KR100386350B1 - Crt display apparatus - Google Patents

Abstract

The present invention provides a Hi- having a cathode and an electron gun including a G1 electrode, a G2 electrode, and a G3 electrode for sequentially drawing electrons from the cathode, and a Gm electrode for modulation is disposed between the G2 electrode and the G3 electrode. In a CRT display device including a Gm tube, by preventing excessive beam current from flowing, the Gm electrode voltage source 10 for generating a voltage applied to the Gm electrode 5 is provided by the Cm electrode current measurement circuit 11. When the value of the current flowing through the measured Gm electrode 5 exceeds the allowable value, the output voltage, that is, the voltage applied to the Gm electrode 5 is lowered in accordance with the value of the measured current, and the cathode is moved from the cathode to the screen. To prevent excessive beam current from flowing.

Description

CRT display device {CRT DISPLAY APPARATUS}

The present invention relates to a display device including a CRT.

9 shows a configuration of a conventional CRT display device. In the figure, reference numeral 18 is a CRT, reference 2 is a cathode, reference 3 is a G1 electrode, reference 4 is a G2 electrode, reference 6 is a G3 electrode, reference 7 is an anode, reference 9 is an image circuit 12 is a flyback transformer (FBT), 13 is an anode current measurement circuit, 14 is a resistor, 15 is a capacitor, and 19 is a variable resistor. The G1 electrode 3, the G2 electrode 4, and the G3 electrode 6 are arranged in an electron gun, and are cylindrical electrodes for withdrawing electrons from the cathode 2, prefocusing, and the like. The focusing electrode or the like disposed after the G3 electrode is omitted for simplicity.

The operation of the apparatus of FIG. 9 will be described. The video signal is amplified by the video circuit 9 and supplied to the cathode 2. The high pressure boosted by the FBT 12 is applied to the anode 7. The voltage obtained by dividing the high voltage applied to the anode 7 by the resistor 19 is applied to the G2 electrode 4. The current is supplied to the FBT 12 via the resistor 14 of the anode current measuring circuit 13, and at this time, the capacitor 15 is charged. The anode current can be measured from the value of the voltage drop caused by the current flowing through the resistor 14. The value of this voltage drop is supplied to the video circuit 9.

The high voltage of about 25 kV applied to the anode 7 is produced by boosting and rectifying the horizontal retrace pulse generated by a horizontal deflection output circuit (not shown) using the FBT 12. The voltage of about 700 V to 1000 V applied to the G2 electrode 4 is made by dividing this high voltage by the resistor 19. Since the current flowing through the G2 electrode 4 is very small, the resistor 19 for dividing the high voltage has a resistance value of about 100 MΩ. By adjusting the voltage applied to the G2 electrode 4, the black level can be varied to perform screen adjustment (coarse cutoff adjustment).

In order to prevent the average electron beam current flowing from the cathode to the screen from exceeding the allowable value, the CRT display device is usually provided with an automatic gradation limit (ACL) circuit (also called an automatic luminance limit (ABL) circuit). Since the anode current is proportional to the electron beam current (hereinafter referred to as beam current), the value of the beam current can be known by measuring the anode current flowing through the FBT 12. The value of the measured anode current is supplied to the ACL circuit. Although various circuits for measuring the anode current have been devised, the apparatus of FIG. 9 measures the anode current from the value of the voltage drop caused by the current flowing through the resistor 14 as described above. The value of this voltage drop is supplied to the video circuit 9 including a preamplifier, an image quality correction circuit, and the like. The video circuit 9 suppresses the amplitude of the video signal supplied to the cathode by reducing the amplification factor of the video signal when the value of the anode current exceeds the allowable value. As a result, the gradation decreases and the beam current is suppressed.

In recent years, there has been a growing demand for improving the luminance and resolution of CRT displays, but Japanese Patent Application Laid-Open No. 11-224618 discloses a high-brightness and high-resolution CRT (hereinafter referred to as Hi-Gm tube) in response to such a requirement. It is. This Hi-Gm tube is characterized by using an electron gun in which a Gm electrode for modulation is newly placed between the G2 electrode and the G3 electrode.

10 shows a configuration of an electron gun used for a Hi-Gm tube. In the figure, reference numeral 20 denotes a G1 electrode, reference numeral 21 denotes a G2 electrode, reference numeral 22 denotes a G3 electrode, reference numeral 23 denotes a cathode, reference numeral 24 denotes an electrospinning material provided on the surface of the cathode, reference numeral 25 denotes Gm Electrode. The configuration of the other focusing electrode or the like disposed after the G3 electrode is the same as that of the conventional electron gun.

11 is a graph showing the potential distribution near the cathode of a Hi-Gm tube electron gun. In this graph, the horizontal axis represents the distance (mm) from the cathode surface, and the vertical axis represents the potential (V), respectively, and the potential distribution curve 26 represents the shape of the potential distribution that is the rotation axis symmetry near the cathode. Incidentally, the arrow indicated by 27 indicates the presence range of the Gm electrode 25 at a distance of about 0.5 mm from the cathode surface.

The potential of the Gm electrode 25 is set to about DC 80V, so that there is a position 28 having a low potential within the existence range 27 of the Gm electrode 25. If the potential of the cathode 23 indicated by the broken line is lower than the potential of this position 28, the electron passes through the position 28 to the screen, but if it is higher than the potential, the electron has the position having the low potential ( 28) It cannot pass through and does not flow towards the screen.

As can be seen from the graph of FIG. 11, between the cathode 23 and the position 28 having a low potential, electrons are always abundant, and the potential gradient behind the Gm electrode 25 is 10 ⁶ (V / m). This is about one order of magnitude larger than the potential gradient between the cathode and the G1 electrode. Therefore, after the electrons have passed through the Gm electrode 25, many of the electrons can be directed to the screen without being affected by the space charge, so that the intensity of the electron beam flowing to the screen passes through the position 28 having a low electric potential. It is determined by the amount of electrons to be made.

For this reason, in the Hi-Gm tube, the change in the beam current when the cathode potential is changed by a certain value is about twice that of the conventional CRT. That is, in the Hi-Gm tube, the fluctuation range of the cathode potential required to change the beam current by a predetermined value can be made less than half the conventional one, and if the fluctuation range of the cathode potential is the same, the amount of change in the beam current compared to the conventional CRT Can be more than doubled. Therefore, by using the Hi-Gm tube, it is possible to easily cope with a high frequency video signal, thereby obtaining a display device with high brightness and high resolution.

12 is a graph showing how each current changes when the cathode voltage is changed in the Hi-Gm tube. In this graph, reference numeral 29 denotes a cathode current, reference numeral 30 denotes a beam current, reference numeral 31 denotes a G2 electrode current, and reference numeral 32 denotes a Gm electrode current. This graph shows a case where the G2 electrode voltage is 500V and the Gm electrode voltage is 80V. From this graph, it can be seen that as the cathode voltage decreases, the beam current increases and the brightness of the screen increases, and since the voltage applied to the Gm electrode is 80V, the beam current starts to flow when the cathode voltage becomes 80V or less. have. In addition, it is understood from the graph that in the Hi-Gm tube, the Gm electrode current and the G2 electrode current increase with the increase of the beam current.

In the display device using the Hi-Gm tube, when the fluctuation range of the cathode voltage is the same as compared with the CRT display device using a normal electron gun, the change amount of the beam current is twice or more, and the likelihood of excessive beam current flowing also increases. . If excessive beam current continues to flow, emission failures occur and the CRT life is shortened. Therefore, in the display device using the Hi-Gm tube, the control of the beam current becomes more important than the prior art. SUMMARY OF THE INVENTION It is an object of the present invention to provide a CRT display device having new means for preventing excessive beam current, in view of the above characteristics of the Hi-Gm tube.

The above and other objects, features, aspects, advantages, and the like of the present invention will become more apparent from the following detailed embodiments described with reference to the accompanying drawings.

1 is a block diagram showing a configuration of a CRT display device according to Embodiment 1 of the present invention;

2 is a block diagram showing a configuration of a CRT display device according to a second embodiment of the present invention;

3 is a block diagram showing a configuration of a CRT display device according to a third embodiment of the present invention;

4 is a block diagram showing a configuration of a CRT display device according to Embodiment 4 of the present invention;

5 is a block diagram showing a configuration of a CRT display device according to a fifth embodiment of the present invention;

6 is a block diagram showing a configuration of a CRT display device according to a sixth embodiment of the present invention;

7 is a block diagram showing a configuration of a CRT display device according to a seventh embodiment of the present invention;

8 is a block diagram showing a configuration of a CRT display device according to Embodiment 8 of the present invention;

9 is a block diagram showing the structure of a conventional CRT display;

10 is an explanatory diagram showing a structure near a cathode of a Hi-Gm tube electron gun;

11 is a graph illustrating a potential distribution in a Hi-Gm tube electron gun;

12 is a graph showing a relationship between a cathode voltage and each current of a Hi-Gm tube.

Explanation of Symbols for Main Part of Invention

1: Hi-Gm tube 2: cathode

3: G1 electrode 4: G2 electrode

5: Gm electrode 6: G3 electrode

7: anode 9: video circuit

10: Gm electrode voltage source 11: Gm electrode current measurement circuit

12 flyback transformer 13 anode current measurement circuit

14 resistance 15 capacitor

16: G2 electrode voltage source 17: G2 electrode current measurement circuit

18: CRT 19: variable resistor

20: G1 electrode 21: G2 electrode

22: G3 electrode 23: cathode

24: electron emitting material 25: Gm electrode

26: potential distribution curve 27: the range where the Gm electrode is present

28: low potential position 29: cathode current

30 beam current 31 G2 electrode current

32: Gm electrode current

The invention according to claim 1 is provided with a cathode, an electron gun including a G1 electrode, a G2 electrode, and a G3 electrode for taking out electrons from the cathode, in order, and a modulation Gm electrode disposed between the G2 electrode and the G3 electrode. A CRT display device comprising a CRT having: a current measuring means for measuring any one of a current flowing through the Gm electrode, a current flowing through the G2 electrode, and a current flowing through an anode of the CRT; and measured by the current measuring means. And control means for controlling the value of the voltage applied to said Gm electrode in accordance with the value of said current.

The invention according to claim 2 includes a cathode, an electron gun provided with a G1 electrode, a G2 electrode, and a G3 electrode for taking out electrons from the cathode in that order, and a Gm electrode for modulation is disposed between the G2 electrode and the G3 electrode. A CRT display device comprising a CRT having: a current measuring means for measuring any one of a current flowing through the Gm electrode, a current flowing through the G2 electrode, and a current flowing through an anode of the CRT; and measured by the current measuring means. And control means for controlling the value of the voltage applied to said G2 electrode in accordance with the value of said current.

The invention according to claim 3 comprises a cathode, an electron gun provided with a G1 electrode, a G2 electrode, and a G3 electrode for taking out electrons from the cathode in that order, and a Gm electrode for modulation is disposed between the G2 electrode and the G3 electrode. A CRT display device comprising a CRT having a CRT and an image circuit for supplying an image signal having an amplitude corresponding to a control signal supplied to the cathode, the current flowing through the Gm electrode, the current flowing through the G2 electrode, and the anode of the CRT. And a current measuring means for measuring the value of any one of the currents flowing through and supplying the measured value as the control signal to the video circuit.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated concretely according to drawing which shows the Example.

(Example 1)

1 is a block diagram showing a configuration of a CRT display device according to Embodiment 1 of the present invention. In the figure, reference numeral 1 denotes a Hi-Gm tube, reference numeral 2 denotes a cathode, reference numeral 3 denotes a G1 electrode, reference numeral 4 denotes a G2 electrode, reference numeral 5 denotes a Gm electrode, reference numeral 6 denotes a G3 electrode, and a reference numeral 7 is an anode, 9 is an image circuit, 10 is a Gm electrode voltage source, 11 is a Gm electrode current measuring circuit. Since the structure after the Gm electrode is the same as the conventional one, the illustration is omitted for simplicity.

The video signal is inverted and amplified by the video circuit 9 and applied to the cathode 2. The Gm electrode voltage source 10 is a voltage source that generates a voltage applied to the Gm electrode 5. The Gm electrode current measuring circuit 11 measures the current flowing through the Gm electrode 5, and supplies the value to the Gm electrode voltage source 10. In Example 1, for example, a high voltage of 0 V is applied to the G1 electrode 3, 500 V to the G2 electrode 4, 5.5 KV to the G3 electrode, 80 V to the Gm electrode, and 25 KV to the anode 6, respectively. have.

As described with reference to FIG. 12, the beam current and the Gm electrode current have a proportional relationship, and in Example 1, the beam current is measured by measuring the Gm electrode current using this characteristic.

When the measured value of the Gm electrode current exceeds the allowable value, the Gm electrode voltage source 10 lowers the output voltage, that is, the voltage applied to the Gm electrode according to the value. The voltage applied to the Gm electrode 5 defines the cathode voltage at which the CRT screen starts to emit light. When the cathode voltage becomes lower than the voltage of the Gm electrode, the electron beam is irradiated onto the screen, and the screen starts to emit light. Therefore, when the Gm electrode voltage is lowered, the point at which the screen for the cathode voltage starts emitting light is lowered, so that the beam current can be suppressed.

In Example 1 described above, the anode current is not measured to measure the beam current, but the current flowing through the Gm electrode 5 from the Gm electrode voltage source 10 having an output voltage of 100 V or less and an output current of 1 mA or less is measured. Therefore, the beam current can be easily measured using a simple circuit. The current flowing through the Gm electrode can be measured by various methods. For example, the voltage drop value of the resistor connected in series to the Gm electrode can be measured as a voltage value.

(Example 2)

2 is a block diagram illustrating a configuration of a CRT display device according to a second embodiment of the present invention. In FIG. 2, the same code | symbol is attached | subjected to the element of the same structure as the element of FIG. In Example 2, similarly to Example 1, the beam current is measured by measuring the Gm electrode current using the characteristic that the beam current and the Gm electrode current are in proportional relationship. Image quality adjustment circuits such as preamplifiers and video chromatic jungles (VCJs) in a video circuit are usually provided with control inputs for control of gradation and the like, and the second embodiment is a Gm electrode current measurement circuit ( 11) differs from the first embodiment in that the measurement result of 11) is supplied to the control input of the video circuit 9 rather than the Gm electrode voltage source 10. FIG.

When the measured value of the Gm electrode current exceeds the allowable value, the video circuit 9 reduces the gain of the amplifier according to the value and decreases the brightness by reducing the amplitude of the video signal supplied to the cathode. This suppresses the beam current. In addition, when the integrating circuit is provided at the output of the Gm electrode current measuring circuit 11, the average beam current is suppressed. However, since the high frequency component of the beam current corresponding to the small-area portion having high brightness on the screen is not so suppressed, the peak peak luminance is sufficient. Is obtained, and an enhanced image is obtained in a moving picture such as a television picture.

In conventional CRT displays or TVs, the anode current is usually measured and the measurement result is supplied to the gradation control circuit of the video circuit. In Example 2, the Gm electrode current is measured and the measurement result. Is supplied to the gradation control circuit of the video circuit. As described above, in the second embodiment, since the beam current is controlled by using the gradation control circuit usually provided in the video circuit, the manufacturing cost can be reduced. In addition, as in Example 1, instead of measuring the anode current to measure the beam current, the current flowing through the Gm electrode 5 from the Gm electrode voltage source 10 having an output voltage of 10 V or less and an output current of 1 mA or less is measured. Using a simple circuit, the beam current can be easily measured.

(Example 3)

3 is a block diagram illustrating a configuration of a CRT display device according to a third embodiment of the present invention. In FIG. 3, the same code | symbol is attached | subjected to the element of the same structure as the element of FIG. Embodiment 3 includes the anode current measurement circuit 13 described with reference to FIG. 9 instead of the Gm electrode current measurement circuit 11, and the measurement result of the anode current measurement circuit 13 is applied to the Gm electrode voltage source 10. FIG. It differs from Example 1 in the point which is supplied.

In the Hi-Gm tube, the anode current increases with increasing beam current. In the third embodiment, the anode current is measured, and according to the measurement result, the output voltage of the Gm electrode voltage source 10 is controlled to prevent excessive beam current from flowing. As described above, the beam current can be measured by measuring the anode current from the value of the voltage drop caused by the current flowing through the resistor 14 of the anode current measurement circuit 13.

When the measured value of the anode current exceeds the allowable value, the Gm electrode voltage source 10 lowers the output voltage, that is, the voltage applied to the Gm electrode 5 according to the value. As already explained, the voltage of the Gm electrode defines the cathode voltage at the point at which the screen starts to emit light. When the cathode voltage becomes lower than the voltage of the Gm electrode 5, the electron beam flows to the screen and the screen starts to emit light. Therefore, when the Gm electrode voltage is lowered, the point at which the screen for the cathode voltage starts emitting light is lowered, so that the beam current can be suppressed. As such, by controlling the voltage applied to the Gm electrode according to the value of the anode current, excessive beam current can be prevented from flowing. The measurement of the anode current in the CRT display device is a method well used in the past for measuring the beam current, and it is easy to introduce this method.

(Example 4)

4 is a block diagram showing a configuration of a CRT display device according to a fourth embodiment of the present invention. In FIG. 4, the same code | symbol is attached | subjected to the component same as the component of FIGS. The fourth embodiment differs from the first embodiment in that the measurement results of the Gm electrode current measurement circuit 11 are supplied to the G2 electrode voltage source 16 instead of the Gm electrode voltage source 10. The G2 electrode voltage source 16 is a voltage source for generating a voltage applied to the G2 electrode, and its output voltage can be changed according to the value of the current measured by the Gm electrode current measurement circuit 11.

As described with reference to FIG. 12, in the Hi-Gm tube, when the beam current increases, the Gm electrode current increases in proportion to it, so that the beam current can be measured by measuring the Gm electrode current.

In a display device having an ordinary CRT, rough adjustment of the cutoff adjustment of the point at which the screen starts to emit light is performed with respect to the cathode voltage called screen adjustment by adjusting the voltage applied to the G2 electrode. Adjusting the cathode bias voltage). In a typical CRT, the relative potential difference with the cathode voltage is reduced by lowering the G2 electrode voltage, and as a result, the beam current can be reduced, but the black level sinks. Even in the Hi-Gm tube, when the G2 electrode voltage is lowered, the relative potential difference with the cathode voltage decreases and the beam current decreases, but since the point at which the screen starts emitting light is determined by the voltage of the Gm electrode, , Black level does not change. Therefore, in the Hi-Gm tube, the beam current can be suppressed without changing the black level by lowering the G2 electrode voltage.

That is, in Example 4, when the measured value of the Gm electrode current exceeds the allowable value, the G2 electrode voltage source 16 lowers the output voltage, that is, the voltage applied to the G2 electrode according to the value. As a result, excessive beam current can be prevented from flowing without changing the black level.

(Example 5)

5 is a block diagram showing a configuration of a CRT display device according to a fifth embodiment of the present invention. In Fig. 5, the same reference numerals are given to the same components as those of Figs. 1 to 4. In FIG. 5, reference numeral 17 is a G2 electrode current measurement circuit connected to the output of the G2 electrode voltage source 16 and measuring the current flowing through the G2 electrode 4. The output of the G2 electrode current measurement circuit 17 is supplied to the G2 electrode voltage source 16. The G2 electrode voltage source 16 is configured to change its output voltage in accordance with the value of the current measured by the G2 electrode current measurement circuit 17.

As described with reference to FIG. 12, in the Hi-Gm tube, as the cathode voltage decreases, the G2 electrode current increases with the increase in the beam current. In Example 5, the beam current is measured by measuring the G2 electrode current using this property.

That is, in the fifth embodiment, when the measured value of the G2 electrode current exceeds the allowable value, the G2 electrode voltage source 16 lowers the output voltage, that is, the voltage applied to the G2 electrode 4 according to the value. As described in the fourth embodiment, in the Hi-Gm tube, the beam current can be lowered by lowering the G2 electrode voltage, and the black level does not change when the beam current is increased by the falling width of the G2 electrode voltage value. Therefore, by lowering the voltage applied to the G2 electrode 4, the beam current can be suppressed without changing the black level.

(Example 6)

6 is a block diagram illustrating a configuration of a CRT display device according to a sixth embodiment of the present invention. In FIG. 6, the same code | symbol is attached | subjected to the element same as the element shown in FIGS. The sixth embodiment differs from the fifth embodiment in that the output of the G2 electrode current measurement circuit 17 is supplied to the control input of the video circuit 9 rather than the G2 electrode voltage source 16.

In Example 6, as in Example 5, in the Hi-Gm tube, the G2 electrode current increases with the increase in the beam current as the cathode voltage decreases, thereby measuring the G2 electrode current to measure the beam current. Is being measured.

When the measured value of the G2 electrode current exceeds the allowable value, the video circuit 9 reduces the gain of the amplifier according to the value, reduces the amplitude of the video signal supplied to the cathode, and lowers the brightness. The beam current is thereby suppressed. In addition, when an integrating circuit is provided at the output of the G2 electrode current measuring circuit 17, the average beam current is suppressed, but since the high frequency component of the beam current corresponding to the small-area portion having high brightness on the screen is not so suppressed, sufficient peak brightness Is obtained, and an improved image is obtained from a moving image such as a television image.

(Example 7)

7 is a block diagram illustrating a configuration of a CRT display device according to a seventh embodiment of the present invention. In FIG. 7, the same code | symbol is attached | subjected to the element same as the element shown in FIGS. Example 7, like Example 3, measures the beam current by measuring the anode current, using the characteristic that the anode current increases with the increase of the beam current, regardless of a normal CRT or Hi-Gm tube. Is different from Example 3 in that the measurement output of the anode current measurement circuit 13 is supplied to the G2 electrode voltage source 16 instead of the Cm electrode voltage source 10.

When the measured value of the anode current exceeds the allowable value, the G2 electrode voltage source 16 lowers the output voltage, that is, the voltage applied to the G2 electrode 4 according to the value. As described in the fourth embodiment, in the Hi-Gm tube, the beam current can be lowered by lowering the G2 electrode voltage, so that the black level is not changed when the voltage drop width of the G2 electrode increases by that much. Therefore, in the Hi-Gm tube, the beam current can be suppressed without changing the black level by lowering the voltage applied to the G2 electrode 4.

(Example 8)

8 is a block diagram illustrating a configuration of a CRT display device according to an eighth embodiment of the present invention. In FIG. 8, the same code | symbol is attached | subjected to the element same as the element shown in FIGS. As already explained, in the Hi-Gm tube, as the cathode voltage decreases, the G2 electrode current increases with the increase of the beam current. Example 8 measures beam current by measuring G2 electrode current using this characteristic similarly to Examples 5 and 6. Example 8 differs from Examples 5 and 6 in that the output of the G2 electrode current measurement circuit 17 is supplied to the Gm electrode voltage source 10.

The Gm electrode voltage source 10 is a voltage source for generating a voltage applied to the Gm electrode, and may change its output voltage according to the value of the current supplied from the G2 electrode current measuring circuit 17. When the measured value of the G2 electrode current exceeds the allowable value, the Gm electrode voltage source 10 lowers the output voltage, that is, the voltage applied to the Gm electrode 5 according to the value.

As already explained, the voltage of the Gm electrode defines the cathode voltage at the point where the screen starts to emit light, and when the cathode voltage is lower than the voltage of the Gm electrode, an electron beam flows to the screen and the screen starts to emit light. When the Gm electrode voltage is lowered, the point at which the screen for the cathode voltage starts to emit light is lowered to suppress the beam current. Thus, by controlling the voltage applied to the Gm electrode according to the value of the G2 electrode current, it is possible to prevent the excessive beam current from flowing.

According to the invention as set forth in claim 1, any one of a current flowing through the Gm electrode, a current flowing through the G2 electrode, and a current flowing through the anode of the CRT, respectively proportional to the beam current, is measured and measured according to the value of the measured current. By controlling the voltage applied, it is possible to prevent excessive beam current from flowing.

According to the invention of claim 2, any one of a current flowing through the Gm electrode, a current flowing through the G2 electrode, and a current flowing through the anode of the CRT, respectively, which is proportional to the beam current, is measured, and the G2 electrode is measured according to the value of the measured current. By controlling the voltage applied, it is possible to prevent excessive beam current from flowing.

According to the invention as set forth in claim 3, an image supplied to the cathode from an image circuit by measuring a value of any one of a current flowing through the Gm electrode, a current flowing through the G2 electrode, and a current flowing through the anode of the CRT, respectively, which is proportional to the beam current Since the amplitude of the signal is controlled in accordance with the measured value, excessive beam current can be prevented from flowing.

As mentioned above, although the invention made by this inventor was demonstrated concretely according to the said Example, this invention is not limited to the said Example and can be variously changed in the range which does not deviate from the summary.

Claims (3)

A CRT comprising a cathode and a CRT having a G1 electrode, a G2 electrode, and a G3 electrode, in order to extract electrons from the cathode, and an electron gun having a Gm electrode for modulation disposed between the G2 electrode and the G3 electrode; In a display device, Current measuring means for measuring any one of a current flowing through the Gm electrode, a current flowing through the G2 electrode, and a current flowing through the anode of the CRT; Control means for controlling the value of the voltage applied to the Gm electrode according to the value of the current measured by the current measuring means CRT display device comprising a. A CRT comprising a cathode and a CRT having a G1 electrode, a G2 electrode, and a G3 electrode, in order to extract electrons from the cathode, and an electron gun having a Gm electrode for modulation disposed between the G2 electrode and the G3 electrode; In a display device, Current measuring means for measuring any one of a current flowing through the Gm electrode, a current flowing through the G2 electrode, and a current flowing through the anode of the CRT; Control means for controlling the value of the voltage applied to the G2 electrode according to the value of the current measured by the current measuring means CRT display device comprising a. A CRT having a cathode, an electron gun provided with a G1 electrode, a G2 electrode, and a G3 electrode for taking out electrons from the cathode in this order, and wherein a Gm electrode for modulation is disposed between the G2 electrode and the G3 electrode; A CRT display device comprising an image circuit for supplying an image signal having an amplitude corresponding to a control signal to the cathode. Current measuring means for measuring the value of any one of the current flowing in the Gm electrode, the current flowing in the G2 electrode and the current flowing in the anode of the CRT, and supplies the measured value as the control signal to the video circuit. CRT display device comprising a.