JPH05333821A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide the liquid crystal display device which maintains picture quality without crosstalk called a shadow even in a high-resolution (high-duty) display with a small operation margin P and obtains a screen of high quality. CONSTITUTION:A driving waveform deviates from a voltage-averaging driving method owing to actual characteristics (frequency characteristics, electrode resistance, connection resistance, driving driver ability, display pattern, etc.) of the liquid crystal display device. Charging and discharging currents to liquid crystal cells of LCDPANEL which are generated by the switching of the driving of a driver are supplied from path controllers C.S1-C.S4, and C.C1-C.C4, fluctuations of the output are reduced, and the characteristics are approximated to the ideal voltage-averaging driving method. Then the driving waveform approach the logical waveform and the screen of high quality having no crosstalk is obtained. Consequently, an inexpensive display which has high picture quality and high definition can be mounted on a word processor, a personal computer, a work station, etc.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a word processor, personal computer,
The present invention relates to a liquid crystal display device that serves as a display unit of an information processing device such as a workstation.

[0002]

2. Description of the Related Art In a conventional liquid crystal display device, as shown in FIG. 13, there is no bypass capacitor in the intermediate liquid crystal power source of V1 to V4 in a place near the driver, and even if there is, it is between V0 and V5, and it is in a place far from the driver. Capacitors were only used to stabilize power supply voltage levels.

[0003]

In the above prior art, the impedance on the layout of the pattern on the substrate cannot be ignored, and the output of the driver fluctuates due to the charging / discharging current to the liquid crystal cell generated by the driving switching. As a result, the deviation from the theoretical voltage averaging drive method is largely caused, which is a cause of causing crosstalk, which is commonly referred to as a shadow. Low resolution area with a large operation margin P of the liquid crystal display element (display duty n = less than 200)
Then, I got a good screen without much trouble. (Here, the liquid crystal display element refers to a portion in which liquid crystal is sandwiched by a pair of electrodes, and the liquid crystal display device refers to the entire portion including a driver portion.) However, in a high resolution region exceeding n = 200. The operating margin P is small (about 7.3
The optimum driving voltage could not be applied to the liquid crystal display element. The theoretical optimum bias ratio β that maximizes the operation margin P is given by the following equation, where n is the display duty.

[0004]

[Equation 1]

However, the actual effective value varies depending on the characteristics of the actual liquid crystal display device (frequency characteristics, electrode resistance, connection resistance, drive driver capability, display pattern, etc.). As a result, crosstalk called threading occurs and the image quality deteriorates, and a high-quality screen cannot be obtained. Therefore, the present invention solves such a problem, and an object of the present invention is to provide an image quality without crosstalk called thread pulling (shadow) even in high resolution (high duty) display in which the operation margin P becomes small. An object of the present invention is to provide a liquid crystal display device that can maintain a high quality screen.

[0006]

A liquid crystal display device according to the present invention is characterized in that a decap having good high frequency characteristics is inserted near a driver in a power supply line of an intermediate level of a liquid crystal power supply.

[0007]

[Operation] Here, the basic driving is confirmed. V0-V
Let 1 be v, which represents the magnitude of the non-selected pulse. The voltage when not selected is v. First, according to the theoretical effective value of the voltage averaging method, the effective value Von of the ON dot is expressed by the following equation.

[0008]

[Equation 2]

The effective value Voff of the OFF dot is shown by the following equation.

[0010]

[Equation 3]

The operation margin P is expressed by the following equation.

[0012]

[Equation 4]

The value β of a at which the operation margin P becomes maximum is the following equation already shown.

[0014]

[Equation 5]

The above is the generally known theoretical formula.

According to the structure of the present invention, the charge / discharge current to the liquid crystal cell generated by the driving switching of the driver is supplied from the decap connected to each power supply level to reduce the fluctuation of the output and to reduce the theoretical voltage. It can approach the averaging drive method. Therefore, even in a high-resolution (high-duty) display in which the operation margin P becomes small, the image quality can be maintained without crosstalk called a threading (shadow), and a high-quality screen can be obtained.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. The driving method will be described.

First, the positive voltage of the liquid crystal power source is given as V (+), and the negative voltage is given as V (-). This voltage is converted into 6-level voltage (V0 to V5) by the elements R1-R2-VR1-R3-R4-R5. V1
Voltage followers OPAMP1 to 4 may be used for V4. R1, R2, R4 and R5 use the same resistance value. The magnitude of the voltage of V0-V5 thus obtained is represented by av, and the magnitude of the pulse applied to the selected ON dot of the liquid crystal display element is represented. FIG. 9 shows a specific display pattern. The driving duty is n and the display capacity is m × n dots. Scan electrode is COM1
~ COMn. Signal electrodes are SEG1 to S
It is represented as EGm. A portion formed by an area where one scanning electrode and one signal electrode intersect is referred to as a display dot. Optical response vs. voltage threshold 2 (Vth2) in FIG.
Display dots that exceed the threshold are shown in black and are called ON dots, and display dots that do not exceed the threshold 1 (Vth1) are shown in white.
It is called FF dot. Display pattern is SEG1
The alphabet "E" is displayed at the intersections of ~ SEG4 and COM1-COM5. Further, SEG5 has no ON dot. SEG6 is ON at the intersection with COM1
Dots are present. SEG7 is ON dot and OFF
Dots are present alternately.

FIG. 10 shows the theoretical SEG1 and COM of FIG.
The applied voltage of the intersection of 1 is shown over the screen writing time (1 frame period T). The reference potential is CO
I am in M1. The voltage of the period av of the selection period tu is applied, the voltage of v is applied during the period of 4tu in which scanning is performed from COM2 to COM5, and the voltage of -v is applied during the period of scanning in the remaining COM6 to COMn. However, due to various characteristics of an actual liquid crystal display device, it is general that the waveform is rounded as shown in FIG. A curve-like change close to an exponential function occurs when each voltage level is switched.
FIG. 5 shows the display dots of the present invention and FIG. 7 of the conventional liquid crystal display device as a simple equivalent circuit. E corresponds to the liquid crystal drive voltage of av or v. R represents electrode resistance, connection resistance, driver resistance, liquid crystal resistance, and the like. C indicates the capacitance of the display dot. Vc5 represents the applied voltage of the display dot of the present invention. Vc7 indicates the applied voltage of the conventional display dot. S
W indicates the switching of the voltage by the driver. C. PA
S indicates the capacitor of the present invention. R. LIN represents the internal resistance of the power supply, the resistance of the wiring (routing), and the like. FIG. 6 shows the present invention, and FIG. 8 shows how the conventional display dot voltages Vc5 and VC7 change with time tu. Area 1 shows the loss voltage for display dot C, and area 2 shows the effective voltage. The voltage Vc5 of the liquid crystal display device of the present invention is C.C. PAS is shown by the following equation as a sufficiently large capacity.

[0020]

[Equation 6]

The voltage Vc7 of the conventional liquid crystal display device is expressed by the following equation.

[0022]

[Equation 7]

Therefore, according to the present invention, as shown in FIG. 6, the liquid crystal display device according to the present invention can rise faster than the conventional liquid crystal display device shown in FIG.

Here, the actual capacitance value will be roughly understood.

First, the electrostatic capacity C of the display dot is expressed by the following equation, where the dot size (horizontal) × (vertical) is xxymm, the distance between electrodes is d, the relative permittivity of the liquid crystal is ε, and the permittivity of vacuum is ε0. Indicated by.

[0026]

[Equation 8]

Therefore, the capacity of the panel (the capacity of the entire screen) C
The panel has the following formula with gn pixels.

[0028]

[Equation 9]

A numerical value is applied to each parameter to calculate the actual capacity of the panel. Resolution 640x
At 480, the pixel pitch is 0.3 × 0.3 mm, the dot gap is 30 μm, ε is 4 and the electrode distance d is 7 μm. The dielectric constant of vacuum is the value of the following formula.

[0030]

[Equation 10]

By substituting the above into the equations 8 and 9, the result of the following equation is obtained.

[0032]

[Equation 11]

It is considered preferable that the decaps attached to each power supply line of this exemplified panel should be about 0.1 μF or more. This calculation is a theoretically simplified case, and the actual required capacitance varies depending on the characteristics of the actual liquid crystal display device (frequency characteristics, electrode resistance, connection resistance, drive driver capacity, display pattern, etc.). Moreover, the cost of a typical ceramic capacitor of the decap increases as the capacitance increases. Therefore, it is necessary to select the optimum value in consideration of the cost and the actual effect when selecting the capacity value. Our actual result is about 0.01 to 10 μF.

In the conventional liquid crystal display device, electric charges are supplied from a power source E as shown in FIG. Therefore, the internal resistance of the power supply and the R.R. Due to the LIN, a large voltage drop occurred near the driver according to the transient current. For this reason, the output voltage of the driver fluctuates greatly every time it is switched, and the ideal voltage level cannot be applied for the ideal period. Further, the currents I71 and I72 that can be supplied cannot be increased because the impedance on the power supply side is large.
Then, as shown in FIG. 8, large waveform rounding occurs. On the other hand, in the present invention, as shown in FIG. Since it is supplied from PAS, the supplied current I51 becomes small, and the internal resistance of the power supply and the routing resistance R.I. The voltage drop due to LIN is small. Further, since the impedance on the power supply side can be lowered, the current I52 that can be supplied becomes large. As a result, as shown in FIG. 6, the output voltage of the driver is stabilized, and it is possible to apply a voltage close to ideal with little waveform rounding.

FIG. 2 shows an embodiment in which a decap is connected to each line of V0 to V5 with V0 as a reference. The effect is great when V (+) is a strong power line.

FIG. 3 shows an embodiment in which a decap is connected to each line of V0 to V5 with V5 as a reference. The effect is great when V (-) is a strong power line.

FIG. 4 shows V0 with reference to both V0 and V5.
It is an example in which a decap is connected to each line of V5.
The effect is great when both V (+) and V (-) are strong power lines.

In addition to the above embodiments, the optimum combination can be applied to individual products.

[0039]

As described above, the present invention provides a liquid crystal display device capable of maintaining a high quality image without crosstalk called "threading" (shadow) even in a high resolution (high duty) display with a small operation margin P and obtaining a high quality screen. Made it possible. As shown in FIG. 5, the charging / discharging current I5 from the power source is
1 can be reduced from the conventional charge / discharge current I71. This is the resistance R. The energy lost in the LIN is reduced, and the power consumption of the liquid crystal display device can be reduced. Furthermore, by preventing the liquid crystal power supply level from reversing, driver latch-up is prevented and reliability is improved. This makes it possible to install inexpensive, high-quality, high-definition, low-consumption, highly reliable displays in word processors, personal computers, workstations, etc.

[Brief description of drawings]

FIG. 1 is a block circuit diagram of an embodiment in which a bypass capacitor is connected between liquid crystal power supply voltage supply lines according to the present invention.

FIG. 2 is a block circuit diagram of an embodiment in which a decap is connected to each line of V0 to V5 with reference to V0 of the present invention.

FIG. 3 is a block circuit diagram of an embodiment of the present invention in which a decap is connected to each line of V0 to V5 with V5 as a reference.

FIG. 4 shows V0 based on both V0 and V5 of the present invention.
FIG. 8 is a block circuit diagram of an embodiment in which a bypass capacitor is connected to each line of V5.

FIG. 5 is a diagram modeling a liquid crystal display device of the present invention.

FIG. 6 is a diagram showing drive waveforms applied to display dots of the present invention.

FIG. 7 is a diagram modeling a conventional liquid crystal display device.

FIG. 8 is a diagram showing drive waveforms applied to conventional display dots.

FIG. 9 is a display pattern diagram illustrating an operation of the present invention.

FIG. 10 is a diagram showing a theoretical drive waveform.

FIG. 11 is a diagram showing an actual drive waveform.

FIG. 12 shows a photoresponse vs. voltage illustrating the operation of the present invention.

FIG. 13 is a block circuit diagram of a conventional liquid crystal power supply voltage supply line.

[Explanation of symbols]

R1 to R5. Fixed resistors OPAMP1-4. Operational amplifier V (+). Liquid crystal positive power supply V (−). Liquid crystal negative power source V0 to V5. Liquid crystal drive voltage level SEGDr1 to. Signal electrode driver COMDr1 to. Scan electrode driver LCD PANEL. Liquid crystal display element SEG1 to m. Signal electrodes COM1 to n. Scan electrode T. 1 screen writing cycle tu. Selection period tu (n-1). Non-selection period E. Power supply modeled on liquid crystal drive voltage R. Resistance component between circuits (driver to liquid crystal cell) related to display dots C. Capacitance component SW of the circuit related to the display dot. A switch that models the driver's function a. Bias ratio P. Operating margin n. Display duty v. Non-selected voltage Von. ON dot effective voltage Voff. Effective voltage of OFF dot R. LIN. Internal resistance and routing resistance of power supply C. S1-C. S4. The bypass capacitor of the present invention placed near the segment driver C.I. C1-C. C4. The common capacitor placed near the common driver of the present invention. S. A conventional bypass capacitor placed near the segment driver. C. A conventional bypass capacitor Vc5. Voltage applied to the display dots of the present invention Vc7. Voltage applied to conventional display dots C.I. PAS. Pass-cap I51 placed near the driver. Current supplied from the power supply of the present invention I52. Current supplied to display dots of the present invention I53. Current supplied from the decap of the present invention I71. Current supplied from conventional power supply I72. Current supplied to a conventional display dot ε. Relative permittivity ε0. Vacuum permittivity x. Horizontal dot size y. Vertical dot size d. Electrode distance Cpanel. Panel capacitance gn. Total number of pixels on the panel

Claims (4)

[Claims] 1. A liquid crystal display device, wherein a bypass capacitor is connected between liquid crystal power source voltage supply lines in the immediate vicinity of a driver. 2. A liquid crystal display device according to claim 1, wherein a decap is connected to each line of V0 to V5 with V0 as a reference. 3. A liquid crystal display device according to claim 1, wherein a decap is connected to each line of V0 to V5 with V5 as a reference. 4. A liquid crystal display device according to claim 1, wherein a decap is connected to each line of V0 to V5 with reference to both V0 and V5.