JPH04155379A - Picture tube driving circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a picture tube drive circuit used in video circuits such as character graphic displays, televisions, and monitors.

[Prior Art] Conventionally, the white balance of a color receiver, which was adjusted at the time of shipment from the factory, changes over time due to changes in the color picture tube such as cathode emissions and circuit drift. There were rjj and ir points that were said to be easy. An automatic white balance adjustment circuit that compensates for such white balance changes is described in, for example, Japanese Patent Laid-Open No. 18087/1987.

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

In FIG. 4, video output circuits 12R, 12(1; and I2B each have the same circuit configuration as a circuit consisting of a collector resistor 26 and a transistor 24 as shown in the video output circuit 12B. Also, the cathode current The detection circuits 9R, 9G, and 9B each include a transistor 28 and a resistor, as shown in the cathode detection circuit 9B.

In FIG. 4, primary color signals of R (red), 6 (green), and 8 (blue) inputted to input terminals IR, IG, and IB pass through signal synthesis circuits 8R, 8G, and 8B, respectively.

Variable gain amplifier circuit 10R for drive adjustment, LOG,
The signal is amplified by 10B and level-shifted by level correction circuits 11R, IIG, and IIB for cutoff adjustment. The video output circuits 12R, 12G, and 12B amplify the amplitude to the extent that the picture tube can be driven, and the cathode current detection circuit 9R
.

Cathode terminals 7R, 7 of picture tube 6 via 9G, 9B
G and 7B are supplied for image display.

The automatic white balance adjustment operation performed at that time will be described below. The signal generation circuit 2 for automatic white balance adjustment is
A reference signal for white balance adjustment is outputted via the reference signal line 4 from the horizontal and vertical blanking pulses input to the input terminals 3H and 3V, respectively; two types of standards are used for cutoff adjustment and drive adjustment. A signal and a gate pulse outputted via the gate signal line 5 are generated.

These generated signals are each sent to a signal synthesis circuit 8R.
.

8G, 8B and sampling circuit 13R, 13G, 1
Supplied to 3B. Focusing on the B 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 130B. . sampling times,
113B is supplied with a gate pulse via the gate signal 1IA5, and by the negative feedback effect by the operational amplifier Wi unit 16B for cutoff adjustment and the operational term # unit 17B for drive adjustment, it is optimal for each adjustment. A control voltage is held in hold capacitors 14B and 15B. In addition,
The R and G primary color signal circuits also have the same circuit configuration as B, and operate in the same manner as B.

By sharing the reference voltages g17 and g18 with the R, G, and B primary color signal circuits, the ratio of the cathode currents of each primary color is controlled to a constant value, and the white balance is stabilized.

[Problems to be Solved by the Invention] In the conventional example shown in FIG.
R, IIG, and IIB are each video output circuit 12R
.

12G and 12B, the signal dynamic range after these video output circuits must be set wide considering the amount of level correction, for example, it is necessary to increase the power supply voltage applied to the terminal 27. In addition, in order to ensure the resolution necessary for a television receiver, it is necessary to suppress the drop in the cutoff frequency of the output circuit, which is determined by the output capacitance consisting of the collector resistor 26 in the video output circuit and the stray capacitance of the wiring. , the collector resistance 26 cannot be set to a high value.

Furthermore, by interposing the cathode current detection circuits 9R, 9G, and 9B between the video output circuit and the picture tube,
The above 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 the desired frequency band.

Therefore, when the power supply voltage terminal 27 is held constant, the current flowing through the collector resistor 26 increases, and the power consumption of the video output circuit increases. In particular, it has been difficult to realize automatic white balance adjustment for high-definition displays that require broadband characteristics.

An object of the present invention is to suppress an increase in power consumption of a video output circuit and realize automatic white balance adjustment for a display.

[Means for Solving the Invention] In order to achieve the above object, a level correction circuit is connected to the output terminal of the video output circuit, a beam current detection circuit is connected to the output terminal of the level correction circuit, and the beam current is A picture tube drive circuit that connects the output terminal of the detection circuit to the picture tube.

[Function] Each component in each of the above technical means has the following functions.

The video output circuit amplifies the video signal to the amplitude necessary to drive the picture tube. The level correction circuit corrects the DC level of the video signal to ensure white balance. By providing the level correction circuit after the video output circuit as described in the above technical means, power consumption in the video output circuit can be reduced. Further, the beam current detection circuit has a function of detecting beam current corresponding to the brightness of each primary color.

[Embodiment 1] An embodiment of the picture tube drive circuit of the present invention will be described below with reference to the drawings. A block diagram of a picture tube drive circuit according to an embodiment of the present invention will be explained with reference to FIG. 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 drive circuit 911 consisting of a level correction circuit 11 and a beam current detection circuit 9 disposed at a subsequent stage is provided at a subsequent stage of a video output circuit 12. By using the configuration shown in FIG. 1, power consumption of the video output circuit 12 can be suppressed. A specific circuit configuration of the block diagram of one embodiment of the present invention shown in FIG. 1 is 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. It is being The video output circuit 12 has a wide band through a cascode configuration formed by transistors 24 and 241, emitter peaking formed by a capacitor 252, and parallel peaking formed by a coil 261. 25 is a resistor that sets the gain of the common emitter amplifier circuit including the transistor 24, and 251 is a resistor that sets emitter peaking characteristics. 27 is a power supply voltage terminal of the video output circuit. 242 is a terminal that applies a bias voltage to the base of the transistor 241 constituting the common base amplifier circuit. Level correction circuit 1
10, the amount of level shift thereof is controlled by a signal transmitted from the control line 20R. The beam current detection circuit is
The cathode current flowing through the emitter of the transistor 28 is guided to the collector side, converted into a current voltage by the detection resistor 29, and outputted to the signal line 30R.

At this time, the cathode current includes not only the beam current but also leakage current from other electrodes of the picture tube 6. Therefore, in order to detect the beam current, the detected beam current is made sufficiently larger than the leakage current, or the leakage current is canceled out by means described later. The diode 282 and the resistor 284 protect the transistor 28 during internal discharge of the picture tube 6. Further, by adjusting the value of the resistor 284, γ correction can be performed.

In the circuit shown in FIG. 2, when the resistor 291 is zero Ω, the frequency characteristics of the drive circuit deteriorate due to the signal line 3 connected via the stray capacitance 71R of the picture tube and the parasitic capacitance 281 of the transistor 28.
This is caused by the stray capacitance 293 of 0R and the parasitic capacitance of the diode 292.

Therefore, in the present invention, the value of the resistor 291 shown in FIG.
and the parallel impedance of the parasitic capacitance of the diode 292. As a result, the stray capacitance 2 acting through the parasitic capacitance 281 of the transistor 28
93 can be eliminated. Further, in FIG. 2, a capacitor 283 has the function of bypassing the video signal in order to compensate for the insufficiency of the picture tube driving ability of the transistor 28 at high frequencies. Because of this bypass effect,
The Miller effect due to the amplification operation of transistor 28 is also eliminated.

In addition, the diode or Zener diode 292 serves 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 increase the collector voltage of the transistor 28. It has the effect of suppressing saturation due to rise. In FIG. 4, a sampling circuit 13R is connected upstream of a comparison circuit 16R, forming a control circuit. However, normally, the control circuit is configured such that a sampling circuit follows the comparison circuits 16R and 17R to which they are connected. Furthermore, as picture tubes become larger and brighter, the driving voltage amplitude and beam current during driving increase. In case transistor 28
The emitter-collector voltage decreases and becomes saturated, which may cause problems such as the picture tube's motion and the beam current detection being intermittent. Therefore, in Figure 3,
The clamping 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 diode 28
The types of 5 and 286 can be arbitrarily selected as long as they meet the absolute rating conditions such as reverse breakdown voltage. For example, Schottky barrier diodes can be used in consideration of high speed, and the types of both diodes are different. You can leave it there. For example, it is possible to improve the saturation prevention effect by using a Baker clamp configuration in which the diode 285 is made of silicon and the diode 286 is made of germanium.

Next, a picture tube drive circuit is installed after the video output circuit,
FIG. 5 shows a block diagram of the configuration of the picture tube drive circuit, in which beam current detection is placed in the first stage and level correction circuit is placed in the second stage. By using the configuration shown in Figure 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. A specific circuit diagram of the block diagram of one embodiment of the present invention shown in FIG. 5 is shown in FIG.

By adopting the circuit configuration shown in FIG. 6, a high-performance element with a low breakdown voltage can be selected as the transistor 28 used in the beam current detection circuit. For example, in Figure 4, 160■
In the above case, an element of 70V or less can be applied. Generally, the amplification ability, good high frequency characteristics, and small parasitic capacitance of an active element conflict with high voltage resistance. For example, by selecting an element with a large amplification degree β for the transistor 28, it is possible to improve the detection accuracy of the beam current and to reduce the minimum detection current. In other words, I cbo can also be reduced. In addition, by improving the high frequency characteristics of the transistor 28 or reducing the parasitic capacitance,
The frequency band of the drive circuit can be expanded. Here, the protection resistor 284 shown in FIG.
If the reliability of 10 can be ensured, the insertion position can be changed between the beam current detection circuit and the level correction circuit, or it can be deleted.

However, in consideration of protection of the level correction circuit 110 and deterioration of frequency characteristics due to capacitance parasitic to this circuit, it is preferable that the protective resistor 28 be inserted 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 constructed 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 clamp transistor 113 via clamp switch 115 to connect coupling capacitor 1
11 is clamped on the picture tube side. The discharge current flowing through the coupling capacitor 111 during clamping is transferred to the transistor 1.
By using a return current between the emitter and the collector of No. 13, fluctuations in the clamp level (black sink) due to discharge current leaking into peripheral circuits are eliminated. In the case of FIG. 7, it is possible to eliminate dark spots caused by the sum of the forward voltage due to the conduction of the diode 282, the forward voltage between the base and emitter of the transistor 28, and the voltage drop across the resistor 26. Resistor 118 serves to raise the base voltage of transistor 113 to the power supply voltage connected to terminal 117 during the non-clamp period when switch 115 is open. Therefore, when not clamped, a reverse voltage is applied to the diode 112, and the emitter of the transistor 113 is disconnected from the coupling capacitor 111. diode 114
is the transistor 11 when not clamped or when the picture tube is discharged.
This is a protection diode that guarantees reverse breakdown voltage conditions between the base and emitter of No. 3. The clamp circuit shown in FIG. 7 is of a synchronous type using the ON/OFF operation of the clamp switch 115, and the power consumption of the circuit that controls the clamp is suppressed. However, in order to reduce the circuit size, switch 11
In the case where the resistor 118 and the resistor 118 are omitted by short-circuiting or opening them, the signal on the signal line 20R may be controlled to switch the voltage of the voltage source 116. Also.

Even if the voltage of the voltage source 116 is not controlled by switching and is constant, the diode 112 and the transistor 113 automatically conduct as the video signal level on the anode side of the diode 112 increases, thereby operating as an asynchronous peak clamp circuit. . Furthermore, even if the voltage source 116 is set to a constant voltage, the high frequency components of the video signal leaked through the diode 112 are detected by the diode 114 due to the influence of the absolute value and time constant of the internal impedance remaining in the voltage source 116. may cause clamp level fluctuations. In that case, diode 1
14. Minimum capacity necessary to cancel the detection effect.

For example, a capacitor on 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 Zener diode or the like with a large parallel parasitic capacitance is used as the diode 114.

In FIG. 7, it is clear that problems such as sag will not occur if the coupling capacitor 111 charged by the detected beam current 7R1 has a capacitance value used in a normal clamp circuit.

Next, we will discuss an embodiment in which cathode current detection is possible at the front stage of the correction circuit even when a bias current other than the beam current is passed through the picture tube drive signal line or when a leakage current flows between the picture tube electrodes. It is shown in Figure 8. As an example of the above-mentioned clamp circuit, a charging bias current may be passed through the coupling capacitor 111 via the resistor 34 or a series connection of the resistor 34 and a diode in order to quickly start up the clamp operation after power is turned on. be. However, with the conventional method, only the beam current cannot be detected due to the addition of the bias current. Therefore, as shown in the 8th episode, using the current controlled current source 31, the above bias current 3
8 to prevent it from flowing to the detection resistor 29. The current controlled current source 3I detects the bias current 38 flowing through its input terminal 32, and functions to supply a current of approximately the same magnitude as this from the output current source 33, but this output current is passed through the beam current path. The above-mentioned current cancellation is made possible by flowing the current to the output point of the detection resistor 29 in the front stage 2, for example, through at least one of the output lines 35, 36 and 37 in the figure. In addition to the beam current component within the picture tube, the cathode current includes leakage current components from other electrodes such as the heater 71R, the first grid, and the second grid.

However, regarding the leakage current components from the electrodes separated between the R, G, and B primary colors, those electrodes are connected to the stage before the detection resistor 29 in the beam current path through a resistor or active element. This can be offset by It goes without saying that the above does not depend on the type of drive electrode of the picture tube, such as the cathode, each grid, or anode.

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 20RO, but it is necessary to flow a control bias current through the resistors 1103 and 1104 and the transistor 1102. Furthermore, although the internal impedance of the voltage source circuit is reduced for high-frequency signals by the bypass capacitor 1101, it depends on the bias current, that is, it is approximately proportional to the bias current of the transistor 1102, and has a value that is not infinitesimal.

In order to suppress the adverse effect of 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 large compared to the beam current. Therefore, in the embodiment shown in FIG. 9, a constant control bias current is passed through the voltage source circuit, and a current equal to this current is drawn from the stage before the detection resistor 29 in the beam current path, thereby increasing the beam current. This makes detection possible. The control bias current has its current value set by the current flowing through the temperature compensation diodes 323 and 325 and the resistor 324, and flows from the transistor 322 to the transistor 331 via the above-mentioned constant voltage circuit or 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 deterioration of the frequency characteristics of the drive circuit.

The collector of transistor 331 is connected to at least one of output lines 35, 36, or 37, for example.

Furthermore, in order to improve the setting accuracy of the control bias current, it is also possible to add series resistances to the emitters of each of the transistors 322 and 331 and to each of the diodes 321 and 322. Furthermore, in order to improve the temperature stability of the control bias current, transistor 322 and diode 323, transistor 331 and diode 3
It is also possible to thermally couple each of the elements 21 or to configure them on the same semiconductor chip, for example, as an IC.

Furthermore, FIG. 10 shows an embodiment in which the clamp circuit used as the level correction circuit in the above embodiments can be applied to a wider-band picture tube drive circuit. In the embodiment of FIG. 10, the collector of the clamp transistor 113 is connected to a switch circuit 39 which is short-circuited only during clamping.
Connect to the drive signal source via. By providing the switch circuit 39, the transistor 11 is used as a drive signal source during the display period when a wideband drive signal is applied to the picture tube 6.
Since the collector-base capacitance and collector stray capacitance described in No. 3 are no longer added, it is possible to further widen the band of the drive circuit. Here, as in FIG. 7, the voltage source 11
The voltage 6 may be controlled by switching for a synchronous type, or may be a constant voltage for an asynchronous type. However, by providing the above-mentioned clamp circuit, the diode 112 is also always connected to the drive signal source and has a capacitance added thereto. If it is necessary to reduce the above-mentioned 8 pins applied via the diode 112, a reverse voltage is applied to the diode 112 during the display period, and as shown in FIG. diode 1
It is also possible to connect the diode 121 and the diode 112 in series with the same polarity.

Next, another embodiment of the switch circuit 39 shown in FIG. 10 is shown in FIG. 12. In the embodiment shown in FIG. 12, since the collector current of the transistor 113 can be considered to be zero when not clamped, the anode voltage of the constant current diode 392 also becomes zero, and a reverse voltage is applied to the diode 391, so that the drive signal source is The collector of transistor 113 is cut off. However, the connection via the junction capacitance of the diode 391 remains. During clamping, the collector current of the transistor 113 becomes a sufficiently larger current value than the current value of the constant current diode 392, so that the anode voltage of the constant current diode 392 increases, the diode 391 becomes conductive, and the above collector current increases. Most of it flows into the coupling capacitor 111, and becomes stable, allowing lamp operation. Diode 391 therefore operates as an automatic switch.

Considering that the diode 391 is made conductive during clamping when the collector current of the transistor 113 increases,
Constant current diode 392 can be replaced with a resistor.

Further, it is also possible to replace the constant current diode 392 with a constant current circuit using an active element such as an FET. Here, the switching speed of the diode 391 is considered to be inversely proportional to the capacitance parasitic to the collector circuit of the transistor 113, and controlled by the slew rate of the collector voltage, which is proportional to the collector current of the transistor 113 during clamping. Therefore, in order to increase the switching speed of the diode 391, a voltage is applied to the cathode of the constant current diode 392 within a range that can always cut off the diode 391 during the non-clamp period and maintain the junction capacitance of the diode 391 at a level that does not pose a problem. It is also possible to connect an offset voltage source with . For example, the cathode of the constant current diode 392 is connected in parallel to the base bias power supply terminal 242 of the common base transistor 241.

Furthermore, in the embodiment shown in FIG. 12, most of the collector current of the transistor 113 is transferred to the coupling capacitor 11.
Although the current component flowing through the constant current diode 392 causes a slight fluctuation in the clamp level, deterioration of clamp accuracy cannot be avoided. Therefore, the 13th embodiment does not involve the above deterioration in clamp accuracy.
As shown in the figure. In FIG. 13, by connecting a resistor 393 between the nimitter 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. Improves clamping accuracy. In other words, the emitter current (collector current) of the transistor 241 decreases by the amount of current flowing through the resistor 393, and the current flows through the coupling capacitor 111 through the transistor 241.
It will flow from 41 collectors. The resistor 393 can be designed with the upper limit being a resistance value that satisfies the switching speed required by the time constant of the collector circuit of the transistor 113, and the lower limit being a resistance value that allows a current large enough to not be cut off by the transistor 241 to be designed6. It is also possible to replace it with a constant current diode (anode connected to the collector of the transistor 113) as shown in FIG. It is better to insert a resistor or inductance in series. It goes without saying that a similar effect can be obtained by connecting the resistor 393 between the emitter of the transistor 24 and the collector of the transistor 113.

Next, a block diagram of a picture tube drive circuit in which the picture tube drive circuit 911 is configured with a cathode current detection and level correction circuit 912 having both level correction and beam current detection functions is shown in the first block diagram.
Shown in Figure 4. The configuration shown in FIG. 14 allows for higher performance such as reduction in circuit scale and improved reliability. A specific circuit configuration of FIG. 14 is shown in FIG. 15. In FIG. 15, by using the transistor of the clamp circuit also for beam current detection, it is possible to provide the level correction circuit with a beam current detection function.

In FIG. 15, the switch circuit 115 remains short-circuited when detecting the beam current, and opens and closes in accordance with the clamp period during other periods to control the synchronous crushing operation. The switch circuit 40 is turned to the drive signal line side only when clamping, thereby enabling the above-mentioned stable ramp operation.

The feature of FIG. 15 is that when detecting the beam current, the voltage of the slightly controlled voltage source 116 is transmitted to the cathode 7R via the switch circuit 115 and the transistor 113, and the DC output of the video output circuit is transmitted by the coupling capacitor 111. Since it can be cut off, accurate level correction that is not affected by the video signal is possible. 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-mentioned discharge within the tube is reduced, and reliability is improved. Furthermore, similar to the embodiment shown in FIG. 10, it is possible to further widen the band of the drive circuit.

Next, another embodiment of the switch circuit 40 shown in FIG. 15 is shown in FIG. 16. In the embodiment shown in FIG.
Similar to the embodiment shown in FIG. 2, the diode 4 is connected only during the clamp period when the collector current of the transistor 113 increases.
Constant current diode 402 so that 01 automatically conducts
is used. Here, the detection beam current flowing through the collector of the transistor 113 and the clamp current will be compared. The charges accumulated in the coupling capacitor 111 due to the beam current flowing during the non-clamp period are intensively discharged during the clamp period. Since the non-clamp period is generally ten times longer than the clamp period, the magnitude of the clamp current is considered to be at least ten times the detection beam current. Therefore, the design of the constant current diode 402 described above is easy, and in some cases, the constant current diode 402 can also be replaced with a resistor.

Next, we will discuss a first example that can improve the accuracy of beam current detection.
It is shown in Figure 7. In the embodiment shown in FIG. 17, by opening the switch circuit 41 only when detecting the beam current, the output of the video output circuit is completely cut off from the cathode 7R from the DC component to the AC component at the time of detection. Beam current detection when the switch circuit 41 is always short-circuited requires a settling time proportional to a time constant approximately determined by the product of the coupling capacitor 111 and the output resistance 26 of the output circuit. By opening it, the above settling time can be ignored.

Furthermore, the switch circuit 4 is connected to the path shown by the broken line in FIG.
2 and switch circuit 42 only when detecting beam current.
By short-circuiting and opening the switch circuit 41, the beam current can be detected while applying the output voltage of the video output circuit to the cathode 7R.

Therefore, the voltage to be applied to the picture tube when detecting the beam current is either supplied by the level-controlled voltage source 116 (by opening the switch circuit 42 and shorting the switch circuit 115), or by supplying it from the video output circuit ( switch circuit 4
2 and open the switch circuit 115) can be selected as appropriate.

Next, another embodiment of the switch circuit 41 shown in FIG. 17 is shown in FIG. 18. In FIG. 18, the coupling capacitor is divided into 110 for high frequency signals and 119 for other signals, and the latter 119 can be isolated from the drive signal source by a diode 411.

The capacitor 119 in the figure indicates an electrolytic capacitor, but the type does not matter. Coupling capacitor 110 for high frequency signals
is set to a capacitance value as small as possible so that the above settling time can be ignored. When the power is turned on, power terminal 4
12 to capacitor 11 via bias resistor 413.
Bias current flows through 0 and 119, and if normal, lamp operation is started. Ideally, zero is better as long as the high frequency impedance of the diode 411 can be sufficiently reduced. When detecting the beam current, the transistor 415 is made conductive by a signal from the detection signal source 416, and its collector voltage is dropped so that the diode 411 is cut off. A resistor 417 is a resistor for setting the base current of the transistor 415.

When performing high-speed control while saturating the transistor 415, a speed-up capacitor 419 and a base current drawing resistor 418 are added. A resistor 414 is inserted as shown in FIG. 18 in order to avoid adding the base-collector capacitance of the transistor 415 and the stray capacitance of the collector circuit to the drive signal line except when detecting the beam current.

Furthermore, FIG. 19 shows an embodiment in which the beam current can be detected 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 sent to the cathodes 7R, 7G of the picture tube 6 via the level correction circuit 11.
, 7B, but as long as the active electrodes of the picture tube 6 are independent electrodes for the three primary colors R, G, and B, the first grid or the like can also be used. Further, in FIG. 19, the beam current detection circuit 9 is connected to the anode 6A of the picture tube 6,
The structure is such that the beam current, which is part of the anode current, is detected. However, the beam current detection circuit 9 can also be connected to electrodes such as the second and third grids, as long as they are electrodes through which a current correlated with the beam current flows. However, when detecting the beam current of a picture tube capable of displaying multiple colors other than a monochrome picture tube from an electrode that is commonly used for multiple colors, the beam current of each color is passed at different timings, etc. Separation for each color is required. FIG. 20 shows an embodiment showing a specific circuit having the above configuration. In FIG. 20, the beam current detection circuit 9 includes a rectifier diode 600, a flyback transformer F B T601, and a voltage dividing resistor R160 for stabilizing high voltage by detecting a high voltage from a terminal 605.
2 and R2603, Rb604 for voltage conversion and detection of the beam current, and voltage source 1 for applying a DC shift to the beam current detection voltage. The above beam current detection voltage is output from the detection terminal 606 to the outside, and this detection voltage is connected to the resistor RAIL and capacitor CABL.
By taking out the beam current average value from the ABL terminal 607 through an integrating circuit consisting of the following, it can be used as the beam current average value ABL control voltage (control voltage for automatic brightness limiting circuit).

The current I PLIT of the flyback transformer 603 to be detected here includes the anode current IA, which is the sum of the beam current and the leakage current component to each terminal of the picture tube 6, and the current flowing through the voltage dividing resistors R1602 and R2603 mentioned above. Ii, distortion current components such as high-order distortion currents in the horizontal deflection period flowing between the ground of each winding of the flyback transformer are included. However, since the amplitude of everything other than the beam current can be considered to be almost constant, the current I
By detecting the peak value, average value, and amount of change in instantaneous value of PLIT.

Beam current can be detected separately. Even if the amplitude of current components other than the beam current mentioned above cannot be said to be sufficiently small with respect to the beam current, the average value can be considered constant, so 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 dynamic load type video output circuit.

In FIG. 21, a 5EPP circuit consisting of transistors 43 and 45 is added as an output buffer to the video output circuit which uses a constant current source or a constant current circuit as the load of the video output transistor 24 to reduce power consumption. The tube 6 is being driven. Although the dynamic load circuit described above can achieve low power consumption in terms of direct current despite the large output voltage by suppressing the power supply current to a small current and making it a constant current, the capacitance of the cathode 7R of the picture tube 6, etc. It is not possible to supply the output current necessary to drive a static load with a large amplitude and wide band signal voltage. For this purpose, the above output buffer 5 is required.
In the EPP circuit as well, the picture tube 6 can be driven by class AB operation in which a relatively large idling current flows through the transistors 43 and 45 used, and by suppressing the cutoff of the transistors to a shallow level. When detecting beam current using the dynamic load type video output circuit described above, if the detection circuit of the above type is placed after the video output circuit, the load capacity of the video output circuit will increase. The advantage of low power consumption is lost.

Therefore, as shown in Fig. 21, the beam current is detected by 5E.
A feature of the present invention is that the transistor 43 of the PP circuit is used. Terminal 48 is a power supply terminal for biasing the 5EPP circuit. However, when detecting current,
It is necessary to cut off the above idling current. Therefore, in the present invention, as shown in FIG. 21, the current of the constant current source or constant current circuit 47 is controlled to reduce the current at the time of current detection, and the bias voltage of the 5EPP circuit is controlled by the voltage drop of the bias impedance 46. By doing so, only the transistor 45 is cut off at the time of current detection. In this case, the diode 44 shown in FIG.
5, but if the detected current is large to some extent, for example 10μ8 or more, it will be deleted (short l!I
) There is no problem.

Next, we will discuss another embodiment that enables beam current detection even when using a dynamic load type video output circuit.
Shown in Figure 2. In FIG. 22, by controlling the current of a constant current circuit consisting of a transistor 471, the diode 44 is turned on and off to detect the beam current. The diodes 462 and 463 constituting the bias impedance compensate for the temperature drift of the idling current. Therefore, the diodes 462 and 463 and the transistors 43 and 45 can be formed on the same semiconductor or can be thermally coupled. Bypass capacitor 464 is 5
Eliminate the directionality of the drive impedance of the EPP circuit.

Resistors 431 and 451 are used to set the idling current and protect transistors 43 and 45, respectively. A resistor 452 is also used to protect the transistor 45 from overcurrent in the event of erroneous contact. Further, the capacitor 500 and the resistor 501 constitute a bypass circuit for compensating for the frequency characteristic deterioration of the drive circuit caused by the protective resistor 284, and exhibit high impedance against the discharge energy within the picture tube 6. Transistor 4 forming a constant current circuit
71 receives the collector current of the transistor 473 controlled by the current detection signal source 416 in a grounded base type that is AC-grounded to a terminal 472 and biased by a resistor 474, and supplies it to the bias impedance of the 5-EPP circuit. do.

The collector current of transistor 473 is adjusted by resistor 475. Since both transistors 473 and 471 are non-saturated, high-speed control is possible. Input resistance 49
0 and the feedback resistor 491, parallel feedback is applied to the output transistor 24, but this feedback is maintained by cutting off only the diode 44 during the current detection period, so that the output voltage of the transistor 43 is stably supplied to the picture tube 6. Supplied.

Furthermore, since the base voltage of the transistor 471 is made negative even when the current detection is switched, leakage of the detection signal from the signal source 416 to the transistor 45 via the capacitor 494 is also suppressed.

Transistor 47 by resistor 495 and capacitor 494
1 is also subjected to negative feedback, resistor 496 and capacitor 497
, a resistor 492 and a capacitor 493 are used for peaking. In addition, Zener diode 25
3 is used to suppress the operating point drop of the input signal source 31 caused by the DC bias of the input resistor 490 and feedback resistor 491 due to the parallel feedback described above, and the bypass capacitor 254 is used to reduce the impedance of the Zener diode 253 and compensate for noise. is being carried out. The operating point drop described above 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 also be maintained.

Next, FIG. 23 shows another embodiment that enables current control of a constant current source or a constant current circuit. In Figure 23,
Current control is performed by controlling the base bias voltage of a transistor 471 constituting a constant current circuit, and portions not shown are similar to the embodiment shown in FIG. 22. This is done by turning on the transistor 51 twice and short-circuiting the resistor 479. The above base bias voltage when resistor 479 is shorted is the voltage at terminal 476 and resistor 4.
77 and 478. A resistor 512 is a base resistor for setting the base current of the transistor 51. In order to improve the switching speed, the value of the above-mentioned base resistor 512 may be adjusted appropriately, or the speed-up capacitor 513 or the base current drawing resistor 511 may be
Use. The breakdown voltage of the transistor 51 can be lower than that of the transistor 473 shown in FIG. 22.

In the embodiments described above, the picture tube is not limited to a cathode ray tube, but also includes a plasma display tube and the like, and therefore, it goes without saying that the drive electrode includes electrodes other than the cathode and the grid. Furthermore, the semiconductors used can be replaced not only with bipolar transistors and diodes, but also with a wide range of active elements such as GaAsFETs. Furthermore, the polarity of the element can also be reversed by reversing the potential relationship.

[Effects of the Invention] Since the present invention is configured as described above, it 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 automatic white balance adjustment can be performed even in wideband video circuits required for ultra-high definition displays. .

(2) According to the present invention, the capacitance added to the picture tube recording signal line due to the addition of the beam current detection circuit can be reduced, so that the frequency characteristics of the picture tube drive circuit due to 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 5EPP circuit can be controlled, a beam current detection function can be added to the 5EPP circuit.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a picture tube drive circuit showing one embodiment of the present invention, FIG. 2 is a specific circuit diagram of FIG. 1 of the present invention, and FIG. 3 is an alternative circuit diagram of FIG. A specific circuit diagram, FIG. 4 is a circuit block diagram showing a conventional automatic white balance adjustment circuit,
FIG. 5 is another picture tube drive circuit block diagram showing an embodiment of the present invention, FIG. 6 is a specific circuit diagram of FIG. 5 of the present invention,
FIG. 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. 10 is a specific circuit diagram of the clamp circuit of the present invention, FIG. 11 is another specific circuit diagram of FIG. 10 of the present invention, and FIG. 12 is a specific circuit diagram of the clamp circuit of the present invention. FIG. 10 is another specific circuit diagram of FIG. 10, FIG. 13 is another specific circuit diagram of FIG. 10 of the present invention, and FIG. 14 is another picture tube ovulation circuit showing an embodiment of the present invention. The block diagram, FIG. 15 is another specific circuit diagram of FIG. 14 of the present invention, FIG. 16 is another specific circuit diagram of FIG. 14 of the present invention, and FIG. 17 is a specific circuit diagram of FIG. 14 of the present invention. 18 is another specific circuit diagram of the present invention shown in FIG. 14, FIG. 19 is another picture tube drive circuit block diagram showing an embodiment of the present invention, 20th
19 is another specific circuit diagram of the present invention, FIG. 21 is a specific circuit diagram showing another embodiment of the present invention, and FIG. 22 is a specific circuit diagram showing another embodiment of the present invention.
This figure is another specific circuit diagram of FIG. 21 of the present invention, and 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...Beam current detection resistor 116...Level-controlled voltage source I for level correction
II...Coupling capacitor 113...Transistor for clamping and beam current detection 40.115...Switch circuit for switching operation between clamp and beam current detection 41 躬 6 圀躬 80 fig. 10 fig. 72 fig. 11 fig.

Claims (1)

[Claims] 1. A level correction circuit that corrects the DC level of the video signal is connected to a video output circuit that amplifies the video signal, and a beam current corresponding to the luminance of each primary color is detected in the level correction circuit. 1. A picture tube drive circuit, comprising: a beam current detection circuit connected to the picture tube; and a picture tube connected to the beam current detection circuit. 2. A beam current detection circuit that detects beam current corresponding to the luminance of each primary color is connected to the video output circuit that amplifies the video signal, and a level correction circuit that corrects the DC level of the video signal is connected to the beam current detection circuit. 1. A picture tube drive circuit, characterized in that the picture tube is connected to the level correction circuit and a picture tube is connected to the level correction circuit. 3. A level correction circuit that corrects the DC level of the video signal and has a beam current detection function that detects the beam current corresponding to the luminance of each primary color is connected to the video output circuit that amplifies the video signal, and the level correction circuit corrects the DC level of the video signal. A picture tube drive circuit characterized in that a picture tube is connected to the circuit. 4. A picture tube drive circuit in which a level correction circuit that corrects the DC level of the video signal is connected to a video output circuit that amplifies the video signal, and a beam current detection circuit that detects the beam current is connected to the picture tube.