JPH10268837A - Liquid crystal display contrast adjusting method, liquid crystal display driving device, and portable information device - Google Patents

Abstract

(57) [Problem] To provide a method of adjusting the contrast of a liquid crystal display, which can reduce the size of a device equipped with the liquid crystal display. SOLUTION: The contrast of the liquid crystal display 21 is changed by changing a voltage value of a driving signal for driving the liquid crystal display output by a driving unit 23 based on a switch operation of operation switches 4a and 4b for adjusting the contrast. In the method of adjusting the contrast of the liquid crystal display to be adjusted, data for contrast control is generated based on the operation of the operation switches 4a and 4b, and a reference voltage is generated by digital-to-analog conversion of the generated data for contrast control. A drive signal is generated based on the generated reference voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of adjusting the contrast of a liquid crystal display for adjusting the contrast of a liquid crystal display in a communication terminal such as a portable telephone, an electronic organizer, and a display device, and a driving of the liquid crystal display. The present invention relates to a device and a portable information device.

[0002]

2. Description of the Related Art The applicant has already developed an LCD module 51 shown in FIG. 8 as a device capable of changing the contrast of a liquid crystal display of this type. An LCD module 51 shown in FIG. 1 can be used for a display unit of a mobile phone, for example, and includes an LCD (liquid crystal) panel 21 capable of displaying various video screens,
X driver 22 that outputs a scanning signal in the column direction of panel 21 in synchronization with input display data XD0 to XD7.
A Y driver 23 for outputting a scanning signal in a row direction of the LCD panel 21 in synchronization with a vertical synchronization signal LP;
The power supply unit 52 includes a level shift circuit 24 for transmitting various signals to a Y driver 23 having a different reference potential from the X driver 22.

In the LCD module 51, an LCD power supply 52 generates various power supplies required to drive the LCD panel 21. Specifically, LCD
First, the power supply unit 52 generates the lowest level of the negative voltage _VEE by the charge pump method based on the input vertical synchronization signal LP. Next, the LCD power supply unit 52
A circuit voltage V _{L of} a negative voltage serving as a ground level of the Y driver 23, a circuit voltage V _H of a positive voltage, which is a signal for driving the LCD panel 21 by the Y driver 23 and having an absolute value equal to the circuit voltage V _L , LCD panel 2 with 22
Various circuit voltages including circuit voltages ± V ₂ and ± V ₃ which are one driving signal are generated.

[0004] Here, the LCD panel 21 is configured so that the contrast is changed by varying the voltage value of the circuit voltage V _L, V _H. Specifically, for example, when the LCD panel 21 is configured by a reflective LCD,
As shown in FIG. 6, when changing the voltage value of the circuit voltage V _L to 0V~ negative voltage V _EE, and the reflection characteristics of the liquid crystal cell of the non-operation shown by curve K1 in the drawing, a curve K2 in FIG The reflection characteristic of the liquid crystal cell in the operating state shown changes, and the reflectance a
The contrast changes depending on the ratio between the reflectance and the reflectance b, that is, the value (b / a). In this case, the contrast is not intended or to increase in proportion to the voltage value of the circuit voltage V _L, as shown in FIG. 7 has a peak value when the circuit voltage V _L of the voltage value with a predetermined ing. Therefore, in the LCD module 51, for example, the contrast can be adjusted by changing the contrast adjustment volume 53 (see FIG. 8) attached to the surface of the mobile phone. Specifically, the LCD power supply unit 5
2 is connected to the first and third terminals of the volume 53 by L
0 V reference potential V _SS input to the CD module 51,
And a negative voltage _VEE . When the user adjusts the volume 53, the circuit voltage V _L1 is output from the second terminal of the volume 53, and the LCD power supply unit 52 outputs the circuit voltage V _L having a voltage substantially equal to the circuit voltage V _L1 and the circuit voltage V _L1. The voltage _VH is generated.

[0005]

However, the LCD module 51 developed by the applicant has the following points to be improved since the contrast adjusting volume 53 is mounted on the surface of the device.

First, since the mechanical volume 53 is used, for example, when the LCD module 51 is mounted on a small portable device such as a portable telephone, the main body of the volume 53 is stored inside the device. As a result, the size of the apparatus tends to be large, and there is a demand for miniaturization.

Second, a knob for changing the contrast adjustment volume 53 must be exposed outside the apparatus. For this reason, for example, L
When the CD module 51 is mounted, clothing or the like may hit the knob before the user knows, and the volume 53 may move. As a result, there is a point to be improved that the contrast may be extremely reduced and characters and the like may not be seen.

Third, since the mechanical volume 53 is used, a contact failure may occur due to long-term use. In such a case, the contrast may not be adjusted, resulting in an improvement in reliability.

On the other hand, in a small portable device, since the display area of the liquid crystal display is generally small, the circuit voltages V _L and V
It is conceivable that the contrast is fixed by setting _H to a constant voltage. However, it is extremely difficult to mass-produce the LCD panel 21 with exactly the same contrast characteristics. For this reason, the semi-fixed volume 53 must be provided inside the apparatus, and each apparatus must be individually adjusted at the time of shipment from the factory. As a result, another problem occurs in that the apparatus cost increases. Also,
In recent years, a mobile phone or the like has been required to have a large display area, and in order to meet such a demand, it is preferable that the contrast be adjusted from outside the apparatus.

SUMMARY OF THE INVENTION The present invention has been made in order to improve such improvements and the like, and a method of adjusting the contrast of a liquid crystal display and a driving apparatus for the liquid crystal display which can reduce the size of a device equipped with the liquid crystal display. , And portable information devices.

[0011]

According to a first aspect of the present invention, there is provided a method for adjusting a contrast of a liquid crystal display, the method comprising the steps of: A contrast control method for adjusting the contrast of the liquid crystal display by changing the contrast based on the switch operation of the operation switch, wherein the contrast control data is generated based on the switch operation of the operation switch; A reference voltage is generated by digital-to-analog conversion of control data, and a drive signal is generated based on the generated reference voltage.

In this method for adjusting the contrast of a liquid crystal display, control data for adjusting the contrast is generated by operating an operation switch. Next, a reference voltage is generated by digital-to-analog conversion of the control data, and a drive signal is generated based on the generated reference voltage. As a result, when the voltage value of the drive signal changes, the contrast of the liquid crystal display changes. As described above, since this adjustment method does not use a mechanical volume or the like, the size of the device can be reduced, and the reliability of the device can be improved.

According to a second aspect of the present invention, in the method of adjusting a contrast of a liquid crystal display according to the first aspect, the contrast control data is generated by operating at least two operation switches. Features.

According to a third aspect of the present invention, in the method of adjusting a contrast of a liquid crystal display according to the first or second aspect, the driving unit includes a liquid crystal display provided in a portable information device. It is characterized by being driven.

According to a fourth aspect of the present invention, there is provided a driving device for a liquid crystal display.
A drive unit that drives a liquid crystal display by outputting a drive signal having a voltage value according to the input circuit voltage, and a voltage value of a reference voltage serving as a reference of the circuit voltage based on a switch operation of an operation switch for contrast adjustment. Voltage driving means for generating a circuit voltage based on the reference voltage and outputting the circuit voltage to the driving section, the reference voltage changing means includes a switch of an operation switch. A power supply comprising: a control data generator for generating contrast control data based on an operation; and a digital-analog converter for generating a reference voltage by digital-to-analog conversion of the generated contrast control data. The unit generates a circuit voltage based on the reference voltage output from the digital-analog conversion unit.

In this liquid crystal display driving device, the control data generator generates contrast control data by operating the operation switch. Next, the digital-analog conversion section converts the control data to digital-to-analog data.
A reference voltage is generated by analog conversion. Thereby, the power supply unit generates a circuit voltage based on the reference voltage. Next, the driving unit drives the liquid crystal display by outputting a drive signal having a voltage value corresponding to the input circuit voltage, so that the contrast of the liquid crystal display changes.
As described above, the liquid crystal display driving device does not use a mechanical volume or the like, so that the size and cost of the device can be reduced and the reliability of the device can be improved.

According to a fifth aspect of the present invention, there is provided a driving device for a liquid crystal display.
5. The liquid crystal display driving device according to claim 4, wherein the liquid crystal display includes a liquid crystal cell having transparent electrodes arranged in a matrix, and the driving unit synchronizes the input display data with the liquid crystal display. A row direction driver that outputs a drive signal in the column direction of the liquid crystal display, and a column direction driver that outputs a drive signal in the column direction of the liquid crystal display in synchronization with the input display data. Is output to at least one of a row-direction driver and a column-direction driver.

According to a sixth aspect of the present invention, there is provided a driving device for a liquid crystal display.
The liquid crystal display driving device according to claim 5, wherein the contrast control data is output to a digital-analog conversion unit via a data bus for transferring the display data.

According to a seventh aspect of the present invention, there is provided a driving device for a liquid crystal display.
7. The liquid crystal display driving device according to claim 4, wherein the operation switch includes at least two switches.

A driving device for a liquid crystal display according to claim 8 is
A portable information device comprising the liquid crystal display driving device according to any one of claims 4 to 7.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the accompanying drawings, a preferred embodiment in which a liquid crystal display adjusting method, a liquid crystal display driving device, and a portable information device according to the present invention are applied to a portable telephone. Will be described. Note that the same components as those of the conventional LCD module 51 are denoted by the same reference numerals, and redundant description will be omitted.

The mobile phone 1 shown in FIG. 1 has an upper housing 2 and a lower housing 3. Inside the upper housing 2, a PCB (Printed Circuit Board) for controlling a keyboard 4 or the like corresponding to an operation switch in the present invention is included. Further, inside the lower housing 3, LPUs such as an MPU (Microprocessor Unit) 11 to be described later and an LCD controller 12 for controlling the LCD module 7 are provided.
A control circuit board 5 on which an SI or the like is mounted and a main board 6 on which the control circuit board 5 is mounted are housed. An LCD module 7 is mounted on the main body substrate 6.
Further, on the surface of the main body substrate 6, there are provided a liquid crystal control IC 8 which constitutes an X driver and a Y driver for driving a liquid crystal and a power supply section for an LCD (these will be described later) arranged inside the LCD module 7. A bus line 9 or the like to be connected is formed as a wiring pattern, and the liquid crystal control IC 8 of the LCD module 7 and the MPU 11 and the LCD on the control circuit board 5 are connected via the bus line 9.
The controller 12 is electrically connected to each other.

Next, an outline of the overall electrical configuration will be described with reference to a comprehensive block diagram of the mobile phone 1.

As shown in FIG. 2, in this portable telephone 1, an MPU 11, a keyboard 4 and an LCD controller 12 are connected to each other by a bus line 9, and
The CD controller 12 is connected to the LCD
Connected to module 7. Here, MPU11
Corresponds to a control data generation unit in the present invention, and has a core role of various controls in the mobile phone 1. For example, various data such as a telephone number input from the keyboard 4 are input, and predetermined processing is executed according to the data in accordance with a program stored in the internal ROM. Specifically, for example, when a telephone number is input from the keyboard 4 during transmission,
The display data is transferred to the LCD controller 12 via the bus line 9 and the L
The telephone number is displayed on the LCD panel 21 (see FIG. 4) of the CD module 7. The MPU 11 outputs the input telephone number to a high-frequency unit (not shown), modulates the high-frequency unit with a high-frequency signal having a predetermined frequency, and outputs the modulated high-frequency signal via the antenna 13 (see FIG. 1). To send.

On the other hand, when an incoming call is received, the MPU 11 demodulates the high-frequency signal input via the antenna 13 to the high-frequency section, and when the demodulated telephone number is the own number, the MPU 11 receives the incoming call from the speaker 14 (see FIG. 1). When sound is emitted and various data are received, the L
The contents of the data are displayed on the CD panel 21. When the key switch 4b is pressed in a state where the predetermined key switch 4a of the keyboard 4 shown in FIG. 1 is pressed, the MPU 11 counts the number of times the key switch 4b is pressed, and counts the count. The contrast of the LCD panel 21 is changed by transferring control data for contrast control according to the value to the LCD module 7 via the bus line 9.

The LCD controller 12 sends an X driver 22 and a Y driver 23 in the LCD module 7 to the LCD driver 7 based on the display data output from the MPU 11.
It generates display data for driving the panel 21 and outputs the display data to the LCD module 7 via the bus line 9.

As shown in FIG. 4, the LCD module 7 includes an LCD panel 21 corresponding to a liquid crystal display according to the present invention, and an X driver 22 and a Y driver 23 constituting a driving device of the liquid crystal display according to the present invention. Level shift circuit 24, LCD power supply unit 25, latch circuit 26,
And a D / A converter 27 corresponding to a digital-analog converter in the present invention. Where L
The CD panel 21 is configured by, for example, arranging a plurality of liquid crystal cells in a matrix of 160 dots in a row direction and 240 dots in a column direction. The X driver 22 constitutes a driving unit in the present invention together with the Y driver 23,
Display synchronization signal XS output from D controller 12
The display data XD0 to XD7 are read and latched in synchronization with CL. In addition, the X driver 22 applies predetermined circuit voltages ± V ₂ and ± V ₃ output from the LCD power supply unit 25 to predetermined liquid crystal cells in the column direction specified by the latched display data XD0 to XD7. A drive signal having a voltage value corresponding to the voltage value is output. The Y driver 23 is an LCD
Circuit voltage V _L which is output from the use power source portion 25, a drive signal having a voltage value corresponding to the voltage value of the V _H, LCD controller 1
2 is output to the liquid crystal cells in the row direction in synchronization with the vertical synchronizing signal YD output from 2.

The LCD power supply unit 25 corresponds to the power supply unit in the present invention, and generates a circuit voltage necessary for the X driver 22 and the Y driver 23. LCD power supply 25
As shown in FIG. 5, a positive-direction 1/2 step-down circuit 31, a negative-direction 1/2 step-down circuit 32, a negative-direction double booster circuit 33, a negative-direction 5 × / 6 booster circuit 34, a Y driver logic circuit A power supply voltage generation circuit 35, a _VH voltage generation circuit 36, and a _VL voltage buffer circuit 37 are provided.

The forward half voltage step-down circuit 31 generates a circuit voltage V ₂ necessary for the X driver 22. Here, the circuit voltage V ₂ is a voltage obtained by halving the input power supply voltage V _DD (for example, 3.3 V) in the positive direction with reference to the ground voltage V _SS . The negative-direction 圧 step-down circuit 32 generates a circuit voltage −V ₂ necessary for the X driver 22. here,
The circuit voltage −V ₂ is a voltage obtained by halving the input power supply voltage _DD in the negative direction with reference to the ground voltage V _SS . Further, the negative direction double boosting circuit 33 is connected to the X driver 22.
To generate a circuit voltage −V ₃ necessary for the operation. Here, the circuit voltage −V ₃ is a voltage that is twice the input power supply voltage V _DD in the negative direction with reference to the ground voltage V _SS . Negative direction 5
The double / 6 booster circuit 34 generates a power supply voltage _VEE required to generate the circuit voltages _VH and _VL required for the Y driver 23. Here, the power supply voltage V _EE is equal to the ground voltage V _SS
, The input power supply voltage V _DD is a voltage that is five or six times in the negative direction. Therefore, the power supply voltage V _EE
Is 16.5 V or 19.8 V with reference to the potential of the input power supply voltage V _{DD in} the above example. Further, the step-up ratio of 5 times or 6 times can be switched by an external setting.

The power supply voltage generation circuit 35 for the Y driver logic circuit generates a circuit voltage V _DDY required for the logic circuit of the Y driver 23. Here, the circuit voltage V _DDY is higher than the circuit voltage _VL by the input power supply voltage V _DD . V _H voltage generating circuit 36 generates a circuit voltage V _H required Y driver 23. Here, the circuit voltage _VH has a positive voltage value equal to the absolute value of the circuit voltage _VL .
The V _L voltage buffer circuit 37 is formed of an emitter follower circuit, and has a circuit voltage V _L output from the D / A conversion unit 27.
By current buffering _L1 , a circuit voltage _VL having a voltage substantially equal to the circuit voltage _VL is generated. Note that the circuit voltage _VL corresponds to the reference voltage in the present invention, and functions as a contrast adjustment voltage of the LCD panel 21.

In FIG. 4, the latch circuit 26
MP to adjust the contrast of the LCD panel 21
The contrast control data (hereinafter, also referred to as control data) XD0 to XD4 output from U11 are latched in synchronization with the falling edge of the latch signal LOAD output from MPU11. Here, the control data X
D0 to XD4 are composed of, for example, 5 bits.
The contrast of the LCD panel 21 can be changed in 32 steps. Further, the control data XD0 to XD4 are
The bus line 9 is the same as the display data XD0 to XD7 output from the MPU 11 via the LCD controller 12.
Transferred on. As a result, the MPU 11
As compared with the case where the data is transferred from the mobile phone, the space for arranging the wiring patterns and the cables can be reduced, whereby the size of the mobile phone 1 can be reduced.

The D / A converter 27 generates a circuit voltage V _L1 by performing digital-to-analog conversion of the control data XD0 to XD4 latched by the latch circuit 26. Specifically, the D / A conversion unit 27 sets an arbitrary range to 32 with the ground voltage V _SS and the power supply voltage V _EE output from the LCD power supply unit 25 as upper and lower limits, respectively.
A voltage value divided in stages can be output, and a voltage value specified by the control data XD0 to XD4 is output to the LCD power supply unit 25 as a circuit voltage V _L1 .

Next, a method of adjusting the contrast of the LCD panel 21 in the mobile phone 1 will be described.

First, when the user presses another specific key switch 4b while pressing a specific key switch 4a in the keyboard 4, the MPU 11 causes the key switch 4 to be pressed.
The number of times b is pressed is counted. Then, MPU11
Are control data XD0 to XD corresponding to the count value.
4 is output to the bus line 9 together with the latch signal LOAD. The control data XD0 to XD4 and the latch signal LOAD
The data is transferred to the CD module 7. LCD module 7
Then, the latch circuit 26 latches the control data XD0 to XD4 in synchronization with the falling edge of the latch signal LOAD, and outputs the latched control data XD0 to XD4 to the D / A converter 27. D / A conversion section 27, a control data XD0~XD4 digital - analog conversion, and outputs the converted circuit voltage V _L1 to the LCD power supply unit 25.

[0035] In LCD power supply unit 25, V _L voltage buffer circuit 37 generates a circuit voltage V _L by a current buffer circuit voltage V _L1. Then, V _H voltage generation circuit 36 generates a circuit voltage V _H on the basis of the circuit voltage V _L. Thereafter, the circuit voltages _VL and _VH are both output to the Y driver 23. On the other hand, when the vertical synchronization signal YD is output from the LCD controller 12, the Y driver 23
In synchronization with the vertical synchronizing signal YD, and the ground voltage V _SS
Is output to the LCD panel 21 with the instantaneous values in the positive and negative directions being the circuit voltage _VL and the circuit voltage _VH , respectively, with the ground voltage as the ground potential. Thereby, in the LCD panel 21, for example, when the circuit voltage _VL is V11, as shown in FIG. 6, the ratio (b) between the reflectance a and the reflectance b
The contrast is changed according to / a).

As described above, according to the mobile phone 1 of this embodiment, the specific key switch 4 of the keyboard 4
The contrast of the LCD panel 21 can be changed by operating the keys a and 4b. Therefore, the size of the mobile phone 1 can be reduced as compared with the case where a mechanical volume is used. Further, since a mechanical volume or the like is not used, a contact failure is unlikely to occur, so that a long-life and highly reliable mobile phone can be configured. Also, as the contrast can be changed only by the simultaneous key operation of the two key switches 4a and 4b, when the user stores the mobile phone 1 in a pocket or the like, clothes or the like touch the key switches 4a and 4b. Even if the user does not know the LCD panel 2
It is possible to reliably avoid the inconvenience that the contrast of 1 changes.

The present invention is not limited to the above embodiment. For example, in the present embodiment, the control data XD0 to XD0
Although XD4 is transferred on the bus line 9, the latch circuit 26 and the D / A converter 27 are
It is configured separately from the D module 7, and the control data XD0 to XD
D4 may be transferred. Further, a circuit for reading the key switch signal of the keyboard 4 may be constituted by a gate array separate from the MPU 11 or the like.

In the present embodiment, the contrast is varied by changing the voltage value of the drive signal by the Y driver 23. However, the voltage value of the drive signal by the X driver 22, or both voltage values are changed. It may be configured as follows. Further, the liquid crystal display may be of a transmission type. Further, as the operation of the operation switch, the contrast may be changed not according to the number of times of pressing but according to the pressing time.

Further, in the present embodiment, the control data for contrast control is 5-bit data, but the present invention is not limited to this, and may be 4-bit or less, or 6-bit or more control data. In the present embodiment, the latch circuit 26 and the D / A conversion unit 27 are configured as independent circuits. However, these may be included in the X driver 22, and each component may be configured as a gate array or the like. The configuration can be changed as appropriate.

In this embodiment, the portable telephone 1
However, the present invention can be suitably applied to electronic devices and information devices such as an electronic organizer, a personal computer, and a liquid crystal television.

[0041]

As described above, according to the method for adjusting the contrast of a liquid crystal display according to the first aspect, the control data for adjusting the contrast is controlled according to the operation of the operation switch without using a mechanical volume or the like. By the generation, the size of the device can be reduced, and the reliability of the device equipped with the liquid crystal display can be improved.

According to the method for adjusting the contrast of a liquid crystal display according to the second aspect, a control switch is generated by operating at least two operation switches. Even when clothing touches the control switch when the clothing is stored in a pocket of clothing, it is possible to avoid such a situation that the contrast is changed.

Further, according to the method of adjusting the contrast of the liquid crystal display according to the third aspect, even when the display area of the liquid crystal display is enlarged, the user can easily adjust the contrast of the liquid crystal display. In addition to the setting, it is possible to effectively prevent the unintended setting deviation of the contrast once set.

Further, according to the liquid crystal display driving device of the present invention, the control data for contrast adjustment generated by the control data generating unit in response to the operation of the operation switch is referenced by the digital-analog converting unit. As a result, the driving unit outputs a drive signal having a voltage value corresponding to the reference voltage, so that the contrast of the liquid crystal display can be changed. As described above, the control data for contrast adjustment is generated in accordance with the operation of the operation switch without using a mechanical volume or the like, so that the device can be downsized and the liquid crystal display is mounted. The reliability of the device can be improved.

According to the driving device for a liquid crystal display of the present invention, when driving a liquid crystal cell having transparent electrodes arranged in a matrix, an output from at least one of a row direction driver and a column direction driver is provided. By changing the voltage value of the drive signal to be performed based on the control data,
The contrast of the liquid crystal display can be reliably changed.

According to the liquid crystal display driving device of the present invention, the control data for contrast control is transferred to the digital-analog conversion unit via the data bus for transferring the display data. As a result, the space for wiring can be reduced as compared with the case where a dedicated line for transferring control data is used, so that the device can be downsized.

Further, according to the portable information device of the present invention, by operating at least two operation switches to adjust the contrast, the portable information device equipped with a liquid crystal display can be used for a clothing pocket or the like. Even when the clothing touches the control switch while the garment is being stored, the situation in which the contrast changes can be avoided.

According to the driving device for a liquid crystal display according to the present invention, the display area of the liquid crystal display is enlarged by applying the driving device for the liquid crystal display to a portable information device. In this case, the user can easily set the contrast of the liquid crystal display device, and it is possible to effectively prevent an unintended setting deviation of the once set contrast.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of a mobile phone according to an embodiment of the present invention.

FIG. 2 is an overall electrical block diagram of the mobile phone according to the embodiment of the present invention.

FIG. 3 is a general block diagram of a mobile phone according to another embodiment of the present invention.

FIG. 4 is an electrical block diagram of the LCD module according to the embodiment of the present invention.

FIG. 5 is a block diagram showing an internal configuration of an LCD power supply unit.

FIG. 6 is an explanatory diagram illustrating the concept of contrast adjustment in a liquid crystal display.

FIG. 7 is a diagram showing a circuit voltage _VL and a contrast curve of the liquid crystal display with respect to the circuit voltage _VL .

FIG. 8 is an electrical block diagram of an LCD module already developed by the applicant.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mobile telephone 4 Keyboard 4a, 4b Key switch 11 MPU 9 Bus line 21 LCD panel 22 X driver 23 Y driver 24 LCD power supply 27 D / A converter

Claims (8)

[Claims] 1. A voltage value of a driving signal for driving a liquid crystal display output by a driving unit is changed based on a switch operation of an operation switch for contrast adjustment,
In the contrast adjusting method for a liquid crystal display for adjusting the contrast of the liquid crystal display, a contrast control data is generated based on a switch operation of the operation switch, and the generated contrast control data is subjected to digital-analog conversion. A method for adjusting a contrast of a liquid crystal display, comprising: generating a reference voltage; and generating the drive signal based on the generated reference voltage. 2. The method according to claim 1, wherein the contrast control data is generated by operating at least two operation switches. 3. The liquid crystal display device according to claim 1, wherein the driving unit drives a liquid crystal display provided in the portable information device.
Or the method for adjusting the contrast of a liquid crystal display according to 2. 4. A driving unit for driving a liquid crystal display by outputting a driving signal having a voltage value according to an input circuit voltage, and an operation for adjusting a voltage value of a reference voltage serving as a reference of the circuit voltage for contrast adjustment A driving device for a liquid crystal display, comprising: a reference voltage varying unit that varies based on a switch operation of a switch; and a power supply unit that generates the circuit voltage based on the reference voltage and outputs the circuit voltage to the driving unit. A reference voltage varying unit configured to generate contrast control data based on a switch operation of the operation switch, and to generate the reference voltage by performing digital-to-analog conversion on the generated contrast control data; A digital-to-analog conversion unit, wherein the power supply unit is output from the digital-to-analog conversion unit. Liquid crystal display apparatus for driving and generating said circuit voltage based on the serial reference voltage. 5. The liquid crystal display comprises a liquid crystal cell having transparent electrodes arranged in a matrix, and the driving unit synchronizes with the input display data in a row direction of the liquid crystal display. A row-direction driver that outputs a drive signal; and a column-direction driver that outputs a drive signal in a column direction of the liquid crystal display in synchronization with the input display data, wherein the power supply unit is based on the reference voltage. 5. The driving device for a liquid crystal display according to claim 4, wherein the circuit voltage generated by the driving is output to at least one of the row direction driver and the column direction driver. 6. The liquid crystal display according to claim 5, wherein the contrast control data is output to the digital-analog conversion unit via a data bus for transferring the display data. Drive. 7. The operation switch according to claim 4, wherein the operation switch comprises at least two switches.
7. The driving device for a liquid crystal display according to any one of items 1 to 6. 8. A portable information device comprising the liquid crystal display driving device according to claim 4. Description: