JPS61289324A - Voltage control system of liquid crystal driving device - Google Patents

Abstract

PURPOSE:To make the dielectric strength of a liquid crystal device (LCD) driver lower than before and to reduce the cost of the LCD driver by varying a bias ratio as a method for varying an effective applied voltage according to variation in the Vth of the LCD. CONSTITUTION:The bias value (a) is varied to vary V(LCD). Namely, a thermistor RV' is inserted and then the bias value (a) varies with temperature, so the effective voltage is varied according to variation in temperature. For example, when the resistance value of the thermistor RV' decreases, reference liquid crystal driving voltage V1 and V4 vary to V1' and V4'. A scanning electrode driving signal varies and when the resistance value of the thermistor RV' increases, reference liquid crystal driving voltage V2 and V3 vary to V2' and V3', so a signal electrode driving signal varies. Therefore, when the temperature falls and the Vth of the LCD increases, the effective voltage V is raised automatically, so the LCD is driven with excellent contrast.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a liquid crystal drive in which the bias ratio is varied as a method of changing the applied effective voltage according to changes in the threshold voltage vth of a liquid crystal display (LCD). It relates to a voltage control method for devices.

[Prior art and its problems 1: Liquid crystal display devices used in liquid crystal television receivers, etc. [(
When performing nxm 7-trix display on the display section of a LCD (LCD), scanning electrode drive signals as shown in FIG. 2(A) and scanning electrode drive signals as shown in FIG. A signal electrode drive signal as shown in (A) is required. However, the threshold voltage vth of such an LCD changes due to changes in ambient temperature and the like. Therefore, in order to drive the LCD with good contrast without being affected by ambient temperature changes, it is necessary to change the effective voltage applied to the LCD in accordance with the change in the threshold voltage vth. As a method of changing the applied effective voltage, a method as shown in FIG. 4 has conventionally been used. FIG. 4 shows a circuit for creating the reference liquid crystal drive voltages ①O to V5. In FIG. 4, Va is a liquid crystal driving power supply, and this power supply Va is applied to both ends of resistors R1 to R5 connected in series via a variable resistor RV.

As a result, the power supply Va is divided into voltages VO-V5.
is created. This voltage VO-V5 is applied to a scanning electrode drive circuit (not shown) and a signal 1! is sent to a pole drive circuit (not shown). Then, the scanning N-pole drive circuit operates at the voltage V
O, V1. Select the voltage of V4゜v5 and display the second voltage on the LCD.
A scanning electrode drive signal as shown in Figure (A) is output. Further, the signal electrode drive circuit operates at the voltages VO, V2°V3. By selecting the voltage V5, a signal electrode drive signal as shown in FIG. 3 (A>) is output to the LCD.

Then, when the threshold voltage of the LCD changes, the variable resistor R
The effective voltages applied to the scan electrode drive signal and the signal electrode drive signal were varied by increasing or decreasing V to change the voltages vO to 5.

However, if the effective voltages applied to the scanning electrode drive signal and signal electrode drive signal applied to the LCD are changed in accordance with changes in the threshold voltage vth, a high drive voltage is required at low temperatures. Driver required. For this reason, when the withstand voltage of the LCD driver is increased,
When integrating an LCD driver, there are disadvantages in that the chip size increases and the IC manufacturing process becomes complicated, leading to increased manufacturing costs.

[Object of the Invention] The present invention has been made in view of the above-mentioned points, and the present invention is made by keeping the driving voltage constant and varying the bias ratio to apply it in response to changes in the threshold voltage vth of a liquid crystal display (LCD). It is an object of the present invention to provide a voltage 1113111 method for a liquid crystal driving device that changes the effective voltage.

[Key Points of the Invention] By using, for example, a temperature compensation element in one of a plurality of series-connected resistors to which a liquid crystal drive power supply is applied, the bias ratio is varied according to concentration changes, and the effective voltage applied to the liquid crystal drive device is adjusted. By changing the voltage, the withstand voltage of the LCD driver is lower than that of the conventional type, and the cost of the LCD driver is reduced.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure shows a circuit for creating the reference liquid crystal drive voltage VO-V5. In FIG. 1, Vb is a driving voltage which is a constant voltage. This driving voltage vb is supplied to both ends of the resistors R11 to R14 and thermistor RV' which are connected in series, and as shown in the figure, the reference liquid crystal driving voltage V
O to V5 is obtained. And this voltage ■0 ~ ■5
Based on the voltages VO, V1 . V4. V5 is selected and a scan electrode drive signal is created, and at the same time voltages VO, V2 . V3. V5 is selected and a signal electrode drive circuit is created.

By the way, the effective voltage V (LCD) of the scanning electrode drive signal and the signal electrode drive signal applied to the LCD is expressed as in the following equation.

Here, N: duty ratio, V: drive voltage, and a: bias ratio.

As is clear from the above equation, V (LCD) can be changed by changing the bias ratio a. That is, since the bias ratio a changes according to the temperature by inserting the thermistor RV', the effective voltage V is varied according to the temperature change. For example, thermistor RV'
When the resistance value becomes small, the reference liquid crystal drive voltage V1
．． Since V4 changes to Vl' and V4', the scanning electrode drive signal changes as shown in Figure 2 (A) to (B), and when the resistance value of thermistor RV' increases, the reference liquid crystal drive Voltage V2. Since V3 changes to V2' and V3', the signal electrode drive signal changes as shown in FIG. 3(A) to (B). Therefore, the temperature decreases and the LCD v
As th increases, the effective voltage (2) is automatically increased, so the LCD is driven with good contrast.

In the above embodiment, a thermistor is used as RV', but the present invention is not limited to this.

[Effects of the Invention] As detailed above, according to the present invention, the liquid crystal display device [(L
As a method of changing the applied effective voltage according to changes in vth of the CD, the bias ratio is varied, so the withstand voltage of the LCD driver is lower than that of conventional ones.
It is possible to provide a voltage control method for a liquid crystal driving device that can reduce the cost of an LCD driver.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing an embodiment of the present invention, Figure 2 (A)
and (8) are diagrams showing scan electrode drive signals, respectively.
Figures (A) and (B) are diagrams showing signal electrode drive signals, the fourth
The figure is a diagram showing a voltage control method of a conventional liquid crystal driving device. R11 to R14...Resistor, RV'...Thermistor. Applicant's agent Patent attorney Takehiko Suzue Figure 2 Figure 3

Claims (1)

[Claims] In a voltage control method for a liquid crystal drive device in which a plurality of reference liquid crystal drive voltages are formed by dividing the voltage obtained from a liquid crystal drive power source, one of the plurality of series-connected resistors to which the liquid crystal drive power source is applied is Using a variable bias ratio element,
A voltage control method for a liquid crystal drive device, characterized in that the applied effective voltage applied to the liquid crystal display device is changed by varying the bias ratio.