Display and method of driving the same

In a display, a first liquid crystal panel has gate bus lines, source bus lines, TFTs, and pixel electrodes, as well as a source driver. A second liquid crystal panel has gate bus lines, source bus lines, TFTs, and pixel electrodes. The source bus lines of the second liquid crystal panel are connected to the associated source bus lines of the first liquid crystal panel through switching TFTs. The source bus lines of the second liquid crystal panel are briefly and repeatedly fed with a predetermined potential when the switching TFTs are off. The invention reduces power consumption of dual panel structure displays and prevents occurrence of an unintended display on the second display panel which is not expected to produce any display.

This Nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2004-123143 filed in Japan on Apr. 19, 2004, Patent Application No. 2005-036949 filed in Japan on Feb. 14, 2005, and the entire contents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to liquid crystal and like displays containing multiple active matrix display panels. The invention relates also to methods of driving these displays.

BACKGROUND OF THE INVENTION

Many recent mobile devices among others, especially foldable mobile phones, have two display panels, or so-called “dual panels.” As an example,FIG. 18shows a circuit diagram of dual panels581comprising a main panel582and a subpanel583.

The main panel582contains a TFT (thin film transistor) substrate584, an opposite substrate585, and a liquid crystal (LC) layer594. The TFT substrate584is a substrate carrying TFTs592thereon. The opposite substrate585is placed opposite the TFT substrate584. The LC594is a display medium interposed between the TFT substrate584and the opposite substrate585.

On the TFT substrate584are there provided gate bus lines588and source bus lines589. A TFT592is formed near each intersection of the gate bus lines588and the source bus lines589. The TFT592is connected to the gate bus line588at the gate, to the source bus line589at the source, and to a pixel electrode at the drain. Voltage is applied across the LC594in a pixel between the pixel electrode and an opposite electrode (COM)593on the opposite substrate585. This mechanism applies to every TFT592across the panel582, which enables image displays.

The main panel582further contains a gate driver590and a source driver591. Lead wires from the gate driver590are connected to the gate bus lines588. Those from the source driver591are connected to the source bus lines589. The gate driver590and the source driver591apply gate signal voltages and display data signals to the bus lines respectively.

In contrast, the subpanel583contains a TFT substrate586, an opposite substrate587, and a liquid crystal (LC) layer594. The TFT substrate586is a substrate carrying TFTs592thereon. The opposite substrate587is placed opposite the TFT substrate586. The LC594is a display medium interposed between the TFT substrate586and the opposite substrate587.

The subpanel583is connected to the main panel582through a FPC (flexible printed circuit; not shown) board. By virtue of this structure, gate signal voltages and display data signals are fed from the gate driver590and the source driver591in the main panel582to the bus lines in the subpanel583through wiring in the main panel582and the FPC board.

On the TFT substrate586are there provided gate bus lines588and source bus lines589. A TFT592is formed near each intersection of the gate bus lines588and the source bus lines589. The TFT592is connected to the gate bus line588at the gate, to the source bus line589at the source, and to a pixel electrode at the drain. Voltage is applied across the LC594in a pixel between the pixel electrode and an opposite electrode (COM)593on the opposite substrate587. This mechanism applies to every TFT592across the panel583, which enables image displays. Both the main panel582and the subpanel583can thus produce image displays.

Examples of prior art literature disclosing concrete dual panel devices include Japanese published patent applications 2001-067049 (Tokukai 2001-067049; published on Mar. 16, 2001), 2001-282145 (Tokukai 2001-282145; published on Oct. 12, 2001), and 2003-131250 (Tokukai 2003-131250; published on May 8, 2003, corresponding to U.S. Patent Application No. 2004/0246428; published on Dec. 9, 2004).

Tokukai 2001-067049 discloses a foldable mobile communications terminal with dual panels: a first liquid crystal display section (first liquid crystal display) and a second liquid crystal display section (second liquid crystal display). The mobile communications terminal is constructed so that a cover section (folder cover) opens/closes on a main body section. The first liquid crystal display section is provided on a face of the cover section which comes inside when the device is folded. The second liquid crystal display section is provided on another face of the cover section which comes outside when the device is folded. The first and second liquid crystal display sections are driven by one driver disposed on the first liquid crystal display section. The driver's outputs are fed to the second liquid crystal display section through the first liquid crystal display section. The second liquid crystal display section is smaller in display area than the first liquid crystal display section. See Tokukai 2001-067049, FIGS. 4, 5. The second liquid crystal display section shows the time and other rudimentary information. The first liquid crystal display section shows various information. In addition, when the cover section is closed, only the second liquid crystal display section produces displays. When the cover section is open, only the first liquid crystal display section produces displays.

Tokukai 2001-282145 discloses a foldable mobile phone with dual panels: a first liquid crystal display section (internal liquid crystal display section) and a second liquid crystal display section (external liquid crystal display section) similarly to Tokukai 2001-067049. The mobile phone is constructed so that a cover section (upper casing) opens/closes on a main body section (lower casing). The first liquid crystal display section is provided on a face of the cover section which comes inside when the device is folded. The second liquid crystal display section is provided on another face of the cover section which comes outside when the device is folded. The first and second liquid crystal display sections are driven by one driver disposed on the first liquid crystal display section. The driver's outputs are fed to the second liquid crystal display section through the first liquid crystal display section. The second liquid crystal display section is smaller in display area than the first liquid crystal display section. See Tokukai 2001-282145, FIGS. 3, 4. When the cover section is closed, only the second liquid crystal display section produces displays. When the cover section is open, only the first liquid crystal display section produces displays.

Tokukai 2003-131250 discloses a foldable mobile phone with dual panels: a first liquid crystal display section (LCD) and a second liquid crystal display section (LCD) similarly to Tokukai 2001-067049. The mobile phone is constructed so that a cover section (lid) opens/closes on a main body section. The first liquid crystal display section is provided on a face of the cover section which comes inside when the device is folded. The second liquid crystal display section is provided on another face of the cover section which comes outside when the device is folded. The first and second liquid crystal display sections are driven by one driver disposed on the first liquid crystal display section. The driver's outputs are fed to the second liquid crystal display section through the first liquid crystal display section. The second liquid crystal display section is smaller in display area than the first liquid crystal display section. See Tokukai 2003-131250, FIGS. 1, 10. The second liquid crystal display section displays a notice of an incoming call, the time and date, and other simple information. The first liquid crystal display section displays major information.

As detailed above, dual panel displays are widely applied to mobile phone and like mobile devices. Demand exists for low power consumption panels. The conventional devices are, however, short of addressing the issue properly.

SUMMARY OF THE INVENTION

The present invention, to address the issue, has an objective to offer a liquid crystal display which achieves sufficient reduction in power consumption and also to offer its drive method.

A display of the present invention is characterized in that it includes:a first display section including: gate signal lines; source signal lines; first switching elements provided near intersections of the gate signal lines and the source signal lines, control terminals for switching operation of the first switching elements being connected to the gate signal lines; and pixel electrodes connected to the source signal lines through the first switching elements;a source signal line drive circuit provided to the first display section to supply display data signals to the source signal lines;second switching elements containing semiconductor elements;a second display section including: the gate signal lines; source signal lines; first switching elements; and pixel electrodes, the source signal lines of the second display section being connected to the associated source signal lines of the first display section through the second switching elements, the second display section sharing the source signal line drive circuit with the first display section; anda predetermined potential supply section briefly and repeatedly supplying a predetermined potential to the source signal lines of the second display section when the second switching elements are off.

Another display of the present invention is characterized in that it includes:a first display section including: gate signal lines; source signal lines; first switching elements provided near intersections of the gate signal lines and the source signal lines, control terminals for switching operation of the first switching elements being connected to the gate signal lines; and pixel electrodes connected to the source signal lines through the first switching elements;a source signal line drive circuit provided to the first display section to supply display data signals to the source signal lines;second switching elements containing semiconductor elements;a second display section including: the gate signal lines; source signal lines; first switching elements; and pixel electrodes, the source signal lines of the second display section being connected to the associated source signal lines of the first display section through the second switching elements, the second display section sharing the source signal line drive circuit with the first display section; anda control section: controlling on/off operation of the second switching elements; causing the second switching elements to carry out recursive temporary switch-on actions where the second switching elements briefly and repeatedly switch on when the second switching elements are off; and causing the source signal line drive circuit to supply a predetermined potential to the source signal lines of the first display elements during the recursive temporary switch-on actions.

A method of driving a display of the present invention is characterized in that the method involves a display including a first display section and a second display section,the first display section including: gate signal lines; source signal lines; first switching elements provided near intersections of the gate signal lines and the source signal lines, control terminals for switching operation of the first switching elements being connected to the gate signal lines; and pixel electrodes connected to the source signal lines through the first switching elements,the second display section including: the gate signal lines; source signal lines; first switching elements; and pixel electrodes,the method including the steps of:connecting the source signal lines of the second display section to the associated source signal lines of the first display section through second switching elements containing semiconductor elements;supplying display data signals to the source signal lines of the second display section through the source signal lines of the first display section; andbriefly and repeatedly supplying a predetermined potential to the source signal lines of the second display section when the second switching elements are off.

Another method of driving a display of the present invention is characterized in that the method involves a display including a first display section and a second display section,the first display section including: gate signal lines; source signal lines; first switching elements provided near intersections of the gate signal lines and the source signal lines, control terminals for switching operation of the first switching elements being connected to the gate signal lines; and pixel electrodes connected to the source signal lines through the first switching elements,the second display section including: the gate signal lines; source signal lines; first switching elements; and pixel electrodes,the method including the steps of:connecting the source signal lines of the second display section to the associated source signal lines of the first display section through second switching elements containing semiconductor elements;supplying display data signals to the source signal lines of the second display section through the source signal lines of the first display section; andcausing the second switching elements to carry out recursive temporary switch-on actions where the second switching elements briefly and repeatedly switch on when the second switching elements are off; and supplying a predetermined potential to the source signal lines of the first display section during the recursive temporary switch-on actions.

According to the arrangement, when the first display section carries out a display operation, and the second display section stops a display operation, the second display section can be isolated from the first display section. Thus, the second display section does not act as an electrical load, and the power consumption can be lowered.

In addition, while the second display section is isolated from the first display section, that is, when the second switching elements are off, a predetermined potential is briefly and repeatedly supplied to the source signal lines of the second display section. Therefore, although even when the second switching elements containing semiconductor elements are turned off, the elements may suffer from current leak, possibly gradually changing the potentials of the source signal lines of the second display section, the source signal lines of the second display section are retained at the predetermined potential. Thus, the potential differences across the pixel electrodes and the opposite electrode become equal to a predetermined level in the second display section carrying out no display operation. No unintended display occurs which otherwise could be caused by the potential difference.

If the second switching elements did not carry out the recursive temporary switch-on actions while the second switching elements are turned off, the leak current through the second switching elements would cause the potentials of the source signal lines of the second display section to become equal to a mean value of the potentials of the source signal lines of the first display section carrying out a display operation. The mean value of the electrical potentials might slightly differ from one source signal line to the other depending on the display image produced on the first display section. In such a case, the potential differences across the pixel electrodes and the opposite electrode of the second display section would become non-uniform, resulting in the display screen of the second display section appearing visually undesirable. These issues are addressed, as described in the foregoing, by the recursive temporary switch-on actions which results in the predetermined potential being supplied to the source signal lines of the second display section.

DESCRIPTION OF THE EMBODIMENTS

The following will describe an embodiment of the present invention in reference to drawings.

FIG. 1shows a circuit diagram of a liquid crystal display (display)1of the present embodiment. The liquid crystal display1, as shown inFIG. 1, has a dual panel structure including a first liquid crystal panel (first display means)10and a second liquid crystal panel (second display means)20.

The first liquid crystal panel10contains a thin film transistor (TFT) substrate11, an opposite substrate12, and a liquid crystal layer. The TFT substrate11carries TFTs25thereon. The opposite substrate12is placed opposite this TFT substrate11. The liquid crystal layer is a display medium interposed between the TFT substrate11and the opposite substrate12. The liquid crystal layer is part of liquid crystal capacitors26.

On the TFT substrate11are there provided gate bus lines (gate signal lines)14and source bus lines (source signal lines)16. A TFT (first switching means)25is formed near each intersection of the gate bus line14and the source bus line16. The TFT25is connected to the gate bus line14at the gate, to the source bus line16at the source, and to a pixel electrode at the drain. Voltage is applied across the liquid crystal capacitor26in a pixel between the pixel electrode and an opposite electrode (COM)27on the opposite substrate12. This mechanism applies to every TFT25across the panel10, which enables image displays.

The second liquid crystal panel20contains a TFT substrate21, an opposite substrate22, and a liquid crystal layer. The TFT substrate21carries TFTs25thereon. The opposite substrate22is placed opposite the TFT substrate21. The liquid crystal layer is a display medium interposed between the TFT substrate21and the opposite substrate22. The liquid crystal layer is part of liquid crystal capacitors26.

On the TFT substrate21are there provided gate bus lines24and source bus lines16. A TFT25is formed near each intersection of the gate bus line14and the source bus line16. The TFT25is connected to the gate bus line24at the gate, to the source bus line16at the source, and to a pixel electrode at the drain. Voltage is applied across the liquid crystal capacitor26in a pixel between the pixel electrode and an opposite electrode (COM)27on the opposite substrate22. This mechanism applies to every TFT25across the panel20, which enables image displays.

InFIG. 1, the suffixes “-L, -M, -N” to the reference numerals for the source bus lines16and the gate bus lines14,24indicate line numbers of the lines. “L, M, N” represent the total number of the lines. The following description will not use the suffixes “-L, -M, -N” if the line in issue does not have to be any particular line.

In the liquid crystal display1of the present embodiment, those source bus lines16on the first liquid crystal panel10correspond respectively to those source bus lines16on the second liquid crystal panel20. To be more specific, those source bus lines16which correspond to the gate bus lines14can conduct to those source bus lines16which correspond to the gate bus lines24, and vice versa, via a switch section19and a FPC (flexible printed circuit) board30. The board30is an example of a flexible connect member. The switch section19is provided on the first liquid crystal panel10. The FPC board30is provided between the first liquid crystal panel10and the second liquid crystal panel20. The location of the switch section19is not limited to the first liquid crystal panel10. The section19may be provided on the second liquid crystal panel20or between the first liquid crystal panel10and the second liquid crystal panel20.

The switch section19contains switching TFTs (second switching means)17and a switching control signal line18. Each source bus line16has its own switching TFT17. The switching TFT17connects/disconnects the source bus line16on the first liquid crystal panel10and the source bus line16on the second liquid crystal panel20. The switching control signal line18is formed in parallel with the gate bus lines14to feed the gates of the switching TFTs17with a switching control signal that turns on/off the switching TFTs17. The switching control signal is supplied from a source driver (source signal line drive circuit, predetermined potential supply means)15to the switching control signal line18.

The first liquid crystal panel10and the second liquid crystal panel20include gate drivers (scan signal line drive circuits)13,23dedicated respectively to drive the gate bus lines14,24. Also, the first liquid crystal panel10and the second liquid crystal panel20share a common source driver15to drive the source bus lines16. The gate drivers13,23output a gate signal (gate select signal) to the gate bus lines14,24. The source driver15outputs display data signals to the source bus lines16. The source driver15is provided on the first liquid crystal panel10and supplies the display data signals to the second liquid crystal panel20via the first liquid crystal panel10.

If the liquid crystal display1is incorporated in a single device, the first liquid crystal panel10is used to produce displays more frequently (more hours) than the second liquid crystal panel20. For example, in the applied device, the first liquid crystal panel10is used to show the time, current status of the device, and other basic information. On the other hand, the second liquid crystal panel20is used to show information in more detail (detailed information) than the first liquid crystal panel10. The display operation of the panel20is triggered by a user input.

Specifically, in a foldable mobile phone40, a cover section (second housing section)42is formed so that it can open/close on the main body section (first housing section)41as shown inFIGS. 2(a),2(b), for example. The first liquid crystal panel10is provided on a face of the cover section42which comes outside when the phone40is folded. The second liquid crystal panel20is provided on a face of the cover section42which comes inside when the phone40is folded.FIG. 3shows a major part of this cover section42in a vertical cross-section. As shown in the figure, the first liquid crystal panel10and the second liquid crystal panel20are disposed back to back inside the cover section42.

As described in the foregoing, in the liquid crystal display1, the source driver15is disposed on the first liquid crystal panel10which is used to produce displays more frequently. The two display panels (first and second liquid crystal panels10,20) are driven by one drive circuit (source driver15). Moreover, the switch section19can electrically isolate the two display panels (first and second liquid crystal panels10,20) from each other.

The cover section42is open while, for example, the user is speaking over the mobile phone40, sending an email, or reading a received email on the mobile phone40. In these events, the display operation of the first liquid crystal panel10is turned off, whereas the display operation of the second liquid crystal panel20is turned on. In contrast, when the mobile phone40is standing by with the cover section42closed (the power supply is turned on), the display operation of the first liquid crystal panel10is turned on, and the display operation of the second liquid crystal panel20is turned off. Generally, the cover section42of the mobile phone40is closed longer than it is open, for example, during a 24 hour period. The result is the first liquid crystal panel10producing displays more frequently than the second liquid crystal panel20.

In the liquid crystal display1, when the cover section42is closed, only the display operation of the first liquid crystal panel10is turned on; the display operation of the second liquid crystal panel20is turned off. In this situation, all the switching TFTs17in the switch section19are turned off by the switching control signal from the source driver15. The source bus lines16on the second liquid crystal panel20are not fed with the display data signals from the source driver15. The gate driver13keeps operating; on the other hand, the gate driver23stops operating.

The source driver15outputs the switching control signal, for example, by the following procedures: The mobile phone40has an open/close detect switch (an example of open/close detect means; not shown). The switch detects, for example, a closed cover section42and sends a detection signal to control means (not shown). The control means produces instructions based on which the source driver15generates the switching control signal for output.

In contrast, when the cover section42is open, only the display operation of the second liquid crystal panel20is turned on; the display operation of the first liquid crystal panel10is turned off. In this situation, all the switching TFTs17in the switch section19are turned on by the switching control signal from the source driver15. The source bus lines16on the second liquid crystal panel20are fed with the display data signals from the source driver15. The gate driver13stops operating; on the other hand, the gate driver23keeps operating.

Next, the display operation of the first and second liquid crystal panels10,20will be described in more detail.

To produce a display on the first liquid crystal panel10, as shown inFIG. 4, the source driver15feeds the source bus lines16with the display data signals. Further, the gate driver13feeds the gate bus lines14with the gate signals switching on/off the TFTs25. In this situation, voltage goes HIGH on a gate bus line14, switching on the TFT25connected to that gate bus line14. The display data signal on the source bus line16is written to the pixel (liquid crystal capacitor26).

To produce a display on the first liquid crystal panel10, the gate bus lines14-1to14-M are addressed a line at a time, while the source bus lines16-1to16-L are being fed with the display data signals. This series of actions produces a frame. The series is repeated.

In this situation, the second liquid crystal panel20produces no displays. So, LOW voltage (switching control signal) is applied from the source driver15to the switching control signal line18. This turns off all the switching TFTs17in the switch section19and electrically isolates the source bus lines16(16-1to16-L) on the second liquid crystal panel20from the source bus lines16(16-1to16-L) on the first liquid crystal panel10. In addition, the gate bus lines24on the second liquid crystal panel20are not driven.

In the above operation, the load in the second liquid crystal panel20is electrically isolated when producing a display on the first liquid crystal panel10which produces displays more frequently. Therefore, the liquid crystal display1achieves lower power consumption.

In contrast, to produce a display on the second liquid crystal panel20, the display data signals are applied from the source driver15to the source bus lines16, and the gate signals are applied from the gate driver23to the gate bus lines24to switch on/off the TFTs25, as shown inFIG. 5. In this situation, as voltage on a gate bus line24goes HIGH, the TFT25connected to that gate bus line24is turned on. The display data signal on the source bus line16is written to the pixel (liquid crystal capacitor26).

To produce a display on the second liquid crystal panel20, the gate bus lines24-1to24-N are addressed a line at a time, while the source bus lines16-1to16-L are being fed with the display data signals. This series of actions produces a frame. The series is repeated.

Although the first liquid crystal panel10is currently producing no display, the display data signals need be applied to the second liquid crystal panel20. So, HIGH voltage (switching control signal) is applied from the source driver15to the switching control signal line18so as to turn on all the switching TFTs17in the switch section19. The gate bus lines14-1to14-M are however not driven.

In the above operation, the load in the first liquid crystal panel10cannot be electrically isolated in producing a display on the second liquid crystal panel20, which requires extra electric power. However, the second liquid crystal panel20is not used so frequently to produce a display. So, this situation happens only infrequently. In contrast, when the first liquid crystal panel10, often used to produce a display, is used for that purpose, the second liquid crystal panel20is electrically isolated. The liquid crystal display1thus achieves overall reductions in power consumption.

The foregoing loads are primarily due to the capacitance of insulating sections where they cross the gate bus lines14and the parasitic capacitance of the TFTs25, among other factors.

The layout of the first liquid crystal panel10and the second liquid crystal panel20in the mobile phone40is not limited to the one described above. An alternative example is, assuming that the mobile phone40is so constructed that the second housing section can open/close on the first housing section, to dispose: the first liquid crystal panel10so that when the second housing section is closed on the first housing section, the display plane of the panel10is on the outside face of either the first or second housing section; and the second liquid crystal panel20when the second housing section is closed on the first housing section, the display plane of the panel20on an inside face of either the first or second housing section. This is equally applicable to the relationship between a subpanel100and a main panel200which will be detailed later.

In the liquid crystal display1of the present embodiment, as described in the foregoing, the second liquid crystal panel20is isolated from the first liquid crystal panel10by the switch section19when producing a display not on the second liquid crystal panel20carrying no source driver15, but only on the first liquid crystal panel10carrying the source driver15. The isolation could entail inconveniences in producing a display on the second liquid crystal panel20. Details follow.

The resistance value of the switching TFT17in the switch section19is at least 1000 times as high when it is switched off as when it is switched on. This does not mean, however, that the switching TFT17would absolutely cease conducting on a switch-off: a certain level of leak current could flow. The leak current would gradually move the potential of the source bus line16on the second liquid crystal panel20which is currently not being driven, until that potential ultimately would become equal to the mean value of the voltage on the source bus line16on the first liquid crystal panel10which is being driven. The gradually changing voltage on the source bus line16would be applied to the drain of the TFT25on the second liquid crystal panel20, and in turn, to the pixel electrode connected to that drain. Resultant variations in the voltage across the pixel electrode and the opposite electrode could change the appearance of the second liquid crystal panel20accordingly. These voltage changes might cause an unintended display to appear on the second liquid crystal panel20which is not being driven. Please be reminded that the opposite electrode is fed with an opposite electrode voltage from, although not shown, an opposite electrode voltage supply circuit.

If the switch section19did not repeat temporary switch-on actions while the switch section19is switched off (while the second liquid crystal panel20is not performing a display operation), the leak current through the switching TFT17in the switch section19could cause the potential of the source bus line16on the second liquid crystal panel20to become equal to a mean value of the potential of the source bus line16on the first liquid crystal panel10which is currently performing a display operation. The mean value of the electrical potential might slightly differ from one source bus line16to the other depending on the display image produced on the first liquid crystal panel10. In such a case, the potential differences across the pixel electrodes and the opposite electrode on the second liquid crystal panel20would become non-uniform, resulting in the display screen of the second liquid crystal panel20appearing visually undesirable.

These problems are solved by the liquid crystal display1: the switch section19is briefly and repeatedly switched on (“recursive temporary switch-on actions”), for example, at a regular cycle, while producing a display on the first liquid crystal panel10, but not on the second liquid crystal panel20. The actions retain the source bus lines16on the second liquid crystal panel20at a predetermined potential.

FIG. 6is a block diagram illustrating an arrangement of the liquid crystal display1carrying out the actions. The source driver15and the gate drivers13,23are fed with necessary voltages from the power supply circuit51. The source driver15and the gate drivers13,23operate under control of the control circuit (control means)52.

FIG. 7is a timing chart illustrating output signals of the source driver15when the first liquid crystal panel10produces a display whereas the second liquid crystal panel20does not. The switch section19is not carrying out the recursive temporary switch-on actions.

InFIG. 7, the control signal S11and the control signal S12are a start signal and a clock signal for the gate driver13respectively. The control signal S21and the control signal S22are a start signal and a clock signal for the gate driver23respectively. The switching control signal S1is transferred to the switching control signal line18so as to control the switch on/off of the switch section19. The video signal S1is transferred to the source bus line16in accordance with information on an image display to be produced.

In the above case, the switching control signal S1stays unchanged at L level, keeping the switch section19switched off. The control signal S21and the control signal S22both stay unchanged at H level, resulting in the second liquid crystal panel20producing no scan signals. As to the video signal S1, each period which is equivalent to the number of the gate bus lines14on the first liquid crystal panel10is a valid image period; the rest is invalid periods. The potentials of the source bus lines16during invalid periods are not particularly specified.

FIG. 8is a timing chart illustrating output signals of the source driver15when the second liquid crystal panel20produces a display whereas the first liquid crystal panel10does not. In this situation, the recursive temporary switch-on actions of the switch section19has of course no relevance.

Consider the case shown inFIG. 8. During the valid image period, the switching control signal S1is at H level, keeping the switch section19switched on. The control signal S11and the control signal S12both stay unchanged at H level, resulting in the first liquid crystal panel10producing no scan signals.

FIG. 9is a timing chart illustrating output signals of the source driver15when the first liquid crystal panel10produces a display whereas the second liquid crystal panel20does not. The switch section19is carrying out the recursive temporary switch-on actions.

In the case, the switching control signal S1goes to H level briefly outside the valid image period. This leads to a recursive temporary switch-on action of the switch section19. The signal S1stays at L level for the rest of time. The video signal S1stays unchanged at a potential level for a period (“predetermined potential supply period”) which stretches at least across that period during which the switching control signal S1is at H level. The switch section19carries out a recursive temporary switch-on action for each vertical interval at a regular cycle outside the valid image period. The control signal S21and the control signal S22both stay unchanged at H level, resulting in the second liquid crystal panel20producing no scan signals.

This series of actions result in supplying a predetermined potential to the source bus lines16on the second liquid crystal panel20which is not expected to produce any displays. That is, the potential differences across the opposite electrode and the drains of the TFTs25, hence the pixel electrodes, are retained at a predetermined level. The appearance of the second liquid crystal panel20which is not expected to produce any displays is uniform across the screen and remains unchanged for some time. Unintended displays do not occur.

The recursive temporary switch-on actions of the switch section19do not necessarily occur at a regular cycle. They may occur at random intervals, provided that the timings offset voltage variations caused by the leak current or reduce such variations to a level where changes in the appearance of the display screen become unnoticeable. Nevertheless, carrying out one action for each vertical interval or for each integral multiple thereof is preferable in facilitating the control of the recursive temporary switch-on actions of the switch section19.

There are no particular limitations on the predetermined potential which is supplied to the source bus lines16on the second liquid crystal panel20as a result of the recursive temporary switch-on actions of the switch section19. The potential may be of any value provided that it makes the second liquid crystal panel20appear uniform (e.g. white, gray, or black) across the screen.

Adopting GND level as the predetermined potential however is preferable because it is easy to do so.

A preferred alternative is to adopt the potential of the opposite electrode as the predetermined potential. When this is the case, there is no potential difference across the opposite electrode and the pixel electrodes. This alternative is preferable for the following advantages: it takes an extended period of time for the leak current to reach a level where resultant potential variations can affect the appearance; the extended period allows for less frequent recursive temporary switch-on actions; and the less frequent actions in turn consumes less power.

In the alternative, the predetermined potential is not necessarily exactly equal to the potential of the opposite electrode. The two potentials can be regarded as being mutually equal if the potential differences across the opposite electrode and the pixel electrodes neither prompt reaction of the liquid crystal nor induce changes in the appearance of the second liquid crystal panel20. For example, TN mode liquid crystal does not react to the difference between the opposite electrode voltage and the predetermined voltage (pixel electrode voltage) on the source bus lines16if the difference is within 1 volt (within ±1 volt). The appearance of the display screen does not change. Other modes have other thresholds for the potential difference; a feasible range of the potential needs be selected in accordance with a particular mode.

The predetermined potential may be equal to the mean value of the voltage on the source bus line16on the first liquid crystal panel10which is being driven. This mean value refers to the voltage level reached by the voltage on the source bus line16on the second liquid crystal panel20due to the leak current if the switch section19does not carry out the recursive temporary switch-on actions as described earlier. Therefore, supplying the mean voltage to the source bus lines16on the second liquid crystal panel20allows for reductions in power dissipation caused by the leak current. The predetermined potential is obtainable with, for example, liquid crystal displays, because the source bus line16is fed with an AC voltage of a cycle, and the mean value of the AC voltage is known. For example, in AC drive where displays are produced while alternating the polarity of the voltage on the source bus line16as is the case with liquid crystal displays, basically, an AC intermediate voltage may be safely regarded as the mean value of the voltage. In DC drive, the mean value of voltage is obtainable, for example, through computation based on input data signals (adding up the data and dividing the sum by the number of lines). These approaches are mere examples. There are many other approaches to obtain the mean voltage value. Any of them may be used.

Furthermore, the predetermined voltage may be, for example, equal to one of the voltages, supplied from the power supply circuit51to the source driver15, which is the closest to the mean voltage value.

This alternative allows for reductions in the power consumed by the liquid crystal display1. If there is provided a separate circuit which gives an accurate mean voltage value, the circuit consumes power. In contrast, power consumption is reduced if the existing power supply circuit51is utilized to obtain one of its output voltages which is the closest to the mean voltage value as the predetermined voltage.

To apply the predetermined voltage (the closest voltage to the mean voltage) via the switch section19(switching TFTs17) from the source bus lines16on the first liquid crystal panel10to the source bus lines16on the second liquid crystal panel20as described in the foregoing, it is preferred to apply the predetermined voltage further to the opposite electrode (COM)27on the second liquid crystal panel20. The structure readily offsets the potential differences across the pixel electrodes and the opposite electrode.

The range of the closest voltage to the mean voltage is, for example, such that the effects of the leak current are not clearly visible across the display screen of the second liquid crystal panel20. For example, in TN mode, this condition is met if the predetermined voltage (pixel electrode voltage) applied to the source bus lines16differs from the opposite electrode voltage by 1 volt or less. If a potential difference across the pixel electrodes and the opposite electrode is 1 volt or less (±1 volt or less), liquid crystal in TN mode does not react to the potential difference, causing no changes in appearance. Other modes have other thresholds for the potential difference; a feasible range of the potential needs be selected in accordance with a particular mode.

The potential of the gate bus lines24is of less importance than the potential of the source bus lines16in preventing the leak current from causing an unintended display on the second liquid crystal panel20when the panel20is not expected to produce any displays. However, if there is such a large potential difference between the gate bus lines24and the opposite electrode that the effects of this potential difference can be seen on the second liquid crystal panel20, the potential of the gate bus lines24can be controlled similarly to the source bus lines16so that the potential of the gate bus lines24is close to that of the source bus lines16. To achieve this, the gate driver23needs to place the gate bus lines24at the same potential as the source bus lines16, while the predetermined potential is being applied to the source bus lines16through the recursive temporary switch-on actions of the switch section19. This prevents a situation where the potential difference between the gate bus lines24and the opposite electrode causes an unintended display near the gate bus lines24, and an uniform appearance is not obtainable across the screen. For the potential at which the gate bus lines24, as well as the source bus lines16, are placed, a similar tolerance range may be specified in accordance with TN or other mode as with the potential applied to the source bus lines16.

The structure where the gate driver23applies the predetermined potential to the gate bus lines24may be as follows. The gate driver23switches its outputs between ON and OFF voltages through the switches in ordinary display operation. Accordingly, the predetermined potential may be supplied as either the ON or OFF voltages with the gate driver23switching the outputs between the voltages through the switches.

The following will describe another embodiment of the present invention in reference to drawings.

A liquid crystal display (display)2of the present embodiment has a structure as inFIG. 10. That is, the liquid crystal display2has a dual panel structure: a subpanel (first display means)100and a main panel (second display means)200. The subpanel100and the main panel200are active matrix panels. The subpanel100and the main panel200include dedicated gate drivers113,123respectively to drive gate bus lines. The subpanel100and the main panel200also include a common source driver (source signal line drive circuit, predetermined potential supply means)115to drive source bus lines.

The outputs of the source driver115, or display data signals, are fed to the source bus lines on the main panel200through the source bus lines on the subpanel100. The source bus lines on the subpanel100are connected to the source bus lines on the main panel200, for example, through a FPC board30which is an example of a flexible connect member interposed between the panels.

The main panel200has more pixels and higher resolution than the subpanel100. Therefore, the main panel200has more source bus lines than the subpanel100. To this end, in the liquid crystal display2, each source bus line on the subpanel100corresponds to more than one source bus line on the main panel200. In other words, in the liquid crystal display2, a display data signal on each source bus line on the subpanel100goes through the time divisional drive section119before being transferred to more than one (e.g. two inFIG. 10) source bus lines on the main panel200. Specifically, the time divisional drive section119is built around selectors. The selector switches a display data signal on a source bus line on the subpanel100between more than one corresponding source bus lines on the main panel200by time division.

Thus, the source driver115provided on the subpanel100with fewer pixels drives the subpanel100by ordinary drive (non-time division drive) and the main panel200with more pixels by time division drive. This enables higher resolution displays on the main panel200than on the subpanel100.

In the liquid crystal display2, the subpanel100includes a TFT substrate11carrying TFTs25thereon, an opposite substrate12, and liquid crystal capacitors26containing a liquid crystal layer, similarly to the first liquid crystal panel10. On the TFT substrate11are there provided gate bus lines14, source bus lines16, and the TFTs25. The TFTs25apply voltage to the liquid crystal capacitors26which make up part of the pixels between pixel electrodes and an opposite electrode (COM)27provided on the opposite substrate12.

The main panel200includes a TFT substrate21carrying TFTs25thereon, an opposite substrate22, and liquid crystal capacitors26containing a liquid crystal layer, similarly to the second liquid crystal panel20. On the TFT substrate21are there provided gate bus lines24, source bus lines28, and the TFTs25. The TFTs25apply voltage to the liquid crystal capacitors26which make up part of the pixels between pixel electrodes and an opposite electrode (COM)27provided on the opposite substrate22.

In the liquid crystal display2of the present embodiment, the time divisional drive section119is disposed on the main panel200. The time divisional drive section119includes multiple switching TFTs17, one for each source bus line28on the main panel200. The switching TFT17is disposed at an end of the source bus line28facing the subpanel100.

In the liquid crystal display2, a display data signal on each one source bus line16on the subpanel100is transferred, for example, to two source bus lines28on main panel200by time division. Every two adjacent switching TFTs17are paired up. Current can be conducted from each source bus line16to the associated two source bus lines28through the pair of switching TFTs17which connects the bus lines16,28.

In addition, the time divisional drive section119includes a first switching control signal line18aand a second switching control signal line18b. The line18ais connected to the gate of a first switching TFT17of each pair. The line18bis connected to the gate of a second switching TFT17of each pair. The first and second switching control signal lines18a,18bare fed with a switching control signal to drive the switching TFTs17by time division. The drive of the switching TFT17connects the two source bus lines28to the associated source bus line16by time division.

Also, the time divisional drive section119is able to electrically separate the subpanel100(the source bus lines16on the subpanel100) from the main panel200(the source bus lines28on the main panel200).

It is preferable to place the time divisional drive section119on the main panel200, for example, for better wiring efficiency. This does not however forbid alternatives: the section119may be placed, for example, on the subpanel100or between the subpanel100and the main panel200.

The subpanel100is used to show the time, current state of the device, and other basic information, for example, in a device to which the subpanel100is applied. The main panel200is used to show information in more detail (detailed information) than the information displayed on the subpanel100. The display operation of the panel200is triggered by a user input.

Specifically, in a foldable mobile phone40, a cover section42is formed so that it can open/close on the main body section41as shown inFIGS. 2(a),2(b), for example. The subpanel100is provided on a face of the cover section42which comes outside when the phone40is folded. The main panel200is provided on a face of the cover section42which comes inside when the phone40is folded. Refer back toFIG. 3for a vertical cross-sectional view of a major part of the cover section42constructed in this manner. As shown in the figure, the subpanel100and the main panel200are disposed back to back inside the cover section42.

As described in the foregoing, in the liquid crystal display2, the source driver115is provided on the lower resolution subpanel100to drive the two display panels (subpanel100and main panel200) singly (by the source driver115). The time divisional drive section119drives the main panel200by time division. In addition, the two display panels (subpanel100and main panel200) can be separated.

The cover section42is open while, for example, the user is speaking over the mobile phone40, sending an email, or reading a received email on the mobile phone40. In these events, the display operation of the subpanel100is turned off, whereas the display operation of the main panel200is turned on. In contrast, when the mobile phone40is either standing by or not being used with the cover section42closed, the display operation of the subpanel100is turned on, whereas the display operation of the main panel200is turned off. Generally, the cover section42of the mobile phone40is closed longer than it is open, for example, during a 24 hour period. The result is the subpanel100producing displays more frequently than the main panel200.

In the liquid crystal display2, when the cover section42is closed, only the display operation of the subpanel100is turned on; the display operation of the main panel200is turned off. In this situation, all the switching TFTs17in the time divisional drive section119are turned off by the switching control signal from the source driver115. The source bus lines28on the main panel200are not fed with the display data signal from the source driver115. The gate driver113keeps operating: on the other hand, the gate driver123stops operating.

In contrast, when the cover section42is open, only the display operation of the main panel200is turned on; the display operation of the subpanel100is turned off. In this situation, the switching TFTs17in the time divisional drive section119operate in accordance with the switching control signal from the source driver115. The TFTs17thus transfers the display data signal from the source driver115to the source bus lines28on the main panel200. The gate driver113stops operating; on the other hand, the gate driver123keeps operating.

Next, the display operation of the subpanel100and the main panel200will be described in more detail.

To produce a display on the subpanel100, as shown inFIG. 12, the source driver115feeds the source bus lines16with the display data signals. Further, the gate driver113feeds the gate bus lines14with the gate signals switching on/off the TFTs25. In this situation, voltage goes HIGH on a gate bus lines14, switching on the TFT25connected to that gate bus line14. The display data signal on the source bus line16is written to the pixel (liquid crystal capacitor26).

To produce a display on the subpanel100, the gate bus lines14-1to14-M are addressed a line at a time, while the source bus lines16-1to16-L are being fed with the display data signals. This series of actions produces a frame. The series is repeated.

In this situation, the main panel200produces no displays. So, LOW voltage is applied from the source driver115to the first and second switching control signal lines18a,18b. This turns off all the switching TFTs17in the time divisional drive section119and electrically isolates the source bus lines28-1to28-2L on the main panel200. In addition, the gate bus lines24-1to24-N on the main panel200are not driven either.

In the above operation, the load in the higher resolution main panel200is electrically isolated when producing a display on the lower resolution subpanel100. Therefore, the liquid crystal display2achieves lower power consumption.

In contrast, to produce a display on the main panel200, the display data signals are applied from the source driver115to the source bus lines16, and the gate signals are applied from the gate driver123to the gate bus lines24to switch on/off the TFTs25, as shown inFIG. 13. In this situation, as voltage on a gate bus line24goes HIGH, the TFT25connected to that gate bus line24is turned on. The display data signal on the source bus line16is written to the pixel (liquid crystal capacitor26).

In the liquid crystal display2, the display data signals from the source driver115are transferred to the source bus lines28on the higher resolution main panel200through the source bus lines16on the lower resolution subpanel100. This is achieved by driving the higher resolution main panel200by time division.

To produce a display on the main panel200, the gate bus lines24-1to24-N are addressed a line at a time, while the source bus lines16-1to16-L are being fed with the display data signals. This series of actions produces a frame. The series is repeated.

Although the main panel200is currently producing no display, the display data signals need be applied to the main panel200. So, the switch on/off of the switching TFTs17in the time divisional drive section119is controlled. Specifically, the switch on/off of the switching TFT17is controlled by the switching control signal on either the first or second switching control signal line18a,18bwhich is connected to that TFT17. The display data signal is thus fed to a pair of source bus lines28, for example, source bus lines28-1,28-2, by time division. The gate bus lines14-1to14-M are however not driven.

In the above operation, the load in the lower resolution subpanel100cannot be electrically isolated in producing a display on the higher resolution main panel200, which requires extra electric power. However, in the dual panel structure, applied to the foldable mobile phone40or the like, which contains the higher resolution main panel200and the lower resolution subpanel100, generally, the lower resolution subpanel100is used for such purposes where display frequency is relatively high, whereas the higher resolution main panel200is used for such purposes where display frequency is relatively low. Therefore, the main panel200produces a display less frequently in the use of the liquid crystal display2. The liquid crystal display2as a whole achieves reductions in power consumption.

The foregoing loads are primarily due to the capacitance of insulating sections where they cross the gate bus lines14and the parasitic capacitance of the TFTs25, among other factors.

FIG. 14shows an alternative structure of the switching TFTs17connected to capacitive loads in the foregoing embodiments. Referring to the figure, each switching TFT17contains a N-channel MOSFET301, a P-channel MOSFET302, and an inverter303. CMOS structures like this are of course preferred to one-channel structure in terms of accuracy of switching actions. It is also preferred in terms of capability of stable control of voltage levels. There are no problems in switching operation if the switching element is of one-channel type.

In the liquid crystal display2, resolutions may be assigned freely to the subpanel100and the main panel200through a suitable number of divisions involved in the time division drive for the main panel200. In the present embodiment, the main panel200is driven by dividing time into two; therefore, the main panel200can be have a resolution up to double that of the subpanel100.

In the liquid crystal display2, the switching TFTs17in the time divisional drive section119play two roles: for time division drive and for isolation of the subpanel100from the main panel200. This dual role structure requires fewer components and is simpler as well as less costly than providing dedicated switches for each role.

In the mobile phone40, the first liquid crystal panel10(subpanel100) carrying the source driver15(115), that is, the first liquid crystal panel10(subpanel100) provided on the outside face of the cover section42, does not have to be structured so that its display operation is turned off when the cover section42is open. The panel (subpanel100) may be structured so that its display operation is always turned on regardless of whether the cover section42is open or closed.

The foregoing embodiments assume that the switching TFTs17are driven by signals from the source driver15or the source driver115. The TFTs17may be driven by another drive circuit.

In the liquid crystal display2of the present embodiment, as described in the foregoing, the main panel200is isolated from the subpanel100by the time divisional drive section119when producing a display not on the main panel200carrying no source driver115, but only on the subpanel100carrying the source driver115. The isolation could entail inconveniences in producing a display on the main panel200similarly to the liquid crystal display1.

The resistance value of the switching TFT17in the time divisional drive section119is at least 1000 times as high when it is switched off as when it is switched on. This does not mean, however, that the switching TFT17would absolutely cease conducting on a switch-off: a certain level of leak current could flow. The leak current would gradually move the potential of the source bus line28on the main panel200which is currently not being driven, until that potential ultimately would become equal to the mean value of the voltage on the source bus line16on the subpanel100which is being driven. The gradually changing voltage on the source bus line28would be applied to the drain of the TFT25on the main panel200, and in turn, to the pixel electrode connected to that drain. Resultant variations in the voltage across the pixel electrode and the opposite electrode could change the appearance of the main panel200accordingly. These voltage changes might cause an unintended display to appear on the main panel200which is not being drive.

If the time divisional drive section119did not repeat temporary switch-on actions while the time divisional drive section119is switched off (while the main panel200is not performing a display operation), the leak current through the switching TFT17in the time divisional drive section119could cause the potential of the source bus line28on the main panel200to become equal to a mean value of the potential of the source bus line16on the subpanel100which is currently performing a display operation. The mean value of the electrical potential might slightly differ from one source bus line28to the other depending on the display image produced on the subpanel100. In such a case, the potential differences across the pixel electrodes and the opposite electrode on the main panel200would become non-uniform, resulting in the display screen of the main panel200appearing visually undesirable.

These problems are solved by the liquid crystal display2: the time divisional drive section119is briefly and repeatedly switched on, for example, at a regular cycle, while producing a display on the subpanel100, but not on the main panel200. The actions retain the source bus lines28on the main panel200at a predetermined potential. Refer back toFIG. 6for an arrangement of the liquid crystal display2carrying out the actions.

FIG. 15is a timing chart illustrating output signals of the source driver115when the subpanel100produces a display whereas the main panel200does not. The time divisional drive section119is not carrying out the recursive temporary switch-on actions.

InFIG. 15, the control signal S11and the control signal S12are a start signal and a clock signal for the gate driver113respectively. The control signal S21and the control signal S22are a start signal and a clock signal for the gate driver123respectively. The switching control signals S1, S2are transferred to the first and second switching control signal lines18a,18brespectively so as to control the switch on/off of the switching TFTs17in the time divisional drive section119. The video signal S1is transferred to the source bus lines16,28in accordance with information on an image display to be produced.

In the above case, the switching control signals S1, S2both stay unchanged at L level, keeping the time divisional drive section119switched off. The control signal S21and the control signal S22both stay unchanged at H level, resulting in the main panel200producing no scan signals. As to the video signals S1, each period which is equivalent to the number of the gate bus lines14on the subpanel100is a valid image period; the rest is invalid periods. The potentials of the source bus lines16during invalid periods are not particularly specified.

FIG. 16is a timing chart illustrating output signals of the source driver115when the main panel200produces a display whereas the subpanel100does not. In this situation, the recursive temporary switch-on actions of the time divisional drive section119has of course no relevance.

Consider the case shown inFIG. 16. During the valid image period, the switching control signals S1, S2alternately go to H level, switching on/off the switching TFTs17in the time divisional drive section119. The control signal S11and the control signal S12both stay unchanged at H level, resulting in the subpanel100producing no scan signals.

In contrast,FIG. 17is a timing chart illustrating output signals of the source driver115when the subpanel100produces a display whereas the main panel does not. The time divisional drive section119is carrying out the recursive temporary switch-on actions.

In the case shown inFIG. 17, the switching control signals S1, S2both go to H level briefly outside the valid image period. This leads to a recursive temporary switch-on action of the time divisional drive section119. The signals S1, S2stay at L level for the rest of time. The video signal S1stays unchanged at a potential level for a period (“predetermined potential supply period”) which stretches at least across that period during which the switching control signals S1, S2are at H level. The time divisional drive section119carries out a recursive temporary switch-on action for each vertical interval at a regular cycle outside the valid image period. The control signal S21and the control signal S22both stay unchanged at H level, resulting in the main panel200producing no scan signals.

This series of actions result in supplying a predetermined potential to the source bus lines116on the main panel200which is not expected to produce any displays. That is, the potential differences across the opposite electrode and the drains of the TFTs25, hence the pixel electrodes, are retained at a predetermined level. The appearance of the main panel200which is not expected to produce any displays is uniform across the screen and remains unchanged for some time. Unintended displays do not occur.

The recursive temporary switch-on actions of the time divisional drive section119do not necessarily occur at a regular cycle, as is the case with the liquid crystal display1. Nevertheless, carrying out one action for each vertical interval or for each integral multiple thereof is preferable in facilitating the control of the recursive temporary switch-on actions of the time divisional drive section119, as is the case again with the liquid crystal display1.

There are no particular limitations on the predetermined potential which is supplied to the source bus lines24on the main panel200as a result of the recursive temporary switch-on actions of the time divisional drive section119. This is again the same case with the liquid crystal display1. The predetermined potential may be selected from the electrical potentials described in relation to the liquid crystal display1.

The potential of the gate bus lines24may be preferably controlled to reduce effects of the potential of the gate bus lines24, as is the case again with the liquid crystal display1.

A display of the present invention can be utilized for desktop or non-mobile devices equipped with multiple display sections and operating primarily from an AC power supply. The display is however particularly suitable for mobile devices equipped with multiple display sections and operating from a battery. The battery-dependent operation is a cause for demand for the lowering of power consumption. Examples of such mobile devices include mobile phones and PDAs (personal digital assistants).

As described in the foregoing, the display and its driving method of the present invention may be arranged so that the recursive temporary switch-on actions are carried out at a cycle equal to an integral multiple of a vertical interval for the second display means.

The arrangement facilitates the control of the recursive temporary switch-on actions.

The display and its driving method of the present invention may be arranged so that the predetermined potential is equal to a potential of an opposite electrode of the second display means.

According to the arrangement, in the second display means carrying out no display operation, in rendering the potential differences between the pixel electrodes and the opposite electrode equal to a predetermined level, the potential differences between the pixel electrodes and the opposite electrode hardly occur, and it takes time for the potential variations caused by leak current to reach a level where the leak current would affect displaying. Therefore, it becomes possible to extend the intervals between the recursive temporary switch-on actions. Electric power consumption in the recursive temporary switch-on actions is reduced.

The display and its driving method may be arranged so that the predetermined potential and a potential of an opposite electrode of the second display means are both equal to GND during the recursive temporary switch-on actions.

According to the arrangement, in rendering the potential differences between the pixel electrodes and the opposite electrode equal to a predetermined level in the second display means carrying out no display operation, the potential for that purpose can be readily obtained.

The display and its driving method of the present invention may be arranged so that the predetermined potential is equal to a mean value of potentials of the source signal lines of the first display means carrying out a display operation.

According to the arrangement, in rendering the potential differences between the pixel electrodes and the opposite electrode equal to a predetermined level in the second display means carrying out no display operation, power loss caused by the leak current in the second switching means can be reduced. In other words, the mean value of the potentials, if the recursive temporary switch-on actions were not carried out, would be equal to the value to which the potentials of the source signal lines of the second display means would approach due to the leak current in the second switching means. Therefore, applying the mean value of the potentials to the source signal lines of the second display means reduces power loss caused by the leak current.

The display may be arranged to include a power supply circuit supplying multiple voltages so that the predetermined potential is equal to one of voltages supplied from the power supply circuit to the source signal line drive circuit, the one of voltages being the closest to a mean value of potentials of the source signal lines of the first display means carrying out a display operation.

The method for driving the display may be arranged so that the predetermined potential is equal to one of voltages supplied to the source signal line drive circuit, the one of voltages being the closest to a mean value of potentials of the source signal lines of the first display means carrying out a display operation.

The arrangement offsets the need for a circuit dedicated to supply the mean value of the potentials, reducing power consumption. In other words, if a circuit is separately provided to produce an accurate mean value of the potentials, power consumption occurs in the circuit. In contrast, electric power consumption in driving a separate circuit is lowered by using an existing power supply circuit and utilizing the closest output voltage to the mean value of the potentials which is selected from multiple output voltages from the existing power supply circuit.

The display and display method may be arranged so that the voltage closest to the mean value of the potentials of the source signal lines of the first display means carrying out a display operation, as the predetermined potential, is simultaneously supplied to an opposite electrode of the second display means.

The arrangement readily offsets the potential differences between the pixel electrodes and the opposite electrode and prevents an unintended display from appearing on the second display means carrying out no display operation in an effective manner.

The display and its driving method may be arranged so that the predetermined potential is supplied to the gate signal lines of the second display means during the recursive temporary switch-on actions.

The arrangement prevents unintended display from appearing on the second display means carrying out no display operation in a more effective manner. In other words, when there are large potential differences between the gate signal lines and the opposite electrode, this potential differences may affect the display on the second display means. Accordingly, supplying the predetermined potential (that is, the potential equal to the potential of the opposite electrode, the GND, the mean value of the potentials of the source signal lines of the first display means carrying out a display operation, or the one of the voltages supplied to the source signal line drive circuit which is the closest to the mean value of potentials of the source signal lines of the first display means carrying out a display operation) to the gate signal lines of the second display means during the recursive temporary switch-on actions prevents the potentials of the gate signal lines from affecting the display on the second display means.

The display may be arranged so that the second display means carries out a display operation less frequently than the first display means.

According to the arrangement, the display data signals are supplied to the source signal lines of the second display means which carries out a display operation less frequently through the source signal lines of the first display means which carries out a display operation more frequently. Therefore, during the use of the display device, the source signal lines of the second display means are connected to the source signal lines of the first display means for a reduced period of time, which further lowers power consumption.

The display may be arranged so that the first display means has fewer pixels than the second display means.

According to the arrangement, in a structure containing the first display means with fewer pixels, that is, with a lower resolution, and the second display means with more pixels, that is, with a higher resolution, typically, the first display means with fewer pixels is used to produce displays more frequently. Therefore, the arrangement is preferable in lowering power consumption.

The display may be arranged so that: the first display means and the second display means are provided in a device in which a second housing section opens/closes on a first housing section; the first display means is provided so that when the second housing section is closed on the first housing section, a display plane of the first display means is on an outside face of either the first or second housing section; and the second display means is provided so that when the second housing section is closed on the first housing section, a display plane of the second display means is on an inside face of either the first or second housing section.

According to the arrangement, when a device with a display in which a second housing section opens/closes on a first housing section is being used, the second housing section is often closed on the first housing section. Therefore, the structure where the first display means is provided so that when the second housing section is closed on the first housing section, a display plane of the first display means is on an outside face of either the first or second housing section; and the second display means is provided so that when the second housing section is closed on the first housing section, a display plane of the second display means is on an inside face of either the first or second housing section is preferable in lowering power consumption.