JPH04331915A - Liquid crystal display unit - Google Patents

Abstract

PURPOSE:To make an image display of high quality even in any temperature environment by switching temperature-driving voltage characteristics which are determined by ranges of ambient temperature. CONSTITUTION:A voltage dividing circuit 10 and 12 which supply a voltage to a liquid crystal driver 15 are provided and switched and used selectively by turning on and off an analog switch 13 according to the switching signal of a liquid crystal bias switching circuit 2. A voltage detector 4 monitors the voltage level of the voltage applied to the liquid crystal driver 15 and a central arithmetic processing unti(CPU) 1 inputs the detected voltage value from a voltage detector 4 and indicates the voltage dividing circuits to be used to the liquid crystal bias switching circuit 6 according to the voltage value. Further, the CPU 1 performs voltage control using the voltage dividing circuit 12 at all time while there is an indication of contrast necessity from a display information generation source, and uses the voltage dividing circuit 10 when the ambient temperature is the room-temperature range and the voltage dividing circuit 12 when not unless there is the indication of the contrast necessity.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display that displays characters and images using liquid crystal.

0002

2. Description of the Related Art FIG. 6 shows a circuit configuration of a control system of a typical conventional liquid crystal display.

In FIG. 6, an AC voltage for application to each liquid crystal is applied from a liquid crystal driver 15 to a liquid crystal panel 16 in which liquid crystals are arranged in a dot matrix form.

A positive voltage generating circuit 3 and a negative voltage generating circuit 6 are provided as power supply sources for the liquid crystal driver 15, and the voltage difference between the voltage generated by the positive voltage generating circuit 3 and the voltage generated by the negative voltage generating circuit 6 is By dividing the voltage by the voltage dividing circuit 10, a driving voltage is supplied to the driver 15 via the amplification buffer 14.

The liquid crystal concentration adjustment circuit 5 variably sets the partial pressure level in accordance with the temperature detected by the temperature sensor 5A in order to adjust the liquid crystal concentration. Characteristic A in FIG. 3 is used for the temperature-voltage characteristic at this time. This characteristic curve is set so that crosstalk is not noticeable and the display contrast is at an optimal level at room temperature. Note that crosstalk is a phenomenon in which the transmittance of the dots above and below the column in which the vertical line is displayed changes from its original value, making the vertical line appear to have tails at the top and bottom.

Transistor 7 receives voltage from liquid crystal concentration adjustment circuit 5 and amplifies current.

Base resistor 8 limits the base current of transistor 7.

[0008]

[Problem to be Solved by the Invention] However, in conventional liquid crystal displays of this type, when temperature-partial-voltage (driving voltage) characteristics are set for the purpose of high-quality display, the partial voltage changes dramatically in a low-temperature environment. As shown in characteristic A of No. 3, the voltage exceeds the permissible voltage range of the liquid crystal driver 15, and the liquid crystal driver becomes unstable. As a result, there was a problem in that the display was distorted.

[0009] In order to eliminate such a problem, as shown in FIG.
It is conceivable to use temperature/partial pressure characteristics such that the partial pressure level at low temperatures falls within the stable operation region of the liquid crystal driver 15, such as the characteristics of the voltage dividing circuit II shown in FIG.

However, in this temperature-partial-pressure characteristic,
New problems arise, such as crosstalk at room temperature and suboptimal contrast conditions.

Therefore, in conventional liquid crystal displays, the voltage dividing ratio of the voltage dividing circuit 10 had to be determined as a compromise, taking into consideration the balance between display quality and temperature environment.

SUMMARY OF THE INVENTION In view of the above-mentioned points, an object of the present invention is to provide a liquid crystal display device capable of displaying the highest quality display even at room temperature or low temperature.

[0013]

[Means for Solving the Problems] In order to achieve the above object, the present invention detects the environmental temperature and variably sets the driving voltage of the liquid crystal display panel in accordance with the detected temperature, thereby adjusting the liquid crystal concentration. In the liquid crystal display device, a voltage detecting means for detecting the driving voltage level and a plurality of different temperature-driving voltage characteristics are determined in advance, and the driving voltage level detected by the voltage detecting means and the plurality of types of temperature-driving voltage characteristics are determined in advance. a comparison means for comparing a switching threshold level determined for each temperature-drive voltage characteristic; and a selection means for selecting a temperature-drive voltage characteristic from among the plurality of temperature-drive voltage characteristics based on the comparison result. and voltage control means for controlling the drive voltage of the liquid crystal panel according to the selected temperature-drive voltage characteristic.

[0014]

[Operation] The present invention prepares a plurality of suitable temperature drive voltage characteristics for each temperature range to be variably set according to the temperature, and selects the characteristics suitable for the current environmental temperature from the detection result of the current drive voltage. The selection is made based on the comparison means and selection means.

[0015]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows the circuit configuration of an embodiment of the present invention.

The same parts as in the conventional circuit configuration shown in FIG. 5 are denoted by the same reference numerals, and detailed explanation thereof will be omitted.

In FIG. 1, in this embodiment, a voltage dividing circuit (numeral 11) and a voltage dividing circuit II (numeral 12) for supplying voltage to the liquid crystal driver 15 are provided in the voltage control circuit.
Based on the switching signal from the liquid crystal bias switching circuit 2, the two voltage dividing circuits are selectively switched and used by opening and closing the analog switch 13. As shown in FIG. 2, the voltage dividing circuit I is configured so that the driving voltage for the liquid crystal driver is partially lower than that of the voltage dividing circuit II.

Voltage detector 4 monitors the voltage level of voltage V5 supplied to the liquid crystal driver.

The central processing unit (CPU) 1 inputs the detected voltage value from the voltage detector 4, and instructs the liquid crystal bias switching circuit 6 which voltage dividing circuit to use based on this voltage value.

The CPU 1 also includes a display information generation source (not shown),
For example, in response to an information signal indicating whether or not contrast is necessary from a document processing device or an image processing device, it also instructs switching of the voltage dividing circuit.

In this embodiment, the switching conditions for voltage dividing circuits I and II are determined as follows.

(i) While there is an external instruction that contrast is "required", voltage control is always performed using the voltage divider circuit II.

(ii) When there is no instruction to contrast "required", the voltage is controlled using the voltage divider circuit I while the environmental temperature is in the normal temperature range, and the voltage is controlled using the voltage divider circuit II while the environment temperature is in the low temperature range. Perform voltage control using

[0025] The CPU 1 for performing such voltage control
The control processing procedure is shown in FIG. 5, and while referring to FIG.
The circuit operation will be explained.

Note that the circuit club shown in FIG. 5, when turned on, supplies voltage divider circuit II (characteristic B in FIG. 3) from the CPU 1 to the liquid crystal bias switching circuit 2 and the liquid crystal adjustment circuit 5.
A signal specifying voltage dividing circuit I (characteristic A in FIG. 3) is held and output when the circuit flag is off.

Further, the CPU 1 executes the control procedure shown in FIG. 5 to control the switching of the voltage dividing circuits I and II.
The control procedure is temporarily interrupted and the signal is held and stored in an internal register.

In FIG. 5, the CPU 1 refers to the contents stored in the internal register, and when it confirms that the contrast "required" is specified, turns off the control flag and prohibits switching of the voltage dividing circuit. Next, the circuit flag is turned on and the voltage dividing circuit II is set to be used (steps S10→S100→S110→S120 in FIG. 5).

[0029] From now on, the contrast "unnecessary" instruction is given to the CP.
Until U1 receives it, the execution procedure repeats the loop process of steps S10 → S100 → S10 due to the contrast “required” signal of the internal register of CPU 1 and the off setting of the circuit flag, and the voltage dividing circuit II is in use. Continue.

When the CPU 2 receives a contrast "unnecessary" signal from the outside in this state, the contents of the signal in the internal register are updated, so the execution procedure in FIG. 5 proceeds from step S10 to step S200. Here, the CPU 1 confirms based on the contents of the control flag that switching of the voltage dividing circuit is currently prohibited, turns on the control flag, and permits switching of the voltage dividing circuit (step 200→S210 in FIG. 5).
).

Next, the CPU 1 performs steps S220 to S2.
Automatic switching control processing S100 for voltage dividing circuit No. 55
Transition to 0.

This control process will be explained next.

After reading the voltage value detected by the voltage detector 4, the CPU 1 refers to the circuit flag to identify which voltage dividing circuit is currently being used.

When the circuit flag is on and the voltage divider circuit II is used, the read voltage value and switching threshold value VV
V (see FIG. 3). As a result of this comparison, if the read voltage value is smaller than the switching threshold VVV,
CPU1 determines that the current environmental temperature is in the normal temperature range,
The circuit flag is turned off and the voltage dividing circuit currently being used is switched to voltage dividing circuit I (step S230→S2
40→S245).

In addition, in the process of identifying the circuit to be used in step S230, if the circuit flag indicates OFF and the voltage dividing circuit I is being used, the read detection voltage and the second switching threshold value VV (see FIG. 3) Compare with. As a result of this comparison,
If the read voltage is larger than the second switching threshold VV, the CPU 1 determines that the current environmental temperature is in the low temperature range, turns on the circuit flag, and switches the voltage divider circuit in use to the voltage divider circuit I.
Switch to I (step SS230 → S250 → S25
5).

[0036] Hereinafter, the CPU 1 performs steps S10→S20.
A loop process of 0→S1000→S10 is executed to perform automatic switching control of the voltage dividing circuit.

For example, when voltage dividing circuit I is used (
Since the detection voltage is smaller than the second threshold value VV while the ambient temperature is below normal temperature (circuit flag off), the execution procedure in step S1000 is from step S220 to S.
230→S250→S10, and the currently used circuit is maintained as it is.

When the environmental temperature falls into the low temperature range, the circuit to be used is automatically switched from the voltage dividing circuit I to the voltage dividing circuit II according to the above-described processing procedure (steps S250→S255) according to an instruction from the CPU 1.

Furthermore, using the voltage dividing circuit II, the detected voltage is greater than the threshold value VVV while the environmental temperature is in the low temperature range, so the execution procedure in step S1000 is as follows: steps S220→S230→S210→S10. The current circuit used is maintained.

As described above, when the environmental temperature shifts to the normal temperature range in this state, the circuit used is switched from the voltage dividing circuit II to the voltage dividing circuit I.

As explained above, in this embodiment, by monitoring the voltage supplied to the liquid crystal driver and switching between two different temperature-voltage characteristics, display defects that conventionally occur in low-temperature environments can be resolved. do.

Furthermore, by making it possible to switch the temperature-voltage characteristic, it is also possible to express contrast based on external instructions.

In addition to this embodiment, the following examples can be given.

(1) In this embodiment, the switching conditions in the CPU 1 are determined based on the detected voltage, but the detected temperature of the temperature sensor 5A may also be used.

In this case, the CPU 1 also instructs the liquid crystal density adjustment circuit 5 as to the type of temperature-voltage characteristic to be used, which has the disadvantage that the number of input/output signals to the CPU 1 increases.

(2) In this embodiment, switching control of the voltage dividing circuit is performed by the CPU, but it goes without saying that the control procedure of FIG. 3 may be implemented by an analog sequence circuit.

(3) In this embodiment, the contrast "required" signal is input from the outside. For example, this signal may be generated when an image processing device handles an image pattern in which crosstalk is difficult to recognize, such as a pattern with few vertical lines, or an image pattern that requires contrast. The generation of the contrast "required" signal may be triggered by an operator's instruction or automatically. In this case, the image processing device side compares the number of black or white pixels in a specific area in the image pattern to be displayed with a threshold value, and based on the comparison result, determines whether or not a contrast "required" signal is generated. do.

[0048]

According to the present invention, since the liquid crystal display panel is driven using the most suitable temperature-drive voltage characteristic determined for each environmental temperature range, the drive voltage does not exceed the allowable range as in the conventional case. A high-quality display image can be obtained without exceeding the limit.

Furthermore, by using a specific temperature-driving voltage characteristic regardless of the environmental temperature based on an instruction from the outside, it is also possible to display a high contrast display.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the circuit configuration of an embodiment of the present invention.

FIG. 2 is a waveform diagram showing driving waveforms of the liquid crystal driver in FIG. 1;

FIG. 3 is an explanatory diagram showing two types of temperature-drive voltage characteristics in an example of the present invention.

FIG. 4 is an explanatory diagram showing the level of a switching signal of the liquid crystal bias switching circuit 2 of FIG. 1 and the type of selected voltage dividing circuit.

FIG. 5 is a flowchart showing the processing procedure of the CPU 1 according to the embodiment of the present invention.

FIG. 6 is a block diagram showing a circuit configuration of a conventional example.

[Explanation of symbols]

1 CPU 2 Liquid crystal bias switching circuit 3 Positive voltage generation circuit 4 Voltage detector 5 Liquid crystal density adjustment circuit 5A Temperature sensor 6 Negative voltage generation circuit 7 Transistor 8 Current limiting resistance 11 Voltage divider circuit I 12 Voltage divider circuit II 13 Analog switch 14 Amplification buffer 15 Driver 16 Liquid crystal display panel 20 Voltage control circuit

Claims (2)

[Claims] 1. In a liquid crystal display device that adjusts liquid crystal density by detecting an environmental temperature and variably setting a driving voltage of a liquid crystal display panel in accordance with the detected temperature, a voltage detecting means for detecting the driving voltage level. and a plurality of different types of temperature-drive voltage characteristics are determined in advance, and the drive voltage level detected by the voltage detection means is compared with a switching threshold level determined for each of the plurality of types of temperature-drive voltage characteristics. a selection means for selecting a temperature-drive voltage characteristic from among the plurality of temperature-drive voltage characteristics based on the comparison result; and a selection means for selecting a temperature-drive voltage characteristic from the plurality of temperature-drive voltage characteristics based on the comparison result; A liquid crystal display comprising voltage control means for controlling. 2. A specific temperature-driving voltage characteristic that provides high contrast in the liquid crystal display panel is determined in advance, and when a signal indicating that contrast is "required" is inputted from the outside, the specific temperature-driving voltage characteristic is determined in advance. 2. The liquid crystal display device according to claim 1, further comprising instruction means for instructing said voltage control means to perform voltage control in accordance with said voltage control means.