JPH02295293A - Projection television - Google Patents

Abstract

PURPOSE:To improve focus performance and contrast by adjusting the screen voltage of the screen electrode of each cathode-ray tube and setting the voltage of each cathode to the optimum value while a beam current is held constant. CONSTITUTION:Variable resistances 25-27 are connected to the output stage of a high voltage generator 20 corresponding to cathode-ray tubes 22-24. A DC voltage generated by the high voltage generator 20 is varied by using those variable resistances 25-27 to adjust the voltages (screen voltage) of 2nd grids G2 (screen electrode) of the cathode-ray tubes 22-24 to set the voltages of the cathodes of the cathode-ray tubes 22-24 as high as possible within a controllable range while the beam currents are held constant. Consequently, the focus performance can be improved and the contrast is improved.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a projection television equipped with an autokine bias circuit (also referred to as an automatic white balance circuit) [Prior Art] is autokine bias (hereinafter abbreviated as A)
My name is KB. ) Regarding circuits, for example, JP-A-61-1
It is described in Publication No. 87487.

The configuration and operation of the AKB circuit will be explained using FIG. 2.

FIG. 2 is a block diagram showing a conventional direct-view television equipped with an AKB circuit.

In Figure 2, 1.2 is a reference voltage power supply, 3 is a variable gain amplifier, 4 is a level shift circuit, 5 is an adder, 6 is a pulse forming circuit, 7 is a blanking pulse generator, and 8 is a current detection resistor. , 9.10 is a comparator, 11 is a horizontal sync separation circuit, 12 is a vertical sync separation circuit, l3 is a sync separation circuit, 1
4 is a luminance signal/color signal (hereinafter abbreviated as Y/C)
Separation circuit, 15 is an amplifier, 16 is a color demodulator, 17 is a matrix circuit, 18 is an output amplifier transistor, 19 is a cathode ray tube, 20 is a high voltage generator, 21 is a gate pulse generator, SWI, SW2 are switches.

In FIG. 2, the video signal is input to the Y/C separation circuit 14, where it is separated into a luminance signal Y and a color signal C. The video signal is input into a matrix circuit 17, where the primary color signals R, G, and blue of red, green, and blue are separated. B is created.

Further, the luminance signal Y is inputted to the sync separation circuit 13, and further to the horizontal sync separation circuit 11 and the vertical sync separation circuit 12 to generate a horizontal sync signal and a vertical sync signal.

Now, the aforementioned primary color signals include three primary colors, R, G, and B. Of these, the primary color signal R will be explained below.

The primary color signal R is added (or replaced) with a reference pulse from a pulse forming circuit 6, which will be described later, in an adder 5. The output of the adder 5 passes through the variable gain amplifier 3 and the level shift circuit 4, and then is input to the output amplifier transistor 18 to drive the red cathode KR of the cathode ray tube 19.

After the other primary color signals G and B are also subjected to similar processing,
For green. Drives blue cathodes KG and KB. As a result, an image is reproduced on the screen of the cathode ray tube 19.

Next, the operation of the AKB circuit will be explained.

The pulse forming circuit 6 generates a reference pulse having a reference level and outputs it to the adder 5 described above. The reference pulses generated at this time usually consist of two types of pulses: one is a black level reference pulse having the black level of the video signal, and the other is a white level reference pulse having the white level. Further, the timing for generating the reference pulse is set during the vertical blanking period based on the input horizontal synchronization signal and vertical synchronization signal.

Further, the gate pulse generator 21 generates a first gate pulse indicating the generation period of the black level reference pulse and a second gate pulse indicating the generation period of the white level reference pulse from the horizontal synchronization signal and the vertical synchronization signal. do.

On the other hand, the output of the adder 5, which is the primary color signal R including the reference pulse, passes through the variable gain amplifier 3 and the level shift circuit 4 as described above, and then passes through the output amplifier transistor 18.
The cathode KR of the cathode ray tube 19 is driven by this.

At this time, a beam current flows according to the voltage of the cathode KR.
The current flows into the resistor for detection through the sun. That is, the voltage across the current detection resistor 8 is proportional to the beam current. The voltages across the current detection resistor 8 are input to the switches SWI and SW2, respectively.

The switch SWI receives the first signal from the gate pulse generator 21.
ONL only during the black level reference pulse generation period based on the gate pulse of , and its output is compared with the reference voltage E of the reference voltage power supply 2 by the comparator 9.

The comparison output is input to the level shift circuit 4, and the DC level of the primary color signal R is shifted according to the magnitude of the comparison output. As a result, the black level reference pulse generation period is controlled so that the DC level of the voltage of the cathode KR becomes the set value.

Further, the switch SW2 is turned ON when a white level reference pulse is generated based on the second gate pulse from the gate pulse generator 21, and its output is compared with the reference voltage E1 of the reference voltage power supply 1 by the comparator IO. Ru. The comparison output is input to the variable gain amplifier 3, and the gain of the variable gain amplifier 3 is changed according to the magnitude of the comparison output to control the amplitude of the primary color signal R. As a result, the white level reference pulse generation period is controlled so that the amplitude of the voltage at the cathode KR becomes the set value.

Note that the set values of the DC level and amplitude of the voltage of the cathode KR are determined by the resistance value of the current detection resistor 8 and the reference voltage E. of the reference voltage power supplies 1 and 2. , Eb.

By the way, the beam current of a cathode ray tube is generally
It is determined by the potential difference between the grating G1 and the second grating G2 (screen electrode) and the potential difference between the first grating G1 and the cathode KR. Here, since the first grating G1 is grounded, when the voltage (screen voltage) of the second grating G2 (screen electrode) is determined, the beam current is transferred to the cathode KR.
It will change according to the voltage.

Therefore, as described above, by controlling the DC level and amplitude of the voltage of the cathode KR to the set values during the black level reference pulse and white level reference pulse generation periods by the AKB circuit, the beam current is controlled to a predetermined value. Can be a value. This eliminates the need for troublesome cutoff adjustments and drive adjustments.

[Problems to be Solved by the Invention] As described above, in the prior art, the beam current can be set to a predetermined value by controlling the DC level and amplitude of the cathode voltage to a set value. This eliminates the need for troublesome cutoff adjustments and drive adjustments.

However, under the condition that the beam current is constant, there is a correlation between the voltage of the second grid (screen electrode) (screen voltage) and the voltage of the cathode (cathode voltage), so the value of the screen voltage There were the following problems.

That is, if the screen voltage is too high, the cathode voltage must also be increased to keep the beam current constant;
However, if the cathode voltage is made too high, the maximum cathode voltage will peak at the power supply voltage of 10B, making control by the AKB circuit impossible, and the dynamic range of the cathode voltage will become narrower, resulting in a decrease in contrast 1. Put it away.

Conversely, if the screen voltage is too low, the cathode voltage must also be lowered to keep the beam current constant; In addition to the deterioration of focus performance, the guinamine range of the cathode voltage is also narrowed, resulting in a decrease in contrast.

As mentioned above, under the condition of keeping the beam current constant, if the screen voltage is not set appropriately, control by the AKB circuit will become impossible, focus performance will deteriorate, or the dynamic range of the cathode voltage will be reduced. There was a problem in that it became narrower and the contrast deteriorated.

The above problems are problems in direct-view televisions equipped with an AKB circuit, but similar problems also occur in projection televisions equipped with an AKB circuit.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the problems of the prior art described above, to enable sufficient control by the AKB circuit, to improve focus performance, and to widen the dynamic range of cathode voltage. Our goal is to provide projection television that is possible.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a projection television equipped with a plurality of cathode ray tubes and a plurality of AKB circuits corresponding to each cathode ray tube. However, a plurality of adjustment means are provided to adjust the screen voltage of the screen electrode in the corresponding cathode ray tube.

[Effect]

A plurality of adjustment means provided corresponding to each cathode ray tube adjusts the screen voltage of the screen electrode in the corresponding cathode ray tube.

In other words, by adjusting the screen voltage of each cathode ray tube using these adjustment means, the cathode voltage of each cathode can be raised as high as possible within the controllable range by the AKB circuit while the beam current is kept constant. (that is, the cant-off level can be set deeply). Therefore, the focusing performance can be improved without making control by the AKB circuit impossible, and the dynamic range of the cathode voltage can also be widened, so that the contrast can be improved. Moreover, since the screen voltage of each cathode ray tube can be adjusted independently, each cathode ray tube can be used in an optimal state.

〔Example] An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a block diagram showing a projection television as an embodiment of the present invention.

In FIG. 1, the same reference numerals as in FIG. 2 are the same as in FIG. 2, and therefore their explanations will be omitted.

In addition, 22, 23, and 24 are cathode ray tubes for red, green, and blue, and 25, 26, and 27 are variable resistors.

This embodiment uses three cathode ray tubes 22 as shown in FIG.
, 23, 24, the basic structure and operation of this embodiment are the same as the direct-view television shown in FIG. 2, so the features of this embodiment will be explained below. do.

In this embodiment, the output stage of the high voltage generator 20 includes variable resistors 25, 26, .
27 are connected. These variable resistors 25, 26.2
7 varies the DC voltage generated from the high-voltage generator 20, and applies the second grid G2 of each of the cathode ray tubes 22, 23, and 24.
(screen electrode) voltage (screen voltage).

Here, as a specific adjustment method using these variable resistors 25, 26.27, each of the cathode ray tubes 22, 23.2
While observing the voltage waveforms of the cathodes KR, KG and KB of 4, check that the black level of each primary color signal R, G, B is equal to
The second grating G2 (
The voltage of the screen electrode (screen voltage) is adjusted independently. At this time, as mentioned above, each primary color signal R
, G, and B are adjusted so that they are close to the power supply voltage 1B, but with some cut-off margin in mind, the black levels are adjusted to be somewhat lower than the power supply voltage 1FB.

Thus, according to this embodiment, the variable resistors 25, 26.2
7, by adjusting the voltage (screen voltage) of the second grid G2 (screen electrode) of each cathode 22, 23, 24, each cathode KR, KG, KB with the beam current constant. The voltage can be set to the optimal value.

That is, by setting the voltages of each cathode KR, KG, and KB as high as possible within the range that can be controlled by the AKB circuit (that is, by setting the cutoff level deeply), without making the control by the AKB circuit impossible, Focus performance can be improved. Moreover, since the dynamic range of the cathode voltage can be widened, the contrast can be improved.

[Effects of the Invention] As explained above, according to the present invention, in a projection television equipped with an AKB circuit, the beam current can be made constant by adjusting the screen voltage of the screen electrode in each cathode ray tube. In this state, the voltage of each cathode can be set to an optimal value.

In other words, by setting the voltage of each cathode as high as possible within the range that can be controlled by the AKB circuit (that is, by setting the cutoff level deep), focus performance can be improved without making control by the AKB circuit impossible. Furthermore, since the dynamic range of the cathode voltage can be widened, the contrast can be improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a projection television as an embodiment of the present invention, and FIG. 2 is a block diagram showing a conventional direct-view television equipped with an AKB circuit. Explanation of symbols 1.2...Reference voltage power supply, 3...Variable gain amplifier,
4...Level shift circuit, 5...Adder, 6...
Pulse forming circuit, 7... planking pulse generator,
8... Resistor for current detection, 9. IO... comparator, 11
... Horizontal synchronization separation circuit, 12 ... Vertical synchronization separation circuit, 13 ... Synchronization separation circuit, 14 ... Y/C separation circuit, 15 ... Amplifier, 16 ... Color demodulator, 17 ...
Matrix circuit, 18... Output amplifier transistor, 19... Braun tube, 20... High voltage generator, 21
...Gate pulse generator, 22...Cathode ray tube for red, 23...Cathode ray tube for green, 24...Cathode ray tube for blue, 25,26.27...Variable resistor, SWI,
SW2...Switch. Agent Patent Attorney Akio Namiki

Claims (1)

[Claims] 1. A plurality of cathode ray tubes, each having a voltage applied to its cathode corresponding to a video signal, and a desired DC level and amplitude of the voltage applied to the cathode of the corresponding cathode ray tube, respectively. In a projection television equipped with a plurality of autokine bias circuits that control the voltage to a value of Projection television featuring