JP3254719B2 - Video display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a television receiver,
The present invention relates to a video display device such as a monitor device, and more particularly to a device capable of automatically controlling a cut-off characteristic of a CRT.

[0002]

2. Description of the Related Art As is well known, in a video display device such as a television receiver, R, G and B phosphors are arranged in a CRT (cathode ray tube) according to a predetermined rule. An image is displayed by emitting light from a body from each electron gun based on R, G, and B image signals.

Meanwhile, the CRT including the electron gun has a lot of manufacturing variations, and the characteristics of the R, G, and B phosphors are not uniform but individually different. Are R, G, and B, respectively. The cutoff characteristic (light emission characteristic) is represented by the cathode current with respect to the cathode voltage, which is shown in FIG.
It is shown in FIG. As can be understood from this figure, the cutoff characteristics do not match in each of the R, G, and B channels. Note that FIG.
Is merely an example, and the cutoff point is not always in the order of R, G, B in the order of the cathode voltage,
The cutoff characteristics are completely irregular for each CRT.

In order to match the cut-off points which do not match, it is necessary to make adjustments in the production process.
That is, a level shift circuit, a gain control circuit, and the like are provided in the signal processing / amplifying circuit system for each of the R, G, and B video signal channels, and these are adjusted so that the cutoff characteristics of each channel match. I was

Further, in order to reduce such a cutoff adjustment step and a gain control circuit, an automatic cutoff adjustment method for automatically performing cutoff adjustment has been proposed. FIG. 16 shows a circuit block of a main part of a television receiver adopting a conventional auto cutoff adjustment method.

When the supplied video signal is demodulated into an R signal, a G signal, and a B signal by a demodulation circuit (not shown),
G and B signals are respectively switched circuit 1R, 1G, 1B
Supplied to In the switch circuits 1R, 1G, 1B,
R, G, reference pulses RP _R in different predetermined positions in the vertical blanking interval of each signal as the B signals shown in FIG. 17, RP _G, is RP _B is added.

As described above, the reference pulses RP _R , R
P _G, a signal is RP _B is added in the level shift circuit 2
Drive circuits 3R, 3G, 3B via R, 2G, 2B
And the electron gun is driven. Of course, it goes without saying that the video display is performed by the signal in the video signal section supplied to the drive circuits 3R, 3G, 3B.
The internal configuration of the drive circuits 3G and 3B is the same as that of the drive circuit 3R, and is not shown. Reference numeral 4 denotes a CRT.

Here, attention is paid to reference pulses RP _R , RP _G and RP _B added during the vertical blanking period. Reference pulses RP _R , RP as in the video signal portion.
_G, RP _B is also amplified in the transistor Q _1, CRT cathode current R _IK, G _IK, but so that the B _IK is obtained,
The cathode currents R _IK , G _IK , and B _IK correspond to the transistor P ₁
Is detected by, it will flow switch circuits 5R, 5G, the resistors R ₁ through 5B. Here, the switch circuits 5R, 5G, and 5B each have a reference pulse RP.
_R, RP _G, are controlled so that the contacts are closed only during a period corresponding to the RP _B, hence the resistance R _1,
As shown in FIG. 18, a voltage having three pulses corresponding to the cathode current generated by the R, G, and B reference pulses RP _R , RP _G , and RP _B is obtained.

This pulse voltage is input to the clamp circuit 6 via the clamp capacitor C _1, and the capacitor is set so that the voltage of the section of the clamp pulse obtained from the clamp pulse generator 6 a becomes V ₁ (see FIG. 18). It is clamped by out current to C _1. The clamped pulse voltage is time-sequentially switched by the switch circuit 7 to each of the comparators 8R, 8G,
8B.

[0010] Comparator 8R, 8G, 8B in is [Delta] V ₁ higher voltage to voltages V ₁ to the other terminal (V ₁ + _{ΔV 1)} is supplied as a comparison reference voltage, DC level is clamped to V ₁ Each pulse voltage is compared to this.

The comparators 8R, 8G, and 8B are controlled so as to perform a comparison operation only during a period in which a pulse voltage is supplied, and a differential output containing an error value between the pulse voltage and the reference voltage as a comparison output. It is configured to obtain an amplifier-like output. This comparator 8
R, 8G, the comparison output of the 8B (i.e. [Delta] V ₁ = current such that [Delta] V ₁ ') each sample hold capacitor C _2R, C _2G, is supplied to the C _2B, the sample hold capacitor C _2R, C _2G, C _2B Is supplied as a control voltage to each of the level shift circuits 2R, 2G, and 2B.

That is, based on the voltages held in the sample and hold capacitors C _2R , C _2G , and C _2B , each of the level shift circuits 2R, 2G, and 2B outputs R,
The black levels of the G and B signals are the reference pulses RP _R and R
P _G, by being controlled to be equal to the height of the RP _B, automatic cutoff adjustment is achieved.

[0013]

However, such a conventional automatic cutoff adjusting circuit has the following problems.

In FIG. 16, a portion 10 surrounded by a dashed line is usually formed in one IC.
The sample and hold capacitors C _2R , C _2G and C _2B must be connected as external components to the IC. For this reason, the number of components is increased, and three extra connection pins for the IC are used, which is inefficient in terms of cost and manufacturing process.

Further, since current flows only in the reference pulse section (1H) in one field to the pins to which the sample and hold capacitors C _2R , C _2G and C _2B are connected, the impedance is very high. However, when the impedance of the substrate is reduced due to a change over time, a leak current is generated, and as a result, the sample and hold operation of the sample and hold capacitors C _2R , C _2G , and C _2B cannot be maintained normally.

[0016]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has been made in consideration of the above problems .
Switch means for adding a reference pulse to a predetermined location different from each other for each field for each field;
Level shift to set the DC level of the output of the switch means
Means and an output of the level shift means.
Cathode current detecting means for detecting a cathode current;
The output of the cathode current detecting means is compared with a predetermined comparison voltage.
And a comparison means for one set in a predetermined period.
Based on count pulses supplied in multiple units between fields
Thus, the counting operation for the output of the comparing means is executed.
Includes an up-down means to the said being by <br/> urchin configured to control the leveled Rushifuto means based on the output of the up-down means, to obtain the control information of the CRT cut-off characteristics
To provide a video display apparatus characterized by being made so that.

Also, for the up / down counting means, from the power-on state to the point in time when the image display operation on the CRT is stabilized, the output of the comparing means is determined based on count pulses supplied in a plurality of units during one field. The counting operation is executed, and the CRT
Stability time of the image display operation in the detection of the cathode current of the whole hand, also constitutes to be determined by the count operation up to a predetermined count value is started from the cathode current detecting time.

[0018]

The pulse voltage converted from the cathode current based on the reference pulse once in one field is compared with a predetermined comparison reference voltage to count up and down.
By converting the count output into an analog signal, the output value is held for one field. That is, control information for the level shift means can be obtained without using the sample / hold con sensor.

Also, when the CRT operation is unstable, there is often a considerable voltage difference between the pulse voltage and the comparison reference voltage, which results in prolonging the convergence time of the cut-off loop. By performing the up / down counting operation a plurality of times per field, the convergence time of the cutoff loop can be shortened.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, referring to FIGS. 1 to 14, (A) an automatic cutoff adjustment operation, (B) a comparison reference hysteresis voltage supply operation, (C) a superposition operation of a reverse polarity signal on a D / A conversion output, Embodiments of the video display apparatus of the present invention will be described in the order of D) color temperature adjustment operation outside the auto cutoff loop, and (E) high-speed stabilization operation of cutoff adjustment by counter pulse control. Note that FIG. 17 and FIG.
Referring to FIG.

(A) Automatic cut-off adjustment operation FIG. 1 is a block diagram showing a main part in a case where a television receiver is an embodiment, and 11R, 11G, 11
B is a switch circuit, which is a demodulated R signal, G signal,
For the B signal, the reference pulse RP as shown in FIG.
_R, RP _G, adds RP _B. 12R, 12G, 12
A level shift circuit B controls the black level of the video signal and adjusts the cutoff characteristics of each of the R, G, and B channels as described later.

Level shift circuits 12R, 12G, 12B
Are output from the drive circuits 13R, 13G, and 13B, respectively.
Supplied is amplified by the transistor Q ₁ in, CRT 14
, Each of the R, G, and B electron guns is driven, and the cathode currents R _IK , G _IK , and B _IK are controlled by the transistor P _1.
Has been made to be detected by.

The cathode currents R _IK , G _IK , and B _IK flow to the resistor R ₁ via the switch circuits 15R, 15G, and 15B. Switch circuits 15R, 15G, 15B is the reference pulse RP each _R, RP _G, are controlled so that the contacts are closed only during a period corresponding to the RP _B, therefore the resistor R _1, as shown in FIG. 18 R , G, the reference pulse RP _R of B, RP _G, R
A voltage having three pulses corresponding to the cathode current by P _B is obtained.

This pulse voltage is input to the clamp circuit 16 via the clamp capacitor C _1, and the capacitor is set so that the voltage of the section of the clamp pulse obtained from the clamp pulse generator 6 a becomes V ₁ (see FIG. 18). It is clamped by out current to C _1. FIG.
The clamped pulse voltage is supplied to the comparator 17 as shown in FIG.

The comparator 17 supplies a voltage (V ₁ +) higher than the voltage V ₁ by ΔV ₁ to the other terminal as a comparison reference voltage.
ΔV ₁ ) is supplied, and each pulse voltage whose DC level is clamped at V ₁ is compared with this, and “H (5
V) ”or“ L (0 V) ”(see FIG. 2).
(B)).

The comparison output of the comparator 17 is supplied to up / down counters 18R, 18G, 18B. Then, each of the up / down counter units 18R, 18
In G and 18B, count clocks R _CK , G _CK and B _CK are given as shown in FIGS. 2C to 2E during a period corresponding to the reference pulse of each channel. If the output is "H", up-counting is performed, and if "L", down-counting is performed. FIGS. 2F to 2H show only the count output LSB. Reference numerals 19R, 19G, and 19B denote D / A converters that convert the outputs of the up / down counter units 18R, 18G, and 18B into analog signals.

Each up / down counter unit and D / A converter (18R, 19R) (18G, 19G) (18B, 1
9B) is specifically configured, for example, as shown in FIG. That is, the output from the comparator 17 is first input to the data terminal of the D flip-flop 30, and the count clock (R _CK , G _CK , B _CK ) is used as a latch clock, and the supplied comparison output is latched. Is output. The latch output is supplied to the up / down counter 31. As described above, by counting the latch output, it is possible to eliminate the influence of the rounded waveform of the output of the comparator 17.

In this case, the count clock (R _CK , G _CK ,
B _CK ) is supplied via the inverter 32, and counts at the rising edge of the output of the inverter 32. In the up-down counter 31 is performed counting of 8 bits, for example, the count output resistance r ₀ ~
is output as an analog voltage value by the D / A converter composed by r _15. The inverter 33 and the switch circuit 34 will be described later.

As described above, a voltage obtained by converting the numerical value counted up / down based on the comparison operation of the comparator 17 into an analog signal, that is, D /
Outputs of the A converters 19R, 19G, and 19B are supplied as control voltages to the level shift circuits 12R, 12G, and 12B, respectively. That is, in each of the level shift circuits 12R, 12G, and 12B, R, G,
The black level of the B signal is equal to the reference pulses RP _R , RP
_G, to be equal to the height of the RP _B by being (i.e., the voltage [Delta] V ₁ 'equal way the [Delta] V ₁ in FIG. 18) control, automatic cutoff adjustment is achieved.

Accordingly, the up / down counter 31 initially continues up counting or down counting in each field, but converges so as to repeat up counting and down counting every field after a predetermined time. That is, at this point, the automatic cutoff adjustment operation is stable.

In this embodiment, since a circuit can be configured in one IC in the area surrounded by the dashed line,
In order to realize the automatic cutoff adjustment operation, an external sample and hold capacitor as in the conventional example shown in FIG. 16 is not required. Therefore, in this embodiment, the number of pins required for the IC, the number of elements, and the like are reduced, and the cost, the manufacturing process, and the like are improved. In addition, the operation of the external sample-and-hold capacitor is not normally maintained due to the influence of aging, so that the auto cut-off adjustment operation does not become unstable.

(B) Supply operation of comparison reference hysteresis voltage By the way, when the automatic cut-off adjustment operation is stable, the up-down counter 31 has the above-mentioned configuration.
Although up-count and down-count must be repeated exactly in, R output of each field For this purpose comparator 17, G, B each reference pulse _{RP R, RP G, RP B} ( reference pulse The condition is that the output of “L” and “H” is repeated with respect to the pulse voltage corresponding to the cathode current detected by the above.

However, in a stable state, the pulse voltage for each field is substantially close to the comparison reference voltage.
The difference is not large enough. For this reason, there is a possibility that an error is likely to occur in the comparison operation of the comparator 17 due to the influence of noise, for example. Since the probability of occurrence of this malfunction is random, the white balance is instantaneously lost due to the malfunction, and color flicker is seen on the screen.

Therefore, in this embodiment, the comparator 17
Are provided with a hysteresis voltage circuit 20R, 20G, 20B for controlling the comparison reference voltage (V ₁ + ΔV ₁ ) supplied to the switch, and a switch circuit 21. Actually, the hysteresis voltage circuits 20R, 20G, 20B and the switch circuit 21 are 40 in FIG.
₂ and the power supply section (V ₁ + ΔV
It can be constituted by ₁₎ and the resistor R _3.

The D flip-flop at the preceding stage of the OR gate 41 corresponds to the D flip-flop 30 in FIG. That is, each of the up / down counter units 18
The D flip-flop 30 in R, 18G, 18B is shown.

The comparator 17 includes transistors P ₁₁ and P _11
The comparison reference voltage (V ₁ + ΔV ₁ ) supplied to the base side of the transistor P ₁₁ and the pulse voltage supplied to the base side of the transistor P ₁₂ are compared by the ₁₂ differential pairs, and the comparison output is the transistor Q ₁₃ As described above, the comparison output is supplied to the D flip-flop 30 in each of the up / down counter units 18R, 18G, and 18B, and the latch is supplied only during the reference pulse section. Clock R _CK , G
_Latched based on _CK and _BCK . The latch output (ie, 5V output or 0V output) of the D flip-flop 30 is supplied to the up / down counter 31 as shown in FIG. 3 and also to the OR gate 41 as shown in FIG. Then, the original comparison reference voltage (V ₁ + ΔV ₁ ) is added by the resistance division by the resistances R ₂ and R ₃ .

As a result, as shown by the dotted line in FIG. 5A, the comparative reference voltage is relatively high after the latch output of the D flip-flop 30 becomes "H".
_R1 and the second output V _R2 is relatively low after the latch output of the D flip-flop 30 becomes “L”. 5B, 5C, and 5D show the pulse voltage supplied to the comparator 17, the latch clock,
The output of the D flip-flop is R,
Only one channel of G or B is shown.
Therefore, the comparison reference voltage of FIG. 5A actually has a waveform in which three channels are combined.

As described above, that is, at the time t _L at which the comparator 17 should output “L”, the comparison reference voltage becomes _VR1 , and the time t _H at which the comparator 17 should output “H”. In the _meantime , the comparison reference voltage _rises and falls based on the output of the comparator 17 so that it becomes VR2. In a state where the comparison result of “L” is to be output, the comparison operation is less affected by noise and the like, and is stable.

(C) Operation of superimposing the reverse polarity signal on the D / A conversion output In this embodiment, in the state where the auto cutoff loop is stable, each of the R, G, and B channels corresponds to The least significant bit of the up / down counter 31 repeats “L” and “H” for each field, but this is the change of the least significant bit when stable (that is, the D / A converters 19R, 19R, 19G,
The level shift is performed in the level shift circuits 12R, 12G, and 12B by an amount corresponding to the change in the voltage value of the minimum bit of 19B). Accordingly, the black level of the video signal rises and falls for each field, and this state is the same for each of the R, G, and B channels, so that an influence appears as a luminance flicker on the screen.

Therefore, in this embodiment, only in the video signal section, the change of the voltage value of the minimum bit of the D / A converters 19R, 19G, 19B is applied to the outputs of the D / A converters 19R, 19G, 19B. The superposition with the opposite polarity prevents the occurrence of luminance flicker. This will be described again with reference to FIG. 3 and FIG.

As described above, the output of the comparator 17 is the latch clock (and the count clock via the inverter 32) R _CK , G in each of the R, G, and B channels.
_{The data} is latched by the D flip-flop 30 based on _CK and _BCK and counted by the up / down counter 31. The state is as shown in FIGS. Here, the polarity of the up / down counter 31 is "H" for up and "L" for down. Constituted D / A output resistance r ₀ ~r ₁₅ of the up-down counter 31
The resistance r ₀ is sent to the converters (19R, 19G, 19B). Normally, the resistance r ₀ is grounded by connecting the switch circuit 34 to the ground terminal. In this state, the D / A converters (19R, 19G, 19B) are connected. 19B) (corresponding to the least significant bit) is as shown in FIG. And this D / A
The level shift circuit (12R, 12R)
G, 12B) is controlled.

Here, the switch circuit 34 is connected to the inverter 3
3B, and connects the signal shown in FIG.
If Figure 6 is inverted through the 3 signals (e) supplying to the resistance r _0, the output of the D / A converter (19R, 19G, 19B) is as shown in FIG. 6 (f), the words, FIG. In 6 (d), the correction waveform is such that the portion (hatched portion) that has been at the L level in the video signal section has been compensated for. That is,
The change of the least significant bit in the output of the D / A converter (19R, 19G, 19B) is canceled. As a result, the black level is kept constant in the video signal section, and the occurrence of luminance flicker on the screen is prevented.

However, if such a correction is made in the reference pulse section (= vertical retrace section) shown in FIG. 6 (g), the auto cut-off operation itself will not be performed. No correction is applied only to the section. That is, the switch circuit 34
Is controlled so that the reference pulse section is grounded and the video signal section is connected to the inverter 33. Thereby, the actual D / A converter (19R, 1
9G and 19B) are as shown in FIG.

Of course, even if the above-described correction is performed by adding the output of the inverter 33 to the grounded resistor r ₀ , the precision of one bit as the level shift control voltage is not affected. FIG. 7 shows D / when no correction operation is performed.
The output of the A converter (equivalent to LSB) is indicated by a dotted line, and the output of the D / A converter (equivalent to LSB) when the correction operation is executed is indicated by a solid line.

(D) Color Temperature Adjustment Operation Outside the Auto Cut-Off Loop Reference numeral 22 shown in FIG. 1 indicates a switch circuit provided for adjusting the color temperature. circuit 12R, 12G, 12B are controlled color temperature adjustment voltage V _3, carried out by changing the DC shift amount of the video signal. However, when controlling the color temperature adjustment voltage V ₃ at the reference pulse section to control the loop of the automatic cutoff that has been described above, the reference pulse RP _R, RP _G, R
The height of the P _B also will vary, automatic cutoff adjustment operation can not function properly. Thus, a reference pulse interval and is controlled to switch circuit 22 selects the fixed voltage V _4.

Hereinafter, each level shift circuit 12R, 1
The color temperature adjustment performed in 2G and 12B will be described. Even if the light emission points of R, G, and B are matched to some extent by the automatic cutoff adjustment operation, it is necessary to adjust the color temperature to make the subtle white appearance uniform on the CRT.

For this reason, in the conventional auto cut-off adjustment method shown in FIG. 16, the color temperature is adjusted by setting the comparison reference voltages of the comparators 8R, 8G, 8B of each channel finely. That is, in the case of the circuit of FIG. 16, when the value of ΔV ₁ is controlled to change the comparison reference voltage, the cut-off adjustment loop increases the pulse voltage at which the cathode current (R _IK , G _IK , B _IK ) is detected. changes, As a result, R, G, reference pulses RP _R and B each channel, RP _G, the height of the RP _B changes.
The black level of the video signal is equal to the reference pulse RP
_R, since they are to be adjusted in RP _G, based on the RP _B, it is possible to adjust the color temperature by setting the comparison reference voltage. The control of the comparison reference voltage for adjusting the color temperature is executed by, for example, a control signal supplied from a system control unit (not shown) via a bus.

However, in the case of the present embodiment, it is not preferable to perform the color temperature adjustment in the cutoff adjustment loop as described above. This is because the present embodiment uses a D / A converter (19R,
19G, 19B), the reference pulse RP
_R, RP _G, but by controlling the height of the RP _B, necessarily a D / A converter (19R, 19G, 19B) the resolution of the bus control signals for bit resolution and color temperature adjustment, consistent Because there is no.

For example, in the relationship between the cathode current of the CRT and the RGB output (= drive amplifier input of the CRT) shown in FIG. 8, the dynamic range of the cathode current required for the auto cutoff adjustment operation is defined as section A. Where D
Assuming that the bit resolution of the / A converters (19R, 19G, 19B) is ΔV _1B indicated by a solid line, and the resolution of the bus control signal for adjusting the color temperature is ΔV _2B indicated by a dotted line, the color temperature adjustment is instructed by the bus control signal. Actually, the adjustment of the black level of the video signal is performed by a D / A converter (19R,
19G, 19B), a dead zone is generated in the color temperature adjustment, and the accuracy is reduced.

Therefore, in this embodiment, the color temperature adjustment is performed outside the automatic cutoff adjustment loop by the level shift circuit 1.
2R, 12G, using the color temperature adjustment voltage V ₃ at 12B,
I try to control it. Each of the level shift circuits 12R, 12G, and 12B in this embodiment is, for example, as shown in FIG.
It is configured as follows.

The video signal in the circuit (R signal, G signal, B signal) is input to the base of the transistor Q _21. The video signal output is obtained from the emitter of the transistor Q ₂₁ through R _20, R _21. Here, a control voltage for automatic cutoff adjustment, that is, a D / A converter (19)
R, 19G, output 19B) is input to the base of the transistor Q _25, is converted into a current I _2. Transistor Q
_{Since 23} and Q ₂₄ constitute a current mirror circuit, the current I ₂ flows through the resistors R ₂₀ and R ₂₁ .

On the other hand, the color temperature adjustment voltage V ₃ or the fixed voltage V
₄ current I ₁ due to the flow through the resistor R _20. This resistor R ₂₀ ,
R ₂₁ will have a function of shifting the DC level of the video signal, DC shift is determined by the current flowing through the resistor R _20, R _21.

[0053] In this case, the transistor Q ₂₂ is an amplifier of the base ground, and the emitter of the potential has become about 0.4 V. Therefore, color temperature adjustment voltage V _3, the values of the resistors R _22, R _23, determines the value of the current I _1. In this case, the resistors R ₂₂ ,
Since the value of R ₂₃ is fixed, the value of the color temperature adjustment voltage V _3, the value of the current I ₁ is controlled. The resistor R ₂₂ 30 k.OMEGA, a resistor R ₂₃ is taken as 2 k.OMEGA, current I ₁ when the color temperature adjustment voltage V ₃ was varied from 1.5 to 3.5 V
Are shown in FIG. Allowing the color temperature adjustment by changing the value of the current I ₁ flowing through this resistor R _20. Then, the adjustment of the current I _1, i.e., adjustment of the color temperature adjustment voltage V ₃ is D / A converter (19R, 19G, 19
Since it does not depend on the bit resolution of B), the color temperature adjustment accuracy is not limited by using the D / A converter, and the adjustment accuracy can be set as desired by the accuracy of the bus control. .

Note that the actual DC level shift amount, that is, the level shift amount as the level shift circuit (12R, 12G, 12B) is determined by the current I flowing through the resistors R ₂₀ and R _21.
It will also depend on the value of ₂ . That is, the video signal inputted from the transistor Q ₂₁ is output a voltage effective amount level shifts of _{{(I 1 + I 2)} × R 20 + I 2 × R 21}.

As described above, in the level shift circuit (12R, 12G, 12B) in the present embodiment, the current I ₂ determined by the auto cutoff adjustment loop and the current I ₁ determined by the color temperature adjustment voltage V ₃ . Although the level shift control systems independent of each other are configured, as described above, the reference pulse section
Since 2 selects the fixed voltage V _4, is not the color temperature adjustment operation is an obstacle to automatic cutoff adjustment operation.

(E) High-speed stabilization operation of cut-off adjustment by counter pulse control By the way, in the case of the above embodiment, the reference pulse RP
_R, RP _G, RP _B are added once per field, the pulse voltages corresponding to cathode current detected by the reference pulse is also obtained once per field are input to the comparator 17. The comparison output is output from each of the up / down counting units 18R, 18G, 18B.
, One count operation is performed per field. For this reason, the level shift operation for cutoff adjustment is controlled with a width corresponding to the minimum bit of the output of the D / A converter per field.

Meanwhile, after the actual CRT in the power-on, the up heater beam radiation is stabilized by an electron gun warms it takes some time, during which in particular based reference pulse RP _R, RP _G, the RP _B The pulse voltage corresponding to the detected cathode current is also determined by the comparator 1
7 often has a considerable voltage difference from the comparison reference voltage (V ₁ + ΔV ₁ ).

Here, if the level shift amounts of the reference pulses RP _R , RP _G , RP _B per field are controlled only by the minimum bit, the stable state (ie, the up / down counter 31 is incremented every field) It takes a considerable time to reach the state where the count / down count is repeated).

In a normal television receiver, blanking is performed so as not to display an image for a certain period of time (about several seconds) after the power is turned on, but before the automatic cutoff adjustment operation reaches a stable state. If the image blanking is canceled, an abnormal image will be displayed. Therefore, the image blanking is continued at least until a stable state is reached. That is, since the cathode current does not flow immediately after the power is turned on, the control signal by the D / A output functions to increase the amount of current and is shifted by the level shift circuit so that the DC component of the video signal output increases. You.

Then, when the CRT warms up after a while and the cathode current is obtained, the DC components of the reference pulse and the video signal output become lower and become stable at a certain point. This is because normal image display is performed only when the stable state is reached. For this reason, prolonging the time required to reach the stable state in the automatic cutoff adjustment operation is inevitably difficult to display an image, which is very undesirable.

For this reason, when the above embodiment is adopted, CR
Until T reaches a stable state, it is desirable that the up / down counter 31 performs a plurality of count operations for one field so that the automatic cutoff adjustment operation can quickly reach a stable state.

Therefore, the up / down counting section 18R,
Count clocks R _CK , G supplied to 18G, 18B
_{The CK} and _BCK generators are configured as shown in FIG. FIG. 12 shows input / output waveforms of each part in FIG. FIG.
, 51, 52, 53 are D flip-flops, 5
4 and 55 are NAND gates, 56 is a switch circuit,
A pulse signal H is input to the input terminal 57 once per horizontal cycle.
_BL (e.g. horizontal sync signal or the horizontal signal of the same frequency generated from the sync signal) is input, and the input terminal 58 a signal H 4 times the signal FH ₄ frequency _BL are input (FIG. 12 (See (a) and (b)).

Signal H_BLIs D free via inverter 59.
Supplied to the flip-flop reset input terminal (FIG.
(C)) and the signal FH_Four Is the D flip-flop 51,
52 and 53 are provided as latch clocks,
Input to the gate 54. D flip-flop
51 Q output (FIG.(D)) is a D flip-flop 5
2 and a NAND gate 54, and a D flip-flop.
Q output of rop 52 (FIG.(E)) is D flip flow
And input to the NAND gate 53 and the NAND gate 55. And D
XQ output of flip-flop 53 (FIG.(G))
Input to the gate 55.

Therefore, from the NAND gate 54FIG.
As shown in (h), a clock having three pulses in one horizontal period.
Output from the NAND gate 55.FIG.
A clock having one pulse in one horizontal period as shown in (i).
Output. Output of these NAND gates 54 and 55
Is selected by the switch circuit 56, and further, each channel is selected.
Timing processing corresponding to the reference pulse
Then, each of the up / down counting units 18R, 18G, 1
8B has a count clock (R_CK, G_CK, B_CK)
Be paid.

Therefore, in each channel, when the output of the NAND gate 55 is selected with respect to the comparison output of the comparator 17 as shown in FIG. 13A input to the up / down counting units (18R, 18G, 18B). In the case where the count clock as shown in FIG. 13B is supplied and the count operation is performed once per field and the output of the NAND gate 54 is selected,
The count clock as shown in (c) is supplied, and the count operation is performed three times per one field. That is,
At the time when the CRT has not reached a stable state, FIG.
By using the count clock of 3 (c), the time until the automatic cutoff adjustment operation reaches a stable state can be shortened.

FIGS. 14A to 14C show that the up / down counter 31 counts three times in one field during the unstable period immediately after the power is turned on, and once in the field after the stable period is reached. , The reference pulse, the count clock, and the outputs of the D / A converters (19R, 19G, 19B) for only one channel are shown. By controlling the count clock in this way, rapid stabilization is realized, and the video blanking time immediately after power-on can be shortened. Although three count pulses are obtained during the horizontal period when the frequency is unstable, a second count or four or more count pulses may be generated.

In this case, in order to obtain the switching timing of the switch circuit 56, means for identifying whether or not the operation of the CRT has reached a stable state is required. For this reason,
In FIG. 11, a counter section 60 counts a predetermined number of vertical blanking pulses supplied to an input terminal 61 from the time of power-on, and outputs count-up information to an AND gate 62. Further, detecting units 63R, 63G, 63B for detecting the presence or absence of the cathode current (R _IK , G _IK , B _IK ) are provided, and information indicating that the cathode current has been detected for all the R, G, B channels is provided. Output via the gate 64.

The detection of the cathode current is performed, for example, by referring to FIGS.
The up / down counting section (18R, 18G, 1
From the state where the count value of the up / down counter 31 in 8B) is reset to “0” at a predetermined point in time immediately after the power is turned on, the count operation accompanying the supply of the pulse voltage by the cathode current based on the reference pulse, for example, “3” ] Can be detected by counting up.

The AND gate 62 outputs information indicating that the cathode current has been detected at least a predetermined time after the power is turned on, and the output of the counter 65 starts counting. And the counter 65
Counts a predetermined time (for example, 0.8 to 1 second), it is determined that the CRT has entered a stable operation, and the switch circuit 56 initially connected to the NAND gate 54 is switched to the NAND gate 55 by the count-up signal. .

In this case, the stabilization of the CRT operation is identified by
Cathode current detection (that is, the CRT warms up)
In this case, the CRT is already warmed, for example, when the power is once turned off and then immediately turned on, for example. In the case where the cathode current detection signal is obtained relatively quickly, unnecessary standby time is eliminated and CR
It is possible to quickly determine whether T has reached a stable state.
Of course, conversely, even when the temperature is low and the CRT does not easily warm up, a sufficient standby time can be obtained by taking the detection of the cathode current into consideration.

The present invention is not limited to the embodiments described above, but can be variously modified within the scope of the invention.

[0072]

As described above, the video display apparatus of the present invention adds a reference pulse to a predetermined portion for each field of a video signal, converts the cathode current obtained by the reference pulse into a pulse voltage, When obtaining the control information of the cut-off characteristic of the CRT based on the output of the comparing means for comparing the voltage with a predetermined reference voltage, the output of the comparing means is counted by the up / down counting means and then D / A converted. Since the cutoff characteristic is controlled by having a level shift means for controlling the DC component of the video signal by the converted output voltage, an auto cutoff adjustment loop can be configured in the IC, and the sample hold as an external component A capacitor can be eliminated. This makes it possible to reduce the number of components and the number of connection pins required for the IC,
This has the effect of increasing efficiency in terms of cost and manufacturing process. Also, there is an advantage that the automatic cutoff adjustment operation does not become unstable due to the influence of aging.

Further, the up / down counting means controls the count clock so that the count operation is performed a plurality of times in one field during a predetermined period, for example, during an unstable period immediately after the power is turned on. This has the advantage that the image blanking time immediately after power-on can be shortened.

The stable operation of the CRT is determined in two stages, namely, the detection of the cathode current and the standby time after the detection, so that it is most appropriate according to the condition of the CRT and the conditions such as the ambient temperature. There is also an effect that a good judgment can be made.

[Brief description of the drawings]

FIG. 1 is a block diagram of a main part of an embodiment of a video display device according to the present invention.

FIG. 2 is an explanatory diagram of a counting operation based on a reference pulse according to the embodiment.

FIG. 3 is a configuration diagram of an up / down counting unit and a D / A converter according to the embodiment.

FIG. 4 is a circuit diagram for explaining a generation unit of a comparison reference hysteresis voltage according to the embodiment.

FIG. 5 is a waveform chart for explaining a comparison reference hysteresis voltage of the example.

FIG. 6 is a waveform chart for explaining a correction operation for the output of the D / A converter according to the embodiment.

FIG. 7 is an explanatory diagram of an output of the D / A converter according to the embodiment.

FIG. 8 is an explanatory diagram of bit accuracy of a control signal for color temperature adjustment according to the embodiment.

FIG. 9 is a circuit diagram of a level shift circuit according to an embodiment.

FIG. 10 is an explanatory diagram of an adjustment operation using a color temperature adjustment voltage according to the embodiment.

FIG. 11 is a block diagram of a count clock generator of the embodiment.

FIG. 12 is a waveform chart for explaining a count clock generation operation of the embodiment.

FIG. 13 is an explanatory diagram of a count operation using a count clock according to the embodiment.

FIG. 14 is an explanatory diagram of a D / A converter output based on a count clock according to the embodiment.

FIG. 15 is an explanatory diagram of cutoff characteristics of R, G, and B channels.

FIG. 16 is a block diagram of an automatic cutoff adjusting unit of a conventional video display device.

FIG. 17 is an explanatory diagram of a reference pulse.

FIG. 18 is an explanatory diagram of a pulse voltage obtained by a cathode current based on a reference pulse.

[Explanation of symbols]

 Reference Signs List 10 IC 11R, 11G, 11B Switch circuit 12R, 12G, 12B Level shift circuit 13R, 13G, 13B Drive circuit 14 CRT 17 Comparator 18R, 18G, 18B Up / down count section 19R, 19G, 19B D / A converter 20R, 20G , 20B hysteresis voltage generator 22 switch circuit 30 D flip-flop 31 up-down counter 51, 52, 53 D flip-flop 60, 62 counter 62R, 62G, 62B detector

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 9/44-9/78

Claims (2)

(57) [Claims] 1. A switch means for adding a reference pulse to a predetermined place different from each other for each demodulated three primary color signals for each field, and a level for setting a DC level of an output of the switch means.
Shift means and a cathode driven by the output of the level shift means
A cathode current detecting means for detecting a current; and comparing an output of the cathode current detecting means with a predetermined comparison voltage.
A comparing means for comparing a plurality of fields in one field during a predetermined period.
Based on the count pulse supplied as a unit, the comparison
Includes an up-down means for counting for the output stage is executed, and on the basis of the output of the up-down means leveled Rushifu
Is configured to control the door means, CRT cut-off
An image display device, wherein characteristic control information is obtained . 2. An output of the comparing means based on count pulses supplied to a plurality of units during one field from a power-on state to a point in time when a video display operation on a CRT is stabilized. with the count operation is executed for a stable time point of the image display operation in the CRT is determined and the detection of the cathode current of the whole hand, by the count operation up to a predetermined count value is started from the cathode current detecting time The image display device according to claim 1, wherein: