JPS6151829B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a matrix display device using liquid crystal, plasma, electroluminescence, etc., and more particularly to a matrix display device that uses digital aperture modulation to display halftones.

The brightness B of a cathode ray tube is proportional to the 2.5 to 3 power of the applied voltage V, but in a liquid crystal display, the brightness is proportional to the effective value of the applied voltage, and in a plasma display, it is proportional to the average value of the applied voltage. By the way, it is said that the human sense of brightness I is proportional to the 1/3 power or logarithm of luminance B. Therefore, when displaying images using a cathode ray tube for television, the voltage applied to the cathode ray tube is applied as is without any correction to the video signal, but the luminance characteristics and sensory I of the cathode ray tube are
are almost canceled out, and a good image in which the relationship between the video signal level and sensation is nearly linear can be obtained. Note that only when gradation accuracy is particularly required, a nonlinear element is inserted into the video amplifier to correct the error (γ
correction). On the other hand, in matrix displays such as liquid crystals and plasma displays, linearity cannot be obtained between the video signal level and the sensation, resulting in an unnatural image in which white parts are compressed.

As a countermeasure for this problem, the input/output characteristics of the video amplifier are corrected in the same way as in conventional cathode ray tube televisions. It will be necessary to do so. This is because it is technically extremely difficult to provide a video amplifier, which is a broadband amplifier from DC to 4MHz, with strong nonlinear input/output characteristics, and even if it were possible, it would not be suitable for mass production and would be expensive.

An object of the present invention is to provide a matrix display device that can easily obtain arbitrary brightness modulation characteristics.

The display device according to the present invention provides a plurality of brightness modulation pulse generators corresponding to the number of gradations, and defines the delay of each brightness modulation pulse from a synchronization signal at irregular intervals to obtain desired brightness modulation characteristics. It is.

FIG. 1 is a block diagram showing one embodiment of the present invention. The video signal V is linearly amplified by a video amplifier AMP to become a video signal A, and then the video signal level is quantized at predetermined intervals by an AD converter (analog-to-digital converter) ADC to produce a digital video signal DV.
and input it to the line memory MEM to store the digital value for one scanning line period. On the other hand, the video signal V is also applied to the sync separation circuit SSP, and the sync signal SY is extracted from the sync separation circuit SSP. scanning circuit SC
is the matrix display panel that receives the synchronization signal SY.
Scan electrode drive pulse X applied to the scan electrode of MXD
occurs. This drive pulse X always selects one scanning electrode and sequentially switches the selection state from top to bottom in synchronization with the synchronization signal SY. The details of the brightness modulation pulse generator PG will be explained later, but the synchronization signal SY
Thus, k (the number of gradation levels) brightness modulation pulses BM delayed by τk (K=1 to N) at unequal intervals are generated. These brightness modulation pulses BM define the brightness B of each pixel of the matrix display panel MXD. The selection switch MPX is composed of multiple integrated circuits called multiplexers or selects, and each multiplexer selects one of the luminance information for one scanning line period stored in the line memory MEM (MEM
one of the parallel video signal PV outputs) is input, and one brightness modulation pulse of the brightness modulation pulses BM is selected according to its digital value and applied to the corresponding column electrode of the matrix display panel MXD. The output of the selection switch MPX is called a signal electrode drive pulse Y, and controls the brightness B of the matrix display panel MXD. Further, the parallel video signal PV is updated every scanning line, and in synchronization with this, the selection state of the signal electrode drive pulse Y is also sequentially switched, so that a two-dimensional image is displayed on the matrix display panel MXD.

FIG. 2 is a specific circuit diagram of the brightness modulation pulse generator PG in a liquid crystal display, and FIG. 3 shows its operating waveforms. In Figure 2, the variable resistor VR, monostable multivibrator MMV, and logic gate EOR (exclusive OR) are the components of the brightness modulation pulse generator PG, and these have a number of gray levels N
When the monostable multivibrator MMV
N pieces of MMV ₁ to MMV _N , N pieces of EOR of EOR ₁ to EOR _N , and N of variable resistors of VR ₁ to VR _N are provided. The pulse width of monostable multivibrator MMV is MMV ₁ to
MMV _N differs from each other, and its pulse width is set at unequal intervals.

The circuit operation of FIG. 2 will be explained in detail using FIG. 3. The synchronizing signal SY is a pulse with a period of 1H (H is one scanning line period) and a width of 0.5H. Monostable multivibrator MMV _k (k = 1 to N) is a synchronization signal
Width τk triggered on the rising and falling edges of SY
generates a pulse PM _k of τk can be set to any value between 0 and 0.5H by variable resistor VR _k , and k=
They differ from each other between 1 and N. Also, logic gate
EOR _k is the output of monostable multivibrator MMV _k
By performing exclusive OR operation of PM _K and synchronization signal SY, brightness modulation pulse BM ₁ as shown in Fig. 3 is obtained.
Output BM ₂ , ...BM _k ...BM _N. That is, BM _k has a waveform obtained by delaying the synchronizing signal SY by τk.

FIG. 4 is a specific circuit diagram of the line memory MEM and selection switch row MPX shown in FIG. 1.

MPX _j and MPX _j+1 are selection switch rows, respectively.
This shows one of the MPX. Here j=
1, 2, 3... The line memory MEM outputs parallel video signals PV j and PV j+1, which are digital values of the line memories LM _j and LM _j+1 , and outputs the parallel video signals PV _j and PV _j+1 , which are the digital values of the line memories LM j and LM j+1, and outputs the parallel video signals PV _j and PV _j+1 according to the line memory MPX _j Decoders DEC _i and DEC _j decode the signal to close one switch in each of MPX _j+1 and select the luminance signal BM to drive signal electrodes to the j column and j+1 column electrodes of the matrix display panel MXD. Add pulses Y _j and Y _j+1 . At this time, the brightness modulation pulse BM _k is selected by the selection switch MPX _j (j=1,
2, 3...) Input. MPX _j is a switch made of semiconductor, which decodes the parallel video signal PV _j (digital code of several bits), closes the corresponding switch, and outputs one of BM ₁ , BM ₂ , BM _k . . . BM _N.
One is connected to the signal electrode drive pulse _Yj .

FIG. 4 shows an example where PV _j = "1" and PV _j+1 = "k". When PV _j = “1”, BM ₁ becomes the output of Y _j ,
When PV _j+1 = “k”, BM _k becomes the output of Y _j+1 .

FIG. 5 summarizes the entire sequence. Figure 5 shows cells (i, j) of the liquid crystal display panel in Figure 1.
This is a sequence exemplified when the cell (i+1, j) has a brightness of k, the cell (i+1, j) has a brightness of 1, and the cell (1+2, j) has a brightness of k. PV _j = “k” in period T ₁ , PV _j = “1” in period T _i+1 , and PV _j = “1” in period T _i+2.
This is an example of “k”.

Furthermore, in FIG. 5, the driving pulse X _i of the i-th scanning electrode, the driving pulse X _i +
The waveforms of the driving pulses X i+ ₂ for the _1st and i+2th scanning electrodes are shown.

During the period _{T i ,} a pulse synchronized with SY exists in the selected state, and the first half 0.5H of T _i has an amplitude of 3 _vp , the second half 0.5H has -vo, and the period T other than the period T _{i i+
1} , T _i+2, etc., the amplitude of X _i becomes vo. X _i+1
During the period T _i+1 , a pulse synchronized with SY exists in the selected state, and the amplitude is 3vo for the first half of 0.5H of T _i+1 , and −vo for the second half of T i+1, except for the period T _i+1. The period T _i ,
At T _i+2 , etc., the amplitude of X _i+1 becomes vo. During the period T _{i+2 ,} a pulse synchronized with SY exists in the selected state, and the first half of T _i+2 is 0.5H with an amplitude of 3vo, and the second half with an amplitude of 3vo.
0.5H becomes -vo, and periods T i and _{T i other} than the period T _{i +2
+1} , etc., the amplitude of X _i+2 becomes vo.

At this time, the driving pulse Y _j of the j-th signal electrode
is the amplitude during 0.5H in periods T _i , T _i+1 , T _i+2
2vo, the amplitude becomes 0 during the other 0.5H. In periods T _i and T _i+2 , corresponding to PV _j =“k”, the Y _j pulse is delayed by the time τk with respect to the SY pulse. In period T _{i +1} , corresponding to PV _j = “1”, τk = 0, and the Y _j pulse is synchronized with the SY pulse.

The voltage applied to the cell (i, j) of the liquid crystal display pulse is (X _i − Y _j ), the voltage applied to the cell (i+1, j) is (X _{i +1} − Y _j ), and the voltage applied to the cell (i+2, j) is The voltage is (X _i+2 −Y _j ), and an example of each waveform is shown in FIG.

The voltage (X
_i - Y _j ), periods T _i+1 , T _i+2 other than the period T _i
etc., the amplitude is constant at ±vo. In period T _i , the amplitude is 3 vo only during τk when the first half is 0.5H, and the amplitude is −3 vo only during τk when the second half is 0.5H.
Here, for example, the brightness B of the liquid crystal cell is determined depending on the actual period of the applied voltage, and for example, the larger the effective value of the applied voltage, the brighter it becomes. From this, in period T _i , the amplitude of |X _i −Y _j | is 3vo only during 2τk.
Therefore, the larger τk is, the larger the effective value becomes, the brightness B becomes higher, and the cell (i, j) has a brightness corresponding to the brightness k.

In the voltage (X _j+1 - Y _j ) applied to the cell ( _{i +1} , j) in FIG _. The amplitude is ±vo in the period of
is constant. That is, the cell (i+1,j) has a brightness corresponding to the darkest brightness (k=1).

In the voltage (X _j+2 - Y _j ) applied to the cell (i+2, j) in FIG. 5, a period T other than the period T _i+2
i , T _i+1, etc., the amplitude is constant at ±vo. In period T _i+2 , the amplitude is only during τk at 0.5H in the first half.
3vo, amplitude -3vo only during τk at 0.5H in the second half
become. From this, in the period T _i+2 , the amplitude of |X _i+2 −Y _j | increases to 3vo only during 2τk, so the larger τk is, the higher the brightness B becomes, and the brightness of the cell (1+2,j) increases. The brightness corresponds to k.

FIG. 6 shows the relationship between τk and brightness modulation characteristics. As shown in FIG. 6, the video amplifier AMP has linear characteristics, and the input V and output A are proportional. Figure 6 2
shows the characteristics of the AD converter ADC, and the output DV
Since is a digital value, it is almost linear except for the fact that quantization errors occur and the input/output characteristics become step-like. FIG. 6 3 shows the characteristics of the brightness modulation pulse generator PG, and the variable resistor VR _k (k
=1 to N) to obtain a nonlinear characteristic (unequal intervals) of ^τk∝k3 . Figure 6 4 shows the relationship between brightness B and human sense of brightness I, where I∝B ^1/3
Then, Fig. 6 5 is a composite characteristic that combines the characteristics shown in Fig. 6 1 to 4, and a proportional relationship holds between the video signal voltage V and the brightness sense I, excluding the quantization error, and the sense You can get more natural images.

Furthermore, the size of the quantization error is visually the same for both white and black parts of the image. On the other hand,
As shown in the graph of the conventional correction in FIG. 7, when the video amplifier AMP is made non-linear, the quantization error in the overall characteristic becomes large near black. Therefore, in the conventional method, it is necessary to further increase the number of gradations in order to make the quantization error less noticeable, whereas in the case of the present invention, the quantization error is less noticeable even with the same number of gradations. The number of display gradations can be reduced by that amount.

In the above embodiments, the case of a liquid crystal display is shown, but it can also be applied to a plasma or EL display. In this case, pulse PM _k
It is the same as a liquid crystal display in that the brightness is determined by the pulse width τk of the control pulse, and the only difference is the driving waveform.

As explained above, in the matrix display device according to the present invention, the luminance of the matrix display panel is adjusted at irregular intervals (nonlinearly) in the luminance modulation pulse generator.
Multiple brightness modulation pulses that can be prescribed to
BM _k is generated and these are generated according to the value of the video signal V.
Since one of the BM _k is selected and the selected pulse is applied to the matrix display pulse, it is easy to obtain nonlinear brightness modulation characteristics by nonlinearizing the brightness modulation pulse generator that handles frequencies as low as the horizontal scanning frequency. can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the matrix display device according to the present invention, FIG. 2 is a circuit diagram showing a specific embodiment of the luminance modulation pulse generator and selection switch in FIG. 1, and FIG. Figure 2 is an operating waveform diagram, Figure 4 is a circuit diagram of the line memory and selection switch row, Figure 5 is an operating waveform diagram of each part, and Figure 6 is the circuit diagram of the line memory and selection switch row.
A graph showing the input/output characteristics of each block in the figure, FIG. 7 is a graph for explaining a conventional matrix display device. V...Video signal, SY...Sync signal, SC...Scanning circuit, AMP...Video amplifier, A...Video signal, PG...Brightness pulse generator, SSP...Sync separation, ADC...A/
D converter, BM...Brightness modulation pulse, DV...Digital video signal, MEM...Line memory, PV...Parallel video signal, MPX...Selection switch row, X...Scanning drive pulse, Y...Signal electrode drive pulse, MXD...Matrix display panel.

Claims (1)

[Claims] 1 A matrix display panel having scanning electrodes and signal electrodes, a scanning circuit that selectively drives the scanning electrodes of this matrix display panel in synchronization with a synchronization signal of a video signal, and a brightness modulation pulse generator that generates N brightness modulation pulses delayed by τk (k = 1 to N);
A matrix display device comprising: a selection switch that selects one of the luminance modulation pulses according to the level of a video signal and applies the selected one to a signal electrode of the matrix display panel.