Liquid crystal driver circuit and liquid crystal display device

Abstract
A matrix type liquid crystal display device has a function of suppressing power consumption without calling for an extra circuit arrangement such as the arrangement of storage capacitance and wiring to storage capacitance and without disposing new external components. A switch is disposed in the liquid crystal display device to temporarily short-circuit both column electrodes and common electrodes sandwiching a liquid crystal between them in synchronism with an alternation timing.
Description




BACKGROUND OF THE INVENTION




This invention relates to a technology for achieving lower power consumption in an active matrix type liquid crystal display device.




To prevent degradation of a liquid crystal, a matrix type liquid crystal display device for controlling a transmission factor (brightness) of each pixel at an effective value of an applied voltage has to employ so-called “alternation” in which the polarity of the applied voltage to the liquid crystal is inversed in a predetermined cycle. Since the liquid crystal is made of a dielectric in this instance, charging and discharging of the liquid crystal consume power in the alternation process described above.




U.S. Pat. No. 5,852,426 describes a method of reducing this power consumption. In this method, a switch is provided to change connection of liquid crystal driving electrodes to a liquid crystal driver circuit or to external storage capacitance. The switch selects the external storage capacitance in the first period of one scanning cycle and the liquid crystal driver circuit in the second period. When the external storage capacitance is sufficiently large, the driving voltage can be shifted to a substantial midpoint of the AC amplitude in the first period without consuming power. In consequence, power consumption can be reduced much more than when no means is employed.




U.S. Pat. No. 5,852,426 needs disposition of the storage capacitance outside the liquid crystal driver circuit. Therefore, to employ this method, a new circuit board design such as the arrangement of the storage capacitance and wiring to the storage capacitance becomes necessary, and the number of components increases, too.




SUMMARY OF THE INVENTION




It is an object of the present invention to provide a matrix type liquid crystal display device, and a driving method thereof, that can save power consumption resulting from alternation without disposing outside any component.




The present invention for solving the problem described above is based on the concept that a charge stored in a liquid crystal can be initialized to 0 (or substantially 0) when an A electrode and a B electrode sandwiching a liquid crystal between them are temporarily short-circuited at a timing of alternation as shown in FIG.


1


. In other words, the sequence having this short-circuit can shift the voltage to a substantial midpoint of alternation amplitude without consuming power. This means that the power-saving effect can be obtained in the same way as in U.S. Pat. No. 5,852,426 without involving the disposition of external components.




The liquid crystal display controller and the liquid crystal display device according to the present invention based on this concept provide switch means for temporarily short-circuiting both of column electrodes and common electrodes sandwiching a liquid crystal in synchronism with the timing of alternation to these electrodes. The present invention includes also means for setting a charge stored in the liquid crystal to or below a predetermined value in synchronism with the timing of alternation. The predetermined value includes 0 (or substantially 0).











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a circuit model of a liquid crystal that represents the concept of the present invention;





FIG. 2

is a block diagram showing a construction of a liquid crystal display device according to the first embodiment of the present invention;





FIG. 3

is a timing chart showing input signals for timing control in the first embodiment of the present invention;





FIG. 4

is a timing chart showing output signals for timing control in the first embodiment of the present invention;





FIG. 5

is a block diagram showing a column electrode driver unit and a common electrode driver unit in the first embodiment of the present invention;





FIG. 6

is a table useful for explaining the operation of a column voltage generation unit in the first embodiment of the present invention;





FIG. 7

is a timing chart showing operations of the column electrode driver unit and the common electrode driver unit in the first embodiment of the present invention;





FIG. 8

is a timing chart showing the operation of a row electrode driver unit in the first embodiment of the present invention;





FIG. 9

is a timing chart showing a liquid crystal applied voltage in the first embodiment of the present invention;





FIG. 10

is a block diagram showing a construction of a liquid crystal display controller according to the second embodiment of the present invention;





FIG. 11

is an explanatory view of input signals of a system interface in the second embodiment of the present invention;





FIG. 12

is a timing chart showing the operation of the input signals of the system interface in the second embodiment of the present invention;





FIG. 13

is a block diagram showing a construction of a cellular telephone set in the second embodiment of the present invention;





FIG. 14

is a timing chart showing the operation of a liquid crystal display device according to the third embodiment of the present invention;





FIG. 15

is a block diagram showing a construction of a row electrode driver unit in the third embodiment of the present invention;





FIG. 16

is a timing chart showing the operation of the row electrode driver unit in the third embodiment of the present invention;





FIG. 17

shows a circuit model that represents a structure of pixels in the fourth embodiment of the present invention;





FIG. 18

is a timing chart showing an applied voltage to a pixel unit in the fourth embodiment of the present invention;





FIG. 19

is a timing chart showing the applied voltage to the pixel unit in the fourth embodiment of the present invention;





FIG. 20

is a timing chart showing the operation of a row electrode driver unit in the fourth embodiment of the present invention; and





FIG. 21

is a timing chart showing an operation of a liquid crystal display device according to the fifth embodiment of the present invention.











DESCRIPTION OF THE EMBODIMENTS




Initially, the first embodiment of the present invention will be explained with reference to

FIGS. 2

to


9


.

FIG. 2

shows a construction of a liquid crystal display device according to the first embodiment. Referring to

FIG. 2

, reference numeral


201


denotes the liquid crystal display device according to the present invention. Numeral


202


denotes a timing control unit. Numeral


203


denotes a column electrode driver unit. Numeral


204


denotes a common electrode driver unit. Numeral


205


denotes a column electrode driver unit. A 3-terminal switch device, a liquid crystal cell and a holding capacitance are arranged at a position corresponding to each pixel of a pixel unit


207


. A drain terminal of the switch device is connected to a column electrode. Its gate terminal is connected to a row electrode and its source terminal, to the liquid crystal cell and the holding capacitance. The other terminal of the liquid crystal cell is connected to a common opposing electrode. The other terminal of the holding capacitance is connected to a common storage electrode. A common electrode driver unit


204


drives both of them. To achieve this connection, the column electrode, the row electrode and the storage electrode are formed in a matrix shape on the inner surface of one of the two transparent substrates that sandwich the liquid crystal between them. The common electrode is formed in a mat shape on the inner surface of the other transparent electrode.




Next, the operation of each block will be explained about the case where so-called “Vcom modulation drive”, in which the applied voltage to the common electrode is allowed to modulate, is conducted by way of example on the assumption that the liquid crystal display device


201


is scanned by a line sequential scanning system.




First, the timing control unit


202


receives a group of standard image input signals in a matrix type liquid crystal using a switch device (hereinafter called merely the “active matrix type liquid crystal”) from an external graphic controller


210


.

FIG. 3

shows a timing chart of the signal group. From the signal group FLM, the timing control unit


202


generates FLM representing a scanning start timing of a front scanning line, CL


1


representing a voltage application start timing to the column electrode and to the common electrode, EN representing a transfer period of effective display data for one scanning line, M representing the polarity of alternation, SHT representing an execution timing of short-circuiting, CL


3


representing a voltage application start timing to the row electrode, CL


2


representing a transfer clock of display data of each column in one scanning line and DT representing display data for one scanning line. The timing control unit


202


outputs these signals to the column electrode driver unit


203


, the common electrode driver unit


204


and the row electrode driver unit


205


. In this embodiment, DT is assumed to have 64 gray-scale information or 6 bits per pixel.




Next,

FIG. 5

shows an internal construction of the column electrode driver unit


203


and the common electrode driver unit


204


. In

FIG. 5

, reference numeral


501


denotes a data latch circuit. Numeral


502


denotes a column voltage generation circuit. Numeral


503


denotes a short-circuit switch A. Numeral


504


denotes a common voltage generation circuit. Numeral


505


denotes a short-circuit switch B. Inputs of the column electrode driver unit


203


are DATA, CL


1


, CL


2


, EN, M, SHT and column voltages V


0


to V


63


corresponding to 64 gray scales. Inputs of the common electrode driver unit


204


are M and VCOMH and VCOML (two kinds of voltage are necessary for alternation) as reference voltages of the common voltage. Incidentally, a power source circuit


206


generates the voltage level of each of V


0


to V


63


, VCOMH and VCOML on the basis of a VCC voltage inputted from outside. The mutual relation of each voltage level has the same setting as that of ordinary Vcom modulation drive, and the voltage is set to an optimal value in accordance with applied voltage-v-transmission factor characteristics of the liquid crystal.




First, in the column electrode driver unit


203


, the data latch circuit


501


stores DT for one row (one scanning line) in the High period of EN by use of CL


2


and repeats the operation of outputting altogether the data stored as LDT


1


to LDTn (hereinafter called generically “LDT”) in synchronism with CL


1


. The column voltage generation circuit


502


selects one of the column voltages V


0


to V


63


corresponding to the gray scale of the pixel in accordance with LDT of each column and the signal M and outputs it as VD (generically representing one of VD


1


to VDn).

FIG. 6

shows an example of this selection operation.




The short-circuit switch A


503


is a switch that selects either one of the terminal from the column voltage generation circuit


502


and the terminal from the common electrode in accordance with the signal SHT. It selects the common electrode when the signal SHT is High and the terminal of the column voltage generation circuit when the signal SHT is Low. The short-circuit switch A


503


outputs VX (generically representing VX


1


to VXn) to the respective column electrode.




Next, in the common electrode driver unit


204


, the common voltage generation circuit


504


selects VCOMH when the input signal M is High and VCOML when the signal M is Low, and outputs the selected signal as VCOMP. The short-circuit switch B


505


is a switch that selects whether or not the terminal from the common voltage generation circuit


504


is to be as such connected, in accordance with the signal SHT. The common voltage generation circuit


504


cuts off the connection when the signal SHT is High, connects the terminal when the signal is Low, and outputs the signal as VCOM to the common electrode and to the storage electrode.





FIG. 7

shows altogether the timing chart of the operations described above. As can be appreciated from

FIG. 7

, VX and VCOM are short-circuited and reach a certain equal potential level when SHT is High, are released from short-circuit when SHT falls thereafter to Low, and execute the ordinary driving operation. This is equal to the above-mentioned operation of saving power consumption.




Next, the operation of the row electrode driver portion


205


will be explained with reference to

FIGS. 2 and 8

. First, inputs of the row electrode driver unit


205


are FLM, CL


3


and VGON and VGOF as the reference voltages of the row voltage. Incidentally, the power source circuit


206


generates VGON and VGOFF on the basis of the VCC voltage that is inputted from outside. VGON has a voltage level at which the gate of the transistor connected to the row electrode is turned ON and VGOFF has a voltage level at which the gate is turned OFF. As shown in the timing chart of

FIG. 8

, the row electrode driver unit


205


acquires High of FLM at the rise of CL


3


, sequentially shifts this FLM in synchronism with CL


3


and outputs it as VY to the row electrode to sequentially shift the scanning line. This operation can be achieved by use of shift registers, for example.




In the liquid crystal display device shown in

FIG. 2

, for example, let's consider the liquid crystal applied voltages VLC


11


and VLC


12


at an intersection P


11


where the column to which VX


1


is applied intersects the row to which VY


1


is applied, and at an intersection P


12


where VX


1


and VY


2


intersect each other. It will be assumed hereby that the display data of P


11


and P


12


are (111111) and (100000) and the mode of the liquid crystal is the NB mode in FIG.


6


.





FIG. 9

shows the applied voltage waveforms of VLC


11


and VLC


12


. As can be seen from

FIG. 9

, after a difference voltage between VCOM and VX


1


is applied during the VGON period of VLC


11


and VLC


12


, the voltages at the end of the VGON period are held. Since the voltages at this time have the voltage levels corresponding to the display data, display can be accomplished in the same way as ordinary Vcom modulation drive.




Incidentally, the switching period of M is one scanning cycle in this embodiment. However, the switching period is not particularly limited but may be a plurality of scanning cycles. In such a case, it is preferred that SHT outputs High and Low for only the first one scanning period after switching of M and remains Low in other periods.




Next, the second embodiment of the present invention will be explained with reference to

FIGS. 10

to


13


. The second embodiment of the present invention represents an application example of the present invention to a liquid crystal display controller of a display memory built-in type. Referring to

FIG. 10

, reference numeral


1001


denotes a liquid crystal display controller. Numeral


1002


denotes a system interface. Numeral


1003


denotes a control register. Numeral


1004


denotes a timing generation unit. Numeral


1005


denotes an address decoder. Numeral


1006


denotes a display memory. Numeral


1007


denotes a column electrode driver unit. Numeral


1008


denotes a common electrode driver unit. Numeral


1009


denotes a row electrode driver unit. Numeral


1010


denotes a power source circuit. Numeral


1011


denotes a pixel unit comprising a plurality of pixels that are arranged in matrix.




First, the interface of the liquid crystal display controller is based on a so-called “MPU6800 Series” bus interface, for example. As shown in

FIG. 11

, CS representing chip selection, RS for selecting the address/data of the control register, E designating the enabling of the operation, RW for selecting write/read of the data and D as the actual value of the address/data are given as signals through a system bus. These control signals have a cycle for designating the address of the control register and a cycle for writing the data. The operations of the control signals in these cycles will be explained with reference to FIG.


12


. In the address designation cycle, CS is set to “Low”, RS, to “Low”, RW, to “Low” and D, to a predetermined address value. Thereafter, E is set to “High” for a predetermined period. In the data write cycle, on the other hand, CS is set to “Low”, RS, to “High”, RW, to “Low” and D, to a desired data. Thereafter, E is set to “High” for a predetermined period. Incidentally, these operations are programmed in advance by an operating system and application software for controlling the overall apparatus.




The system interface


1002


is the portion that decodes the control signals described above. The system interface


1002


outputs the signal for bringing the corresponding address into the write state in the address designation cycle to the control register


1003


and a data to be written in the data write cycle to the control register


1003


.




The control register


1003


brings the register having the designated address into the write state and stores the data in this register. Incidentally, the data to be written into the control register


1003


are various driving parameters such as resolution of the liquid crystal panel, the display data and the display position data. These data are written to separate addresses, respectively. The driving parameters stored in the control registers


1003


are outputted to each block, and the display data is outputted to the display memory


1006


.




The timing generation unit


1004


is a portion that generates by itself the timing signal group on the basis of the driving parameters given from the control register


1003


, and its content is substantially equal to the timing signal group shown in FIG.


4


. At the same time, the timing generation unit


1004


generates a read address of the display memory and outputs it to the address decoder


1005


.




The address decoder


1005


decodes the display position data given from the control register


1003


at the time of write of the display data and selects the bit line and the word line inside the corresponding display memory


1006


. The address decoder


1005


then outputs the display data given from the control register


1003


to the data line of the display memory


1006


and completes the write operation. At the time of read-out, on the other hand, the address decoder


1005


decodes the read address outputted by the timing generation unit


1004


and selects the word line inside the corresponding display memory. Thereafter, the display data for one line is collectively outputted from the data line of the display memory


1006


.




Incidentally, the read address described above is switched one line by line from the address at which the data of the leading line of the screen panel is stored, for example, and after the address of the final line, this operation is repeated while returning again to the leading line. The address switch timing of each line is in synchronism with CL


1


and the timing for outputting the address of the leading line is in synchronism with FLM. The address decoder


1005


has a so-called “arbitration function” that assigns priority for either of the write operation and the read operation when they occur simultaneously.




The column electrode driver unit


1007


is the portion that converts the display data of each column of one line read out from the display memory


1006


to a predetermined column voltage, and selects and outputs either one of the voltage output and the terminal from the common electrode. This unit


1007


can be accomplished by use of the column voltage generation circuit in combination with the short-circuit switch in the same way as the column voltage driver circuit


203


of the first embodiment shown in FIG.


5


.




The common electrode driver unit


1008


and the row electrode driver unit


1009


have the same construction and execute the same operation as those of the common electrode driver unit


204


and the row electrode driver unit


205


in the first embodiment. Therefore, the detailed explanation will be omitted. The timing generation unit


1004


and the power source circuit


1010


provide the input signal and the input voltage necessary for each block, respectively.




The operation of the liquid crystal display controller


1001


described above can accomplish the temporary short-circuit operation between the column electrode and the common electrode at the alternation timing as the feature of the present invention. Therefore, this embodiment can achieve lower power consumption in the same way as in the first embodiment.




The liquid crystal display controller


1001


according to the second embodiment can be applied to a cellular telephone set, for example.

FIG. 13

shows a block construction of the cellular telephone set. Referring to

FIG. 13

, reference numeral


1301


denotes a liquid crystal module including the liquid crystal display controller of this invention and the pixel unit. Numeral


1302


denotes an ADPCM CODEC circuit for compressing/expanding speech. Numeral


1303


denotes a speaker. Numeral


1304


denotes a microphone. Numeral


1305


denotes a keyboard. Numeral


1306


denotes a TDMA circuit for time division multiplexing the digital data. Numeral


1307


denotes EEPROM for storing a registered ID number. Numeral


1308


denotes ROM for storing a program. Numeral


1309


denotes SRAM for temporarily storing the data and providing a work area of a microcomputer. Numeral


1310


denotes a PLL circuit for setting a carrier frequency of a wireless signal. Numeral


1311


denotes an RF circuit for transmitting and receiving the wireless signals. Numeral


1312


denotes a system controlling microcomputer. In

FIG. 13

, the aforementioned driving parameters and display data are given from the system controlling microcomputer


1312


. These data are stored in ROM


1308


and SRAM


1309


, respectively. The detailed explanation of each block will be hereby omitted, but the construction shown in

FIG. 13

makes it possible to apply the liquid crystal display controller of the second embodiment to the cellular telephone unit.




Next, the third embodiment of the present invention will be explained with reference to

FIGS. 14

to


16


. To achieve lower power consumption at the row electrode driver unit, this embodiment contemplates to apply the short-circuit operation of the present invention. In the driving system of the ordinary active matrix type liquid crystal, the GON voltage shown in

FIG. 8

is higher than GND and GOFF is lower than GND. If the row voltage is temporarily short-circuited to GND on the basis of this voltage relationship as shown in

FIG. 14

, power consumption with the voltage shift to GND does not exist, and power consumption of the row voltage driver unit can be reduced. Therefore, the construction of the row electrode driver unit and its construction for accomplishing this operation will be explained with reference to

FIGS. 15 and 16

.





FIG. 15

shows the internal construction of the row electrode driver unit according to the third embodiment of the present invention. Numeral


1501


denotes the row electrode driver unit. Numeral


1502


denotes a row selection circuit. Numeral


1503


denotes a switch controlling circuit. Numeral


1504


denotes a short-circuit switch C. First, the row selection circuit


1502


is a portion that outputs VGON/VGOFF in the same way as the row electrode driver unit


205


in the first embodiment of the present invention. The row selection circuit


1502


acquires High of FLM at the rise of CL


3


, sequentially shifts the signal FLM in synchronism with CL


3


and outputs the signal so shifted as R (generically representing R


1


to Rm). The switch controlling circuit


1503


is a portion that controls the short-circuit switch C


1504


. Its inputs are FLM, CL


3


and SHTR. The switch controlling circuit


1503


outputs as such SHTR during the scanning period in which VGON is applied to the row and during one previous period, and outputs Low in other periods. The short-circuit switch C


1504


selects GND when the control signal SR (generically representing SR


1


to SRm) outputted by the switch controlling circuit


1503


is High, selects the terminal from the row selection circuit


1502


when the control signal SR is Low and outputs VY (generically representing VY


1


to VYm).

FIG. 16

shows altogether the operation timing chart of the operation for VY


2


, by way of example. As can be appreciated from

FIG. 16

, the row electrode driver unit


1501


according to the third embodiment of the present invention can accomplish the operation shown in FIG.


14


.




When combined with the first liquid crystal display device and the second liquid crystal display controller according to the present invention, the row electrode driver unit according to the third embodiment can further reduce power consumption.




Next, the fourth embodiment of the present invention will be explained with reference to

FIGS. 17

to


20


. Besides the structure shown in

FIG. 2

, the structure in which the terminal of the holding capacitance is connected to a preceding row of a given row is known as the pixel structure of the active matrix type liquid crystal as shown in FIG.


17


. When such a pixel structure is employed, it is customary to change the voltage waveform of GOFF in the same amplitude as that of the common voltage in order to keep the same potential relationship between the holding capacitance and the liquid crystal cell as shown in FIG.


18


. When the short-circuit operation of the present invention is applied to this driving method, the potential relationship between VCOM and VY becomes different in the short-circuit period in which SHT is High as shown in FIG.


19


. As a result, the charge stored in the holding capacitance migrates and power consumption increases. To solve this problem, the output of VY is brought into the high impedance (Hi-Z) state during the short-circuit period as shown in

FIG. 20

, for example. This operation can be easily accomplished when a switch is disposed inside the row electrode driver unit, for example, and connection of VY is cut off in match with High of SHT. In

FIG. 20

, VY becomes VGON in synchronism with the second CL


3


pulse and write of the column voltage is executed. The output is not brought into the Hi-Z state during this period because it does not have much technical meaning.




The fourth embodiment described above can acquire the power consumption saving effect in the same way as in the first to third embodiments in the pixel structure in which the terminal of the holding capacitance is connected to the row of a preceding stage of a given stage.




Though the foregoing embodiments have been explained about Vcom modulation drive by way of example, the present invention can be applied also to dot inversion drive and column inversion drive on the basis of the same concept.

FIG. 21

shows the voltage waveforms of the column voltage and common voltage in the drive systems as the fifth embodiment of the present invention.




The embodiments of the present invention provide the following effects in the active matrix type liquid crystal display device in which the effective value of the applied voltage controls the transmission factor (brightness) of each pixel:




The voltage can be substantially shifted to the midpoint of alternation magnitude without consuming power when the column electrode and the common electrode sandwiching the liquid crystal between them are temporarily short-circuited at the timing of alternation;




Power consumption can be saved when the applied voltage to the row electrode as the signal for selecting the row is temporarily short-circuited to GND; and




The power consumption reduction methods described above can be applied without unnecessary power consumption to the pixel structure for connecting the terminal of the holding capacitance to the row of a preceding stage of a given stage when the applied voltage to the row electrode is brought into the high impedance state during the short-circuit period described above.



Claims
  • 1. An active matrix type display device comprising:a display panel including column electrodes and row electrodes arranges in a matrix form, a common electrode disposed opposite to the column electrodes and the row electrodes, and pixel units disposed at intersection points between the column electrodes and the row electrodes, a pixel unit being connected to a column electrode, a row electrode and the common electrode; a common electrode driver circuit for outputting a common voltage to the common electrode, the common voltage being in common to the pixel units; a column electrode driver circuit for selecting a column voltage corresponding to display data applied externally, from among a plurality of column voltages corresponding to a plurality of gray-scales, and outputting the column voltage selected to the column electrodes; a row electrode voltage driver circuit for outputting a row voltage to the row electrodes, the row voltage causing the pixel units to be in an “ON” state; a power supply circuit for generating the common voltage, the plurality of column voltages and the row voltage, and for outputting the common voltage, the plurality of column voltages and the row voltage to the common electrode driver circuit, the column electrode driver circuit and the row electrode driver circuit, respectively; a first switching circuit disposed on the column electrodes between the pixel units and the column electrode driver circuit; and a second switching circuit disposed on the common electrode between the pixel units and the common electrode driver circuit, wherein: the first switching circuit switches into either connection between the column electrodes on a side of the pixel units and the common electrode, or connection between the column electrodes on the side of the pixel units and the column electrode driver circuit, when the second switching circuit is turned “OFF”, the first switching circuit makes connection between the column electrodes on the side of the pixel units and the common electrode without making connection between the column electrodes on the side of the pixel units and the column electrode driver circuit, and when the second switching circuit is turned “ON”, the first switching circuit makes connection between the column electrodes on the side of the pixel units and the column electrode driver circuit without making connection between the column electrodes on the side of the pixel units and the common electrode.
  • 2. The display device according to claim 1, wherein, when the first switching circuit makes connection between the column electrodes on the side of the pixel units and the common electrode, the column electrodes on the side of the pixel units and the common electrode are short-circuited with each other.
  • 3. The display device according to claim 1, wherein, for every one or more scanning periods, the first switching circuit makes connection between the column electrodes on the side of the pixel units and the common electrode during a predetermined period, and thereafter makes connection between the column electrodes on the side of the pixel units and the column electrode driver circuit.
  • 4. The display device according to claim 1, wherein:the pixel units perform switching operation of a potential to alternate between a positive polarity and a negative polarity for every one or more scanning periods, and the first switching circuit, in synchronism with the switching operation, makes connection between the column electrodes on the side of the pixel units and the common electrode during a predetermined period, and thereafter makes connection between the column electrodes on the side of the pixel units and the column electrode driver circuit.
  • 5. The display device according to claim 4, wherein, where the switching operation is performed for every plural scanning periods, the predetermined period is a first scanning period.
  • 6. A display driver circuit for driving an active matrix type display panel including column electrodes and row electrodes arranged in a matrix form, a common electrode disposed opposite to the column electrodes and the row electrodes, and pixel units disposed at intersection points between the column electrodes and the row electrodes, a pixel unit being connected to a column electrode, a row electrode and the common electrode, the display driver circuit comprising:a column electrode driver circuit for selecting a column voltage corresponding to a display data applied externally, from among a plurality of column voltages corresponding to a plurality of gray-scales generated by a power supply circuit; a first switching circuit disposed on the column electrodes between the pixel units and the column electrode driver circuit; and a second switching circuit disposed on the common electrode between the pixel units and a common electrode driver circuit; wherein: the first switching circuit switches into either connection between the column electrodes on a side of the pixel units and the common electrode, or connection between the column electrodes on the side of the pixel units and the column electrode driver circuit, when the second switching circuit is turned “OFF”, the first switching circuit makes connection between the column electrodes on the side of the pixel units and the common electrode without making connection between the column electrodes on the side of the pixel units and the column electrode driver circuit, and when the second switching circuit is turned “ON”, the first switching circuit makes connection between the column electrodes on the side of the pixel units and the column electrode driver circuit without making connection between the column electrodes on the side of the pixel units and the common electrode.
  • 7. The display driver circuit according to claim 6, wherein, when the first switching circuit makes connection between the column electrodes on the side of the pixel units and the common electrode, the column electrodes on the side of the pixel units and the common electrode are short-circuited with each other.
  • 8. display driver circuit according to claim 6, wherein, for every one or more scanning periods, the first switching circuit makes connection between the column electrodes on the side of the pixel units and the common electrode during a predetermined period, and thereafter makes connection between the column electrodes on the side of the pixel units and the column electrode driver circuit.
  • 9. The display driver circuit according to claim 6, wherein:the pixel units perform switching operation of a potential to alternate between a positive polarity and a negative polarity for every one or more scanning periods, and the first switching circuit, in synchronism with the switching operation, makes connection between the column electrodes on the side of the pixel units and the common electrode during a predetermined period, and thereafter makes connection between the column electrodes on the side of the pixel units and the column electrode driver circuit.
  • 10. The display driver circuit according to claim 9, wherein, where the switching operation is performed for every plural scanning periods, the predetermined period is a first scanning period.
Priority Claims (1)
Number Date Country Kind
2001-036303 Feb 2001 JP
US Referenced Citations (5)
Number Name Date Kind
5448384 Uchino et al. Sep 1995 A
5774099 Iwasaki et al. Jun 1998 A
5852426 Erhart et al. Dec 1998 A
5929847 Yanagi et al. Jul 1999 A
6172663 Okada et al. Jan 2001 B1
Foreign Referenced Citations (1)
Number Date Country
11-326863 Nov 1999 JP