JPH04213969A - Quadrupole coil drive circuit - Google Patents

Abstract

PURPOSE:To correct deterioration in the focus characteristic due to a large change in a beam spot shape in a center area of a screen of a cathode ray tube having a laterally long and large sized display screen by generating a quadrupole current for beam spot correction. CONSTITUTION:A 1st resonance circuit comprising C1, LOP, L1 generating a quadrupole current for beam spot correction increasing rapidly as a scanning position of an electron beam is parted from the center of the display screen when the electron beam scans the screen end area of the display screen and a 2nd resonance circuit comprising C22, LOP, L1 generating a quadrupole current for beam spot correction increasing gradually as a scanning position of an electron beam is parted from the center of the display screen when the electron beam scans the screen center area of the display screen are provided to the quadrupole coil drive circuit 20 to generate the quadrupole current for beam spot correction increasing rapidly at the end of the display screen and increasing gradually in the center of the display screen thereby correcting properly the beam spot shape over the entire display screen.

Description

[Detailed description of the invention]

0001

【table of contents】

The present invention will be explained in the following order. Conventional examples of industrial application fields (Figs. 3 to 5) Problems to be solved by the invention (Figs. 3 to 5) Means for solving the problems (Figs. 1 and 2) Effects (Figs. 1 and 2) Example (Figures 1 and 2) Effects of the invention

0002

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quadrupole coil drive circuit, and is particularly suitable for use in correcting the beam spot shape of a cathode ray tube.

0003

2. Description of the Related Art Conventionally, in a display device using a cathode ray tube, a quadrupole coil is provided around a beam gun. This is designed to prevent focus shift caused by the beam spot 3 becoming elliptical when obliquely hitting the surface.

A quadrupole coil drive circuit for driving this quadrupole coil has a drive circuit 1 as shown in FIG.
The base of a transistor Q1 is connected to the output terminal of the transistor Q1, and the damper diode D1 is connected to the collector of the transistor Q1.

Further, a resonant capacitor C1 is connected in parallel to the transistor Q1 and the damper diode D1, and a quadrupole coil LOP and a coil L1 are respectively connected in parallel to the resonant capacitor C1. By supplying the power output through R1, the drive circuit 12 drives the transistor Q1.
While the transistor Q1 is on, energy is accumulated in the resonant circuit consisting of the quadrupole coil LOP, the coil L1, and the resonant capacitor C1, and in this state, the transistor Q1
When the coil LOP turns off, resonance occurs between the quadrupole coil LOP, the coil L1, and the resonant capacitor C1.

Therefore, as shown in FIG. 5A, the voltage VC across the resonant capacitor C1 increases between time points t1 and t3 and between times t4 and t6 when the transistor Q1 turns off and enters a resonant state. is the resonant voltage waveform VC1
shows.

Therefore, as shown in FIG. 5(B), at times t1 and t4 when resonance starts, the quadrupole current IOP1 flowing through the quadrupole coil LOP increases, and the voltage value across the resonant capacitor C1 rises. Falling points t2 and t5
At this time, the clamp diode D2, which is connected to the quadrupole coil LOP along with the ringing removal capacitor C3, is turned off, so that the quadrupole coil LOP is turned off.
The quadrupole current IOP1 flowing through OP decreases.

[0008] Therefore, a mountain-shaped waveform IMA having a maximum value at times t2 and t5 is formed.

Furthermore, at times t3 and t6 when the transistor Q1 turns on and the resonance state ends, the DC cut capacitor C2 and the clamp diode D2, which are connected in series to the quadrupole coil LOP and the coil L1, The quadrupole current IOP1 remains at 0 level until the subsequent resonance state starts.

Therefore, the waveform of the quadrupole current IOP1 at time t
After decreasing while drawing a predetermined curve between 2 and t3, it is maintained at 0 level at time t3 and t4, and further decreases at time t
4 to t5, a so-called bathtub waveform is formed that increases along a predetermined curve.

Therefore, by adjusting the timing of turning on and off the transistor Q1 by the drive circuit 12 to the scanning timing of the electron beam, the effective display screen DIS1 from the left end L to the right end R of the display screen of the cathode ray tube can be changed.
In (FIG. 5(B)), near the left end L and right end R (i.e., the screen edge area of the display screen 2), the quadrupole current I increases as the distance from the center of the screen increases.
By flowing OP1 to the quadrupole coil LOP, the shape of the beam spot is corrected, and the effective display screen DIS
In the central part of the screen CENT1, the quadrupole current IO
By not making P1 conductive, the shape of the beam spot is not corrected.

0012

[Problem to be Solved by the Invention] However, when attempting to correct the beam spot shape using such a bathtub waveform, in the 0 level area of the bathtub waveform (i.e., the center area CENT1 of the screen in FIG. 5(B)), teeth,
Since the shape of the beam spot cannot be corrected, there is a problem in that even though the shape of the beam spot gradually changes from the center of the screen to the periphery, it cannot be corrected.

[0013] In particular, cathode ray tubes compatible with high-definition so-called high-vision systems use, for example, a horizontally long and large display screen with an aspect ratio of 16:9.
As the horizontal length of the display screen becomes longer, even if a quadrupole current IOP1 having a bathtub waveform with an uncorrected area (CENT1 in Fig. 5(B)) is passed as in the conventional case, the center area of the screen (CENT1 in Fig. 5(B)) is 5 (B) CENT 1), there was a problem that the focus characteristics deteriorated due to the large change in the shape of the beam spot.

The present invention has been made in consideration of the above points, and aims to propose a quadrupole coil drive circuit that can generate a quadrupole current that can appropriately correct beam spots over the entire display screen. It is something.

[0015]

[Means for Solving the Problems] In order to solve the problems, in the present invention, in the quadrupole coil drive circuit 20 for correcting the beam spot shape of the cathode ray tube, the scanning position of the electron beam is shifted from the center of the display screen 2. The first resonant circuits C1, LOP, and L1 generate a quadrupole current IMA for beam spot shape correction that increases rapidly as the electron beam moves away, and gradually increases as the scanning position of the electron beam moves away from the center of the display screen 2. a second resonant circuit C22 that generates a quadrupole current IPA for beam spot shape correction;
LOP, L1, and switching means Q1, D1 for switching and operating the first resonant circuit C1, LOP, L1 and the second resonant circuit C22, LOP, L1, respectively, so that the electron beam can reach the screen edge of the display screen 2. A quadrupole current IOP2 for correcting the beam spot shape is generated, which changes rapidly when scanning an area and slowly changes when the electron beam scans the central area of the display screen 2.

[0016]

[Operation] High-frequency resonance is generated by the first resonant circuit LOP, L1, and C1 in the screen edge area of the display screen, and the second resonant circuit LOP, L1, and C22 is generated in the screen center area of the display screen. Therefore, by generating resonance with a low frequency, the electron beam that scans the edge area of the display screen changes rapidly, and the electron beam that scans the center area of the display screen changes gradually. A quadrupole current for correcting the shape of the beam spot can be generated.

In this manner, the shape of the beam spot can be appropriately corrected depending on the irradiation position of the electron beam.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

In FIG. 1, in which parts corresponding to those in FIG. A resonant circuit is formed, and a resonant capacitor C2 is connected to the quadrupole coil LOP and the coil L1.
2 are connected in series to form a second resonant circuit.

The resonant capacitor C22 is a capacitor with a smaller capacity than the conventional DC cut-off capacitor C2 (FIG. 4), and when the transistor Q1 is turned on, the resonant capacitor C22 and the quadrupole coil LOP, Low frequency resonance is caused between the coils L1.

[0021] Also, a resistor R1 is connected at the output terminal of the power supply VCC.
The coil L2 is connected in series to the resonant capacitor C22, thereby changing the combined impedance of the resistor R1 and the coil L2 to the resonant capacitor C22.
The impedance is made larger than the impedance of the Therefore, when the transistor Q1 turns on, the power supply VC
The output of C is configured so as not to be returned to the ground side of the power supply VCC via the ground GND, and thus a constant current source is constituted by the resistor R1 and the coil L2.

In the above configuration, the quadrupole coil drive circuit 20 is supplied with power output from the power supply VCC via the resistor R1 and the coil L2, and the transistor Q1 is turned on by the drive circuit 12 at a predetermined timing. While the transistor Q1 is turned on, energy is accumulated in the resonant circuit made up of the quadrupole coil LOP, the coil L1, and the resonant capacitor C1, and then the electron beam is transmitted to the edge area of the display screen (i.e. When the transistor Q1 is turned off by the drive circuit 12 at the timing of scanning the peripheral area on the display screen,
Quadrupole coil LOP, coil L1 and resonant capacitor C
1, high frequency resonance occurs.

Therefore, as shown in FIG. 2(A), by turning off the transistor Q1, the first resonant circuit L
Time t11 to t1 when OP, L1 and C1 reach a resonance state
3 and between time points t14 and t16, the voltage VC across the resonant capacitor C1 (FIG. 2(B)) shows a resonant voltage waveform VC1.

Therefore, the time t at which high frequency resonance begins
At times t12 and t15, the quadrupole current IOP2 (Fig. 2(D)) flowing through the quadrupole coil LOP increases rapidly, and at times t12 and t15, the voltage value across the resonance capacitor C1 falls. When the clamp diode D2 connected to the LOP together with the ringing removal capacitor C3 is turned off (Fig. 2(C)), the quadrupole current IOP2 flowing through the quadrupole coil LOP (Fig. 2(D)) ) decreases rapidly.

Accordingly, a chevron-shaped waveform IMA having a maximum value at time t12 and t15 is formed.

Furthermore, at the timing when the electron beam scans the central area of the display screen, the transistor Q1 is turned on by the drive circuit 12, thereby creating a resonance state between the quadrupole coil LOP, the coil L1, and the resonant capacitor C1. At time points t13 and t16 when , low frequency resonance occurs between the quadrupole coil LOP and coil L1 and the small-capacitance resonant capacitor C22 connected in series with the quadrupole coil LOP and coil L1. As a result, the quadrupole current IOP2 forms a so-called parabolic waveform that gradually changes along a predetermined curve until time t14 when the continuing resonance state starts.

Therefore, the waveform of the quadrupole current IOP2 is
After rapidly decreasing while drawing a predetermined curve between 12 and t13, a gentle parabolic waveform IPA is formed between time t13 and t14, and then rapidly increasing while drawing a predetermined curve between time t14 and t15, At time points t12 to t13 and time points t14 to t15, a part of the mountain-shaped waveform IMA in the conventional bathtub waveform (IPO1) is formed, and at time points t13 to t14, a parabolic waveform IPA that changes gradually is formed. The heavy pole current IOP2 as a whole can form a so-called parabolic bathtub waveform, which is a combination of the bathtub waveform's chevron-shaped waveform IMA and parabolic waveform IPA.

Therefore, in the effective display screen DIS2 (FIG. 2(D)) from the left end L to the right end R of the display screen of the cathode ray tube, as the distance from the center of the screen increases near the left end L and right end R, By flowing a quadrupole current consisting of a rapidly increasing mountain-shaped waveform IMA to the quadrupole coil LOP, the shape of the beam spot is greatly corrected according to the amount of sudden change, and the screen of the effective display screen DIS2 is In the central area CENT2, by flowing a quadrupole current with a parabolic waveform IPA that gradually increases as the distance from the center of the screen increases to the quadrupole coil LOP, the beam spot shape can be adjusted according to the amount of gradual change in the shape of the beam spot. You can make corrections little by little.

In this manner, in a cathode ray tube having a horizontally long and large display screen, the spot shape can be appropriately corrected in response to changes in the shape of the beam spot depending on the irradiation position of the beam spot.

According to the above configuration, the quadrupole coil LOP
and constitutes a first resonant circuit that generates high frequency resonance by the coil L1 and the resonant capacitor C1, and
Quadrupole coil LOP and coil L1 and resonant capacitor C
22 constitutes a second resonant circuit that generates low frequency resonance, and when correcting the shape of the beam spot that changes greatly near the edge of the display screen, the first resonant circuit is used to generate low frequency resonance. In order to generate a quadrupole current having a chevron-shaped waveform IMA that changes greatly with respect to the amount of change in distance, and to correct the beam spot shape that changes small in the central area CENT2 of the display screen,
The second resonant circuit generates a quadrupole current having a parabolic waveform IPA that changes small with respect to the amount of change in distance from the center of the display screen, and the quadrupole current IOP2 causes a quadrupole coil to be generated. By driving, the shape of the beam spot can be appropriately corrected by the quadrupole coil LOP according to the irradiation position of the beam spot.

In this way, it is possible to correct the shape of the beam spot that changes little by little in the intermediate region between the center and the periphery of the display screen, thereby further improving the focus characteristics.

Note that in the above embodiment, the power supply VCC
Although the case has been described in which the coil L2 is connected as a method of adding impedance to the side, the present invention is not limited to this, and the impedance of the resistor R1 may be increased.

Furthermore, in the above embodiment, the case where the present invention is applied to a cathode ray tube display device with an integrated display screen has been described, but the present invention is not limited to this, but can be applied to various other cathode ray tubes such as a projector device, etc. It can be widely applied to quadrupole coil drive circuits of display devices.

[0034]

As described above, according to the present invention, in a quadrupole coil drive circuit that corrects the beam spot shape of a cathode ray tube, when the electron beam scans the edge area of the display screen, a first resonant circuit that generates a quadrupole current for beam spot correction that increases rapidly as the scanning position moves away from the center of the display screen; By configuring a second resonant circuit that generates a quadrupole current that gradually increases as the scanning position moves away from the center of the display screen, the current changes rapidly in the edge areas of the display screen and gradually increases in the center area of the display screen. A quadrupole coil drive circuit that can generate a quadrupole current for beam spot correction that varies as follows, thereby realizing a quadrupole coil drive circuit that can appropriately correct the beam spot shape over the entire display screen.

[Brief explanation of the drawing]

FIG. 1 is a connection diagram showing an embodiment of a quadrupole coil drive circuit according to the present invention.

FIG. 2 is a signal waveform diagram for explaining the operation of the embodiment.

FIG. 3 is a schematic diagram showing distortion of a beam spot on a display screen.

FIG. 4 is a connection diagram showing a conventional quadrupole coil drive circuit.

FIG. 5 is a signal waveform diagram for explaining the operation according to the conventional example.

[Explanation of symbols]

2... Display screen, 10, 20... Quadrupole coil drive circuit, C1, C22... Resonance capacitor, C2... DC cut capacitor, LOP... Quadrupole coil, D1...
Damper diode, D2... Clamp diode, L2
...Coil for adding impedance.

Claims (1)

[Claims] 1. In a quadrupole coil drive circuit for correcting the beam spot shape of a cathode ray tube, the quadrupole current for beam spot shape correction increases rapidly as the scanning position of the electron beam moves away from the center of the display screen. The first occurrence
a second resonant circuit that generates a quadrupole current for beam spot shape correction that gradually increases as the scanning position of the electron beam moves away from the center of the display screen;
switching means for respectively switching and operating the first resonant circuit and the second resonant circuit; the electron beam changes rapidly when scanning an edge area of the display screen; A quadrupole coil drive circuit, characterized in that the quadrupole coil drive circuit generates a quadrupole current for correcting the shape of the beam spot that changes gradually when scanning the central area of the display screen.