Liquid crystal display with a liquid crystal touch panel having photo-sensing elements

A liquid crystal display includes a light source for emitting light, a first substrate, a second substrate parallel to and facing the first substrate, and a plurality of pixel units formed between the first substrate and the second substrate. At least one pixel unit comprises a reflecting element disposed on the first substrate for reflecting light from the light source, and a photo-sensing element, formed on the second substrate, for outputting a sensing parameter based on light reflected from the reflecting member. Each reflecting element is extended out of the first substrate and faces to one of the plurality of photo-sensing elements. A position of the force applied on the first substrate is determined by detecting a variation of the sensing parameter outputted by the photo-sensing element.

BACKGROUND OF INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display, and particularly relates to a touch-control liquid crystal display.

2. Description of Prior Art

More and more advanced-function displays have found their applications in current consumer electronic products. In particular, liquid crystal displays (LCDs) having a high-resolution color screen are more widely applied in various electronic devices, such as televisions, mobile phones, personal digital assistances (PDAs), digital cameras, desktop computer screens, and notebook computer screens.

To facilitate portability and usage of these devices, the LCDs with an LCD touch panel to allow direct touch by the users have become the trend in the LCD market. Conventional resistor type or capacitor type LCD touch panels, which are configured by disposing additional resistors or capacitors on the panels, determine the coordinate positions of touch-points by detecting the voltage variation at the touch positions. However, since the resistors and capacitors are directly disposed on the panels, light transmittance through the LCD panel will be decreased and the overall thickness of the LCD panel will be increased. Another type of LCD touch panel, called an optical touch panel, is configured by disposing a large amount of light sources and corresponding optical detecting elements around an LCD panel. The position of a touch-point is determined when determining the position of an optical detecting element has failed to receive light rays from a corresponding light source. Although this design would not decrease the overall light transmittance through the panel, the product size is significantly increased.

Accordingly, a touch-control LCD with detecting elements incorporated into a touch panel thereof is desirable to decrease the weight and volume of the LCD and thus meets the compact demand of the LCD market.

SUMMARY OF INVENTION

It is therefore an object of this invention to provide a touch-control LCD having photo-sensing elements directly disposed within the liquid crystal panel that allows direct touch by the user. A position of a touch point of the LCD panel which the force is applied on is determined by using the photo-sensing element to detect the light intensity.

In another aspect of the present invention, there is provided a liquid crystal display comprising a light source for emitting light, a first substrate, a second substrate parallel to and facing the first substrate, and a plurality of pixel units formed between the first substrate and the second substrate. At least one pixel unit comprises a reflecting element disposed on the first substrate for reflecting light from the light source, and a photo-sensing element, formed on the second substrate, for outputting a sensing parameter based on light reflected from the reflecting member. A position of the force applied on the first substrate is determined by detecting a variation of the sensing parameter outputted by the photo-sensing element.

DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1is a schematic diagram of a liquid crystal display100in accordance with one embodiment of the present invention. The liquid crystal display100comprises a light source (not shown inFIG. 1), a gate driver102, a source driver104, a decision unit106, and a liquid crystal panel (LCD panel)110, all of which are enclosed by a case (not shown). The gate driver102is used for providing a scanning signal to the LCD panel110via scan lines112. The source driver104is used for providing a data signal voltage to the LCD panel110via data lines114. The decision unit106, coupled to the LCD panel110via transmission lines116, is used for determining a position of the LCD panel110on which a force is applied. The light source may be Cold Cathode Fluorescent Lamps (CCFLs) for generating required backlight for the LCD panel110.

Referring toFIG. 2illustrating a circuit diagram of the LCD panel110and the decision unit106depicted inFIG. 1, the LCD panel110comprises a plurality of pixel units200, and each pixel unit contains a switch transistor202, a storage capacitor204, and a liquid crystal capacitor206. The liquid crystal capacitor206is formed by two electrodes, in which one electrode is coupled to a common voltage end Vcom, and the other electrode is coupled to the switch transistor202. Liquid crystal molecules are sandwiched between the two electrodes. When the gate of the switch transistor202receives the scan signal generated by the gate driver102via the scan line112, the data signal voltage generated by the source driver104is conducted to the liquid crystal capacitor206through the data line114. According to the voltage difference between the common voltage at the common voltage end Vcom and the data signal voltage, the liquid crystal molecules of the liquid crystal capacitor206are reoriented for controlling the light intensity transmitted through the liquid crystal molecules. The storage capacitor204is adapted to store the data signal voltage, so that the liquid crystal capacitor206may still maintain the voltage difference between the data signal voltage and the common voltage even when the switch transistor202is turned off, thereby maintaining the light intensity transmitted through the liquid crystal molecules. The LCD panel110has a plurality of transistors211and a plurality of photo-sensing elements218for generating sensing parameter based on the received light intensity. The photo-sensing element218, such as a photo transistor, is coupled to a bias end Vbias and is used for generating a sensing current (i.e. the sensing parameter) based on the received light intensity. The transistor211is used for conducting the sensing current generated by the photo-sensing element218when turned on. Additionally, the pixel unit200further comprises a storage capacitor219for storing the sensing current generated by the photo-sensing element218.

With reference toFIG. 3illustrating a partial structure of the liquid crystal panel110depicted inFIG. 1, andFIG. 4showing a diagram of the LCD panel110applied by the force A, the LCD panel110comprises a first substrate150, a second substrate152and a black matrix layer156. Preferably, the first substrate150and the second substrate152are transparent conducting substrates. The pixel units200are formed between the first substrate150and the second substrate152. Each pixel unit200comprises a photo-sensing element218formed on the second substrate152, and a reflecting element154extended out of the first substrate150for reflecting light emitted from the light source130. Each reflecting element154is facing one of the photo-sensing elements218. Preferably, the reflecting element154is made of metal with high reflecting coefficient. The black matrix layer156, which may be made of resin, is formed on the first substrate150but not facing the plurality of photo-sensing elements218, for blocking the light emitted from the light source130. Liquid crystal molecules120are sandwiched between the first substrate150and the second substrate152. As shown inFIG. 3, if there is no pressure on the first substrate150, the photo-sensing element218can easily receive light from the light source130. By contrast, as shown inFIG. 4, when the force A is applied on a touch point on the first substrate150, the distance between the first substrate150and the second substrate152at the touch point is shortened. In the meantime, light from the light source130is reflected outwardly by the reflecting element154, thereby causing a less amount of light to be received by the photo-sensing element218. The photo-sensing element218can generate sensing current based on the light intensity. In other words, the greater the light intensity is, the stronger the sensing current generated by the photo-sensing element218is. As a result, the photo-sensing element218can output stronger sensing current when the force A not to be applied on the touch point (as depicted inFIG. 3) than the force to be applied on the touch point (as depicted inFIG. 4).

Referring toFIG. 2, the photo-sensing element218generates a sensing current based on different light intensity, and outputs the sensing current to a conversion circuit212. The conversion circuit212includes an operational amplifier214, a feedback capacitor Cf and a switch unit216. The operational amplifier214has a first input terminal221, a second input terminal222and an output terminal223. The first input terminal221is coupled to a reference voltage terminal Vrefthat is adapted to provide a direct current reference voltage, e.g. 5V. The conversion circuit212may be regarded as an integrating circuit. When the scan line112delivers a scan signal, the switch unit216will be turned off. In contrast, when the scan line112does not deliver a scan signal, the switch unit216will be turned on, whereby a short circuit occurs between the second input terminal222and the output terminal223, resulting in the voltage at the output terminal223is equal to the reference voltage Vref. When the switch unit216is turned off, the output Vout at the output terminal223of the operational amplifier214is expressed by:

where Vc indicates the voltage across the capacitor Cf, I indicates the sensing current generated by the photo-sensing element218, and t indicates a time period.

Afterwards, the operational amplifier214converts the sensing current generated by the photo-sensing element218into a sensing voltage. Because a smaller amount of sensing current is generated by the photo-sensing element218corresponding to the touch point which a force is applied on, a smaller amount of the sensing voltage is converted by the operational amplifier214. Consequently, the decision-making unit250receives all the sensing voltages outputted by the operational amplifiers214, and determines the corresponding position of the touch point of the LCD panel110which the force is applied on.

Forces with different magnitude applied on the first substrate150cause variations of distance between the first substrate150and the second substrate152, as well as the light intensity received by the photo-sensing element218and its output sensing current. Accordingly, the output voltage of the operational amplifier214is also varied based on the output sensing current of the photo-sensing element218. Consequently, in addition to determining the position of the touch point of the LCD panel110, the decision-making unit250also can determine the magnitude of the force which is applied on the touch point based on the output voltages of the operational amplifiers214.

The liquid crystal display, according to the present invention, integrates a plurality of photo-sensing elements into a liquid crystal panel thereof. By detecting the voltage variations resulting from the light intensity differences, corresponding coordinate positions of the touch point of the liquid crystal panel can be determined. Since the photo-sensing elements are integrated into the liquid crystal panel, not only the weight and size of the liquid crystal display are decreased as compared with conventional liquid crystal display using an optical type touch panel, but also the current compact trend of liquid crystal display products is matched as well.