JPH10207429A - Display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a display device having a display mode for suppressing power consumption as much as possible by displaying the information display of a picto-display area for displaying minimum information only with a power supply voltage (main switch is OFF). SOLUTION: Based on display data converted into a liquid crystal driving voltage level inputted from a level shifter circuit 11, a segment driver circuit 12 selects an LCD power supply voltage signal (V0, 1/5V0 to 4/5V0, VSS) inputted from an LCD power source circuit 4 in a normal display mode where a main switch MS is ON, selects an LCD power supply voltage signal (VDD, VSS and 1/2VDD) inputted from the LCD power source circuit 4 in a power conservation display mode where the main switch MS is OFF and then a signal electrode in a liquid crystal display panel 15 is driven.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device using a reflective or transflective liquid crystal panel.

[0002]

2. Description of the Related Art In conventional portable electronic devices such as electronic organizers and mobile phones, many display devices equipped with a reflective or semi-transmissive liquid crystal panel (hereinafter simply referred to as a liquid crystal panel) have become widespread. I have. As described above, in the liquid crystal display panel mounted on the portable electronic device, for example, a dot display area for displaying arbitrary information such as various kinds of information processed after the power is turned on, and an antenna mark or a clock mark indicating the radio wave reception status are displayed. And a pictogram display area that displays fixed information such as

The display state of the liquid crystal panel on which the dot display area, the pictogram display area, and the like are formed is such that when the power of the portable electronic device is turned off, the light is completely turned off (a state in which no voltage is applied). No information is displayed.

[0004]

However, in a portable electronic device equipped with such a conventional reflective or transflective liquid crystal panel, a dot display area or a pictogram display area is formed on the liquid crystal panel. As a result, arbitrary information or fixed information is displayed, but the display state of the liquid crystal panel is determined by turning off the power of the portable electronic device.
If the power is turned off, no information is displayed because the lamp is completely turned off (no voltage is applied), so the information is not transmitted through the liquid crystal panel unless the power of the portable electronic device is turned on. There was a problem that it could not be obtained.

[0005] That is, in order to always display some information, the power of the portable electronic device is always turned on.
In such a case, the portable electronic device and the liquid crystal panel consume unnecessary power, and the built-in battery is consumed. In order to display information on the liquid crystal panel, the power supply voltage generated by the battery is boosted for the liquid crystal drive voltage, so its power consumption is the largest among portable electronic devices, which greatly affects battery life .

SUMMARY OF THE INVENTION It is an object of the present invention to provide a display having a display mode capable of minimizing power consumption by enabling information display in a pictogram display area for displaying minimum information only by a power supply voltage (main switch is in an OFF state). It is to provide a device.

[0007]

According to a first aspect of the present invention, there is provided a display panel including a plurality of pixels, a booster for boosting a power supply voltage, and the display panel using a boosted voltage from the booster. And a second display state in which only a specific pixel of the display panel is driven using the power supply voltage by selectively switching between a first display state in which the display panel is driven to perform normal display and a second display state in which only a specific pixel is driven using the power supply voltage. And drive control means for controlling driving.

According to the display device of the first aspect of the present invention, the drive control means boosts the power supply voltage via the boosting means, and drives the display panel including a plurality of pixels by using the boosted voltage. Then, a first display state in which normal display is performed and a second display state in which only a specific pixel of the display panel is driven using the power supply voltage are switched and controlled.

Therefore, for example, if the main switch is O
In the N state, the display mode is set to the normal display mode in which the display panel is driven by the boosted voltage obtained by boosting the power supply voltage.
In the F state, each display mode can be set as a power saving display mode in which the display panel is driven by the power supply voltage.

In this case, as in the second aspect of the present invention, in the display device according to the first aspect, the drive control means may control the first display state and the second display state in response to a signal from an external circuit. It is effective to have switch means for switching the display state.

According to the display device of the present invention, the drive control means switches between the first display state and the second display state in accordance with a signal from an external circuit. Means.

Therefore, the driving power in the power saving display mode is suppressed to be lower than the driving power in the normal display mode. Can always display necessary information.

Further, as in the invention described in claim 3,
3. The display device according to claim 2, wherein the external circuit is a timer circuit that outputs a switching signal when a time during which the display state of the display panel table 1 is not changed reaches a predetermined time or more.

According to the display device of the third aspect of the present invention, the external circuit outputs a switching signal when the time during which the display state of the display panel table 1 does not change reaches a predetermined time or more. It is.

Therefore, even when the main switch is turned off by the timer operation in the electronic device on which the display device is mounted, it is possible to always display necessary information on the display panel.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings.

(First Embodiment) FIGS. 1 to 7 are views showing a first embodiment of a liquid crystal display device 100 to which the present invention is applied.

First, the configuration will be described.

FIG. 1 is a block diagram showing a main configuration inside a liquid crystal display device 100 according to the first embodiment. In FIG. 1, a liquid crystal display device includes a power supply voltage adjusting circuit 1,
Step-up circuit 2, constant voltage circuit 3, LCD power supply circuit 4, oscillation circuit 5, frequency dividing circuit 6, address counter 7, common timing generating circuit 8, address switching circuit 9, display RAM 1
0, level shifter circuit 11, segment driver circuit 1
2, level shifter circuit 13, common driver circuit 14,
It comprises a liquid crystal display panel 15, an excitation circuit 16, and the like.

The power supply voltage adjusting circuit 1 is a circuit which adjusts the voltage level of the power supply voltage (VDD, VSS, VREF) supplied from an external power supply (not shown) and supplies the voltage to the constant voltage circuit 3. The booster circuit (boost means) 2 is a circuit that boosts a power supply voltage (VDD, VSS) supplied from an external power supply unit (not shown) and supplies the boosted power supply to the constant voltage circuit 3.

An external main switch MS for turning on / off an electronic device such as an electronic desk calculator on which the liquid crystal display device 100 is mounted is provided at an intermediate portion of the wiring connecting the booster circuit 2 and the constant voltage circuit 3. ON / OFF by the excitation circuit 16 which is excited / de-energized according to the / OFF operation
The operating contact S is connected and the main switch MS
Is connected between the booster circuit 2 and the constant voltage circuit 3 when the main switch MS is in the OFF state.
And the constant voltage circuit 3 is opened.

That is, the excitation circuit (drive control means) 16
When the main switch MS is turned on, it is excited by an exciting voltage supplied from a power supply unit (not shown) to turn on the contact S, thereby connecting the booster circuit 2 and the constant voltage circuit 3 to boost the voltage. The boosted voltage signal supplied from the circuit 2 is supplied to the constant voltage circuit 3, and when the main switch MS is turned off, the excitation voltage supplied from a power supply unit (not shown) is cut off, and the contact S is turned off. Then, the voltage between the booster circuit 2 and the constant voltage circuit 3 is opened, and the power supply voltage supplied from the power supply voltage adjustment circuit 1 is supplied to the constant voltage circuit 3.

The constant voltage circuit 3 generates a constant voltage signal of a constant voltage level from a boosted voltage signal supplied from the booster circuit 2 or a power supply voltage signal (VDD, VSS) supplied from the power supply voltage adjusting circuit 1. This is a circuit for supplying to the LCD power supply circuit 4. The LCD power supply circuit 4 generates an LCD power supply voltage signal required for driving the liquid crystal based on a constant voltage signal (a boost signal or a power supply voltage signal) supplied from the constant voltage circuit 3 to generate a segment driver circuit 12 and a common driver circuit 14.
Circuit. When the main switch MS is in the OFF state, the LCD power supply circuit 4 is in a power saving display mode described later, and the constant voltage signals supplied from the constant voltage circuit 3 are power supply voltage signals (VDD, VSS). LCD power supply voltage signals (VDD, VSS, 1/2 V
DD) is generated and supplied to the segment driver circuit 12 and the common driver circuit 14.

The oscillating circuit 5 is supplied with power supply voltages VDD and VSS from a power supply (not shown), and oscillates a reference oscillating signal which takes the timing of time-division driving which is the basis of the liquid crystal driving control to divide the frequency. 6 The frequency dividing circuit 6 divides the frequency of the reference oscillation signal supplied from the oscillation circuit 5 to generate an address count timing signal necessary for address counting, and supplies it to the address counter 7. The address counter 7 counts up a count value corresponding to a display address in the display RAM 10 in accordance with an address count timing signal input from the frequency dividing circuit 6, and sends the count value to the common timing generating circuit 8 and the address switching circuit 9. Output.

The common timing generation circuit 8 sequentially generates a common drive signal for driving a common line of the liquid crystal display panel 15 according to the count value input from the address counter 7, and passes the generated common drive signal through a level shifter circuit 13 to a common driver. By sequentially transferring the scan electrodes to the circuit 14, the scan electrodes of the liquid crystal display panel 15 are sequentially driven by the common driver circuit 14 based on the generated common drive signal.

The address switching circuit 9 has a display RAM 10 according to the count value inputted from the address counter 7.
Switch the display address to be accessed within. R for display
As shown in FIG. 2, the AM (DDRAM) 10 has a vertical pixel × a horizontal 128 bit of a pictogram unit 15a which displays a predetermined design or symbol with a single pixel, which is a display screen configuration of a liquid crystal display panel 15 described later. Pictogram part 15 which corresponds one-to-one to
a display memory 10a, a dot-part display memory 10b corresponding to the vertical 32 bits × horizontal 128 bits of the dot part 15b on a one-to-one basis, and a vertical bit 1 × horizontal 12 of the pictogram part 15c.
It has a memory configuration of the display memory 10c for the pictogram portion 15c corresponding to 8 bits on a one-to-one basis.
In the a and the pictogram part 15c, the display address is set from left to right in the figure in units of 1 bit in the vertical direction, and the display address is set in the dot part from the left to right in the figure in units of 16 bits in the vertical direction. Then, display data input from an external controller (not shown) in 1-bit or 16-bit units corresponding to the display address is sequentially advanced and accessed for each display address switched by the address switching circuit 9 and sequentially accessed. The stored data for display is sequentially transferred to the level shifter circuit 11. Each bit of the display data stored in the display RAM 10 is stored as “1” or “0”.
“1” corresponds to “lighting” of the liquid crystal display element (1 bit), and “0” corresponds to “non-lighting” of the liquid crystal display element (1 bit).

The level shifter circuit 11 includes a display RAM 1
The display data input from 0 is converted into a liquid crystal drive voltage level and output to the segment driver circuit 12. The segment driver circuit 12 is input from the LCD power supply circuit 4 based on the display data converted into the liquid crystal drive voltage level input from the level shifter circuit 11 when the main switch MS is in the normal display mode in the ON state. L
CD power supply voltage signal (V0, 1 / 5V0 to 4 / 5V0, V
SS) and in the power saving display mode in which the main switch MS is in the OFF state, the LCD power supply voltage signals (VDD, VSS, 1 / 2VD) input from the LCD power supply circuit 4 are set.
D) is selected to drive the signal electrodes in the liquid crystal display panel 15.

The level shifter circuit 13 converts the common drive signal input from the common timing generation circuit 8 into a liquid crystal drive voltage level and outputs the same to the common driver circuit 14. The common driver circuit 14 includes the level shifter circuit 13
In the normal display mode in which the main switch MS is ON at the timing of the common drive signal converted to the liquid crystal drive voltage level input from the LCD, the LCD power supply voltage signal (V0, 1 / 5V0-4 /
5V0, VSS) and the main switch MS is OFF
In the power saving display mode, the power supply voltage signal (VDD,
(VSS, 1/2 VDD) to sequentially drive the scanning electrodes in the liquid crystal display panel 15.

The liquid crystal display panel (display panel) 15 is composed of a simple matrix type liquid crystal panel, and its display screen is configured as shown in FIG. Pictogram part 15 on the lower side in the figure
c and a dot section 15b for displaying arbitrary information.
Each of the pictograms 15a and 15c has a display area of 1 bit vertically × 128 bits horizontally,
b has a display area of 32 bits vertically × 128 bits horizontally. The liquid crystal display panel 15 includes the segment driver circuit 1
2 (the main switch MS is OFF)
In the F state, the LCD power supply voltage signals (VDD, VSS, 1 /
2VDD)), the signal electrode is driven, and the drive voltage (main switch MS) input from the common driver circuit 13
Is OFF, the LCD power supply voltage signals (VDD, VS
(S, 1/2 VDD)), the scanning electrodes are driven to display fixed information such as marks on the pictogram portions 15a and 15c, and also display characters and images on the dot portions 15b. The dot portion 15b in the liquid crystal display panel 15
Is a full dot type display, but may be a liquid crystal display element for character display.

Next, the operation of the first embodiment will be described.

In the liquid crystal display device 100 of the present embodiment,
When the main switch MS is ON, the liquid crystal display panel 1 is driven by the liquid crystal driving voltage whose power supply voltage has been boosted by the booster circuit 2.
5 is driven, and when the main switch MS is in the OFF state, the power supply voltage (VD
D, VSS) alone to drive the liquid crystal display panel 15 for display.

First, the operation of the liquid crystal display device 100 in the normal display mode will be described.

In the liquid crystal display device 100, when the main switch MS is turned on, the exciting circuit 16 is in an excited state, the contact S is turned on, and the booster circuit 2 is connected to the constant voltage circuit 3. In the booster circuit 2, when the power supply voltages (VDD, VSS, VREF) supplied from an external power supply (not shown) are boosted and supplied to the constant voltage circuit 3, the power supply voltage is converted into a constant voltage signal in the constant voltage circuit 3. It is adjusted and supplied to the LCD power supply circuit 4. In the LCD power supply circuit 4, an LCD power supply voltage signal required for driving the liquid crystal is generated from the constant voltage signal supplied from the constant voltage circuit 3, and supplied to the segment driver circuit 12 and the common driver circuit 14, and the liquid crystal in the normal display mode is generated. Driving is started.

The segment drive signal output from the segment driver circuit 12 and the common drive signal output from the common driver circuit 14 in the normal display mode will be described with reference to a timing chart shown in FIG.

FIG. 4 shows the pictograph section 15 of the liquid crystal display panel 15 from the common driver circuit 14 in the normal display mode.
a and the respective common drive signals (FIGS. 9A and 9B) output to the pictogram section 15c, and output from the segment driver circuit 12 to the pictogram sections 15a and 15c of the liquid crystal display panel 15. 5 shows an example of the segment drive signal (FIG. 4C).

Each of the common drive signals shown in FIGS. 3A and 3B output from the common driver circuit 14 to the pictogram portions 15a and 15c of the liquid crystal display panel 15, and from the segment driver circuit 12 to the liquid crystal display panel. The segment drive signal output to the 15 pictograms 15a and 15c shown in FIG.
/ 34, bias value 1 / 5V0, voltage amplitude V0 to VSS
Is shown. Here, the voltage level V0 is a liquid crystal drive voltage level boosted by the booster circuit 2, the constant voltage circuit 3, and the LCD power supply circuit 4.

The common drive signal and the segment drive signal are applied to the scanning electrodes and the signal electrodes of the pictogram portions 15a and 15c of the liquid crystal display panel 15, so that the voltage level V0 or the voltage shown in FIG. The portion to which the segment drive signal of the level VSS is applied is turned on, and fixed information is displayed.

Next, the operation of the liquid crystal display device 100 in the power saving display mode will be described.

In the liquid crystal display device 100, when the main switch MS is turned off, the excitation circuit 16 is de-energized, the contact S is turned off, and the booster circuit 2 is separated from the constant voltage circuit 3, and the constant voltage circuit 3 A power supply voltage signal (VDD, VSS) supplied from the power supply voltage adjustment circuit 1 is supplied to the LCD power supply circuit 4 as a constant voltage signal. In the LCD power supply circuit 4, the LCD power supply voltage signals (VDD, VSS) are supplied from the constant voltage signal supplied from the constant voltage circuit 3 to the segment driver circuit 12 and the common driver circuit 14 as the LCD power supply voltage signal, thereby saving the power. The liquid crystal drive in the power display mode is started.

The segment drive signal output from the segment driver circuit 12 and the common drive signal output from the common driver circuit 14 in the power saving display mode will be described with reference to a timing chart shown in FIG.

In FIG. 5, each segment drive signal output from the segment driver circuit 12 to the pictogram sections 15a and 15c of the liquid crystal display panel 15 in the power saving display mode (FIGS. 5C to 5F). And the pictogram portion 15 of the liquid crystal display panel 15 from the common driver circuit 14
a, each common drive signal output to the pictogram section 15c and the dot section 15b ((a), (b), (g) in the same figure)
An example is shown.

Each of the common drive signals shown in FIGS. 7A and 7B output from the common driver circuit 14 to the pictogram portions 15a and 15c of the liquid crystal display panel 15 when turned on has a duty ratio of 1/34, The case where the voltage value takes two values of VDD and VSS is shown, and the common drive signal shown in FIG. 9G which is output when the dot portion 15b is not turned on has a constant voltage level of 1/2 VDD. I have.

Further, from the segment driver circuit 12 to the pictogram portions 15a and 15c of the liquid crystal display panel 15,
Each of the segment drive signals shown in FIGS. 3 (c) to 3 (f) is output to the pictogram unit 15a and the pictogram unit 15c.
a segment drive signal output when lighting both c
(D) is a segment drive signal output when the pictogram section 15a is turned on and the pictogram section 15c is turned off, and (e) is output when the pictogram section 15a is turned off and the pictogram section 15c is turned on. The segment drive signal (f) is a segment drive signal output when both the pictogram unit 15a and the pictogram unit 15c are turned off, and the duty ratio is 1/3.
4. Bias value 1 / 2VDD, voltage value is VDD, 1 / 2VDD
The figure shows a case where three values of D and VSS are taken.

The pictogram section 15a and the pictogram section 1 in FIG.
FIG. 6 shows a relationship between an effective value based on the common drive signal and the segment drive signal applied when the dot portion 15c is turned on / off, and an effective value based on the common drive signal and the segment signal applied when the dot portion 15b is not turned on.

FIG. 6A shows a composite waveform (COM-SEG) of the common drive signal and the segment drive signal applied when the pictogram portions 15a and 15c are turned on. The value can be obtained by the following equation (1).

[0046]

(Equation 1)

From this equation (1), the effective value when the pictogram portions 15a and 15c are turned on is "0.79 VDD".

FIG. 6B shows a composite waveform (COM-SEG) of the common drive signal and the segment drive signal applied when the pictogram portions 15a and 15c are turned off. The effective value can be obtained by the following equation (2).

[0049]

(Equation 2)

From this equation (2), the effective value when the pictogram portions 15a and 15c are not lit is "0.354 VDD".

FIG. 6C shows a composite waveform (COM-SEG) of the common drive signal and the segment drive signal applied when the dot section 15b is turned off, and the effective value of the composite waveform is shown. Can be obtained by the above equation (2). Therefore, the effective value when the dot section 15b is not lit is "0.354 VDD".

Here, assuming that VDD = 3V, 0.79 × 3 = 2.37 (V) at the time of lighting and 0.354 at the time of non-lighting.
× 3 = 1.06 (V). So, in this case,
The threshold voltage for turning on / off the liquid crystal display element is 1.06
By setting the voltage to (V) or more and 2.37 (V) or less, the pictogram unit 15a and the pictogram unit 15 can be used without using the booster circuit 2.
c can be displayed.

As a result, since the liquid crystal display element can be driven with low power consumption, the liquid crystal display device 10 of the first embodiment can be driven.
0 can be used to display information such as a clock display that is always lit, and the power consumption of an electronic device equipped with the liquid crystal display device 100 of the first embodiment can be reduced to extend the battery life. Can be made.

The liquid crystal display device 10 of the first embodiment
0, a power saving display mode is provided in addition to the normal display mode. In this power saving mode, the segment driver circuit 12
The segment drive signal output from the controller is VDD, VSS, 1
Although the description has been given of the case where the common drive signal output from the common driver circuit 14 takes two values of VDD and VSS, the method of taking the voltage value is opposite between the segment side and the common side. It may be. That is, FIG.
As shown in (b), the common drive signal applied to the pictogram section 15a and the common drive signal applied to the pictogram section 15c take three values of VDD, VSS, and 1 / 2VDD.
As shown in (d), the segment drive signal at the time of lighting and the segment drive signal at the time of non-lighting may take two values of VDD and VSS.

However, in this case, the liquid crystal display element is turned on / off.
The effective range of the non-lighting threshold voltage is narrower than in the case of the first embodiment.

(Second Embodiment) In the liquid crystal display device 100 of the first embodiment, the liquid crystal display panel 15
In addition to providing the pictogram portions 15a and 15c, a power saving display mode is provided in addition to the normal display mode. In this power saving mode, the segment drive signals output from the segment driver circuit 12 are three of VDD, VSS and 1/2 VDD. The common drive signal output from the common driver circuit 14 takes two values, VDD and VSS.
As a configuration in which the pictogram portion of the liquid crystal display panel 15 shown in FIG. 3 is reduced to one line, a configuration in which the segment drive signal output from the segment driver circuit 12 takes two values of VDD and VSS is also possible.

Since the liquid crystal display device of the second embodiment has the same configuration as the liquid crystal display device 100 shown in FIG. 1 of the first embodiment, illustration and description of the configuration are omitted. I do. However, the display screen configuration of the liquid crystal display panel 15 includes one pictograph part 15a having a display area of 1 × 128 bits and a dot section 15b having a display area of 32 × 128 bits. Shall have.

In the same power saving display mode as described above,
FIG. 8 shows an example in which the segment drive signal output from the segment driver circuit 12 takes two values, VDD and VSS. In FIG. 8, the common drive signal shown in FIG. 8A output from the common driver circuit 14 to the pictogram portion 15a of the liquid crystal display panel 15 at the time of lighting is a duty ratio of 1
/ 34, the case where the voltage value takes two values of VDD and VSS,
The common drive signal shown in FIG. 3D that is output when the dot section 15b is not lit indicates a case where the voltage level is constant at 1/2 VDD.

Each of the segment drive signals shown in FIGS. 7B and 7C output from the segment driver circuit 12 to the pictogram section 15a of the liquid crystal display panel 15 is as shown in FIG.
Is a segment drive signal output when the pictogram section 15a is turned on, and (c) is a segment drive signal output when the pictogram section 15a is turned off. The duty ratio is 1/34 and the voltage value is VDD and This shows a case where two values of VSS are taken.

The pictogram section 15a in FIG.
FIG. 9 shows a relationship between an effective value based on the common drive signal and the segment drive signal applied when the dot portion 15b is not lit, and an effective value based on the common drive signal and the segment signal applied when the dot portion 15b is not lit.

FIG. 9A shows a composite waveform (COM-SEG) of the common drive signal and the segment drive signal applied when the pictogram section 15a is turned on, and the effective value of this composite waveform is given by the following equation. It can be obtained in (3).

[0062]

(Equation 3)

From the equation (3), the effective value when the pictogram portion 15a is turned on is "VDD".

FIG. 9B shows a composite waveform (COM-SEG) of the common drive signal and the segment drive signal applied when the pictogram section 15a is turned off, and the effective value of this composite waveform is " 0 ".

FIG. 9C shows a composite waveform (COM-SEG) of the common drive signal and the segment drive signal applied when the dot section 15b is turned off, and the effective value of this composite waveform is shown. Can be obtained by the following equation (4).

[0066]

(Equation 4)

From this equation (4), the effective value when the dot portion 15b is not lit is "1 / 2VDD".

As in the first embodiment, VDD = 3
(V), 1 / 2VDD = 1.5 (V), and the threshold voltage for turning on / off the liquid crystal display element is 1.5 (V).
As described above, by setting the voltage to 3.0 (V) or less, display of the pictogram portion 15a can be similarly performed without using the booster circuit 2. Further, the voltage values of the segment drive signal are VDD and V
In order to take two values of SS, the circuit configuration in the segment driver circuit 12 is simplified as compared with the case where the voltage value of the segment drive signal takes three values of VDD, 1 / 2VDD and VSS in the first embodiment. can do.

When the input LCD power supply voltage VDD is low, the power supply voltage of 0.353 VDD to 0.353 VDD in the first embodiment is applied.
Although there may be a case where the threshold voltage range of 0.79 VDD cannot be satisfied (threshold voltage does not become 0.79 VDD or less), the second embodiment can operate even when the threshold voltage is VDD or less, so that the power supply voltage can be reduced. The second embodiment is more advantageous for lowering the voltage of the second embodiment.

Therefore, since the liquid crystal display element can be driven with low power consumption, the liquid crystal display device 1 of the second embodiment can be driven.
00 can be used to display information such as a clock display that is always lit, and to reduce the power consumption of an electronic device equipped with the liquid crystal display device 100 of the second embodiment to extend the battery life. Can be made.

In the power saving display mode, the segment drive signal output from the segment driver circuit 12 has a voltage value of two values of VDD and VSS. The circuit configuration in the driver circuit 12 can be simplified.

Further, in the liquid crystal display device 100 according to the second embodiment, the threshold voltage for turning on / off the liquid crystal display element can be set to not less than 1/2 VDD and not more than VDD, so that the threshold voltage is not more than VDD. However, the display of the pictogram portion 15a becomes possible, which can contribute to the reduction of the power supply voltage.
The power consumption of an electronic device equipped with the liquid crystal display device 100 of the second embodiment can be further reduced, and the battery life can be further prolonged.

In each of the above embodiments, the switching between the normal display mode and the power saving display mode is performed in conjunction with the ON / OFF operation of the main switch MS.
When the ON / OFF operation of the main switch MS is configured to be linked to the timer operation, the normal display mode and the power saving display mode are switched between the ON / OFF operation of the main switch MS linked to the timer operation. Switching can also be performed. In this case, it is possible to always display necessary information on the display panel even when the main switch is turned off by the timer operation in the electronic device in which the liquid crystal display device is mounted.

[0074]

According to the display device of the first aspect of the present invention, the normal display mode in which the display panel is driven by the boosted voltage obtained by boosting the power supply voltage, and the power saving in which only the specific pixels of the display panel are driven by the power supply voltage. The display mode can be selectively switched, so that the power consumption of the display device can be reduced.

According to the display device of the second aspect of the present invention,
The drive power in the power saving display mode is suppressed to be lower than the drive power in the normal display mode, so that the display panel is always required even if the main switch is OFF in the electronic device on which the display device is mounted. It is possible to display information.

According to the display device of the third aspect of the present invention,
Even when the main switch is turned off by a timer operation in an electronic device on which the display device is mounted, it is possible to always display necessary information on the display panel.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a main part in a liquid crystal display device 100 according to a first embodiment to which a display device of the present invention is applied.

FIG. 2 is a diagram showing a memory configuration in a display RAM 10 of FIG. 1;

FIG. 3 is a diagram showing a display screen configuration of a liquid crystal display panel 15 of FIG.

FIG. 4 is a timing chart of drive signals output from the segment driver circuit 12 and the common driver circuit 14 in FIG. 1 in a normal display mode.

5 is a timing chart of drive signals output from the segment driver circuit 12 and the common driver circuit 14 in FIG. 1 in a power saving display mode.

FIG. 6 is a view showing a relationship between effective values based on a composite waveform of each drive signal in FIG. 5;

7 is a diagram showing another example of a timing chart of each drive signal output from the segment driver circuit 12 and the common driver circuit 14 in FIG. 1 in the power saving display mode.

FIG. 8 shows a segment driver circuit 12 in a liquid crystal display device 100 according to a second embodiment to which the display device of the present invention is applied.
4 is a timing chart of each drive signal output from the common driver circuit 14.

FIG. 9 is a diagram showing a relationship between effective values based on a composite waveform of each drive signal in FIG. 8;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power supply voltage adjustment circuit 2 Booster circuit (boost means) 3 Constant voltage circuit 4 LCD power supply circuit 5 Oscillator circuit 6 Divider circuit 7 Address counter 8 Common timing generation circuit 9 Address switching circuit 10 Display RAM (DDRAM) 10a Pict part 1 Display memory 10b Display memory for dot section 10c Display memory for pict section 2 11, 13 Level shifter circuit 12 Segment driver circuit 14 Common driver circuit 15 Liquid crystal display panel (display panel) 15a, 15c Pict section 15b Dot section 16 Excitation circuit (drive) Control means) 100 liquid crystal display device MS main switch

Claims (3)

[Claims] 1. A display panel comprising a plurality of pixels, a booster for boosting a power supply voltage, and a first display for driving the display panel using the boosted voltage from the booster to perform normal display. Drive control means for selectively switching between a display state and a second display state in which only a specific pixel of the display panel is driven using the power supply voltage to control the driving of the display panel. A display device characterized by the above-mentioned. 2. The apparatus according to claim 1, wherein said drive control means includes switch means for switching between said first display state and said second display state in accordance with a signal from an external circuit. Item 2. The display device according to Item 1. 3. The external circuit according to claim 2, wherein the external circuit is a timer circuit that outputs a switching signal when a time during which the display state of the display panel table 1 is not changed reaches a predetermined time or more. Display device.