JPS5820436B2 - Focus voltage automatic adjustment device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic focus voltage adjustment device for a CRT.
In particular, the present invention relates to an automatic focus voltage adjustment device for a CRT used in a character display as a terminal device of an electronic computer or the like.

A conventional CRT focus voltage adjustment device has a circuit configuration as shown in FIG.

That is, 1 is a horizontal output switching transistor, 2 is a flyback transformer, 3 is a flyback transformer resonance capacitor, 4 is a deflection yoke, 5 is a deflection yoke resonance capacitor, 6 is a size coil, 7 is a linearity coil, and 8 is a Damper diode, 9 is power supply voltage application terminal, 1
0 is a diode for anode voltage rectification, 11 is a focus voltage rectification diode, 12 is a smoothing capacitor, 13 is a fixed resistor, 14 is a sliding resistor, 15 is a CRT, and 16 is a video signal application terminal.

With this configuration, the horizontal output from the transistor 1 is applied to the primary winding 271 of the flyback transformer 2, and the pulse voltage generated here is boosted by the anode voltage winding 2-2, and the anode voltage is Rectifier diode 1
It is rectified with 0 and applied to the anode of the CRT 15.

On the other hand, the voltage boosted by the focus voltage winding 2-3 of the flyback transformer 2 is rectified by the focus voltage rectifier diode 11, and smoothed by the capacitor 12 to obtain a voltage slightly higher than the required focus voltage.

This voltage is divided between the fixed resistor 13 and the sliding resistor 14, and a refocus voltage is obtained from the sliding terminal of the sliding resistor 14.
The electron beam is supplied to the focus grid of the CRT 15 and is modulated by a video signal applied to the cathode from the video signal application terminal 16 to control the electron beam.

Then, the position of the sliding terminal of the sliding resistor 14 is adjusted using an external operation section to obtain the optimum focus voltage.

However, in general, the optimum focus voltage of a CRT changes depending on the current density of the beam current flowing when the electron beam hits the fluorescent surface of the CRT.

It is known that the optimum focus voltage changes as shown in FIG. 2 due to this change in current density.

Therefore, in a CRT with a large deflection angle, the difference between the bending radius of the fluorescent surface and the distance from the center of deflection to the fluorescent surface becomes larger at the periphery of the fluorescent surface, and the difference between the center and peripheral portions of the fluorescent surface increases. The moving distance of the scanning point for the same deflection angle is different between and.

Therefore, the current density of the beam current differs between the central part and the peripheral part of the fluorescent surface.

Therefore, the above-mentioned conventional focus voltage adjusting device has the disadvantage that the optimum focus voltage can only be obtained at one specific point on the fluorescent surface, and the optimum focus cannot be obtained at other scanning points.

This invention was made in view of the above circumstances, and is an automatic focus voltage adjustment device that detects the distance from a predetermined position on a fluorescent surface to a scanning point of an electron beam, and automatically adjusts a focus voltage based on this distance. It provides:

An embodiment of the present invention will be described in detail below.

Figure 3 shows the arrangement of characters on the fluorescent surface of a CRT employing this embodiment.As shown in Figure a, there are 96 characters in the main scanning direction (X direction) of the electron beam (in the sub scanning direction (Y direction)). on 27
Characters shall be displayed.

A square on the fluorescent surface represents one pixel, and one character is displayed within this one pixel.

One character is displayed with 7 dots in the horizontal direction and 9 dots in the vertical direction, ie, 63 dots, as shown in FIGS.

Further, the space between the pixels is one dot in the main scanning direction and three dots in the sub scanning direction.

Note that P is the center point of the fluorescent surface.

FIG. 4 is a block diagram of this embodiment, and the same parts as in FIG. 1 are designated by the same numbers.

In the same figure, 20 is an electron beam scanning position detection block, and in the above block formation, 21 is an oscillator that oscillates at a reference frequency.

This oscillator 21 sequentially includes an octal counter 221, a hexadecimal counter 222, a hexadecimal counter 223, and a hexadecimal counter 2.
31.27-decimal counters 232 are connected in cascade.

Then, the hexadecimal counter 222 and the hexadecimal counter 22
The count value of 3 is supplied to the subtraction circuit 24 as a subtracted number.

This subtraction circuit 24 is coupled with a code generator 25 that generates a code of "48" as a subtractive number, and the subtraction result is converted into a voltage by a DA (digital-to-analog) conversion circuit 26 and then converted into a voltage. Sent to Nanatsuku I.

On the other hand, the decimal counter 231 and the 27-decimal counter 23
The count value of 2 is supplied to the subtraction circuit 27 as a subtracted number.

A code generator 28 that generates a code of "162" as the minuend is coupled to this subtraction circuit 27, and the subtraction result is converted into a voltage by a DA conversion circuit 29 and sent to block U. .

The block U is detected by the block υ, and the scanning position of the electron beam represented by the voltage is set to the center point P of the fluorescent surface.
This function converts the distance from The multiplied sum voltage is supplied to "Block".

"Blocking" is CR in response to the signal from block U above.
This block adjusts the focus voltage applied to the focus grid of T15.

The output voltage of the block U is connected to a negative terminal of an OP amplifier 41, and a positive terminal of this OP amplifier 41 is connected to a cathode of a Zener diode 42 whose anode is grounded for generating a reference voltage.

The output of the OP amplifier 41 is supplied to the base of a transistor 43, and the collector of this transistor 43 is connected to a load resistor 44.

Further, the emitter of this transistor 43 is connected to a negative power supply via a resistor 45, and the emitter of the transistor 43 is connected to a negative power supply via a resistor 45.
It is connected to the emitter of 6.

The base of this transistor 46 is grounded via a load resistor 47, and its collector is connected to a load resistor 48.

In this way, the transistors 43, 46 are connected to the resistors 44, 45,
Together with 47 and 48, it constitutes a differential amplifier.

The output of this differential amplifier, ie, the collector of transistor 46, is connected to the base of transistor 49.

This transistor 49 is Darlington connected to the transistor 50.

This Darlington connected transistor group 49 and 5
The collector of 0 is connected to the cathode of the Zener diode 42 via the resistor 51 and the resistors 44 and 48.
It is further connected via a resistor 52 to the intersection of the diode 11 and the capacitor 12, that is, to a high voltage source obtained from the focus voltage winding 2-3 of the flyback transformer 2.

Further, the emitter of the transistor 50 is grounded via a resistor 53 and supplies a focus voltage to the focus grid of the CRT 15.

Next, the operation of the embodiment configured as described above will be explained.

The oscillator 21 has a frequency of, for example, 14. Generates MHz clock pulses.

Note that the video signal applied to the video signal application terminal 16 is composed of an on/off signal or a modulation signal synchronized with this clock pulse.

The above 14MHz clock pulse is generated by the octal counter 221.
This count is synchronized with the scanning of one character in the main scanning direction of the electron beam.

The pulses output from the octal counter 221 one by one for each character scan are sent to the hexadecimal counter 22 at the next stage.
2 is input.

From the rear end of the hexadecimal counter 222, one pulse is output for every 16 output pulses of the octal counter 221.

That is, when the electron beam completes scanning for 16 characters in the main scanning direction, one pulse is output, and the output pulse is input to the hexadecimal counter 223 at the next stage.

The hexadecimal counter 223 outputs one pulse when six pulses output from the rear end of the hexadecimal counter 222 are input.

That is, when the electron beam completes scanning for 16×6=96 characters (=1 main scanning) in the main scanning direction, one pulse is output.

Note that the output pulse from the hexadecimal counter 223 is used as a horizontal synchronization signal.

On the other hand, the output pulse from the hexadecimal force counter 223 is input to a hexadecimal counter 231, which counts 12 human force pulses and outputs one pulse.

This pulse is synchronized with the scanning of one character in the sub-scanning direction.

The output pulse from the 12-decimal counter 231 is input to the 27-decimal counter 232 at the next stage.
One pulse is output for every seven pulses counted.

That is, scanning of 27 characters (=1 frame) in the sub-scanning direction is completed and one pulse is output.

The output pulse from this 27-ary counter 232 is used as a vertical synchronization signal.

The scanning position of the electron beam can be detected by the combination of the counters shown above.

That is, the output from the hexadecimal counter 222 and the hexadecimal counter 223 makes it clear which character is being scanned in the X direction, and the output from the hexadecimal counter 231 and the 27-decimal counter 232 makes it clear how many sub-scans are being scanned. It becomes clear that

The signals representing the contents of the hexadecimal counter 222 and the hexadecimal count 223 are each input as a subtracted number to the subtraction circuit 24, while the code for the minuend 48 is input from the code generation circuit 25 to the subtraction circuit 24, and subtraction is executed. .

For example, if the content of the hexadecimal counter 222 is 5 and the content of the hexadecimal counter 223 is 2, the electron beam will be 16X2 in the X direction.
+5=The 37th character is being scanned, and the center point P of the fluorescent surface is determined from the output from the subtraction circuit 24 (48-37=11).
It can be detected that the position is the 11th position on the left.

For example, if the output of the hexadecimal counter 222 is 10 and the output of the hexadecimal counter 223 is 4, the output from the subtraction circuit 24 is (48-(16X4+10))=-26, which is the 26th point to the right from the center point of the fluorescent surface. It can be detected that the position of

As described above, in this embodiment, the position is displayed by dividing the main scanning direction into two areas, right and left, with the center line passing through the center point P of the fluorescent surface as the boundary.

Further, signals representing the contents of the hexadecimal counter 231 and the hexadecimal counter 232 are input to the subtraction circuit 27 together with the minutand code 162 output from the code generation circuit 28.

In the same way as described above, for example, if the output of the hexadecimal counter 231 is 6, and the output of the 27-decimal counter 232 is 8, it can be detected that the electron beam 18.8X12+6=102nd sub-scanning is being performed, and this output is subtracted. Subtraction in circuit 25 (
162-102=60), it is possible to detect that the 60th line is on the upper side counting from the center point P of the fluorescent surface.

For example, if the output of the hexadecimal counter is 8 degrees and the output of the 27-decimal counter is 16, the output from the subtraction circuit 25 is (16
2-(12X16+8))=-38, and it can be detected that this is the 38th line on the lower side counting from the center point P of the fluorescent surface.

In this way, in this embodiment, the sub-scanning direction is set to the center point P of the fluorescent surface.
The position is displayed in two areas, upper and lower, with the center line passing through as the boundary.

Therefore, in this example, as shown in FIG. 3, the fluorescent surfaces are
The position is displayed in four areas: , ■, and ■.

As described above, the scanning position of the electron beam from the center point of the fluorescent surface is detected separately in the main scanning direction and the sub-scanning direction, and the outputs of the subtraction circuits 24 and 27 are respectively detected by the DA conversion circuits 26 and 27. 29, it is converted into an analog quantity (voltage).

In this way, the scanning position of the electron beam from the center point P of the fluorescent surface is detected digitally, and this position detection signal is converted into an analog quantity, that is, a predetermined voltage, and then this voltage is used in the block U to generate the fluorescent light. It is converted into a voltage corresponding to the distance from the center point P of the surface.

That is, in the block turtle, the input signals from the DA conversion circuits 26 and 29 are each multiplied by a constant, and the sum voltage is outputted from the OP amplifier 31.

This voltage corresponds to the distance (XA + YA) from the center point P of the fluorescent surface to the electron beam scanning position detected in block 1, for example, point A in FIG.

Note that xA and YA are the distances from the center point P to the point A in the X and Y directions.

After converting the scanning position of the electron beam into a voltage value corresponding to the distance from the center point of the fluorescent surface to the scanning position of the electron beam in this way, a focus voltage is applied to the focus grid of the CRT 15 in accordance with this distance. "Block"
Adjust with.

In block 0, an OP amplifier 41 compares the output voltage from block U with a reference voltage generated by a Zener diode 42, and detects fluctuations in the output voltage of block I.

The comparison output is amplified by a differential amplifier consisting of transistors 43 and 46, and the output of the differential amplifier is supplied to the base of transistor 49.

Therefore, the current is supplied from the focus voltage winding 2-3 of the flyback transformer 2 through the resistor 52 to the collectors of the transistors 49 and 50 connected in Darlington, and the current output from the emitter of the transistor 50 is the base current, that is, the differential voltage. It changes depending on the current output from the amplifier.

The output current of the emitter flows through the resistor 53, and the voltage generated there is applied to the focus grid of the CRT 15 as a focus voltage.

Suppose that the electron beam is currently scanning a point A on the fluorescent surface (for example, point A is the 4th character of the second character in the main scanning direction).
277th character in the sub-scanning direction), one pulse is input to the subtraction circuit 24 as a subtractive number as a signal representing the contents of the hexadecimal counter 222.

On the other hand, the subtraction circuit 24 receives the subtracted number 48 from the code generation circuit 25 and performs the calculation (48-(8X1+4)).

Furthermore, 2 is used as a signal representing the contents of the hexadecimal counter 231.
The 26 pulses are each input to the subtraction circuit 27 as a subtractive number as a signal representing the contents of the 27-decimal counter 232.

On the other hand, the subtraction circuit 27 receives the subtractable number 162 from the subtracted number command circuit 28, and performs the calculation (162-(12X26+2)).

The calculation results of the subtraction circuits 24 and 27 are "36" and [-
152J are respectively input to the D-A conversion circuits 26 and 29, and voltage information (
XA, YA, ).

Electron beam scanning position information converted to this analog quantity (
XA, YA) is converted into voltage information (XA+YA) corresponding to the distance from the center point of the fluorescent surface in block I, and a focus voltage corresponding to this distance information is generated at 40 and applied to the focus grid of the CRT 15. That's why.

Note that the electron beam scanning position detection means υ of the above embodiment
In the above, position detection in the main scanning direction was performed character by character, but it may also be performed dot by dot.

In this case, the minuend of the code generation circuit 25 is % (8X96)
-384, and the count signal of the octal counter 221 may also be input to the subtraction circuit 24.

Similarly, position detection in the sub-scanning direction may also be performed character by character.

In this case, in the above embodiment, the number of displayed characters in the sub-scanning direction is an odd number, which is inconvenient, but for example, if there are 26 characters, the minuend of the code generation circuit 28 is 26/2=13, and the 27-decimal counter 232 is converted into a 26-decimal counter. It is sufficient to input to the subtraction circuit 27 only from the digit counter.

Further, the circuit configurations of blocks U and I are not limited to the above embodiments, and various circuit configurations can be considered to obtain the same effect.

Furthermore, although the above embodiment has been explained using a character display as an example, the present invention can be applied to any digitally driven CRT.

As described in detail above, the present invention uses an output signal from an oscillator with an oscillation frequency synchronized with the carrier frequency of a video signal applied to the cathode of a CRT as a clock pulse, and counts these clock pulses to perform scanning in the main scanning direction and sub-scanning direction. The scanning position of the electron beam in the direction is detected, and based on this detection signal, the scanning position of the electron beam is converted into position information from a predetermined position on the fluorescent surface. After converting this position information into an analog signal, The present invention provides an automatic focus voltage adjustment device that converts the scanning position of the beam into distance information from a predetermined position on the fluorescent surface and adjusts the focus voltage based on this distance information, and adjusts the focus voltage for each scanning point. is adjusted optimally, so the focus of the entire screen is correct.

Further, there is an advantage that there is no need to adjust the focus voltage from the outside.

[Brief explanation of drawings]

Figure 1 shows a conventional focus voltage adjustment device, Figure 2 shows a CR
FIG. 3 is a graph showing the relationship between the focus voltage of T and the beam current density. FIG. 3 is a plan view of the fluorescent surface showing the arrangement of characters on the fluorescent surface as an embodiment of the present invention. FIG. 1 is an automatic focus voltage adjustment device according to an embodiment of the present invention. υ・・・Electron beam scanning position detection block, ■・
...Block for detecting the distance from the center point of the fluorescent surface to the scanning position of the electron beam, 40......Block that detects the distance from the center point of the fluorescent surface to the scanning position of the electron beam Block to adjust focus voltage.

Claims (1)

[Claims] A clock pulse generating means for generating a clock pulse with an oscillation frequency synchronized with the carrier frequency of an I CRT, a digitally detecting scanning position of the electron beam by counting the clock pulses, and a detection signal of the scanning position of the electron beam. scanning position detection means for converting the scanning position of the electron beam into positional information from a predetermined position on the fluorescent surface based on the scanning position of the electron beam; An automatic focus voltage adjustment device comprising: means for converting into distance information from a predetermined position on a surface; and means for generating an optimum focus voltage for the distance information. 2. In the automatic focus voltage adjustment device according to claim 1, the predetermined position of the fluorescent surface is set as the center point of the fluorescent surface, and the scanning position detecting means is arranged in the main scanning direction of the electron beam. One or more counters for counting the number of pixels or dots distributed in the electron beam, and one or more counters for calculating the number of pixels or sub-scanning lines distributed in the sub-scanning direction of the electron beam. , the count signal from each of the above counters is used as a subtraction signal, and one half of the number of pixels or one half of the number of dots arranged in the main scanning direction of the electron beam and one half of the number of dots arranged in the main scanning direction of the electron beam are used. 1/2 of the number of pixels or 1/2 of the number of sub-scanning lines is input as the subtracted number.
A focus voltage automatic adjustment device comprising: a subtraction circuit.