JPH06319146A - Electromagnetic focus circuit - Google Patents

Abstract

PURPOSE:To obtain the electromagnetic focus circuit in which deterioration in the focus due to the effect of a temperature change in a focus coil is not caused (the magnetic field generated by a magnet is changed attended with a temperature rise in a core and the magnet in the inside of the focus coil resulting in causing deterioration in the focus of an electron beam). CONSTITUTION:A temperature sensor 14 (15) is provided in a core (magnet) in the inside of a focus coil respectively, and while a VP is in operation, the temperature of the core and the magnet is always sensed, a temperature compensation signal to generate a magnetic field to compensate a change in the magnetic field generated from the magnet is generated and added to a static focus signal, the resulting signal is supplied to a static focus coil 13 so that the focus magnetic field generated by the focus coil 13 is made constant independently of temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a CRT type video projector (hereinafter referred to as "VP")
The present invention relates to an electromagnetic focus type focus circuit in which a focus coil is installed in a CRT neck portion of a focus circuit for focusing an electron beam on an RT fluorescent screen to generate a focus magnetic field to focus the electron beam.

[0002]

2. Description of the Related Art FIG. 10 is a block circuit diagram showing a structure of a conventional electromagnetic focus type dynamic focus circuit. In the figure, 51 is a drive circuit for main deflection,
Reference numeral 52 is a main deflection coil, 53 is a feedback resistor in the main deflection circuit for detecting a current flowing through the main deflection coil 52, 54 is a sub deflection drive circuit for performing convergence adjustment, and 55 is a sub deflection drive circuit.
Is a sub-deflection coil, 56 is a feedback resistor in the sub-deflection circuit that detects the sub-deflection current, 57 is an adder circuit that adds the deflection amount signals, 58 is a deflection bias amount correction circuit that corrects the raster deviation, and 59 is A focus correction waveform signal generation circuit, 60 is an amplification stage (output circuit) of the focus correction signal, and 13 is a focus coil installed in the CRT neck portion. The horizontal and vertical correction signal generation circuits have basically the same configuration.

Next, the operation will be described. When the VP operates, a deflection current (sawtooth waveform) having a horizontal or vertical cycle flows through the main deflection coil 52, and a convergence correction signal flows through the sub deflection coil 55. This main deflection current waveform is output as a voltage waveform across the feedback resistor 53. The sub-deflection current waveform is also output as a voltage waveform across the feedback resistor 56. The main deflection and sub-deflection current waveforms represent the actual horizontal and vertical main deflection and sub-deflection amounts, but there is a difference in sensitivity between the main deflection and the sub-deflection.
Addition circuit 5 replacing each sensitivity difference with addition gain
Add at 7. This added output signal becomes a deflection amount information signal that represents the actual deflection amount in the horizontal and vertical directions. next,
The horizontal and vertical deflection amount information signals are capacitively coupled to cancel the DC level of the deflection amount information signals, the amplitude level at the center position of the sawtooth wave is set to zero, and it is output to the next stage. Although not shown in FIG. 10, the coupling capacitor is included in the adding circuit 57.

Next, in order to correct the deflection bias amount which is the horizontal and vertical DC shift amount of the raster, the deflection bias amount correction circuit 58 performs addition and subtraction of the DC signal which is the deflection bias amount to the output signal of the adder circuit 57. , To the focus correction signal generation circuit 59 in the next stage. This output signal is a signal representing the actual deflection amount, where the position where the amplitude level is zero corresponds to the non-deflection point.

The focus correction signal generation circuit 59 first performs square calculation of horizontal and vertical sawtooth waves to create a secondary waveform signal (parabolic waveform). This signal is a parabolic waveform whose center is at zero level. Next, in order to adjust the focus level, the parabolic signal amplitude is controlled using a volume or the like to adjust the level of the parabolic signal. This level adjusting operation is also performed in the focus correction signal generating circuit 59.

The level-adjusted vertical dynamic focus correction signal has a vertical frequency of several tens Hz (60 H).
Since this is a general value around z), the frequency band of this signal is low, so the static focus signal (DC signal) is added by an adder circuit and put together into one focus coil (static focus coil). Apply focus correction current to. This addition is also performed by the focus correction signal generation circuit 59 and output to the next stage. Note that FIG. 11 shows a dynamic focus correction signal waveform obtained by this circuit. 11A is a horizontal dynamic focus waveform, FIG. 11B is a vertical dynamic focus waveform, and FIG. 11C is a dynamic focus correction waveform obtained by magnetic field synthesis excluding static components.

The horizontal and vertical cycle dynamic focus correction signals are created as described above, and the horizontal and vertical correction signals are current-amplified in the respective amplification stages 60, and the horizontal dynamic focus correction signals are dynamically generated by the focus coil 13. The static focus correction signal is supplied to the static focus coil of the focus coil 13 as a dynamic focus correction current to the coil.
By being flown together with the C signal, respective dynamic and static focus magnetic fields are generated, and these magnetic fields are vector-combined to form a focus magnetic field, and the electron beam converging operation is performed.

Since three RRTs, one for R, one for G, and one for B, are installed in the VP, the dynamic focus circuit is the R, G, B circuit described above.
This means that circuits for one channel each and a total of three channels are provided.

Since the focus current always flows in the static focus coil of the focus coil 13, the focus coil generates heat, and this heat is transmitted to the core of the focus coil 13 and the magnet, and the temperature of the core and the magnet rises. When the temperature of the magnet rises, the amount of magnetic field generated changes, which causes the amount of static magnetic field generated to change, deteriorating the focus. This symptom is called focus deterioration due to temperature drift of the focus coil.

[0010]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and prevents the focus deterioration caused by the temperature rise of the core of the focus coil and the magnet, and the influence of the temperature change. The purpose is to obtain an electromagnetic focus circuit in which focus deterioration does not occur.

[0011]

A temperature detecting method for a core of a focus coil and a magnet according to the present invention is such that a temperature sensor is installed in the core of the focus coil and a magnet portion, and the temperature sensor is always the core of the focus coil and the magnet. Temperature is generated, and based on this detected temperature signal, a temperature compensation signal that compensates for the amount of change in the magnetic field generated by the magnet is created, and the temperature compensation signal is added to the static focus signal and sent to the static focus coil. Then, the focus deterioration due to the temperature change is compensated.

[0012]

The relationship between the amount of magnetic field generated by the focus coil magnet and the temperature is shown in FIG. As can be seen from the figure, when the temperature of the magnet rises, the amount of magnetic field generated by the magnet decreases. Therefore, when the temperature of the focus coil magnet or the core rises, the amount of static magnetic field generated by the magnet decreases. On the other hand, the amount of magnetic field generated by the dynamic focus coil and the static focus coil is determined by the focus current value flowing through the coil, so it is irrelevant to the temperature of the focus coil magnet and core, and if the focus current value is constant It is constant. Therefore, the total amount of magnetic field generated by the focus coil is determined by the vector addition of the above-mentioned generated magnetic fields. Therefore, when the temperature of the focus coil rises, the amount of focus magnetic field required to focus the electron beam on the phosphor screen cannot be obtained, resulting in focus blurring. Occurs.

The amount of magnetic field generated by the magnet of the focus coil is about 300 gauss. From FIG. 12, the temperature change of the generated magnetic field is about 0.1% of the total magnetic field for a temperature change of 1 ° C. is there. However, during the VP setting operation, the temperature of the focus coil rises by 20 to 40 ° C., so the amount of change in the generated magnetic field amount becomes 2 to 4%. Conventional NT
In the SC-only VP, since the received image is mainly moving images, focus deterioration was not a problem with this kind of change in the magnetic field.
In a VP set showing a video mainly composed of still images, focus deterioration is detected, which is a problem.

Further, since the temperature characteristic of the generated magnetic field amount of the magnet described above varies depending on the magnet material, depending on the magnet material, the magnetic field variation amount is larger than that in the example shown in FIG. In addition, there is something whose relationship with temperature cannot be expressed by a linear expression. In addition,
In fact, there is no magnet material that produces a constant amount of magnetic field with respect to temperature.

For the temperature compensation signal according to the present invention, the temperature characteristic data of the magnetic field amount of the focus coil magnet to be used is checked in advance, and the insufficient focus magnetic field amount is generated as the temperature compensation signal in accordance with the temperature characteristic data. . Furthermore, gain conversion of the amount of current flowing through the focus coil and the amount of magnetic field generated by the focus coil is performed,
Create a temperature compensation signal for generating an insufficient magnetic field, add the temperature compensation signal to the static focus correction signal, and send it as a focus current to the static focus coil of the focus coil, so that the amount of magnetic field generated by the focus coil magnet is independent of temperature. Keep it constant.

[0016]

【Example】

Example 1. Embodiment 1 of the present invention will be described below with reference to the drawings. FIG. 1 is a block circuit diagram of an electromagnetic focus circuit showing the first embodiment, in which 1 is a horizontal phase adjustment circuit, 2 is a dynamic focus correction signal generation circuit,
3 is a dynamic focus level adjusting means, 4 is a magnet temperature detection circuit installed inside the focus coil 13, 5 is a core temperature detection circuit installed inside the focus coil, 6 is a static focus correction signal generation circuit, 7 is a magnet temperature correction signal level adjusting circuit, 8 is a core temperature correction signal level adjusting circuit, 9 is a static focus level adjusting circuit, 10 is a static focus signal adding circuit, 11 is a dynamic focus output circuit, 12 is a static focus output circuit, 14 is a core temperature detection sensor of the focus coil 13, 15 is a magnet temperature detection sensor of the focus coil 13, 16 is a CRT, 17 is a vertical synchronization signal input terminal,
Reference numeral 18 is a horizontal synchronizing signal input terminal, 19 is a horizontal sub deflection amount detection circuit, and 20 is a vertical sub deflection amount detection circuit. In addition,
In FIG. 1, only one set of focus circuit component blocks is shown, but in the actual VP, one set is provided for each of R, G, and B, and there are a total of three set components.

FIG. 8 is a vertical sectional view showing the internal structure of the focus coil 13 installed in the neck portion of the CRT 16, wherein 21 is installed in the neck of the CRT 16 and 22 is installed in the focus coil 13. To generate a static magnetic field, 23 is a focus coil 1
Reference numeral 3 denotes a core, 24 denotes a static focus coil for flowing a static focus current, and 25 denotes a dynamic focus coil for flowing a dynamic focus current.

FIG. 9 is a vertical sectional view showing the internal structure of the focus coil 13 having an internal structure different from that of FIG. 8, in which the installation positions of the dynamic and static coils 24 and 25 are different. Further, the core temperature detecting temperature sensor is composed of the two cores 23 of the focus coil 13.
In order to detect the average temperature of the above, one is installed for each and a total of two are installed. There are many other focus coils having a structure different from the structures shown in FIGS. 8 and 9, but they are omitted here.

Next, the operation will be described. The dynamic focus correction signal is a dynamic correction signal according to the screen position synchronized with the main deflection, and the dynamic focus correction signal generation circuit 2 receives the horizontal and vertical synchronization signals input from the horizontal and vertical synchronization signal input terminals 17 and 18. On the basis of the above, a parabolic correction signal is generated. In addition,
The horizontal phase adjustment circuit 1 is composed of a mono-multi circuit that delays the horizontal synchronization signal for the purpose of adjusting the phase of the horizontal dynamic focus correction signal.

Next, the level of the dynamic focus correction signal generated by the dynamic focus correction signal generating circuit 2 is adjusted by the level adjusting means 3, which is the best focus while watching the image projected on the screen. Will be adjusted to a level. Finally, the output signal of the level adjusting means 3 is the dynamic focus output circuit 11
The current is amplified by and is passed through the dynamic focus coil 25 of the focus coil 13.

During the operation of the VP, the focus current flows through the dynamic coil 25 and the static coil 24 of the focus coil 13, but each coil generates heat, and the heat is transmitted to the core 23 and the magnet 22, and the temperature of these is changed. The amount of static magnetic field generated by the magnet 22 rises and changes. The core temperature detection sensor 14 and the magnet temperature sensor 15 are DCs proportional to the actual temperatures of the core 23 of the focus coil 13 and the magnet 22.
Since the voltage is output, the voltages corresponding to these temperatures are output from the sensors 14 and 15 during the VP setting operation. This output voltage is guided to the temperature detection circuits 4 and 7, and the actual temperature of the core 23 and the magnet 22 is detected from the voltage value thereof.

Next, there are two methods for generating the temperature compensation signal. In the first method, if the temperature T is used as a parameter in FIG. 12, the temperature compensation signal can be expressed by a linear expression. Since the temperature sensors 14 and 15 installed on the core 23 of the focus coil 13 and the magnet 22 output a voltage proportional to the temperature, a temperature compensation signal can be created by multiplying the output signals of the temperature sensors 14 and 15 by a coefficient K.
The operation of multiplying this coefficient can be realized by giving a gain to the buffer circuit of the output signals of the temperature sensors 14 and 15.

This method can be used in the case of a magnet material in which the generated magnetic field amount and the temperature compensation signal have a linear relationship, and the temperature compensation signal can be created with the simplest circuit configuration.

The second method is to RO the temperature compensation signal data.
The temperature sensors 14 and 1 are stored in M as data.
A data read address signal for the ROM is created from the output signal of No. 5, and the temperature compensation signal is obtained by reading the temperature compensation signal data in the ROM by the address signal and performing D / A conversion.

This method is effective for a magnet material in which the relationship between the amount of magnetic field generated by the magnet and the temperature compensation signal cannot be expressed by a linear expression.

Next, the static focus correction circuit 10 adds the temperature compensation signal created by any of the above methods and the static focus correction signal. The output signal is a focus correction signal in which the static focus correction signal and the temperature compensation signal are added, and the current is amplified by the static focus output circuit 12 and sent to the static focus coil of the focus coil 13. As a result, the sum of the static magnetic field generated by the magnet 22 and the temperature compensation magnetic field of the magnet generated magnetic field is the sum of the magnet 2
It is always constant regardless of the temperature of 2. Further, the static focus magnetic field and the dynamic focus magnetic field are vector-wise magnetically added to form a focus magnetic field for focusing the electron beam.

The operation of each focus circuit installed for R, G, and B is exactly the same, and there is a total of three focus circuits, one set for each color, and one set for each color. A constant required focus magnetic field is generated regardless of the temperature of the focus coil 13.

Example 2. FIG. 2 is a block circuit diagram of a second embodiment of the present invention. An electromagnetic focus circuit for detecting a horizontal deflection amount and a vertical deflection amount and a sub deflection amount, and using the detection signals to generate a dynamic focus correction signal. Is shown. In the figure, the same reference numerals as those in FIG. 1 denote the same parts, and 26 is a horizontal main deflection amount detection circuit,
27 is a vertical main deflection amount detection circuit.

The operation of the second embodiment is the same as that of the temperature compensation signal generation circuit, except that the method of producing the dynamic focus correction signal in the dynamic focus correction signal generation circuit 2 of the electromagnetic focus circuit of the first embodiment is different. . Therefore, only the operation of the dynamic focus correction signal generation circuit 2 will be described.

The dynamic focus correction signal is a dynamic correction signal according to the screen position. In the second embodiment, this correction signal is created from the actual horizontal and vertical deflection amounts. The horizontal and vertical deflection amounts are represented by the respective deflection currents, so the horizontal and vertical deflection amount detection circuits 26 and 27 are shown.
Each deflection current is detected by, and the sub-deflection amount is detected by the sub-deflection amount detection circuits 19 and 20, and the horizontal and vertical deflection amounts are added to detect the actual horizontal and vertical deflection amounts. Square calculation is performed to create a dynamic focus correction signal. Thereafter, a correction current is passed through the dynamic coil of the focus coil 13 via the level adjusting means 3 and the output circuit 11.

During the operation of the VP, the focus current flows through the dynamic focus coil 25 and the static focus coil 24 of the focus coil 13,
Both coils generate heat, and this heat is generated by the core 23 and the magnet 22.
Since the temperature rises and the static magnetic field amount generated by the magnet 22 decreases, these temperatures are detected by the core and magnet temperature sensors 14 and 15, and a temperature compensation signal is created. The method of generating the temperature compensation signal and the method of correction are the same as those described in the first embodiment.
The same effect as the electromagnetic focusing circuit of the first embodiment can be obtained.

Example 3. 3 is a block circuit diagram of a third embodiment of the present invention, and the same reference numerals as those in FIG. 1 denote the same parts. In the third embodiment, in the electromagnetic focus circuit described in the first embodiment, the dynamic focus correction signal is capacitively coupled and output to the output circuit 11, and the AC component of the dynamic focus correction signal is input to the focus coil 13.
, And the DC component is added to the static focus correction signal and the focus coil 13
It is configured to flow to the static coil of. The difference from the first embodiment is that a coupling capacitor 28 is added between the dynamic focus correction signal level adjusting circuit 3 and the dynamic focus output circuit 11. The coupling capacitor 28 serves to block the DC component of the dynamic focus correction signal and output only the AC component. The DC component of the dynamic focus correction signal will be added to the static focus correction signal. Others have exactly the same configuration as the electromagnetic focus circuit described in the first embodiment, and therefore, the same operation as in the first embodiment and the same effect can be obtained.

Example 4. 4 is a block circuit diagram of a fourth embodiment of the present invention, and the same reference numerals as those in FIG. 2 denote the same parts. In the fourth embodiment, in the electromagnetic focus circuit described in the second embodiment, the dynamic focus correction signal is capacitively coupled and output to the output circuit 11, and the AC component of the dynamic focus correction signal is input to the focus coil 1.
It is made to flow in the dynamic coil of 3 and the DC component is
The static focus correction signal is supplied to the static coil of the focus coil 13 together with the static focus correction signal. Like the third embodiment, a coupling capacitor is provided between the dynamic focus correction signal level adjusting circuit 3 and the dynamic focus output circuit 11. 28 is added. The coupling capacitor 28 serves to block the DC component of the dynamic focus correction signal and output only the AC component. The DC component of the dynamic focus correction signal is added to the static focus correction signal. Others are exactly the same as the electromagnetic focusing circuit described in the second embodiment, and therefore, the same operation as the second embodiment and the same effect can be obtained.

Example 5. 5 is a block circuit diagram of a fifth embodiment of the present invention, the same reference numerals as those in FIG. 1 denote the same parts. The fifth embodiment is configured such that, in the electromagnetic focus circuit described in the first embodiment, the temperature compensation signal is not added to the static focus signal but is added to the dynamic focus correction signal to perform temperature compensation.
An adder circuit 29 adds the dynamic focus correction signal and the temperature compensation signal. Focus correction signal,
The method of creating the temperature compensation signal is exactly the same as the electromagnetic focus circuit described in the first embodiment, and the same operation as the electromagnetic focus circuit described in the first embodiment is performed and the same effect is obtained.

Example 6. 6 is a block circuit diagram of a sixth embodiment of the present invention, and the same reference numerals as those in FIG. 2 denote the same parts. In the sixth embodiment, in the electromagnetic focus circuit described in the second embodiment, the temperature compensation signal is added to the dynamic focus correction signal instead of being added to the static focus signal to perform temperature compensation. Is a dynamic focus addition circuit that adds the dynamic focus correction signal and the temperature compensation signal. The method of creating the focus correction signal and the temperature compensation signal is exactly the same as the electromagnetic focus circuit described in the second embodiment, and the same operation as the electromagnetic focus circuit described in the first embodiment is performed and the same effect is obtained. .

Example 7. In each of the above embodiments, the temperature of the core of the focus coil and the temperature of the magnet are detected and the temperature compensation signal is created by the temperature change, but a temperature sensor for detecting the ambient temperature in which the focus coil 13 is installed. May be installed, and a temperature compensation signal may be created based on this ambient temperature signal to perform temperature compensation. In this case, the number of temperature sensors and temperature detection circuits is increased by one, and only one kind of signal is added by the adder circuit of the core and magnet temperature compensation signals, and other configurations are the same as those in the above-mentioned respective embodiments. The same effect as the embodiment can be obtained.

Example 8. FIG. 7 is a block circuit diagram of an eighth embodiment of the present invention. In each of the above-mentioned embodiments, the electromagnetic focus circuit in which the dynamic focus correction signal and the static focus correction signal are all generated by analog circuits has been described. The eighth embodiment applies the present invention to an electromagnetic focus circuit that generates a dynamic focus correction signal and a static focus correction signal by calculating digital data.

In FIG. 7, the same reference numerals as those in FIG. 1 denote the same parts, and 30 denotes a dynamic / static focus correction signal generation circuit for generating a dynamic focus correction signal and a static focus correction signal by digital signal processing, 31 Is a phase adjustment signal generation circuit for adjusting the phase of horizontal and vertical focus, 32 is a ROM in which digitalized digitalized temperature compensation signal data is stored, 33 is a read address of the ROM 32 from the output signals of the temperature sensors 14 and 15. Address signal generation circuits for generating signals, and 34 and 35 are D / A conversion circuits for converting the dynamic focus correction digital data signal and the static focus correction digital data signal into analog signals.

The temperature compensating signal is created by creating a read address signal of the ROM according to the temperature detected by the sensor,
ROM storing temperature compensation data with this address signal
The temperature compensation signal data is read from 32. Next, the temperature compensation data signal read out as described above is added to the static focus correction signal (digital data state signal, level adjustment completed state). This addition can be performed simply by adding digital numerical data.
All the above operations are performed in the dynamic / static focus correction signal generation circuit 30.

Finally, the output data of the dynamic / static focus correction signal generation circuit 30 (two types of data signals, dynamic and static, are output) are converted into analog signals in the D / A conversion circuits 34 and 35, respectively. Then, it is guided to the output circuits 11 and 12, where current amplification is performed, and a focus current is supplied to the dynamic focus coil and the static coil of the focus coil 13 to obtain a focus magnetic field.

Even if the electromagnetic focusing circuit is constructed as described above, like the above-mentioned respective embodiments constructed by analog circuits,
It is possible to obtain an electromagnetic focus circuit in which the focus characteristic does not change by compensating the change in the magnetic field generated by the focus coil magnet due to the change in the temperature of the focus coil.

[0042]

As described above, according to the present invention, since the focus signal for generating the magnetic field for compensating the change in the focus magnetic field generated with the temperature rise of the focus coil is generated, the temperature rise of the focus coil can be prevented. This has the effect of obtaining an electromagnetic focus circuit that is free from focus deterioration caused by the cause.

[Brief description of drawings]

FIG. 1 is a block circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a block circuit diagram showing a second embodiment of the present invention.

FIG. 3 is a block circuit diagram showing a third embodiment of the present invention.

FIG. 4 is a block circuit diagram showing a fourth embodiment of the present invention.

FIG. 5 is a block circuit diagram showing a fifth embodiment of the present invention.

FIG. 6 is a block diagram showing a sixth embodiment of the present invention.

FIG. 7 is a block circuit diagram showing an eighth embodiment of the present invention.

FIG. 8 is a vertical cross-sectional view showing the internal structure of a focus coil.

FIG. 9 is a vertical cross-sectional view in which the internal configuration of the focus coil is different.

FIG. 10 is a block circuit diagram showing a configuration of a conventional electromagnetic focus circuit.

FIG. 11 is a focus correction signal waveform diagram obtained by a conventional electromagnetic focus circuit.

FIG. 12 is a temperature characteristic diagram of a magnetic field amount generated by a focus coil magnet.

[Explanation of symbols]

1 horizontal phase adjustment circuit 2 dynamic focus correction signal generation circuit 3 dynamic focus level adjustment means 4 magnet temperature detection circuit 5 core temperature detection circuit 6 static focus correction signal generation circuit 7 magnet temperature correction signal level adjustment circuit 8 core temperature correction signal level adjustment Circuit 9 Static focus level adjustment circuit 10 Static focus signal addition circuit 11 Dynamic focus output circuit 12 Static focus output circuit 13 Focus coil 14 Core temperature detection sensor 15 Magnet temperature detection sensor 16 CRT 19 Horizontal sub deflection amount detection circuit 20 Vertical sub deflection amount Detection circuit 22 Magnet 23 Core 24 Static focus coil 25 Dynamic focus coil 26 Horizontal main deflection amount detection circuit 2 7 Vertical Main Deflection Detection Circuit 28 Coupling Capacitor 29 Adder Circuit 30 Dynamic / Static Focus Correction Signal Generation Circuit 31 Phase Adjustment Signal Generation Circuit 32 ROM 33 Address Generation Circuit 34 D / A Conversion Circuit 35 D / A Conversion Circuit 51 Main Deflection Drive circuit

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[Procedure amendment]

[Submission date] June 29, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction content]

Since the focus current always flows in the static focus coil of the focus coil 13, the focus coil generates heat, and this heat is transmitted to the core and the magnet of the focus coil 13, and the temperature of the core and the magnet rises. When the temperature of the magnet rises, the amount of magnetic field generated changes, which causes the amount of static magnetic field generated to change, deteriorating the focus. This symptom is called focus deterioration due to temperature drift of the focus coil.

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 5

[Correction method] Change

[Correction content]

[Figure 5]

[Procedure 3]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 6

[Correction method] Change

[Correction content]

[Figure 6]

Claims (6)

[Claims] 1. In an electromagnetic focus circuit of a CRT system video projector, a focus coil equipped with a core of a focus coil for generating a focus magnetic field and a means for detecting the temperature of the magnet installed in a CRT neck portion, and the temperature detection. A circuit for generating a temperature compensation signal for the magnetic field generated by the magnet based on the output signal of the means, and an adder circuit for adding the temperature compensation signal to the static focus signal are provided, and the focusing coil performs an electron beam focusing operation. Characteristic electromagnetic focus circuit. 2. An electromagnetic focus circuit of a CRT type video projector, comprising: a focus coil having a core of a focus coil for generating a focus magnetic field installed at a CRT neck portion; A circuit for generating a temperature compensation signal of the magnetic field generated by the magnet based on the output signal of the means, and an adder circuit for adding the temperature compensation signal to the dynamic focus signal are provided, and the focusing operation of the electron beam is performed by the focus coil. Characteristic electromagnetic focus circuit. 3. A dynamic focus correction signal is capacitively coupled to output only its AC component to a dynamic output circuit, and the temperature compensation signal of the magnetic field generated by the magnet inside the focus coil is added to the static focus signal. What is claimed is: Claim 1
The electromagnetic focusing circuit according to the item. 4. An atmosphere temperature detection circuit for detecting an ambient temperature of a focus coil for generating a focus magnetic field installed in a CRT neck portion, and a temperature compensation signal for a magnet generated magnetic field based on an output signal of the atmosphere temperature detection circuit. 4. The electromagnetic focus circuit according to claim 1 or 3, further comprising a circuit for generating the ambient temperature compensation signal and a circuit for adding the ambient temperature compensation signal to the static focus signal. 5. An atmosphere temperature detecting circuit for detecting an ambient atmosphere temperature of a focus coil for generating a focus magnetic field installed in a CRT neck portion, and a temperature compensating signal for a magnetic field generated by a magnet based on an output signal of the atmosphere temperature detecting circuit. 3. The electromagnetic focus circuit according to claim 2, further comprising a circuit for generating the ambient temperature compensation signal and a circuit for adding the ambient temperature compensation signal to the dynamic focus signal. 6. A core of a focus coil for generating a focus magnetic field installed in a CRT neck portion in an electromagnetic focus circuit in which a dynamic focus correction signal and a static focus correction signal are created by calculating digital data by a microprocessor. And a focus coil having means for detecting the temperature of the magnet, means for converting the output signal of the temperature detecting means into a digital signal, and means for creating a temperature compensation signal for the magnet generated magnetic field from the detected temperature data signal, An operation circuit for adding the temperature compensation signal to the dynamic focus signal or the static focus signal and a circuit for converting the focus correction data signal into an analog signal are provided, and the focusing coil performs an electron beam focusing operation. The electromagnetic focus circuit according to any one of claims 1 to 5, wherein: