JPH07112248B2 - Display device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device using a CRT.

[0002]

2. Description of the Related Art Display devices using CRTs include, for example, computer terminals and TV receivers. In the video circuits used in these devices, the cutoff adjustment of a CRT electron gun and the background utilizing a back raster are used. Brightness control is performed.

An example of a conventional video circuit is shown in FIG.

In FIG. 4, reference numeral 1 is an analog video signal generation source for outputting an analog video signal. The analog video signal from the source 1 has a direct current component removed by a capacitor 2 and a maximum of 7 V _PP by an intermediate amplifier 3.
It is amplified to the extent. The analog video signal output from the intermediate amplifier 3 is superposed with a DC voltage responsive to a clamp pulse applied at a timing to be described later for determining a DC voltage level, that is, a black level by the DC reproducing unit 4, and an amplification factor is obtained. Is amplified to a cathode drive level of about 50 V _{PP at the} maximum by the inverting type final stage amplifier 5 of about 7 times and output. The analog video signal for driving the cathode from the final stage amplifier 5 is applied to the cathode of the CRT through the DC shift type cutoff adjusting circuit 6.

The cutoff adjusting circuit 6 is composed of a Zener diode 7, a cutoff adjusting variable resistor 8, a stabilizing capacitor 9 and a resistor 10. The shift amount of the DC voltage between the input and output ends of the cutoff adjustment circuit 6 is the maximum potential difference across the Zener diode 7 and is 0 at the minimum, and the resistance division ratio of the cutoff adjustment variable resistor 8 is between them. Depends on

In a color CRT, there are three primary colors, namely R (Red), G (Green) and B (Blue).
FIG. 4 for each of the three electron gun cathodes for e).
A video circuit such as The cutoff adjustment of the electron gun in the cutoff adjustment circuit 6 is performed for the following reason.

In the color CRT, the three electron guns for R, G, and B are mainly used for machining and assembling accuracy.
The difference in each distance between one common control grid G1 and the three cathodes cannot be zero. Therefore, when a predetermined voltage is applied to the control grid G1, the difference in the distance becomes the difference in the electric field, and as a result, the cutoff voltage of each cathode becomes different. Therefore, the cutoff adjustment circuit 6 individually adjusts the cutoff bias of each cathode to cut off each electron gun. This matches the black or darkest level of each color analog video signal to the cutoff voltage at the cathode of each electron gun. The difference in the cutoff bias potential of each cathode between the three electron guns is
Although it increases in proportion to the set voltage of the G2 grid, there is generally a difference of about 27V. From this, the Zener diode 7 in the cut-off adjustment circuit 6 has 2
A Zener voltage of about 7V to 30V is selected.

In FIG. 4, the direct current reproduction section 4 determines the direct current voltage in the analog video signal by using a feedback clamp method using a pulse generated within a horizontal blanking period. In FIG. 4, the analog video signal output from the final stage amplifier 5 is voltage fed back from the middle point of the resistors 11 and 12 via the error amplifier 13 and the DC regenerating unit 4. That is, the error amplifier 13 has the resistors 11 and 12 during the period of the pulse generated in the horizontal blanking period.
The error voltage between the midpoint voltage and the changeable reference voltage 14 is amplified and applied as a clamp pulse to the DC regeneration unit 4.

The brightness control of the CRT, that is, the brightness level control of the back raster as the background on the CRT screen is performed by changing the voltage level of the clamp pulse in the DC reproducing section 4 to change the DC voltage level. The black level of the analog video signal at the input side of the final stage amplifier 5, which is determined by the voltage level of the clamp pulse when the background is not illuminated at all on the CRT screen, is set to the limit of the dynamic range of the final stage amplifier 5. It is desirable to do. When the final stage amplifier 5 is, for example, a transistor-based input type amplifier, the black level on the input side of the final stage amplifier 5 is set to 0.6V to 1V. This is because when the black level is completely set to 0V, the gray scale of low gradation becomes non-linear due to the diode characteristics of the transistor that constitutes the final stage amplifier. On the contrary, if the black level is set to 1 V or higher, for example, 2 V, the dynamic range of the final stage amplifier 5 is narrowed, and the final stage amplifier 5 wastes power.

As described above, for example, the black level on the input side of the final stage amplifier 5 having an amplification factor of about 7 is set to a maximum of 1 V in the state where the background is not illuminated at all on the CRT screen, and the background on the CRT screen is changed. When the light is emitted at the maximum level, a potential difference of about 21V occurs with respect to the power supply voltage of the final stage amplifier 5 on the output side of the final stage amplifier 5.

[0011]

In the above video circuit, the following voltage must be secured as the power supply voltage for the final stage amplifier 5. That is, a voltage for ensuring the maximum level of the white background of the CRT screen after securing a maximum of 1 V as the black level on the input side of the final stage amplifier: 21 V The maximum amplitude voltage of the analog video signal for driving the cathode: 50V Maximum voltage for compensating the difference of cutoff voltage of each cathode between 3 electron guns: 30V.

Therefore, as the power supply voltage of the final stage amplifier 5, it is necessary to secure about 100 V obtained by summing these.

However, when the frequency of the analog video signal becomes high, the load resistance value in the final stage amplifier 5 must be lowered in order to secure the necessary amplification factor. Therefore, a large current flows through the final stage amplifier 5. As a result, the following problem occurs in the final stage amplifier 5. That is, power loss increases and heat is generated.

The amount of electromagnetic radiation increases.

Reliability is reduced.

Further, in the cutoff adjusting circuit 6,
Since there is a variable resistor 8 on the line through which the analog video signal flows, CR is controlled by DC voltage control or digital control.
The cutoff of the T electron gun cannot be adjusted. That is, it is not possible to support the fully automatic adjustment of the video circuit by digital control.

Further, since the cathode current flows through the resistor 10 having a relatively high resistance value in the cutoff adjusting circuit 6, the voltage across the resistor 10 changes in response to the change in the cathode current, and as a result, the cathode The cutoff bias shifts.

Therefore, an object of the present invention is to solve the above problems and to provide a display device in which the power supply voltage of the final stage amplifier is low.

Another object of the present invention is to provide a display device in which the cutoff bias does not fluctuate due to changes in the current flowing through the cathode of the CRT.

Still another object of the present invention is to provide a display device capable of fully automatic adjustment of a video circuit by digital control.

[0021]

To achieve the above object, the present invention provides a means for amplifying an analog video signal and a CR.
Means for generating a DC background brightness voltage in response to a background brightness control voltage for T, and receiving the amplified analog video signal from the amplifying means, removing the DC component of the analog video signal, and the DC component It is characterized by comprising clamp means for superimposing the direct current background luminance voltage on an analog video signal not including, and the CRT connected to the clamp means.

[0022]

According to the present invention, the final-stage amplifier only amplifies the analog video signal to a level required for driving the cathode, and the CRT cutoff adjustment, brightness adjustment, etc. are separated from the final-stage amplifier by a DC circuit. Done by

Therefore, the power supply voltage of the final stage amplifier becomes lower than in the conventional case.

[0024]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. The video circuit shown in FIG. 1 is common to the R, G and B channels. As shown in FIG. 1, the analog video signal from the analog video signal generation source 1 has a DC component removed by a capacitor 2 and is amplified by an intermediate amplifier 3 to a maximum of about 7 V _PP . The analog video signal output from the intermediate amplifier 3 is applied to the DC reproducing unit 4. The pulse P is generated during the horizontal blanking period. The error amplifier 13 generates a clamp pulse during this pulse P. This clamp pulse is supplied to the DC reproducing section 4 to determine the DC level of the analog video signal. This DC level is the lower limit level of the dynamic range of the inverting type final stage amplifier 5, that is, 0.6 to 1V. Then, the analog video signal is amplified to a maximum of about 50 V _PP by the final stage amplifier 5 having an amplification factor of about 7 times, and output.

The analog video signal output from the final stage amplifier 5 is taken out from the midpoint of the resistors 11 and 12. The error amplifier 13 amplifies and outputs the error voltage between the midpoint voltage of the resistors 11 and 12 and the fixed reference voltage 141 only for the period of the pulse P within the horizontal blanking period, and outputs it to the DC regeneration unit 4 as a clamp pulse. Apply. The reference voltage 141 is determined at the input side of the final stage amplifier 5 so that the reference DC level of the analog video signal is 0.6 to 1V. The power supply voltage B1 of the final-stage amplifier 5 may be a value that secures the reference DC level after amplification of the analog video signal and the dynamic range necessary for the analog video signal to be amplified, that is, about 60V.

The analog video signal from the final stage amplifier 5 has a direct current component removed by a capacitor 15, a direct current voltage is superimposed as described below, and is supplied to the cathode of the electron gun of the corresponding color of the CRT by an output line 16. To be done. The anode of the diode 17 is connected to the output line 16, and the cathode of the diode 17 is connected to the collector of the transistor 18. The capacitor 15 and the diode 17 form a very general clamp circuit 19. Two
Reference numeral 0 is a buffer circuit, which includes a transistor 18 and a resistor 21 for applying a power supply voltage B2 to the collector of the transistor 18. The clamp circuit 19 clamps the reference DC level of the analog video signal on the output line 16, and the clamp voltage determination circuit 22 determines this clamp voltage. The power supply voltage B1 is equal to or larger than the power supply voltage B2.

The clamp voltage determining circuit 22 includes resistors 23,
24, 25, variable resistance 26, transistors 27, 28,
It has open collector type inverters 29 and 30.
The resistor 23 applies the power supply voltage B2 to the base of the transistor 18 and both collectors of the two transistors 27 and 28. This application point is point B. Transistor 27
A voltage for controlling the brightness of the background of the CRT screen is applied to the base (here, point A). A direct current voltage for adjusting the cutoff of the electron gun of the CRT is applied to the base of the transistor 28 (here, point C) via the variable resistor 26. At the input terminals of the two inverters 29 and 30,
The pulse P generated during the horizontal blanking period as described above is commonly applied, and the output ends of the two inverters 29 and 30 become the ground (GND) level, that is, the reference potential when the pulse P is applied, and other than that. Time reaches an open (floating) level. The output end of one inverter 29 and the emitter of one transistor 27 are connected via a resistor 24, and the output end of the other inverter 30 and the emitter of the other transistor 28 are connected via a resistor 25. The pulse P is also supplied to the same components (the error amplifier 13 and the inverters 29 and 30) in the video circuits of the other color channels.

Next, the cutoff adjustment of the electron gun of the CRT will be described. That is, a DC voltage (referred to as V _C ) is applied to the base of the transistor 28, that is, the point _C via the variable resistor 26 for cutoff adjustment. Ignoring the voltage drop of V _BE of the transistor 28, when the pulse P is applied to the inverter 30, the output terminal of the inverter 30 becomes the GND level, and the voltage V _C is generated across the resistor 25. If the value of the resistor 25 is r25, a current i ₁ = V _C / r25 flows through the collector of the transistor 28. Therefore, at the point B, if the value of the resistor 23 is r23, a voltage fluctuation of (r23 / r25) · V _C occurs. Since r23 and r25 are fixed, the voltage at the point B can be changed by changing V _C, and as a result, the clamp voltage in the clamp circuit 19 is shifted down from the power supply voltage B1 via the buffer circuit 20. The cutoff of the electron gun of the CRT can be adjusted by controlling the cutoff direction. In this way, the black level of the analog video signal on the output line 16 can be matched to the cutoff voltage of the cathode of the electron gun. Since the voltage range for cutoff adjustment in the clamp circuit 19 is approximately 30 V, in a changeable range of V _C, V _C ·
R23 and r such that (r23 / r25) = 30 holds.
Determine the ratio with 25. Instead of the variable resistor 26, by applying an analog voltage from a D / A converter for inputting digital data to the base of the transistor 28, cutoff adjustment by digital data is possible. Since only the diode 17 and the transistor 18 having low impedance are inserted between the cathode of the CRT and the GND, the fluctuation of the cathode bias due to the flow of the cathode current can be suppressed to a small level.

Next, the background brightness control of the CRT screen will be described. In addition to the cutoff adjustment as described above, the background brightness of the CRT screen can be controlled by applying the background brightness control voltage V _A to the base of the transistor 27, that is, point _A. Assuming that the value of the resistor 24 is r24, when the pulse P is applied to the inverter 29, the current i ₂
= V _A / r24 flows to the collector of the transistor 27,
The voltage fluctuation width of the point B becomes _{(r23 / r24) · V A} . When the pulse P is applied to the two inverters 29 and 30, and V _A and V _C are applied, a current i ₁ + i ₂ flows through the resistor r23 according to the addition rule, and thus B2-r23 · {(V _A / _{r24) + (V C / r25} ) voltage V _B represented by} occurs B point.

The buffer circuit 20 will be described. This circuit 20 is an emitter follower circuit having a resistor 23 as an input resistor. Resistor 2 when pulse P is not applied
The terminal 24a of 4 and the terminal 25a of the resistor 25 are floating, so that the voltage B2 is applied to the base and emitter of the transistor 18 and the cathode of the diode 17, so that the transistor 18 and the diode 17 are not conducting. When the pulse P is applied, as described above, the terminal 24a
And 25a become the reference potential, the voltage at point _B is switched to V _B , and transistor 18 becomes conductive. Since the voltage drop between the base and the emitter is small, if this is ignored, the emitter of the transistor 18, that is, the diode 1
A voltage V _B is applied to the cathode of the diode 7, whereby the diode 17 becomes conductive, an AC current flows from the power supply voltage B1 to the point B through the final stage amplifier 5, the capacitor 15 and the diode 17, and the potential of the line 16 becomes V. _When equal to _B , diode 17 is turned off so that the voltage on line 16 is clamped to voltage V _B. Thus, the line 16 is clamped to the voltage V _B during the pulse P generated during the horizontal retrace period, and this voltage V _B is converted into the analog video signal supplied to the line 16 during the horizontal scanning period. It is superimposed as a DC component.

When the value r24 of the resistor 24 is made common in the video circuits of the R, G, and B channels, the brightness control voltage V _{A at the} point A for making the background of the CRT screen white is mutually different. Will be different. That is, CRT
This is because the types of phosphors used for the screen, the differences in the R, G, and B emission efficiencies, the specifications of the chromaticity of white balance, and the like influence. Therefore, in the video circuit of each channel of R, G, B, for the resistor 24, use the value r24 calculated individually based on the data such as the luminous efficiency of the R, G, B phosphors and the white balance chromaticity. The brightness control voltage V at point A
_A can be shared by each video circuit. On the other hand, the value r24 of the resistor 24 is made common in each video circuit, and A
The point brightness control voltage V _A can also be adjusted individually.
The brightness control voltage V _A is a D / A input with digital data.
The output of the converter can be used.

Further, as shown in FIG. 2, the two inverters 29 and 30 in FIG. 1 can be replaced by one transistor 31.

Next, a second embodiment of the present invention is shown in FIG. In FIG. 3, the same components as those in FIG. 1 are designated by the same reference numerals. In the first embodiment shown in FIG. 1, the black level of the analog video signal on the output line 16 is configured to shift down from the power supply voltage B1, but in the second embodiment, the black level on the output line 16 is changed. The black level of the analog video signal is shifted up from the power supply voltage B1. However, in the second embodiment, the relationship of power supply voltage B1 <power supply voltage B2 is satisfied.

Reference numeral 191 denotes a clamp circuit provided on the output line 16, and the capacitor 15 and the cathode are connected to the output line 16.
And a diode 171 connected to. A buffer circuit 201 includes an NPN transistor 32 having a collector connected to the power supply voltage B2 and an emitter connected to the anode of the diode 171, and a resistor 33 connected between the point B and the base of the transistor 32. Become.
Reference numeral 221 denotes a clamp voltage determination circuit, which includes resistors 23 and 2
4, 25, 35, variable resistance 26, transistors 27, 2
8, open collector type inverters 29 and 30, and open collector type buffer (non-invert) 34.

The power supply voltage B2 is commonly applied to the collectors of the two transistors 27 and 28 via the resistor 23. A pulse P is applied to the input end of the buffer 34, and the output end of the buffer 34 is connected to the two transistors 27 and 28 via the resistor 35.
Commonly connected to the emitters of. During periods other than when the pulse P is generated, the outputs of the inverters 29 and 30 are floating, while the output end of the buffer 34 is at the GND level, and the power supply voltage B2, the resistor 23, the transistor 2
The current I _A flows to the GND level through 7 and 28 and the resistor 35, and the voltage at the point B, that is, the voltage at the input end of the buffer circuit 201 is (power supply voltage B1−the maximum amplitude voltage of the analog video signal at the cathode). The value of the resistor 35 is set to be lower. As a result, the output end of the buffer circuit 201 is connected to the clamp circuit 19
It goes below the voltage on output line 16 at 1 and the clamp circuit does not operate.

On the other hand, when the pulse P is generated, the output of the buffer 34 floats, and the inverters 29, 30 and the transistors 27, 28 operate as in the first embodiment, and the currents i ₂ and i ₁ flow. , B point voltage rises according to the voltage at point A and the voltage at point C. As a result, the capacitor 15 in the clamp circuit 191 is charged via the buffer circuit 201 in accordance with the increase in the voltage at the point B, and the black level of the analog video signal on the output line 16 is shifted up from the power supply voltage B1.

As described above, the power supply voltage B2 is equal to the power supply voltage B1.
taller than. The current I _A flowing through the resistor 23 when the pulse P is not applied is larger than the current i ₁ + i ₂ flowing through the resistor 23 when the pulse P is applied. The voltage at the point B generated by the current I _A becomes lower than the voltage equal to (power supply voltage B1−the maximum amplitude voltage of the analog video signal of the cathode) as described above, while the voltage B generated by the current i ₁ + i ₂ The voltage at the point is the power supply voltage B2-r23 (i ₁ + i
₂ ) The voltage becomes equal to. The voltage at point B is higher than the power supply voltage B1.

[0039]

As described above, according to the present invention, the following effects can be obtained.

(1) The power supply voltage of the final stage amplifier can be lowered to about half the value of the conventional one. Therefore, all the problems to be solved, which have been the problems in the past regarding the final stage amplifier, are solved.

(2) Since the cathode current does not flow through the high resistance portion, the fluctuation of the cathode bias can be suppressed.

(3) It is required to set the DC voltage high depending on the cutoff condition of the CRT and the demand of the drive circuit. The circuit of FIG. 3 can accomplish this.

(4) Since the CRT cutoff can be adjusted by digital data, fully automatic adjustment by the digital data of the video circuit is possible.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing a part of another example of the clamp voltage determination circuit in the embodiment.

FIG. 3 is a circuit diagram of a second embodiment of the present invention.

FIG. 4 is a circuit diagram of a conventional display device.

[Explanation of symbols]

 4 DC recovery unit 5 Final stage amplifier 19 Clamp circuit 20 Buffer circuit 22 Clamp voltage determination circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaki Kobayashi 1623 Shimotsuruma, Yamato-shi, Kanagawa 14 Yamabe Works, IBM Japan, Ltd. (56) Reference JP-A-61-242472 (JP, A) ) Actual Kaihei 2-79666 (JP, U)

Claims (1)

[Claims] 1. A signal amplifying means for amplifying an analog video signal, and a clamp voltage for generating a DC clamp voltage corresponding to the sum of both control voltages in response to a background brightness control voltage and a beam cutoff control voltage for a CRT. Receiving the amplified analog video signal from the generating means and the signal amplifying means, removing the DC component of the analog video signal,
The clamp voltage generating means includes: clamp means for superimposing the DC clamp voltage on the analog video signal not containing the DC component; and the CRT connected to the clamp means. A connected output resistance, and (b) a first current, which is connected between the other end of the output resistance and a reference potential, and which is proportional to the background brightness control voltage from the power supply voltage through the output resistance to the reference potential. And (c) a second current, which is connected between the other end of the output resistor and the reference potential, and which is proportional to the beam cutoff control voltage from the power supply voltage through the output resistor. A display device including a second current path for flowing to the reference potential.