JP2516098B2 - Image display device - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to an image display device (display device using a cathode ray tube), and particularly to an average image level (AP) of an input video signal.
L) and an image display device capable of displaying an optimum image.

[Prior art]

It is well known that the maximum allowable average anode current value is defined for the cathode ray tube, and that the cathode ray tube is not allowed to be used in a state of exceeding the maximum allowable average anode current value described above in terms of reliability. It is as follows. Therefore, in an image display device configured using a cathode ray tube (display device using a cathode ray tube), no matter what the content of the video signal input to it, or the brightness of the operator (viewer). Regardless of the adjustment state such as adjustment or contrast adjustment, it is necessary that the average anode current value flowing in the operating cathode ray tube is equal to or less than the above-mentioned maximum allowable average anode current value. To be done. Therefore, when the average anode current value of the cathode ray tube exceeds a predetermined average anode current value, the amplitude of the video signal is reduced to limit the average anode current value of the cathode ray tube. An image display device provided with a current limiting circuit has been put to practical use in the past, and an example configuration thereof is shown in FIG. In FIG. 4, 1 is an input terminal for a video signal (image signal) to be displayed, 2 is a video gain control circuit, 3 is a video output circuit, 4 is a cathode ray tube, 5 is an average anode current detection circuit, and 6 Is an anode current limiting circuit, 8 is a gain control voltage supply terminal, and 9 is a variable resistor for manually adjusting the image gain. A power source (not shown) is connected to both ends of the variable resistor 9 for manual adjustment of the image gain described above, and the gain control voltage supply terminal 8 is connected to the variable resistor 9 according to the adjustment of the slider of the variable resistor 9. The gain control voltage is output. The video signal supplied to the input terminal 1 is the operator (viewer)
Then, the gain is adjusted (contrast adjusted) by using the variable resistor 9 for manual adjustment, and then it is supplied to the cathode ray tube 4 and displayed as an image on the fluorescent screen. When a color image is displayed by the cathode ray tube 4,
It goes without saying that a cathode ray tube for displaying a color image is used as the cathode ray tube 4, and a color image signal is supplied to the cathode ray tube 4. In the average anode current detection circuit 5 described above, the cathode ray tube 4 is used.
The average value of the anode current flowing in the cathode ray tube 4 corresponding to the brightness of the fluorescent surface of the
Supply to. The anode current limiting circuit 6 generates a gain control signal when the average value of the anode current of the cathode ray tube 4 detected by the above-mentioned average anode current detection circuit 5 exceeds a preset maximum anode current value, By supplying it to the image gain control circuit 2, gain control is automatically performed in the image gain control circuit 2 so that the average value of the anode current of the cathode ray tube 4 is previously set. Make sure that the maximum anode current value is set. The relationship between the average image level (APL) of the input signal and the average anode current in the conventional image display device having the anode current limiting circuit described with reference to FIG. 4 is illustrated in FIG. This is represented by such a curve, and the average anode current of the cathode ray tube 4 is controlled so as not to exceed the value indicated by a in FIG.

[Problems to be Solved by the Invention]

However, in the conventional image display device illustrated in FIG. 4, the relationship between the average image level (APL) of the input signal and the average anode current in the standard adjustment state is shown by the curve in FIG. 5, for example. If it is such that the average image level of the input signal (AP
Considering a case where the relationship between L) and the average anode current is changed to the state shown by the curve in FIG. 5, for example, at the point b when the average image level is low, the operator makes a manual adjustment. Gain adjustment (contrast adjustment) can be performed using the variable resistor 9, but it is often desired to perform gain adjustment, and a video signal in a relatively high average luminance state, for example, c in FIG. The point is that the gain adjustment cannot be performed.

[Means for solving problems]

The present invention provides a means for detecting an average anode current of a cathode ray tube and an average anode of the cathode ray tube by automatically controlling a gain of an image amplification circuit when the average anode current of the cathode ray tube exceeds a predetermined current value. In an image display device provided with a means for controlling a current, when an external adjusting means is operated to change the gain of the video amplification circuit up or down, the average anode current of the cathode ray tube is limited. The limit value of the average anode current of the cathode ray tube set in the means,
There is provided an image display device provided with means for changing the gain of the video amplifier circuit up and down in response to the change of the gain.

[Action]

Operate external adjustment means to increase the gain of the video amplifier circuit,
The limit value of the average anode current of the cathode ray tube, which is set in the means for limiting the average anode current of the cathode ray tube when changed to the lower side, corresponds to the above-mentioned change of the gain of the video amplifier circuit. Since the change is made up and down, the relationship between the average image level (APL) of the input signal and the average anode current is shown by the curve in FIG. 3 by the operator (viewer) adjusting the contrast. When the state is changed to such a state that the average image level is relatively high, the operator manually adjusts the variable resistor 9 even at the point c.
Can be used to perform gain adjustment (contrast adjustment).

【Example】

Hereinafter, specific contents of the image display device of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a block diagram of an image display device of the present invention, FIG. 2 is a partial specific circuit diagram, and FIG. 3 is an average image level (APL) of an input signal in the image display device of the present invention. It is a curve figure which shows the relationship with an average anode current. In the image display device of the present invention shown in FIG. 1, 1 is an input terminal for a video signal (image signal) to be displayed,
2 is a video gain control circuit, 3 is a video output circuit, 4 is a cathode ray tube, 5 is an average anode current detection circuit, 6 is an anode current limiting circuit, 7 is an anode current limiting level control circuit, 8
Is a gain control voltage supply terminal, 9 is a variable resistor for manually adjusting the image gain, and a power source (not shown) is connected to both ends of the variable resistor 9 for manually adjusting the image gain. . The variable resistor 9 outputs the gain control voltage to the gain control voltage supply terminal 8 in accordance with the adjustment of its slider. The image display device of the present invention shown in FIG. 1 has a configuration mode in which an anode current limit level control circuit 7 is added to the conventional image display device described above with reference to FIG. In the image display device shown in FIG. 1, the video signal supplied to the input terminal 1 is adjusted by the operator (viewer) using the variable resistor 9 for manual adjustment as necessary. After the adjustment), it is supplied to the cathode ray tube 4 and displayed as an image on the phosphor screen. When a color image is displayed by the cathode ray tube 4, a cathode ray tube for displaying a color image is used as the cathode ray tube 4, and a color image signal is supplied to the cathode ray tube 4. This is similar to the case of the conventional image display device shown in FIG. In the image display device shown in FIG. 1, in the average anode current detection circuit 5, the cathode current of the cathode ray tube 4 is supplied to the cathode ray tube 4 corresponding to the cathode current of the cathode ray tube 4 supplied to its terminal 5a. The average value of the flowing anode current is detected and supplied from the output terminal 5b to the terminal 6a of the anode current limiting circuit 6, and in the anode current limiting circuit 6, the cathode ray tube 4 detected by the average anode current detecting circuit 5 is detected. The average value of the anode current of the anode current control circuit 6
When the maximum anode current value set in is exceeded, a gain control signal is generated, and the gain control signal is supplied from the output terminal 6c to the video gain control circuit 2 so that the video gain control circuit 2
In (1), the gain control is automatically performed so that the amplitude of the video signal is reduced so that the average value of the anode current of the cathode ray tube 4 is suppressed to the preset maximum anode current value. By the way, in the above-mentioned anode current limiting circuit 6 in the image display device of the present invention, the maximum anode current value preset in the anode current limiting circuit 6 is the anode current limiting level control circuit 7 for the terminal 6b thereof. Output terminal
It is designed to be changed by the signal supplied from 7b. The anode current limit level control circuit 7 responds to the adjustment of the slider of the variable resistor 9 when the operator performs the gain adjustment (contrast adjustment) using the variable resistor 9 for manual adjustment. The gain control voltage output to the gain control voltage supply terminal 8 is supplied to the input terminal 7a, so that an output signal corresponding to the supplied gain control voltage is output from the output terminal 7b to the terminal of the anode current limiting circuit 6. 6b, whereby the maximum anode current value preset in the anode current limiting circuit 6 is changed in a predetermined manner, that is,
When the operator performs gain adjustment (contrast adjustment) using the variable resistor 9 for manual adjustment to change the gain of the image amplification circuit up or down, the operator is set in the anode current limiting circuit 6 of the cathode ray tube. As the limiting value of the average anode current of the cathode ray tube, the characteristic curve typically shown in FIG. , It is adapted to be updated in a changing manner that changes downward. Therefore, in the image display device of the present invention shown in FIG. 1, the relationship between the average image level (APL) of the input signal and the average anode current is adjusted by the operator (viewer) adjusting the contrast. Even at the point c where the average image level is relatively high when the state is changed to the state shown by the curve in FIG. 3, the operator uses the variable resistor 9 for manual adjustment to adjust the gain (contrast). Adjustment). Next, referring to FIG. 2, an average anode current detection circuit 5, an anode current limiting circuit 6, and an anode current limiting level control circuit 7 in the image display device shown in FIG.
Specific configuration contents of each component such as will be described. The constituent parts shown by broken line frames 5, 6, 7 in FIG. 2 are the constituent parts shown by solid line frames 5, 6, 7 in FIG. 1, that is, the average anode current detection circuit 5
And an anode current limiting circuit 6 and an anode current limiting level control circuit 7, etc. are shown respectively. Further, in order to clarify the correspondence between the respective components in FIGS. The output terminals are shown correspondingly. In FIG. 2, the average anode current detection circuit 5 is a power source V
It is composed of 1, resistor R1, R2, capacitor C1,
The anode current Ik of the cathode ray tube 4 from the high voltage winding of the high voltage transformer flows through the terminal 5a. In this average anode current detection circuit 5, one end of the resistor R1, the non-grounded terminal of the capacitor C1 and the output terminal 5b are connected to the other end of the resistor R2 whose one end is connected to the positive electrode of the power source V1 whose negative electrode is grounded. They are connected at the connection point α, and the other end of the resistor R1 is connected to the terminal 5a. The terminal 6a of the anode current limiting circuit 6 is connected to the output terminal 5b of the average anode current detecting circuit 5 described above, and the diode D is connected to the terminal 6a of the anode current limiting circuit 6.
Is connected to the terminal 6b, and the anode of the diode D is connected to one end of the resistor R3 and the base of the transistor Q1 (connection point β). The other end of the resistor R3 is connected to the collector of the transistor Q1 and the power supply Vcc, and the emitter of the transistor Q1 is connected to the non-ground terminal of the resistor R4 and the output terminal 6c (connection point γ ) Has been. The signal output from the output terminal 6c of the anode current limiting circuit 6 is supplied to the video gain control circuit 2 as a gain control signal (gain control voltage). Further, the output terminal 7b of the anode current limit level control circuit 7 is connected to the terminal 6b of the anode current limit circuit 6 described above, and the output terminal 7b of the anode current limit level control circuit 7 is connected to the output terminal 7b of the transistor Q2. The collector is connected. The input terminal 7a is connected to the base of the transistor Q2, and the transistor Q2
One end of a resistor R5 is connected to the emitter of, and the positive electrode of a power source V2 whose negative electrode is grounded is connected to the other end of the resistor R5. In the circuit arrangement shown in FIG. 2, when the anode current Ik (FIG. 2) flows through the cathode ray tube 4 in FIG. 1, the anode current Ik is the average anode current detection circuit 5
At the ground → power supply V1 → resistor R2 → connection point α → resistor R1 → terminal 5a → circuit. Therefore, the voltage value of the connection point α in the average anode current detection circuit 5 described above is determined by the capacitor C1 connected thereto.
Therefore, a voltage value corresponding to the average anode current value of the cathode ray tube 4 is obtained, which corresponds to the average anode current value of the cathode ray tube 4 generated at the connection point α. The voltage is supplied from the output terminal 5b of the average anode current detection circuit 5 to the terminal 6a of the anode current limiting circuit 6. As described above, the cathode of the diode D is connected to the terminal 6a of the anode current limiting circuit 6, and the output terminal 7b of the anode current limiting level control circuit 7 is also connected via the terminal 6b. In the diode D, the voltage value relationship between the voltage Vα at the connection point α in the average anode current detection circuit 5 and the voltage Vβ at the connection point β in the anode current limiting circuit 6 is Vα>
In the case of Vβ, it is in a non-conducting state, and in the case where the relationship between the voltage values of the two voltages Vα and Vβ is Vα <Vβ, it is in a conducting state. Therefore, when the average anode current Ik of the cathode ray tube is within the allowable range, the voltage Vα at the connection point α in the average anode current detection circuit 5 is the anode of the diode D provided in the anode current limiting circuit 6. The voltage value V1 of the power source V1 described above so as to be higher than the side voltage Vβ,
If the voltage value Vcc of the power source Vcc is set in advance in a relationship such that V1> Vcc, the diode D becomes non-conductive when the average anode current Ik of the cathode ray tube 4 is within the allowable range. Done. Since the anode current limiting circuit 6 is in a state irrelevant to the average anode current detecting circuit 5 and the limiting level control circuit 7 for the anode current when the diode D is in the non-conducting state, Transistor Q1 whose base is supplied with voltage Vβ at connection point β
The emitter voltage Vγ is kept constant, and this voltage is supplied as a gain control voltage to the video gain control circuit 2 via the output terminal 6c. The resistance increases as the average anode current value of the cathode ray tube 4 increases.
Since the voltage drop of R2 becomes large, the voltage Vα of the connection point α in the average anode current detection circuit 5 decreases, and when the average anode current Ik of the cathode ray tube 4 exceeds the allowable range, the average anode current Ik The voltage V at the connection point α in the detection circuit 5
α makes the diode D conductive. In addition, the reason why the diode D becomes conductive as described above is
This is when the voltage value Vα at the connection point α becomes a voltage value lower than the voltage Vβ on the anode side of the diode D provided in the anode current limiting circuit 6 by the forward voltage of the diode D or more. When the diode D becomes conductive, the voltage V applied to the base of the transistor Q1 due to the voltage drop caused by the conduction current of the diode D flowing through the resistor R3 connected in the base circuit of the transistor Q1.
β decreases. As a result, the voltage Vγ of the emitter of the transistor Q1 connected to the emitter follower decreases, and the voltage Vγ is supplied to the video gain control circuit 2 via the output terminal 6c as a gain control voltage, thereby decreasing the gain of the video gain control circuit 2. Let Then, by the automatic control operation by the circuit consisting of the image gain control circuit 2, the image output circuit 3, the average anode current value of the cathode ray tube, the average anode current detection circuit 5, the anode current limiting circuit 6, and the image gain control circuit 2, The maximum average anode current of the cathode ray tube is limited to a predetermined current value. The description of the circuit operation as described above performed with respect to the circuit arrangement shown in FIG.
It was for the case where the transistor Q2 of the limiting level control circuit 7 for the anode current, which is connected to the cathode side of the through the terminals 6b and 7b, is cut off. The variable resistor 9 is adjusted by the user (viewer), and the gain control voltage appearing at the gain control voltage supply terminal 8 is adjusted according to the adjustment of the slider of the variable resistor 9. And the limit level control circuit 7 for the anode current, so that the transistor Q2 of the limit level control circuit 7 for the anode current is turned on. The variable resistor 9 for manual adjustment of the video gain is adjusted by the user (viewer), and the gain control represented by the gain control voltage supply terminal 8 is adjusted in accordance with the adjustment of the slider of the variable resistor 9. Terminal 7a of limit level control circuit 7 whose voltage is the anode current
Is supplied to the base of the transistor Q2 of the limiting level control circuit 7 for the anode current. As the gain control voltage output to the gain control voltage supply terminal 8 increases in accordance with the adjustment of the slider of the variable resistor 9 for manual adjustment of the image gain described above, the video gain decreases. The user (viewer) adjusts the slider of the variable resistor 9 for manually adjusting the image gain in order to reduce the contrast (reduce the image gain). Sometimes, the gain control voltage applied to the base of the transistor Q2 via the terminal 7a of the anode current limit level control circuit 7 causes the transistor
When Q2 changes from the cut-off state to the conductive state, grounding in the average anode current detection circuit 5 → power supply V1 → resistor R2 → connection point α → terminal 5b → terminal 6a → terminal 6b → terminal 7b → transistor Q2
Flows through the circuit of collector → same emitter → resistor R5 → power supply V2 → ground. Therefore, the voltage value of the connection point α in the average anode current detection circuit 5 depends on the voltage drop generated in the resistor R2 in the average anode current detection circuit 5 due to the current flowing in the transistor Q2 in the above-mentioned anode current limit level control circuit 7. Although changing, the gain control voltage output to the gain control voltage supply terminal 8 becomes high in accordance with the adjustment of the slider of the variable resistor 9 for manually adjusting the image gain as described above. Accordingly, in the case where the video gain is controlled to decrease, the user (viewer) tries to lower the cotrust (low video gain) and slides the variable resistor 9 for manual adjustment of the video gain. By adjusting the pendulum, the voltage value of the connection point α in the average anode current detection circuit 5 is lowered as the contrast is lowered, so that the image display of the present invention. On the other hand, when the external adjusting means such as the variable resistor 9 for manually adjusting the image gain is operated to change the gain of the image amplifying circuit up or down, the average anode current of the cathode ray tube is limited. Since the limit value of the average anode current of the cathode ray tube set in the circuit 6 is changed to up and down in correspondence with the up and down changes of the gain of the video amplification circuit, the operator (viewing / listening) By adjusting the contrast, the relationship between the average image level (APL) of the input signal and the average anode current becomes higher than the standard contrast from the state of the curve in FIG. 3 corresponding to the case of the standard contrast. The limit value of the average anode current of the cathode ray tube when it is changed to the lowered state, for example, the state shown by the curve in FIG. 3, is indicated by a'in FIG. The average image level is changed to a state lower than a in FIG. 3 showing the limit value in the average anode current of the cathode ray tube as shown by the curve in FIG. 3 in the state of quasi-contrast. The operator can perform the gain adjustment (contrast adjustment) by using the variable resistor 9 for manual adjustment even at the relatively high point c.

【The invention's effect】

As is clear from the above description, the image display device of the present invention is a means for detecting the average anode current of the cathode ray tube, and when the average anode current of the cathode ray tube exceeds a predetermined current value. In an image display device having means for automatically controlling the gain of the video amplifier circuit to limit the average anode current of the cathode ray tube, an external adjusting means is operated to increase the gain of the video amplifier circuit. The limit value of the average anode current of the cathode ray tube, which is set in the means for limiting the average anode current of the cathode ray tube when changed to the lower side, corresponds to the above-mentioned change of the gain of the video amplifier circuit. An image display device comprising means for changing up and down, when the image display device of the present invention operates an external adjusting means to change the gain of the video amplifier circuit up and down. To The limit value of the average anode current of the cathode ray tube, which is set in the means for controlling the average anode current of the cathode ray tube, changes up and down in correspondence with the above-mentioned change of the gain of the video amplifier circuit. Since the operator (viewer) adjusts the contrast, the relationship between the average image level (APL) of the input signal and the average anode current is changed to the state shown by the curve in FIG. 3, for example. In this case, the operator can perform the gain adjustment (contrast adjustment) using the variable resistor 9 for manual adjustment even at the point c where the average image level is relatively high. However, the conventional problems described above can be solved well.

[Brief description of drawings]

FIG. 1 is a block diagram of an image display device of the present invention, FIG. 2 is a part of a concrete circuit diagram, and FIG. 3 is an average image level (APL) and an average anode of an input signal in the image display device of the present invention. FIG. 4 is a block diagram of a conventional example of an image display device, and FIG. 5 is an average image level (APL) of an input signal in the conventional image display device of FIG.
It is a curve figure which shows the relationship between and an average anode current. 1 ... input terminal of video signal (image signal) to be displayed, 2 ... video gain control circuit, 3 ... video output circuit, 4 ... cathode ray tube, 5 ... average anode current detection circuit, 6 ... Anode current limiting circuit, 7 ... Anode current limiting level control circuit, 8 ... Gain control voltage supply terminal, 9 ... Variable resistor for manual adjustment of video gain,

Claims (1)

(57) [Claims] 1. A means for detecting an average anode current of a cathode ray tube, and a gain of an image amplifying circuit is automatically controlled when the average anode current of the cathode ray tube exceeds a predetermined current value. In an image display device provided with a means for limiting the average anode current, the average anode current of the cathode ray tube is changed when the gain of the video amplifier circuit is changed up or down by operating an external adjusting means. An image comprising means for changing the limit value of the average anode current of the cathode ray tube set as the limiting means to up and down in correspondence with the up and down changes of the gain of the video amplifier circuit. Display device