. FIG. 6 shows a specific circuit of the block diagram of one embodiment of the present invention shown in FIG.

With the circuit configuration shown in FIG. 6, a high-performance element having a low withstand voltage can be selected for the transistor 28 used in the beam current detection circuit. For example, in FIG. 4, an element of 70 V or less instead of 160 V or more can be applied. In general, the amplifying ability, high-frequency characteristics, and small parasitic capacitance of active elements are contrary to high withstand voltage. For example, by selecting an element having a large amplification degree β for the transistor 28, the detection accuracy of the beam current can be improved and the minimum detection current can be reduced. That is, Icbo can be reduced. In addition, the high frequency characteristics of the transistor 28 are improved or
By reducing the parasitic capacitance, the frequency band of the driving circuit can be expanded. Here, when the reliability of the level correction circuit 110 can be ensured, the protection resistor 284 shown in FIG. 6 can change or delete the insertion position between the beam current detection circuit and the level correction circuit. it can. However, in consideration of the protection of the level correction circuit 110 and the deterioration of the frequency characteristic due to the parasitic capacitance of this circuit, the insertion position of the protection resistor 28 is preferably immediately before the picture tube as shown in FIG.

Next, FIG. 7 shows an embodiment in which the level correction circuit 110 of FIG. 6 is configured using a clamp circuit. In the circuit configuration shown in FIG. 7, the level-controlled clamping voltage source 116
Is connected to the base of the clamp transistor 113 via the clamp switch 115 to clamp the picture tube side of the coupling capacitor 111. By using the discharge current flowing through the coupling capacitor 111 during the clamp as the return current between the emitter and the collector of the transistor 113, fluctuations in the clamp level (black sun) due to leakage of the discharge current into peripheral circuits are eliminated. In the case of FIG. 7, a diode
The black sun phenomenon caused by the sum of the forward voltage due to the conduction of 282 and the forward voltage between the base and the emitter of the transistor 28 and the voltage drop in the resistor 26 can be eliminated. Resistance 118
Operates to raise the base voltage of the transistor 113 to the power supply voltage connected to the terminal 117 during the unclamping period when the switch 115 is opened. Therefore, when unclamping, a reverse voltage is applied to the diode 112, and the transistor 1
The 13 emitters are released from the coupling capacitor 111. The diode 114 is a protection diode that guarantees a reverse withstand voltage condition between the base and the emitter of the transistor 113 when unclamped or when the picture tube is discharged. The clamp circuit shown in FIG. 7 is of a synchronous type based on the ON / OFF operation of the clamp switch 115, and the power consumption of the circuit for controlling the clamp is suppressed. Normally, the clamp switch 115 is turned on once during the blanking interval. However, when the switch 115 and the resistor 118 are short-circuited / opened and omitted to reduce the circuit scale, the signal on the signal line 20R may be controlled to switch the voltage of the voltage source 116. Further, even if the voltage of the voltage source 116 is constant without switching control, the diode 112 and the transistor 113 are automatically turned on by an increase in the video signal level on the anode side of the diode 112. Operate. Further, even when the voltage source 116 is set to a constant voltage, the high-frequency component of the video signal leaked through the diode 112 is detected by the diode 114 due to the influence of the absolute value of the internal impedance remaining in the voltage source 116 and the time constant. May cause fluctuations in the clamp level. In such a case, a minimum necessary capacitance to cancel the detection effect on the diode 114, for example, a capacitor of the order of several tens of pF that does not adversely affect the frequency band of the drive circuit is added in parallel, or a parallel parasitic capacitance is added to the diode 114. A zener diode having a large value is used.

In FIG. 7, it is clear that the coupling capacitor 111 charged by the detected beam current 7R1 does not cause a problem such as sag as long as the capacitance value is used for an ordinary clamp circuit.

Next, an embodiment in which the cathode current can be detected in the preceding stage of the correction circuit even when a bias current other than the beam current flows through the picture tube driving signal line or when a leak current flows between the picture tube electrodes. It is shown in FIG. As an example of the above-described clamp circuit, in order to rapidly start up the clamp operation after turning on the power supply, there is a case where a charging bias current is supplied to the coupling capacitor 111 via the resistor 34 or the series connection of the resistor 34 and the diode. is there. However, in the conventional method, only the beam current cannot be detected due to the application of the bias current. Therefore, as shown in FIG. 8, the bias current 38 is canceled by using the current control current source 31 so that the current does not flow through the detection resistor 29. Current control current source
31 detects the above-mentioned bias current 38 flowing to the input terminal 32 and supplies a current of the same magnitude as that from the output current source 33, but this output current is detected by the detection resistor in the beam current path. The above-described current cancellation can be performed by flowing the current to the output point via at least one of the output lines 35, 36, and 37 in the figure before the step 29, for example. In addition to the beam current component in the picture tube, the cathode current
Includes leakage current components from other electrodes such as 71R, the first grid, and the second grid. However, regarding the leakage current component from the electrode separated between the R, G, and B primary colors, the electrode is connected to the preceding stage of the detection resistor 29 in the above beam current path via a resistor or an active element. Can be offset. The above is the kind of the driving electrode of the picture tube, for example, the cathode,
It goes without saying that it does not depend on each grid, anode or the like.

Next, another embodiment for supplying a bias current to the level correction circuit is shown in FIG. In FIG. 9, the level correction circuit is constituted by a current control voltage source circuit using a transistor 1102. The voltage of this voltage source circuit is controlled by the current flowing between the input terminals 20R1 and 20R2 of the photocoupler 20R0.
4. It is necessary to flow to the transistor 1102. The internal impedance of the voltage source circuit is
Thus, although the value is reduced for a high-frequency signal, the value depends on the bias current, that is, is almost proportional to the bias current of the transistor 1102, and is not infinitely small. To suppress the adverse effect of the internal impedance on the voltage of the voltage source circuit, it is necessary to make the control bias current constant or to make it sufficiently larger than the beam current.
Therefore, in the embodiment shown in FIG. 9, a constant control bias current is supplied to the above-mentioned voltage power supply circuit, and a current equal to this current is extracted from a stage preceding the detection resistor 29 in the beam current path. Detection is possible. The control bias current is the temperature compensation diode 323.
325 and the current flowing through the resistor 324, the current value is set, and the current flows from the transistor 322 to the transistor 331 via the above constant voltage circuit and the like. In this case, the resistor 34 connected to the collector of the transistor 322 has the function of separating the parasitic capacitance on the collector side of the transistor 322 from the drive signal source and suppressing the deterioration of the frequency characteristics of the drive circuit. The collector of the transistor 331 is connected to at least one of the output lines 35, 36 and 37, for example. In order to improve the setting accuracy of the control bias current, the transistors 322 and 3
It is also possible to add a series resistor to each of the 31 emitters and each of the diodes 321 and 322. In order to further improve the temperature stability of the control bias current, the transistor 322 and the diode 323, and the transistor 331 and the diode 321 are thermally coupled, or these components are formed on the same semiconductor chip, for example, an IC. It is also possible.

FIG. 10 shows an embodiment in which the clamp circuit used as the level correction circuit in the above embodiment can be applied to a wider-band picture tube driving circuit. In the embodiment of FIG. 10, the collector of the clamp transistor 113 is
It is connected to a drive signal source via a switch circuit 39 that is short-circuited only during clamping. By providing the switch circuit 39, during the display period in which the broadband drive signal is applied to the picture tube 6, the collector of the transistor 113 is used as the drive signal source.
Since the base-to-base capacitance and the floating capacitance of the collector are not added, it is possible to further widen the bandwidth of the drive circuit. Here, as in FIG. 7, the voltage of the voltage source 116 may be switching-controlled for a synchronous system or may be a constant voltage for an asynchronous system. However, by providing the clamp circuit described above, the diode 112
Is always connected to the drive signal source and the capacitance is added. When it is necessary to reduce the parasitic capacitance added via the diode 112, a reverse voltage is applied to the diode 112 during the display period, so that the
As shown, another diode 1121 is connected to the diode 112.
It is also possible to connect them in series with the same polarity.

Next, another embodiment of the switch circuit 39 shown in FIG. 10 is shown in FIG. In the embodiment shown in FIG. 12, since the collector current of the transistor 113 can be regarded as zero at the time of unclamping, the anode voltage of the constant current diode 392 also becomes zero, a reverse voltage is applied to the diode 391, and the driving signal source supplies The collector of the transistor 113 is shut off.
However, the connection via the junction capacitance of the diode 391 remains.
At the time of clamping, the collector current of the transistor 113 becomes a current value sufficiently larger than the current value of the constant current diode 392, so that the anode voltage of the constant current diode 392 rises, the diode 391 conducts, and the collector current Most of the current flows to the coupling capacitor 111, and a stable clamping operation can be performed. Therefore, the diode 391 operates as an automatic switch. Considering that the diode 391 is made conductive at the time of clamping when the collector current of the transistor 113 becomes large, the constant current diode 392 can be replaced with a resistor. Further, the constant current diode 392 can be replaced with a constant current circuit using an active element such as an FET. Here, the switching speed of the diode 391 is
It is considered that it is inversely proportional to the parasitic capacitance of the collector circuit of the transistor 113 and is governed by the slew rate of the collector voltage proportional to the collector current of the transistor 113 at the time of clamping. Therefore, in order to increase the switching speed of the diode 391, the cathode of the constant current diode 392 always shuts off the diode 391 during the non-clamp period, and a voltage within a range where the junction capacitance of the diode 391 can be maintained at a level that does not cause a problem. It is also possible to connect an offset voltage source having the following. For example, the cathode of the above constant current diode 392 is connected in parallel to the base bias power supply terminal 242 of the common base transistor 241.

In the embodiment shown in FIG.
Although most of the collector current 113 flows to the coupling capacitor 111 to perform a stable clamping operation, a current component flowing to the constant current diode 392 causes a minute change in the clamp level, and inevitably deteriorates the clamp accuracy. Therefore, FIG. 13 shows an embodiment that does not involve the deterioration of the clamping accuracy.
In FIG. 13, by connecting the resistor 393 between the emitter of the transistor 241 and the collector of the transistor 113, the current component flowing through the resistor 393 for switching the diode 391 can be returned to the coupling capacitor 111 again. Clamping accuracy is improved. That is, the emitter current (collector current) of the transistor 241 decreases by the amount of the current flowing through the resistor 393, and the corresponding current flows into the coupling capacitor 111 from the collector of the transistor 241. The resistor 393 can be designed so that the upper limit is a resistance value that satisfies the switching speed at which the time constant of the collector circuit of the transistor 113 satisfies the required switching speed, and the lower limit is a resistance value at which a current that does not interrupt the transistor 241 flows. The resistor 393 is
As shown in the figure, a constant current diode (the anode is connected to the collector of the transistor 113) can be replaced. In this case, however, a resistor or an inductance is required to suppress a high-frequency signal leaking through the parallel parasitic capacitance of the constant current diode. Should be inserted in series. It goes without saying that the same effect can be obtained even if the resistor 393 is connected between the emitter of the transistor 24 and the collector of the transistor 113.

Next, FIG. 14 shows a block diagram of a picture tube driving circuit in which the picture tube driving circuit 911 is composed of a cathode current detection and level correction circuit 912 having both functions of level correction and beam current detection. The configuration shown in FIG. 14 enables high performance such as reduction in circuit scale and improvement in reliability. FIG. 15 shows a specific circuit configuration of FIG. In FIG. 15, the level correction circuit can be provided with a beam current detection function by also using the transistor of the clamp circuit for detecting the beam current.

In FIG. 15, the switch circuit 115 is kept in a short-circuit state when the beam current is detected, and is opened and closed by a clamp cycle in other periods to control the cycle clamp operation.
The switch circuit 40 is tilted toward the drive signal line only during clamping to enable the above-described stable clamping operation.

The feature of FIG. 15 is that the voltage of the voltage source
Since the DC output of the video output circuit is transmitted to the cathode 7R via 3 and can be cut off by the coupling capacitor 111, accurate level correction not affected by the video signal can be performed. In addition, since the transistor 113 can be used for both clamping and beam current detection, the circuit scale is reduced, and at the same time, the number of locations that are damaged during the above-described discharge in the tube is reduced, thereby improving reliability. Further, as in the embodiment shown in FIG. 10, the drive circuit can be further widened in bandwidth.

Next, another embodiment of the switch circuit 40 shown in FIG.
Figure 16 shows. In the embodiment shown in FIG. 16, similarly to the embodiment shown in FIG. 12, a constant current diode 402 is used so that the diode 401 automatically conducts only during the clamp period when the collector current of the transistor 113 becomes large. I have. Here, a comparison is made between the detection beam current flowing through the collector of the transistor 113 and the clamp current. The electric charge stored in the coupling capacitor 111 by the beam current flowing during the non-clamp period is intensively discharged during the clamp period. In general, the non-clamp period is at least ten times as long as the clamp period, and thus the magnitude of the clamp current is considered to be at least ten times or more the detection beam current. Therefore, the design of the constant current diode 402 is easy, and in some cases, the constant current diode 402 can be replaced with a resistor.

Next, an embodiment capable of improving the accuracy of beam current detection will be described.
As shown in FIG. In the embodiment shown in FIG. 17, the switch circuit 41 is opened only when the beam current is detected, so that the output of the video output circuit from the DC component to the AC component is completely cut off from the cathode 7R at the time of detection. Switch circuit 41
When the beam current is always short-circuited, a settling time proportional to the time constant determined substantially by the product of the coupling capacitor 111 and the output resistance 26 of the output circuit is required, but the switch circuit 41 must be opened. As a result, the settling time can be ignored.

Further, the switch circuit 42 is connected to the path indicated by the broken line in FIG.
Is inserted, and the switch circuit is short-circuited and the switch circuit 41 is opened only when the beam current is detected, whereby the beam current can be detected while applying the output voltage of the video output circuit to the cathode 7R. Therefore, the voltage applied to the picture tube when detecting the beam current is changed to the level-controlled voltage source 116.
(The switch circuit 42 is opened and the switch circuit 115 is short-circuited) or supplied from the video output circuit (the switch circuit 42 is short-circuited and the switch circuit 115 is opened).
Can be appropriately selected.

Next, another embodiment of the switch circuit 41 shown in FIG.
See Figure 18. In FIG. 18, the coupling capacitor is divided into 110 for high-frequency signals and 119 for other signals so that the latter can be cut off from the drive signal source by the diode 411 of 119. In the figure, the capacitor 119 indicates an electrolytic capacitor, but may be of any type. The high-frequency signal coupling capacitor 110 has a capacitance value as small as possible so that the settling time can be ignored. When the power is turned on, a bias current flows from the power supply terminal 412 to the capacitors 110 and 119 via the bias resistor 413, and a normal clamping operation is started. If the high-frequency impedance of the diode 411 can be reduced sufficiently, zero is originally good. At the time of beam current detection, the transistor 415 is turned on by a signal from the detection signal source 416, and its collector voltage is reduced so that the diode 411 is cut off. Resistor 417 is transistor 4
This is a resistor for setting 15 base currents. When performing high-speed control while saturating transistor 415,
A speed-up capacitor 419 and a base current extraction resistor 418 are added. Except during the detection of the beam current, the resistor 411 is used to avoid adding the base-collector capacitance of the transistor 415 or the stray capacitance of the collector circuit to the drive signal line.
Is inserted as shown in FIG.

FIG. 19 shows an embodiment in which the beam current can be detected also from the current of an electrode other than the cathode electrode of the picture tube. In FIG. 19, the output of the video output circuit 12 is applied to the cathodes 7R, 7G, 7B of the picture tube 6 via the level correction circuit 11, but the drive electrodes of the picture tube 6 are R, G, B 3
The first grid or the like can be used as long as the electrodes are primary color and independent electrodes. In FIG. 19, the beam current detection circuit 9 is connected to the anode 6A of the picture tube 6, and is configured to detect a beam current which is a part of the anode current. But,
The beam current detection circuit 9 can be connected to electrodes such as the second and third grids as long as an electrode through which a current correlated with the beam current flows. However, the beam current of a picture tube capable of displaying multiple colors, excluding the monochrome picture tube,
In the case of detection from an electrode commonly used for a plurality of colors, it is necessary to separate each color by, for example, flowing a beam current of each color at a different timing. FIG. 20 shows an embodiment showing a specific circuit having the above configuration. 20, the beam current detection circuit 9 includes a rectifier diode 60.
0, flyback transformer FBT601, voltage dividing resistors R1 602 and R2 603 for stabilizing high voltage by detecting high voltage from terminal 605, Rb604 for converting beam current to voltage and detecting beam current detection voltage constituted by a voltage source V _R for providing a DC shift to. The above-described beam current detection voltage is output to the outside from the detection terminal 606.By extracting this detection voltage from the ABL terminal 607 through an integration circuit including the resistor R _ABL and the capacitor C _ABL , the beam current average value ABL control is performed. Voltage (control voltage for automatic brightness limiting circuit)
Can be used as

Here, the current I _FBT of the flyback transformer 603 to be detected, the anode current I _A and the partial pressure plus the leakage current components of the respective terminals of the picture tube 6 to the beam current resistance R1 6
02 and R2 the current flowing through the 603 I _R, include distortion current component of the higher-order distortion current of the horizontal deflection period flows to the ground during such a flyback transformer winding. However, since the amplitude other than the beam current can be regarded as almost constant amplitude, the peak value and average value of the current _IFBT ,
By detecting the amount of change in the instantaneous value, the beam current can be separately detected. Even when the amplitude of the current component other than the beam current is not sufficiently small with respect to the beam current, the average value can be regarded as constant. Therefore, the beam current can be easily detected by using the above method. .

Next, FIG. 21 shows an embodiment in which the present invention is applied to a video output circuit of a dynamic load system. In FIG. 21, the video output transistor 24 is loaded with a constant current source or a constant current circuit to reduce the power consumption, and a SEPP circuit composed of transistors 43 and 45 is added as an output buffer for image reception. The tube 6 is being driven. The above dynamic load circuit can reduce the power consumption in terms of direct current regardless of the large output voltage by suppressing the power supply current to a small current and making the current constant, but the capacitive load of the cathode 7R and the like of the picture tube 6 can be reduced. The output current required to drive the load with a large-amplitude broadband signal voltage cannot be supplied. In the above-mentioned SEPP circuit for output buffer, which is required for this purpose, the picture tube 6 can be driven by controlling the cutoff of the transistor to a shallow level as a class AB operation in which a somewhat large idling current is passed to the transistors 43 and 45 used. ing. When the beam current is detected using the video output circuit of the dynamic load method described above, if the effect circuit of the above-described method is arranged at the subsequent stage of the video output circuit, the load capacity of the video output circuit increases. The advantage of low power consumption is lost.

Therefore, as shown in Fig. 21, beam current detection is
It is a feature of the present invention that the operation is performed using the transistor 43 of the circuit. Terminal 48 is a power supply terminal for biasing the SEPP circuit. However, at the time of current detection, it is necessary to cut off the idling current. Therefore, in the present invention, a constant current source or a constant current circuit as shown in FIG.
By controlling the current of 47 and reducing the current at the time of current detection, and controlling the bias voltage of the SEPP circuit due to the voltage drop of the bias impedance 46, only the transistor 45 is cut off at the time of current detection. In this case, the diode 44 shown in FIG. 21 functions to stably shut off the transistor 45 even when the detected beam current is extremely small, but is deleted when the detected current is somewhat large, for example, 10 μA or more. There is no problem even if a short circuit occurs).

Next, another embodiment that enables beam current detection even when a dynamic load video output circuit is used will be described.
See Figure 22. In FIG. 22, by controlling the current of a constant current circuit including a transistor 471, the conduction and cutoff of the diode 44 are switched to detect the beam current.
Diodes 462 and 4 constituting bias impedance
63 compensates the temperature drift of the idling current, so that the diodes 462 and 463 and the transistors 43 and 45 can be formed on the same semiconductor or thermally coupled. The bypass capacitor 464 eliminates the directionality of the drive impedance of the SEPP circuit. The resistors 431 and 451 are used for setting the idling current and protecting the transistors 43 and 45, respectively. The resistor 452 is also used for overcurrent protection of the transistor 45 at the time of erroneous contact. Further, the capacitor 500 and the resistor 501 constitute a bypass circuit for compensating for deterioration of the frequency characteristic of the drive circuit by the protection resistor 284, and have a high impedance with respect to the discharge energy in the picture tube 6. Transistors that make up a constant current circuit
Reference numeral 471 denotes a collector current of the transistor 473 controlled by the current detection signal source 416, which is AC grounded to a terminal 472, receives the base current biased by a resistor 474, and supplies it to a bias impedance of the SEPP circuit.
The collector current of the transistor 473 is adjusted by the resistor 475. Since both the transistors 473 and 471 are unsaturated, high-speed control is possible. Input resistance 490 and feedback resistance 491
Thus, parallel feedback is applied to the output transistor 24. However, even during the current detection period, only the diode 44 is shut off, and this feedback is maintained, so that the output voltage of the transistor 43 is stably supplied to the picture tube 6. In addition, since the base voltage of the transistor 471 is kept constant during current detection switching, leakage of the detection signal from the signal source 416 to the transistor 45 via the capacitor 494 can be suppressed. Negative feedback is also applied to transistor 471 by resistor 495 and capacitor 494,
Each of the resistor 496 and the capacitor 497 and the resistor 492 and the capacitor 493 are used for peaking. In addition, the Zener diode 253 has an input resistance of 4 due to the parallel feedback.
The bypass capacitor 254 is used to reduce the operating point drop of the input signal source 31 caused by the DC bias of the feedback resistor 491 and 90, and the bypass capacitor 254 reduces the impedance of the zener diode 253 and performs noise compensation. The above operating point drop is also compensated for by using resistor 498. In this embodiment, since there is no output capacitance added for current detection,
The large output broadband characteristics of the drive circuit can be maintained.

FIG. 23 shows another embodiment capable of controlling the current of a constant current source or a constant current circuit. In FIG. 23, current control is performed by controlling a base bias voltage of a transistor 471 constituting a constant current circuit. Portions not shown are the same as those in the embodiment shown in FIG. This is performed by switching the transistor 51 and short-circuiting the resistor 479. When the resistor 479 is short-circuited,
The bias voltage is set by the voltage at terminal 476 and resistors 477 and 478. The resistor 512 is a base resistor for setting the base current of the transistor 51. To improve the switching speed, the value of the base resistor 512 is appropriately adjusted, or a speed-up capacitor 513 or a base current extracting resistor 511 is used. The breakdown voltage of the transistor 51 can be lower than that of the transistor 473 shown in FIG.

In the embodiments described above, the picture tube includes not only a cathode ray tube but also a plasma display tube and the like, and it is needless to say that the driving electrode includes other electrodes than the cathode and the grid. Also, the semiconductor used can be replaced not only with bipolar transistors and diodes but also with a wide range of active elements such as GaAs FETs. Further, the polarity of the element can be inverted by reversing the potential relation.

[Effects of the Invention] The present invention is configured as described above and has the following effects.

(1) According to the present invention, automatic white balance adjustment can be performed without increasing the power consumption of the video output circuit, so that automatic white balance adjustment can be performed even in a wideband video circuit required for an ultra-high definition display. .

(2) According to the present invention, the capacitance added to the picture tube driving signal line can be reduced with the addition of the beam current detection circuit, so that the frequency characteristic of the picture tube driving circuit with the addition of the beam current detection function can be reduced. Deterioration can be suppressed.

(3) According to the present invention, since the idling current of the SEPP circuit can be controlled, a beam current detection function can be added to the SEPP circuit.

[Brief description of the drawings]

FIG. 1 is a block diagram of a picture tube driving circuit showing an embodiment of the present invention, FIG. 2 is a specific circuit diagram of FIG. 1 of the present invention, and FIG. 3 is another circuit diagram of FIG. FIG. 4 is a specific circuit diagram, FIG. 4 is a circuit block diagram showing a conventional automatic white balance adjustment circuit,
FIG. 5 is another block diagram of a picture tube driving circuit showing one embodiment of the present invention, FIG. 6 is a specific circuit diagram of FIG. 5 of the present invention,
7 is another specific circuit diagram of FIG. 5 of the present invention, FIG. 8 is another specific circuit diagram of FIG. 5 of the present invention, and FIG. 9 is another specific circuit diagram of FIG. 5 of the present invention. FIG. 10 is a specific circuit diagram showing a clamp circuit of the present invention, and FIG. 11 is a specific circuit diagram of the present invention.
Another specific circuit diagram of FIG. 10, FIG. 12 is another specific circuit diagram of FIG. 10 of the present invention, FIG. 13 is another specific circuit diagram of FIG. 10 of the present invention, 14 is a block diagram of another picture tube driving circuit showing one embodiment of the present invention, FIG. 15 is another specific circuit diagram of FIG. 14 of the present invention, and FIG. 16 is a diagram of FIG. 14 of the present invention. Another specific circuit diagram, FIG. 17 is another specific circuit diagram of FIG. 14 of the present invention, FIG. 18 is another specific circuit diagram of FIG. 14 of the present invention,
FIG. 19 is a block diagram of another picture tube driving circuit showing an embodiment of the present invention, FIG. 20 is another specific circuit diagram of FIG. 19 of the present invention, and FIG. FIG. 22 is another specific circuit diagram of FIG. 21 of the present invention,
FIG. 23 is another specific circuit diagram of FIG. 21 of the present invention. 9: Beam current detection circuit 11: Level correction circuit 12: Video output circuit 29: Resistor for beam current detection 116: Voltage source whose level is controlled for level correction 111: Coupling capacitor 113: Clamp Beam current detection transistors 40, 115 ... Switch circuit for switching operation of clamp or beam current detection

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yoshio Amamiya 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Yokohama, Japan Inside Yokohama Plant, Hitachi, Ltd. (56) References JP-A-60-96981 (JP, A) JP-A Sho 61-187487 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G09G 1/00 H04N 9/73

Claims (8)

(57) [Claims] 1. A video output circuit for amplifying a video signal,
A beam current detection circuit for detecting a beam current corresponding to the luminance of each primary color is connected, and a level correction circuit for correcting the DC level of the video signal is connected to the beam current detection circuit,
An image display device, wherein the level correction circuit is connected to a cathode of a picture tube. 2. A video output circuit for amplifying a video signal,
An image characterized by connecting a level correction circuit for correcting a DC level of a video signal, comprising a means for detecting a beam current corresponding to the luminance of each primary color, and connecting the level correction circuit to a cathode of a picture tube; Display device. 3. A video output circuit for amplifying a video signal, a level correction circuit for correcting a DC level of the video signal is connected, the level correction circuit is connected to a cathode of a picture tube, and an anode of the picture tube is connected to the video output circuit. An image display device to which a beam current detection circuit for detecting a beam current is connected. 4. The level correction circuit according to claim 1, wherein a clamp voltage source is connected to the base of the transistor, one end of the coupling capacitor is connected to the emitter, and the other end of the coupling capacitor is connected to the collector via switch means. 3. The image display device according to claim 2, comprising a circuit. 5. The level correction circuit according to claim 1, wherein a voltage source for clamping is connected to a base of the transistor, one end of a coupling capacitor is connected to an emitter, a collector is connected to the other end of the coupling capacitor, and a base of the transistor is connected to the base of the transistor. 3. The image display device according to claim 2, wherein a diode is connected in parallel with the emitter. 6. The level correction circuit supplies a beam current of a cathode of the picture tube to a detection resistor via a clamp circuit connected to a cathode of the picture tube and a clamp circuit when a beam current is detected. And a second switch circuit for supplying a level-controlled voltage to the clamp circuit when the beam current is detected and at other lamp periods. 4. The image display device according to 3. 7. A control apparatus according to claim 1, wherein a third switch is provided in a line connecting an output of said video output circuit to a cathode of said picture tube, and said third switch is controlled to be opened when said beam current is detected. The image display device according to claim 2, wherein: 8. An image display device in which a picture tube is connected to a video output circuit for amplifying a video signal, wherein the video output circuit connects the emitters of two transistors having opposite polarities to each other and connects the emitter to the picture tube. Connecting the bases of the two transistors to each other via a bias impedance, connecting a variable current source to the bias impedance, and connecting a beam current detection circuit of the picture tube to one collector of the two transistors. An image display device characterized by comprising: