JPH07120142B2 - Flat cathode ray tube - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flat cathode ray tube (flat type CRT) for applying and driving a video signal to a G1 electrode.

[0002]

2. Description of the Related Art Conventionally, there is known a flat cathode ray tube in which a fluorescent screen is formed so as to be inclined at a relatively small angle with respect to a central axis of an electron gun. FIG. 5 shows a drive system of this flat cathode ray tube.

In the figure, 1 is a flat cathode ray tube,
K is a cathode electrode, G1 is a first grid electrode, G2 is a second grid electrode forming an accelerating electrode, G3 is a third grid electrode forming a focus electrode, and 2 is a fluorescent screen.
The phosphor screen 2 has a flyback transformer (hereinafter, “FB”).
A high voltage HV obtained by rectifying the pulse voltage output from the T.) is applied.

As the cathode electrode K, unlike the indirectly heated electrode used in a general cathode ray tube, a directly heated electrode which operates at low power and has a quick rising is adopted. A pulse voltage is supplied as a heater voltage 3 from the FBT to the cathode electrode K, and so-called pulse ignition is performed.

In this case, since the FBT winding is connected to the cathode electrode K, the stray capacitance of the cathode electrode K increases, and when the cathode drive system for applying a video signal to the cathode electrode K is adopted, Loss increases. In other words, in order to improve the frequency characteristics, it is necessary to reduce the impedance of the output stage of the video circuit so that the influence of the stray capacitance can be ignored, and the emitter follower configuration or the like will be adopted. Will lead to an increase.

Therefore, a G1 drive system is adopted in which a video signal is applied to the first grid electrode G1 having a relatively small stray capacitance. That is, 4 is an NPN type transistor which constitutes a video amplifier.
The video signal SV is supplied from the terminal 5 to the base of the.
The emitter of this transistor 4 is grounded via a parallel circuit of a resistor 6 and a capacitor 7, and its collector is connected to a power supply terminal + B (for example, 50V) via a resistor 8. Then, the video signal obtained at the connection point of the collector of the transistor 4 and the resistor 8 is applied to the first grid electrode G1 of the cathode ray tube 1 via the capacitor 9.

Voltage source + B1 (for example, 900V)
Is grounded via a series circuit of a variable resistor 10 for focus adjustment, a variable resistor 11 for cutoff adjustment, and a resistor 12. The voltage obtained at the movable terminal of the variable resistor 10 is applied to the third grid electrode G3 of the cathode ray tube 1 via the resistor 13. The mover of the variable resistor 11 is grounded via the capacitor 14, and the voltage obtained at the connection point between the mover and the capacitor 14 is applied to the second grid electrode G2 of the cathode ray tube 1.

Voltage source + B2 (for example, 140V)
Is grounded via a semi-fixed resistor 15 for adjusting the sub-brightness, a resistor 16, a variable resistor 17 for adjusting the brightness and a resistor 18 forming a constant current circuit. The voltage obtained at the mover of the variable resistor 17 is applied to the cathode electrode K via the resistor 19.

The cutoff adjustment of the cathode ray tube 1 is performed by changing the voltage applied to the second grid electrode G2 and the cathode electrode K. That is, the voltage applied to the second grid electrode G2 is varied by the variable resistor 11 to determine the cutoff of the cathode ray tube 1 and the semi-fixed resistor 15
Therefore, the sub-brightness is determined by changing the voltage applied to the cathode electrode K.

As described above, since the voltage applied to the cathode electrode K is varied by the sub-brightness adjustment by the semi-fixed resistor 15 and the brightness adjustment by the variable resistor 17, the resistance value of the resistor 19 is relatively high, for example, 10
It is set to 0 KΩ. However, as is well known, since a beam current proportional to a video signal flows into the cathode electrode K, it is necessary to lower the circuit impedance. Therefore, the cathode electrode K of the cathode ray tube 1 is grounded via the capacitor 20 to lower the impedance in terms of AC.

Reference numeral 21 is a horizontal blanking pulse HBL.
K is supplied to the terminal, 22 is a vertical blanking pulse VB
This is the terminal to which LK is supplied. The terminal 21 is connected to the base of the NPN transistor 25 via the resistor 23 and the diode 24. The terminal 22 is connected to the base of the transistor 25 via the resistor 26. The base of this transistor is grounded via a resistor 27, its emitter is grounded, and its collector is connected via resistor 28 to the junction of transistor 4 and resistor 8.

During the horizontal and vertical blanking periods, a blanking pulse (positive pulse) HBL is applied to the terminals 21 and 22.
Since K and VBLK are supplied, the transistor 25 is turned on. As a result, the voltage at the connection point between the transistor 4 and the resistor 8 becomes approximately 0V, and the blanking operation is performed.

[0013]

In the example of FIG. 5,
When adjusting the cutoff, the voltage applied to the second grid electrode G2 is varied by the variable resistor 11 to determine the cutoff of the cathode ray tube 1, and the semifixed resistor 15 is applied to the cathode electrode K. The sub-brightness is determined by changing the applied voltage, which causes a problem of increasing the number of adjustment steps.

Further, the voltage applied to the cathode electrode K is varied during the cutoff adjustment, and therefore the resistance value of the resistor 19 is increased, so that the cathode electrode K is grounded via the capacitor 20. As a result, the impedance is lowered AC-wise, and there is a problem that the number of parts increases and the cost increases.

The voltage applied to the second grid electrode G2 is variable when the cutoff adjustment is performed.
The cutoff adjustment may deteriorate the resolution.

Therefore, it is an object of the present invention to provide a flat cathode ray tube which can reduce the number of adjustment steps and the number of parts and can perform cutoff adjustment without deteriorating the resolution.

[0017]

The present invention provides a flat cathode ray tube in which a fixed voltage is applied to the cathode electrode K and the second grid electrode G2, and a video signal is applied to the first grid electrode G1 for driving. A fixed voltage is applied to the cathode electrode from a low impedance power source, and a DC voltage is applied to the first grid electrode G1 from the low impedance power source through a high impedance circuit forming a voltage dividing circuit.

[0018]

The DC voltage applied to the first grid electrode G1 is changed by changing the voltage division ratio of the high impedance circuit. This makes it possible to adjust the cutoff of the cathode ray tube. Further, since a fixed voltage is applied to the cathode electrode K from the low impedance power source, it is not necessary to connect a capacitor that lowers the impedance in an AC manner between the cathode electrode K and the ground. In addition, a DC voltage is applied to the first grid electrode G1 from a low impedance power source through a high impedance circuit, so that the potential change due to the cathode current flowing into the first grid electrode G1 does not occur. Further, since the voltage is applied to the cathode electrode K and the first grid electrode G1 from the same low impedance power source, the potential relationship between the cathode electrode K and the first grid electrode G1 is always constant even if the voltage changes. Kept in. Further, since the fixed voltage is applied to the second grid electrode G2, the voltage applied to the second grid electrode does not change due to the cutoff adjustment.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 and 2, parts corresponding to those in FIG. 5 are designated by the same reference numerals, and detailed description thereof will be omitted.

First, the high voltage generating circuit 30 shown in FIG. 2 will be described. Reference numeral 31 is a terminal to which a horizontal drive pulse output from a horizontal drive circuit (not shown) is supplied, and this terminal 31 is connected via a capacitor 32 to the base of an NPN transistor 33 which constitutes a switching element. A clamp diode 34 is connected to the base of the transistor 33.

The emitter of the transistor 33 is grounded,
The collector is connected to the intermediate tap P1 of the primary coil 35a of the FBT 35. A damper diode 36 and a resonance capacitor 37 are connected in parallel between the collector of the transistor 33 and the ground. One end of the primary coil 35a is connected to a power supply terminal + Vcc via a low pass filter composed of a coil 38 and a capacitor 39.

The intermediate tap P2 of the primary coil 35a of the FBT 35 is connected to the rectifying / smoothing circuit 40. In the rectifying / smoothing circuit 40, the pulse voltage obtained at the intermediate tap P2 is rectified and smoothed, and the DC voltage E1 (for example, 50 V) output from the rectifying / smoothing circuit 40 is led to the terminal 41.

The other end of the primary side coil 35a and the other end of the secondary side coil 35b of the FBT 35 are commonly connected, and the connection point P3 is connected to the rectifying / smoothing circuit 42. In the rectifying / smoothing circuit 42, the pulse voltage obtained at the connection point P3 is rectified and smoothed, and the DC voltage E2 (for example, 140 V) output from the rectifying / smoothing circuit 42 is led to the terminal 43.

Further, one end side of the secondary coil 35b of the FBT 35 is connected to a rectifying circuit 44 having a multiple voltage. The pulse voltage obtained at one end of the secondary coil 35b is rectified by the rectifier circuit 44, and the high voltage HV output from the rectifier circuit 44 is led to the terminal 45.

The intermediate tap P4 of the secondary coil 35b of the FBT 35 is connected to the rectifying / smoothing circuit 46. In the rectifying / smoothing circuit 46, the pulse voltage obtained at the intermediate tap P4 is rectified and smoothed to obtain a DC voltage (for example, 900V). The output side of the rectifying / smoothing circuit 46 is grounded via a series circuit of a variable resistor 47 and a resistor 48 for focus adjustment. The DC voltage EG3 obtained at the mover of the variable resistor 47 is led to the terminal 50 via the resistor 49. The connection point of the variable resistor 47 and the resistor 48 is grounded via the capacitor 51, and the DC voltage EG2 (500 V, for example) obtained at this connection point is led to the terminal 52.

The other coils 35a, 3 of the FBT 35 are also
One end and the other end of the secondary coil 35c insulated from 5b are connected to terminals 53a and 53b. This secondary coil 35
c is for obtaining a pulse voltage applied to the cathode electrode K of the cathode ray tube 1 as described later. 2
One end of the secondary coil 35c has a low resistance value (for example, 100Ω).
Is connected to the output side of the rectifying / smoothing circuit 42 via the resistor 54. Thereby, as will be described later, the flat cathode ray tube 1
A fixed DC voltage is applied to the cathode electrode K of.

Next, the drive system of the flat cathode ray tube 1 of FIG. 1 will be described. To the cathode electrode K of the cathode ray tube 1, the pulse voltage derived to the terminals 53a and 53b of the high voltage generating circuit 30 described above is applied as a heater voltage, and
The DC voltage E2 output from the rectifying / smoothing circuit 42 is applied. The second grid electrode G2 of the cathode ray tube 1 has a DC voltage E led to the terminal 52 of the high voltage generating circuit 30 described above.
G2 is applied. To the third grid electrode G3 of the cathode ray tube 1, the DC voltage EG3 led to the terminal 50 of the high voltage generating circuit 30 described above is applied. Further, the high voltage HV led to the terminal 45 of the high voltage generating circuit 30 described above is supplied to the cathode ray tube 1, and this high voltage is applied to the fluorescent screen 2 and the like.

Further, in FIG. 1, 60 is a CRT drive circuit, and 61 is a terminal to which the video signal SV is supplied. The terminal 61 is connected to the base of the NPN transistor 63 via the capacitor 62. A series circuit of resistors 64 and 65 is connected between the power supply terminal + Vcc and the ground, and the connection point of the resistors 64 and 65 is connected to the base of the transistor 63, whereby the base bias is supplied to the transistor 63. It

The collector of the transistor 63 is connected to the power supply terminal + Vcc, and the emitter of the transistor 63 is grounded via the resistor 66 to form an emitter follower structure. The connection point between the emitter of the transistor 63 and the resistor 66 is grounded through a series circuit of a variable resistor 67 for contrast adjustment, a resistor 68 and a capacitor 69, and the connection point of the resistor 68 and the capacitor 69 is an emitter-coupled differential. It is connected to the base of one NPN transistor 70 which constitutes an amplifier. The mover of the variable resistor 67 is connected to the base of the other NPN transistor 71 which constitutes the emitter-coupled differential amplifier.

The collector of the transistor 70 is a resistor 72.
Is connected to the terminal 73 via. The DC voltage E1 led to the terminal 41 of the high voltage generating circuit 30 described above is supplied to the terminal 73. The collector of the transistor 71 is connected to the power supply terminal + Vcc. And transistor 7
A series circuit of resistors 74 and 75 is connected between the emitters of 0 and 71, and the connection point of these resistors 74 and 75 is the series of collector / emitter of NPN transistor 76 and resistor 77 that form a constant current source. Grounded via a circuit.

A series circuit of a resistor 78, a resistor 79 and an NPN type transistor 80 is connected between the power supply terminal + Vcc and the ground, and the connection point of the resistors 78 and 79 is connected to the base of the transistor 76. The collector and base of the transistor 80 are connected to form a diode connection, and the transistors 76 and 80 constitute a current mirror circuit as a constant current source.

81 is a horizontal blanking pulse HBL
A terminal to which K (for example, a positive pulse having a pulse width of 10 to 12 μsec) is supplied, and 82 is a vertical blanking pulse VBLK
(For example, a positive pulse having a pulse width of 1 msec) is supplied to the terminal. The terminal 81 is grounded via a series circuit of resistors 83 and 84, and the connection point of these resistors 83 and 84 is connected to the base of the transistor 76 via a diode 85. The terminal 82 is also connected to the base of the transistor 76 via the resistor 86.

The connection point between the collector of the transistor 70 and the resistor 72 is connected to the first grid electrode G1 of the cathode ray tube 1 via the capacitor 87 and the terminal 88. Further, 89 is the terminal 43 of the high voltage generating circuit 30 described above.
This is a terminal to which the DC voltage E2 derived to (3) is supplied. A series circuit of a resistor 90, a variable resistor 91 for brightness adjustment, and a variable resistor 92 for cutoff adjustment is connected between this terminal 89 and ground. For example, the resistance value of the resistor 90 is 270 KΩ, and the resistance value of the variable resistor 91 is 47 K.
Ω, and the resistance value of the variable resistor 92 is 1 MΩ. The mover of the variable resistor 91 is connected to the capacitor 87 via the resistor 93.
And the terminal of the variable resistor 92, and the mover of the variable resistor 92 is grounded. In this case, the resistor 90 and the variable resistors 91 and 92 form a high impedance circuit as a voltage dividing circuit.

In the above structure, the same DC voltage is supplied as a bias from the emitter output of the transistor 63 to the bases of the transistors 70 and 71. A video signal is supplied to the base of the transistor 71 from the mover of the variable resistor 67. for that reason,
An amplified video signal is obtained at the connection point between the collector of the transistor 70 and the resistor 72, and this video signal is transmitted via the capacitor 87 to the first grid electrode G1 of the cathode ray tube 1.
Applied to. Here, by moving the position of the mover of the variable resistor 67, the magnitude of the video signal supplied to the base of the transistor 71 changes, and the contrast can be adjusted accordingly.

When the blanking pulses HBLK and VBLK are supplied to the terminals 81 and 82, the transistor 76 is turned on and the collector current of the transistor 70 increases, so that the collector of the transistor 70 and the resistor 7 are connected.
A voltage of blanking level (retrace line erasing voltage) is obtained at the connection point of 2, and a blanking operation is performed.

FIG. 3 shows an equivalent circuit of the emitter-coupled differential amplifier. Si is the input video signal supplied to the base of the transistor 71, and So is the transistor 7
It is the output video signal obtained at the junction of the collector of 0 and the resistor 72. In the figure, the base bias voltage of the transistors 70 and 71 is VB, the base-emitter voltage of the transistor 76 is VBE1, the base-emitter voltage of the transistor 80 is VBE2, and the resistors 72, 74, 75,
The resistance values of 77, 78, 79 are RL, Re2, Re respectively.
1, Re3, R1 and R2.

Here, the collector current Ic flowing through the transistor 76 is as shown in equation 1.

[0038]

[Equation 1]

Further, the gain A of the amplifier is represented by the equation 2, and the output video signal So is determined by the equation 3.

[0040]

[Equation 2]

[0041]

[Equation 3]

By the way, FIG. 4 shows static characteristics of the flat cathode ray tube 1. The characteristic shown is that the high voltage HV is 7.
5KV, the voltage EG2 of the second grid electrode G2 is 500V,
It is a graph showing the relationship between the cathode current IK and the voltage EG1 of the first grid electrode G1 when the voltage of the cathode electrode K is 140V. In the figure, a curve a shows a low cutoff voltage, a curve b shows an average cutoff voltage, and a curve c shows a high cutoff voltage.

In the present example, the DC voltage EG1 applied to the first grid electrode G1 of the cathode ray tube 1 is changed by moving the mover position of the variable resistor 92, so that the cathode ray tube 1 is cut. Off adjustment can be performed. For example, in the cathode ray tube 1 having the characteristics of curves a, b, and c in FIG. 4, the DC voltage EG1 is EG1a,
By adjusting to EG1b and EG1c, the cutoff level becomes 5
Can be set to μA. As described above, the resistance value of the variable resistor 92 is much larger than the resistance value of the variable resistor 91 for brightness adjustment, and the adjustable range is widened. This cutoff adjustment is performed at the time of factory shipment, for example.

As described above, in this example, the cut-off adjustment can be performed only by changing the DC voltage EG1 applied to the first grid electrode G1, and the second grid electrode G2 and the cathode electrode K can be adjusted as in the conventional case. The adjustment process can be reduced as compared with the case where the cutoff adjustment is performed by changing the applied DC voltage, and the adjustment becomes easy.

The DC voltage applied to the cathode electrode K is the DC voltage E2 output from the rectifying / smoothing circuit 42, and a fixed voltage can be supplied from a low impedance voltage source. It is not necessary to connect a capacitor or the like for lowering the impedance in terms of AC between the grounds, and the number of parts can be reduced.

Further, the high impedance circuits 90 to 9 from the low impedance power source 42 are connected to the first grid electrode G1.
A DC voltage is applied via 2 and it is possible to prevent a potential change due to the cathode current flowing into the first grid electrode G1. Further, a voltage is applied to the cathode electrode K and the first grid electrode G1 from the same low impedance power source 42, and the potential relationship between the cathode electrode K and the first grid electrode G1 is always maintained even if a voltage change occurs. Is kept constant. Therefore, the circuit system becomes stable and the image quality can be improved. Further, the fixed DC voltage EG2 is applied to the second grid electrode G2, and the voltage applied to the second grid voltage is not changed by the cutoff adjustment as in the conventional case, but is adjusted by the cutoff adjustment. Therefore, there is no fear that the resolution will deteriorate.

In the emitter-coupled differential amplifier composed of the transistors 70 and 71, a blanking pulse HBL is applied to the base of the transistor 76 which constitutes a constant current source.
K and VBLK are supplied to turn them on to obtain a blanking level voltage, and a stable blanking operation is performed, and the blanking operation affects the frequency characteristics and response characteristics. Never,
Higher image quality can be achieved.

[0048]

According to the present invention, the cut-off adjustment can be performed only by changing the voltage division ratio of the high impedance circuit and changing the DC voltage applied to the first grid electrode G1, and the adjustment steps can be reduced. it can. Further, since a fixed voltage is applied to the cathode electrode K from the low impedance power source, it is not necessary to connect a capacitor that lowers the impedance in an AC manner between the cathode electrode K and the ground, and the number of parts can be reduced. In addition, the first grid electrode G
1, a DC voltage is applied from a low impedance power source through a high impedance circuit, and there is no potential change due to the cathode current flowing into the first grid electrode G1. Further, since the voltage is applied to the cathode electrode K and the first grid electrode G1 from the same low impedance power source, the potential relationship between the cathode electrode K and the first grid electrode G1 is always constant even if the voltage changes. Kept in. Therefore, the circuit system becomes stable and the image quality can be improved. Furthermore, since a fixed voltage is applied to the second grid electrode G2, the voltage applied to the second grid electrode G2 is not changed by the cutoff adjustment as in the related art, and the resolution is improved by the cutoff adjustment. There is no danger of getting worse.

[Brief description of drawings]

FIG. 1 is a connection diagram showing an embodiment (cathode ray tube drive system) of an embodiment of a flat cathode ray tube according to the present invention.

FIG. 2 is a connection diagram showing an embodiment (high voltage generating circuit) of a flat cathode ray tube according to the present invention.

FIG. 3 is a diagram showing a part of an equivalent circuit of the example of FIG.

FIG. 4 is a diagram showing a relationship between a first grid voltage and a cathode current.

FIG. 5 is a connection diagram showing a drive system of a flat cathode ray tube.

[Explanation of symbols]

 1 Flat Cathode Ray Tube 2 Fluorescent Screen 30 High Voltage Generation Circuit 60 CRT Drive Circuit 92 Variable Resistor for Cutoff Adjustment G1 First Grid Electrode G2 Second Grid Electrode G3 Third Grid Electrode K Cathode Electrode

Claims (1)

[Claims] 1. A cathode electrode K and a second grid electrode G2
In the flat cathode ray tube in which a fixed voltage is applied to the first grid electrode G1 and a video signal is applied to and driven by the first grid electrode G1, a fixed voltage is applied to the cathode electrode from a low impedance power source, and the first grid electrode G1 is applied to the first grid electrode G1. Is a flat cathode ray tube, wherein a DC voltage is applied from the low impedance power source through a high impedance circuit forming a voltage dividing circuit.