JPH06168207A - Display driving voltage generating circuit for liquid crystal display device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a control volume for varying the maximum display drive voltage itself in a display drive voltage generation circuit of a liquid crystal display device used for small electronic devices such as a calculator and an electronic notebook. The purpose is to lower the required power supply voltage, eliminate the booster circuit, and extend the life of the battery power supply by reducing power consumption. [Structure] An output stage V2 divided into a plurality of stages between an output stage V1 of the highest drive voltage VLCD and an output stage V6 of the lowest drive voltage.
In V5, the contrast adjusting volume VR is directly interposed between the third and fourth output stages V3 and V4, and the other output stage V
1 to V2, V2 to V3, V4 to V5, and V5 to V6, the voltage level between the output stages is adjusted by adjusting the potential difference by the resistance ratio with each fixed resistor R interposed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display drive voltage generating circuit for a liquid crystal display device used in small electronic equipment such as a calculator and an electronic notebook.

[0002]

2. Description of the Related Art In general, a liquid crystal display panel used for a calculator, an electronic notebook, etc. is a display medium utilizing light transmittance, and therefore has a property that it is difficult to obtain a wide viewing angle.
Therefore, even if the viewing angle is slightly changed, the contrast is changed and it becomes difficult to see.

Therefore, normally, a contrast adjusting volume is provided on the main body of the apparatus, and the user obtains an appropriate contrast display state by adjusting the volume.

The liquid crystal display section generally drives a plurality of segments in a time division manner, and in order to perform the time division drive, a plurality of levels of drive voltages divided into a plurality of stages of potential differences are required.

FIG. 2 shows the structure of a conventional display drive voltage generating circuit of a liquid crystal display device. In FIG. 2, R is a fixed resistor having a preset resistance value, and VR is the contrast adjusting volume. The variable resistor C is a capacitor that smoothes the voltage waveforms of the drive voltage output stages V1 to V6, the LCD is a liquid crystal display unit, the D / D is a display driver, and the CPU is a display control unit.

Here, assuming that the applied voltage Vcc = 7 (V), VR = 0 (Ω) and the highest voltage output stage V1 = 7.
(V), minimum voltage output stage V6 = 0 (V), for example VR = 2 (kΩ), maximum voltage output stage V1 = 6 (V),
The minimum voltage output stage V6 becomes 0 (V).

That is, the maximum drive voltage VLCD of the liquid crystal display LCD is adjusted in the range of 6 to 7 (V), and the drive voltages obtained in the other voltage output stages V2 to V5 are also compressed and expanded according to the adjustment. To be done.

The display driver D / D is
The liquid crystal display unit receives the output voltages of six levels from the six voltage output stages V1 to V6, creates a scanning signal and a data signal that combine the voltage waveforms of the above six levels according to a display control command from the display control unit CPU. It is supplied to the LCD to drive the display.

[0009]

However, in the above-mentioned conventional display drive voltage generation circuit, the highest drive voltage VLCD itself in the highest voltage output stage V1 is variably adjusted by the contrast control volume VR, and the lowest voltage output stage below that. Since the drive voltage of each of the output stages V2 to V5 divided between V6 and V6 is changed, a higher applied voltage Vcc in consideration of the voltage drop due to the volume VR is required, which requires a booster circuit and power consumption. Is a big problem.

The present invention has been made in view of the above problems,
Display of a liquid crystal display device that can lower the required power supply voltage, eliminate the booster circuit, and extend the life of the battery power supply by reducing the power consumption without providing a control volume that changes the maximum drive voltage itself. An object is to provide a drive voltage generation circuit.

[0011]

That is, a display drive voltage generating circuit of a liquid crystal display device according to the present invention generates a drive voltage of a predetermined stage required for time-divisional driving of a liquid crystal display unit. One of a plurality of output stages between the voltage output stage and the lowest voltage output stage that generates the lowest drive voltage among the predetermined drive voltage output stages and the highest voltage output stage that generates the highest drive voltage. A variable resistor interposed between the output stages and adjusted from the outside of the device is provided, and by adjusting the variable resistor, the minimum drive voltage of the minimum voltage output stage and the maximum drive voltage of the maximum voltage output stage remain constant. The configuration is such that the generated drive voltage in each output stage is increased or decreased.

[0012]

In other words, a variable resistor is directly arranged between any one of the output stages having the highest drive voltage and the lowest drive voltage to adjust the potential difference between the output stage and the other output stage. The voltage level obtained from the stage will also be adjusted,
It is not necessary to arrange a volume for adjusting the maximum drive voltage itself.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of a display drive voltage generating circuit of a liquid crystal display device. Six voltage output stages V1 to V6 are provided separately between a power supply applied voltage Vcc and a ground voltage.

Between the highest voltage output stage V1 and the second voltage output stage V1, which are directly connected to the power source applied voltage Vcc, between the second voltage output stage V2 and the third voltage output stage V3, and the ground voltage. Between the lowest voltage output stage V6 and the fifth voltage output stage V5 which are directly connected to the fifth voltage output stage V5 and the fourth voltage output stage V5.
A fixed resistor R having the same preset resistance value (for example, 2 kΩ) is interveningly connected to each other. And
A contrast control volume VR is connected between the third voltage output stage V3 and the fourth voltage output stage V4.

Here, the resistance value variable range in the contrast adjusting volume VR is, for example, “2 (kΩ) ≧
VR> 0 ”, and is set in a range that does not cause a short circuit even with the lowest adjustment value. In addition, the above six voltage output stages V1, V2,
Smoothing capacitors C having the same preset capacitance value are connected to V3, V4, V5 and V6, respectively.

The display driver D / D receives 6-level output voltages from the 6 voltage output stages V1 to V6, and scans a combination of the 6-level voltage waveforms according to a display control command from the display control unit CPU. A signal and a data signal are created and supplied to the liquid crystal display unit LCD.

That is, when the power supply voltage Vcc = 6 (V), the highest drive voltage V obtained in the highest voltage output stage V1 is obtained.
The LCD has a fixed voltage of 6 (V), and the minimum drive voltage obtained at the minimum voltage output stage V6 is fixed at 0 (V).

When the contrast control volume VR interposed between the third voltage output stage V3 and the fourth voltage output stage V4 is adjusted to its maximum value "2 (kΩ)", the maximum drive voltage VLCD = 6 (V) is six output stages V1 to V
The voltage is equally divided between 6 and about 4.8 in the second voltage output stage V2.
(V), about 3.6 (V) at the third voltage output stage V3,
A driving voltage of about 2.4 (V) is obtained at the voltage output stage and a driving voltage of about 1.2 (V) is obtained at the fifth voltage output stage V5.

On the other hand, the contrast adjusting volume V
When R is adjusted to its minimum value "100 (Ω)", the maximum drive voltage VLCD = 6 (V) is equal to the six output stages V1 to V1.
The voltage is divided according to the resistance ratio between 6 and between V1 and V2,
A potential difference of about 1.48 (V) occurs between V2 and V3, between V4 and V5, and between V5 and V6, and V3 to V3.
Since a potential difference of about 0.07 (V) occurs between 4 and
The voltage output stage V2 has approximately 4.51 (V), the third voltage output stage V3 has approximately 3.03 (V), and the fourth voltage output stage has approximately 2.
96 (V), about 1.48 (V) in the fifth voltage output stage V5
Drive voltage can be obtained.

Therefore, according to the display drive voltage generating circuit of the liquid crystal display device having the above structure, the output stages V2 to V5 are divided into a plurality of stages between the output stage V1 of the highest drive voltage VLCD and the output stage V6 of the lowest drive voltage. Among the third to fourth output stages V
The contrast adjustment volume VR is directly interposed between 3 and V4, and other output stages V1 to V2, V2 to V3 and V4 to V are provided.
By adjusting the potential difference by the resistance ratio with each fixed resistor R interposed between V5, V5 and V6, the voltage level between the output stages is adjusted, and the maximum drive voltage itself required conventionally is adjusted. It is possible to realize a long life of the battery power source by lowering the voltage Vcc applied to the power source, abolishing the booster circuit, and reducing the power consumption without requiring a volume.

In the above embodiment, the variable resistor adjusted from the outside is used. However, for example, transistors having different ON resistances may be connected in parallel and the resistance value may be changed by turning on any one of them. .

[0023]

As described above, according to the present invention, a drive voltage of a predetermined stage required for time-divisional driving of a liquid crystal display unit is generated, and a drive voltage output stage of a predetermined stage and a drive voltage of the predetermined stage. A variable resistor interposed between any one of a plurality of output stages between the lowest voltage output stage that generates the lowest drive voltage and the highest voltage output stage that generates the highest drive voltage among the output stages. Since the minimum drive voltage of the lowest voltage output stage and the highest drive voltage of the highest voltage output stage are fixed by adjusting the variable resistance, the generated drive voltage in each output stage during that period is increased or decreased, It is possible to reduce the required power supply voltage, eliminate the booster circuit, and extend the life of the battery power supply by reducing the power consumption, without providing a control volume that varies the maximum drive voltage itself.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a display drive voltage generating circuit of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a conventional display drive voltage generation circuit of a liquid crystal display device.

[Explanation of symbols]

LCD: liquid crystal display, D / D: display driver,
CPU ... Display control unit, VCC ... Applied voltage, VLCD ... Maximum driving voltage, V1 to V6 ... Voltage output stage, R ... Fixed resistance, VR
… Contrast control volume, C… Smoothing capacitor.

Claims (1)

[Claims] 1. A display drive voltage generating circuit of a liquid crystal display device for generating a drive voltage of a predetermined stage required for time-division driving of a liquid crystal display unit, wherein a drive voltage output stage of a predetermined stage and a drive voltage output stage of the predetermined stage. Of the plurality of output stages between the lowest voltage output stage that generates the lowest drive voltage and the highest voltage output stage that generates the highest drive voltage. However, by adjusting the variable resistance means, the minimum drive voltage of the lowest voltage output stage and the highest drive voltage of the highest voltage output stage are kept constant, and the generated drive voltage in each output stage in the meantime is increased or decreased. Display drive voltage generation circuit for liquid crystal display device.