JP2630961B2 - Display device - Google Patents

Description

The present invention relates to a display device, and more particularly, to a display device using a ferroelectric liquid crystal for a display panel.

[Summary of Disclosure] The present specification and the drawings relate to a display device using a ferroelectric liquid crystal for a display panel, a voltage holding circuit that holds a plurality of set voltages based on a plurality of voltage setting information in a power supply unit,
A plurality of operational amplifiers for generating a positive potential or a negative potential based on the fixed potential by obtaining a differential from the fixed potential, and a drive voltage using these set potentials as applied voltage information Output from each unit to each electrode drive unit, without increasing the withstand voltage of the information electrode drive unit, a potential generation method that effectively outputs the maximum drive voltage within the withstand voltage. It discloses a technique for preventing a decrease in operation speed and performing appropriate temperature compensation of a drive voltage.

[Prior art] At present, when a TN (Twisted Nematic) type liquid crystal is used for a display panel, especially for a large display panel in which scanning electrodes and information electrodes are arranged in a matrix, the driving voltage generation method is usually as follows. It is like. That is, as shown in FIG. 7A, the display electrode 71 is provided on the display panel 71.
And the information electrode driving unit 73 are connected so that a source voltage V _DD and a drain voltage V _SS are respectively applied thereto. Here, as shown in FIG. 7 (b), a plurality of resistors are connected in series between the voltage V _DD and the voltage V _SS, and the divided voltage values V ₂ , V ₅ , V ₄ , V ₃ , to generate a V _6. Figure R _V is a trimmer for changing the voltage applied to the liquid crystal, the partial pressure value by adjusting the trimmer R _V is V ₂ ~V ₆ to stretch the V _DD = V ₁ as the top voltage. The scan electrode driving unit 72 supplies divided voltage values V ₁ , V ₂ , V ₅ , V
₆ is supplied, the information partial pressure value V ₁ was to the electrode driving portion 73, V _2, V
_3, V ₄ is supplied. Trimmer R _V is used to adjust the contrast. At this time, since (V _DD -V _SS ) is applied as the power supply voltage of the scan electrode driver 72 and the information electrode driver 73, the voltage applied to the liquid crystal pixels at the time of selection is (V ₁ -V ₂ ). The maximum applied voltage to the pixel depends on the breakdown voltage of both driving units. Normally, a withstand voltage of, for example, about 18v to 22v is practically used, and the liquid crystal is driven within this range.

On the other hand, various proposals have been made for a driving method of a ferroelectric liquid crystal. For example, in Japanese Patent Application Laid-Open Nos. 59-193426 and 60-33535, a driving method as shown in FIG. It is shown. In FIG. 8, the scanning electrode driving and the information electrode driving are centered on the applied voltage central potential V _C , and V ₁ : V ₂ : V ₃ : V
₄ = 2: 2: 1: 1 is performed with a fixed ratio waveform, the amplitude of the scan electrode drive waveform is (V ₁ −V ₂ ), and the amplitude of the information electrode drive waveform is (V ₃ −V ₄ ). That is, (V ₁ −V ₂ ) / 2. V in the figure
Is the applied voltage of the electric field applied to the pixel, and ΔT is the application time required to reverse the orientation of the pixel. Here, similarly to the driving method of the TN type liquid crystal, V _DD (V ₁ ) is fixed to the highest potential, and the divided voltage values V ₃ , V _C , V ₄ , V ₂ are generated to generate the ferroelectric liquid crystal. When driving is considered, the maximum applied voltage that can be applied to the pixel is (V ₁ −V ₄ ). Specifically, V _DD -V _SS = 22v
Then, V ₁ = 22v, V ₃ = 16.5v, V _C = 11v, V ₄ = 5.5v, V ₂ = 0
With v, the maximum applied voltage to the pixel is 16.5v.

As described above, even if the withstand voltage of the driving unit is the same (for example, 22 V), the maximum applied voltage to the pixel differs between the TN type liquid crystal and the ferroelectric liquid crystal due to the difference in the driving method. Will be smaller.

[Problems to be Solved by the Invention] The characteristics of the ferroelectric liquid crystal require high-speed switching and further improvement of a wide operating temperature range, but they greatly depend on an applied voltage.

FIG. 9 is a characteristic graph showing the relationship between the drive voltage and the application time, and FIG. 10 is a characteristic graph showing the relationship between the temperature and the drive voltage. In FIG. 9, the horizontal axis represents the drive voltage shown as the applied voltage V in FIG. 8, and the vertical axis represents the pulse width also shown as the application time ΔT. As can be seen from the figure, the higher the drive voltage V, the shorter the pulse width ΔT may be. In FIG. 10, the temperature Temp is plotted on the horizontal axis, the drive voltage V is plotted on the horizontal axis, and the threshold voltage _Vth accompanying the temperature change is shown with the pulse width ΔT fixed, but as the temperature Temp drops. It is clear from the figure that the threshold voltage _Vth rises. According to FIGS. 9 and 10, when the applied voltage is increased, higher-speed switching and a wider operating temperature range can be obtained.

However, if a driver IC with a higher withstand voltage is designed to obtain a drive voltage required for driving, another problem occurs in that the operation speed of the logic circuit unit in the information electrode driver becomes slow. The reason is that, in general, when the design is made to increase the breakdown voltage, the pattern width of the driver IC and the size of the active element become large, the capacitance component becomes huge, and the propagation delay time becomes long. When the operation speed is reduced, the amount of video information that can be transferred within a predetermined horizontal scanning period decreases, and as a result, it becomes difficult to realize a large-sized and high-definition liquid crystal display having a large number of pixels.

According to FIGS. 9 and 10, appropriate temperature compensation must be performed in consideration of the threshold value in controlling the drive voltage. In this case, the pulse width ΔT That is, the driving conditions in which the driving voltage V and the like are related to each other greatly vary depending on the temperature, and the range of the driving conditions allowed at a predetermined temperature is narrowly limited. Finely manually adjusting the pulse width and drive voltage for changing temperatures is a very difficult task and wastes time and effort.

SUMMARY OF THE INVENTION The present invention has been made in view of such a problem, and a drive voltage is reduced by a potential generation method that effectively outputs a maximum drive voltage within a general withstand voltage without increasing a withstand voltage of an information electrode drive unit. It is another object of the present invention to provide a ferroelectric liquid crystal display device that prevents a decrease in operation speed due to an increase in breakdown voltage and that performs appropriate temperature compensation of a drive voltage.

[Means for Solving the Problems] In the present invention, a display panel, a scan electrode drive unit and an information electrode drive unit for driving the display panel, and a scan electrode drive unit and an information electrode drive unit A power supply unit for supplying a voltage for driving the display panel, wherein the power supply unit samples and holds a plurality of set voltages set based on a plurality of voltage setting information, and the plurality of settings A plurality of operational amplifiers that take a difference between the voltage and the fixed voltage, and a first voltage having a positive polarity and a second voltage smaller than the first voltage corresponding to each difference with reference to a reference potential; What is claimed is: 1. A display device comprising: a circuit for generating a third voltage having a negative polarity and a fourth voltage smaller than the third voltage, wherein the scan electrode drive circuit and the information electrode drive circuit are provided from the power supply unit. When the voltage of the reference potential is supplied to the In addition, the first voltage and the third voltage are supplied only to the scan electrode driver among the scan electrode driver and the information electrode driver, and the second and third voltages are supplied to the information electrode driver. 4. A display device characterized by supplying a voltage of 4 with respect to the fixed potential, in which two of the four types are on the positive side with respect to the fixed potential and the other two are on the negative side. Is set in the power supply section,
When the display panel has a temperature sensor, the control unit instructs each drive unit and the power supply unit to perform a change setting corresponding to the temperature measurement data, and a current amplifier is provided at each of a plurality of drive voltage output stages of the power supply unit. The present invention is a display device which is a suitable display device, and whose main object is that the optical modulation element is a ferroelectric liquid crystal element.

[Operation] In the present invention, in a power supply unit to be supplied to a drive unit, four set voltages generated from four kinds of voltage setting information are differentiated from a predetermined fixed potential with each set voltage. Accordingly, the V ₁ and V ₃ as a positive units, based on the solids potential V _C, generates a V ₂ and V ₄ as a negative potential, to generate these four potential as the driving voltage, further, the display panel And the set voltage is changed and set in accordance with the temperature.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a configuration diagram showing an example of a display device embodying the present invention. In FIG. 1, a display device uses a ferroelectric liquid crystal as an optical modulation element, a display panel 1 in which scanning electrodes and information electrodes are arranged in a matrix, a scanning electrode driving unit 2 for driving those electrodes, and an information electrode. A driving unit 3;
A control unit 4 for controlling the driving units 2 and 3;
And a power supply unit 5 for supplying a voltage to the power supply 2 and 3. The power supply unit 5
Voltages V _DD1 , V _SS1 , V _DD2 , GND, V _SS2 , V required for operation of the driver
_SS3 and voltages V ₁ , V ₃ , V _C , V ₄ , and V ₂ required for the pixel are generated based on voltages + V and −V from an external power supply (not shown) and supplied to the driving units 2 and 3. .

Each of the scan electrode drive unit 2 and the information electrode drive unit 3 includes a logic circuit unit and an output stage circuit unit (both not shown). In the scan electrode drive unit 2, (V _DD1 −V _SS1 )
The logic circuit section is operated at a voltage of (V _DD1 −V _SS3 ), and the output stage circuit section is operated at a voltage of (V _DD1 −V _SS3 ).
_The logic circuit section is operated at the voltage of ( _DD2- GND), and the output stage circuit section is operated at the voltage of ( _VDD2 - _VSS2 ).

In the present embodiment, the operation speed of the logic circuit unit in the scan electrode drive unit 2 is about 30 KHz, the maximum use rating is a 36V breakdown voltage process IC, and the operation speed of the logic circuit unit in the information electrode drive unit 3 is 5 MHz. Is an 18V breakdown voltage process IC. Thereby, the relationship between the operating potential and the driving potential was set as shown in FIG. In the figure, the control signals S ₁ as an input level (+ 5V-GND) voltage, (V _DD1
−V _SS1 ) = (14V−9V), (V _DD1 −V _SS3 ) = (14V − (−
22V)), (V _DD2 -GND) = (5V-0V), (V _DD2 -V _SS2 )
= (5V-(-13V)). From the operating potential setting as described above, the fixed potential among the driving potentials is
V _C was determined to be −4V. Therefore, each variable range is V ₁ =
_{-4V~ + 14V, V 3 = -4V~} + 5V, V 4 = -4V~-13V, V 2 = -4
V to -22V.

In this embodiment, the display panel 1 is provided with a temperature sensor 6. A temperature-sensitive resistance element is used as the temperature sensor 6, the measurement result is detected by the A / D converter 7, and the temperature measurement data is taken into the control unit 4. In the control unit 4, temperature measuring data is compared with data table which is prepared in advance, the pulse width ΔT is determined to be the optimum drive condition by the comparison value, the scan electrode driving from the control unit 4 in the form of control signals S ₁ It is output to the section 2 and the information electrode driving section 3. At the same time, the driving voltage V which is the optimum driving condition
Is also determined, output from the control unit 4 to the D / A converter 8, converted into an analog value by the D / A converter 8, and then input to the power supply unit 5. The power supply unit 5 includes a voltage holding circuit 51, an operational amplifier 52, and a current amplifier 53.
1, a V _1, for V _2, for V _3, made independent four circuits for V _4, the operation of which a desired V _1, V _2, V ₃ and V ₄ is D / A
When the voltage is sequentially output from the converter 8, the voltage is sampled and then held, whereby an operation is performed in which four potentials are set.

The data table is created in consideration of the characteristics shown in FIGS. 9 and 10, and FIG. 3 is a characteristic graph obtained by plotting the data. In FIG. 3, the horizontal axis represents the temperature Temp, and the vertical axis represents the drive voltage V and the frequency f (f = 1 / ΔT). Here, if the fixed frequency f in the temperature range (A), the temperature Temp is the drive voltage V is lowered increases, exceeds the V _min. Therefore, if a larger frequency f is set to a fixed value at the temperature point (D) in the figure, the drive voltage V is determined correspondingly, and the temperature range (B), (C) and the temperature point (E) are hereinafter determined. However, the same operation is repeated.

The shape of the curve formed as described above differs depending on the characteristics of the liquid crystal, and the linearity of the frequency f and the drive voltage V can be set as appropriate. In particular, fine control is usually performed on the drive voltage V, and various proposals have been made. However, as in the conventional example shown in FIG. 8, V ₁ : V ₂ : V ₃ : V ₄ has a fixed ratio. Instead, there is also a driving method implemented with a variable ratio potential relationship. There is also a drive system that also employs a variable ratio for temperature compensation.

FIG. 4 is a circuit diagram showing an example of the power supply unit of the present invention. The power supply unit in FIG. 4 is provided with a means for changing the drive voltage according to a change in temperature, and is composed of four stages: an amplifier, a voltage holding circuit, an operational amplifier, and a current amplifier. As already mentioned, set voltage data D _i, after being converted to an analog value is transmitted in the form of a digital signal from the control unit 4 to the D / A converter 8, V ₁ V ₂ amplifier 50a and V ₃ V ₄
The voltage is input to the voltage holding circuit 51 via the amplifier 50b.

FIG. 5 is a procedure diagram showing an example of a control operation of sampling the set voltage and holding the voltage in the voltage holding circuit 51. Control procedures, as shown in FIG. 5, first, in advance by setting the set voltage for V ₁ to the D / A converter 8, from the control unit 4
By outputting a sampling signal V ₁ to V ₁ voltage holding circuit 51a, and sampling hold to the circuit 51a, to hold the set voltage upsilon ₁ for V _1. Below, voltage holding circuit
51b, 51c, in 51d, repeating a similar operation, each set voltage upsilon _2, upsilon _3, holds the upsilon _4.

Now, the voltage holding circuit 51a, 51b, 51c, voltage upsilon ₁ was set to _{51d, υ 2, υ 3,} υ 4 includes an operational amplifier 52a, 52 shown in FIG. 4
b, 52c, 52d. Operational amplifiers 52a, 52b, 5
Reference numerals 2c and 52d denote differential amplifiers that take a difference with the fixed potential V _C = −4 V. In the present embodiment, each holding voltage is −4 V ≦ υ ₁ , υ ₂ ≦ 14 V,
-4 V ≦ upsilon _3, has a voltage range upsilon ₄ ≦ 5V. Therefore, the potential generated by the operational amplifiers 52a, 52b, 52c, 52d is −4V ≦ V
_{1 ≦ 14V, -4V ≦ V 2} ≦ 22V, -4V ≦ V 3 ≦ 5V, -4V ≦ V 4 ≦ -13V
The potential in the range shown below is taken.

The operational amplifier 52a, occurred 52 b, 52c, at 52d and V _C voltage follower OP amplifier 52e potential, current amplifier 53a connected to the respective, 53b, 53c, 53d, through 53e, the output V ₁ , V _C , V ₂ are supplied to the scan electrode driver 2 and output
V ₃ , V _C , and V ₄ are supplied to the information electrode driving unit 3. Current amplifier
53a, 53b, 53c, 53d, 53e are provided to stably supply required power.Since TN type liquid crystals generally have a small capacitive load, simply provide a parallel capacitor for each voltage dividing resistor. However, in the case of ferroelectric liquid crystal, the voltage drop due to load switching cannot be ignored because it takes a very large capacitance value.In order to eliminate this, the power supply capacity must be increased and regulation must be improved. Therefore, a current amplifier must be provided. Although not shown, in order to prevent a voltage drift, an ordinary circuit configuration feeds back the output of each current amplifier to the buffer OP amplifier of the differential amplifier.

In the above embodiment, the circuit configuration for holding the analog voltage as the voltage holding method, the present invention is of course not limited to this, and it holds the digital voltage setting data D _i from the control unit 4 It is also possible to set the voltage. FIG. 6 is a circuit diagram of a voltage holding circuit showing such a configuration example. In FIG.
When a sampling signal SH ₁ -SH ₄ is sent from the control unit 4, V
For _1, a V _2, for V _3, the data register 61a for V _4, 61b, 61c, 61
The voltage setting data _Di is stored in d. The data of the data register is stored in the D / A converters 62a, 62b, 62c, 6
Through 2d, the holding voltage _{υ 1, υ 2, υ 3} , are outputted as upsilon _4.

According to the present invention described above, for V _1, for V _2, V
For _3, upsilon ₁ generated from the voltage configuration information for _{V 4, υ 2, υ 3} , υ 4
Voltage holding and the fixed potential V _C, referenced to a fixed potential V _C by take a differential, respectively, V _1, V ₃ is positive potential
When, it is possible to generate and V _4, V ₂ is a negative potential, according to this generation method, the breakdown voltage of the scan electrode driver and the information electrode driver Unlike min pressure system of the conventional resistor is different Also, the maximum drive voltage can be output effectively within the respective breakdown voltages. Further, since the four types of drive potentials can be independently varied, the degree of freedom of drive voltage control in temperature compensation is increased. Furthermore, since it is not necessary to increase the withstand voltage of the information electrode drive unit more than necessary, it is not necessary to consider a high withstand voltage IC process that lowers the operation speed.

[Effects of the Invention] As described above, according to the present invention, the drive voltage can be reduced by the potential generation method that effectively outputs the maximum drive voltage within the general withstand voltage without increasing the withstand voltage of the information electrode drive unit. In addition, it is possible to prevent a decrease in operation speed due to an increase in breakdown voltage, and to provide a ferroelectric liquid crystal display device that performs appropriate temperature compensation of a drive voltage.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of one embodiment of the present invention, FIG. 2 is an explanatory diagram of operating potential and driving potential, FIG. 3 is a temperature characteristic diagram of driving voltage and frequency, and FIG. FIG. 5 is a circuit diagram of a voltage holding circuit of the present invention, FIG. 7 is a circuit diagram of a voltage holding circuit of the present invention, FIG. 7 is a configuration diagram of a conventional example, and FIG. FIG. 9 is a characteristic diagram of drive voltage and application time, and FIG. 10 is a characteristic diagram of temperature and drive voltage. 1,71 display panel, 2,72 scanning electrode drive unit, 3,73 information electrode drive unit, 4 control unit, 5 power supply unit, 6 temperature sensor, 7 A / D converter, 8 D / A converter, 51 voltage holding circuit, 52 operational amplifier, 53 current amplifier.

Claims (5)

(57) [Claims] 1. A display panel, a scan electrode drive section and an information electrode drive section for driving the display panel, and a power supply for supplying a voltage for driving the display panel to the scan electrode drive section and the information electrode drive section A voltage holding circuit that samples and holds a plurality of set voltages set based on a plurality of voltage setting information; and a plurality of units that obtains a difference between the plurality of set voltages and a fixed voltage. And a first voltage having a positive polarity, a second voltage smaller than the first voltage, a third voltage having a negative polarity, and a third voltage corresponding to each difference with respect to the reference potential. A circuit for generating a fourth voltage smaller than the third voltage, wherein the power supply unit supplies a voltage of the reference potential to the scan electrode drive circuit and the information electrode drive circuit unit. And the scanning electrode driving section and the information electrode. A display characterized in that the first voltage and the third voltage are supplied only to the scan electrode driving unit among the driving units, and the second and fourth voltages are supplied to the information electrode driving unit. apparatus. 2. The display device according to claim 1, wherein said power supply section includes a current amplifier for current-amplifying an output of said operational amplifier to generate said positive and negative voltages. 3. The display device according to claim 1, wherein said voltage setting information changes according to an output from a temperature sensor. 4. The voltage holding circuit according to claim 1, wherein said voltage holding circuit includes a register for storing said voltage setting information and a D / A converter.
The display device according to item. 5. The display device according to claim 1, wherein said display panel is a ferroelectric liquid crystal display panel.