Abstract:
A thin film transistor liquid crystal display (TFT-LCD) capable of adjusting its light source utilizes at least one thin film transistor (TFT) disposed in a peripheral region of a bottom substrate as a photo sensor for detecting ambient illumination. Then, a light source modulator can enhance, weaken, open or close the light source of the TFT-LCD to an optimal brightness level that depends on the ambient illumination spontaneously.

Description:
BACKGROUND OF INVENTION 
     1. Field of the Invention 
     The present invention relates to a thin film transistor liquid crystal display (TFT-LCD) capable of adjusting its light source, and more particularly, to a TFT-LCD having a photo sensor. 
     2. Description of the Prior Art 
     Display devices that have a back light source such as a liquid crystal display (LCD) are usually used in portable electronic devices such as a notebook, an electronic dictionary, and a personal digital assistant (PDA) etc. When users utilize the display device that has the back light source, ambient illumination affects the ability of the users to view the display device directly. Therefore, the above-mentioned portable electronic devices need a suitable light source adjusting mechanism to adjust the back light source. 
     The prior art light source adjusting mechanism is mainly a manual light source adjusting mechanism. The users can adjust the back light source of the display devices by way of a specific light source adjusting knob or keys of a keyboard disposed on the device. However, the prior art mechanism has two disadvantages. First, when the LCD is used in portable electronic products, the portable electronic products are usually in various background environments, such as in a moving car. Therefore the users must adjust the back light source often, causing inconvenience for the user. Second, the users could adjust the back light source to a brighter brightness level to prevent the operational inconvenience, but this leads to high power consumption. 
     Please refer to FIG.  1 . FIG. 1 is a circuit diagram of a prior art back light adjusting circuit  10 . The back light adjusting circuit  10  includes a back light source  12  for generating backlight, a photo sensor  14 , an amplified circuit  16 , a decisive circuit  18 , and a DC/AC inverter  20 . The back light source  12  and the inverter  20  are composed of a back light module, and the back light module generates the backlight with various brightness levels depending on ambient illumination  22 . 
     When the photo sensor  14 , such as a photosensitive resistance or a charge coupled device (CCD) senses the ambient illumination  22 , the photo sensor  14  generates a corresponding photocurrent i p  that depends on the ambient illumination  22 . Since photocurrent i p  generated from the photo sensor  14  is very weak, the amplified circuit  16  is used to amplify the photocurrent i p  to conveniently perform the subsequent signal processes. The amplified circuit  16  includes a transistor Q 1 , a resistance R 1  and a resistance R 2 , functioning as an amplifier, and a voltage source V DC  for providing a bias voltage. When a base of the transistor Q 1  receives a voltage signal converted from the photocurrent i p  by the resistance R 1 , an amplified signal  24  is sent from a collector of the transistor Q 1  to the decisive circuit  18  to calculate the ambient illumination  22 . 
     The decisive circuit  18  includes a photo diode D 1 . An anode of the photo diode D 1  receives the amplified signal  24 , and then a back light control signal  26  is calculated and sent from a cathode of the photo diode D 1  to the inverter  20 . The inverter  20  receives the back light control signal  26  and transforms it into a current, which is used to drive the back light source  12 . The inverter  20  includes a transistor Q 2  for receiving a driving voltage and producing a switching voltage, a transformer T 1  for transforming the switching voltage to a loading voltage for providing to the back light source  12 , a pulse width modulation (PWM) controller  28  that generates a pulse width modulate signal  29  corresponding to a pulse width according to the received back light control signal  26  and transfers the pulse width modulate signal  29  to the base of the transistor Q 2 . By turning on and off the transistor Q 2 , a voltage source V M  is indirectly connected to the transformer T 1 . And a corresponding driving current is produced so that the back light source  12  generates a corresponding back light. 
     When the prior art back light adjusting circuit  10  is applied to a display device (not shown), an output circuit of the inverter  20  can be modulated according to the back light control signal  26  sent from the decisive circuit  18  to adjust the back light source  12  spontaneously when the back light source  12  of the display device is turned on. However, the prior art back light adjusting circuit  10  has several disadvantages. First, the prior art back light adjusting circuit utilizes the additional photo sensor, increasing costs and volume of the display device. Second, the back light adjusting circuit is applied to the display device which has the back light source. However, for display devices which have a front light source, the ambient illumination and the front light source are on same side. Therefore, if variations of the ambient illumination are acute enough, the ability of users to view the display device will be severely affected. 
     SUMMARY OF INVENTION 
     It is therefore a primary objective of the claimed invention to provide a thin film transistor liquid crystal display (TFT-LCD) capable of adjusting its light source that depends an ambient illumination spontaneously, without consuming power and causing eyestrain. 
     It is another objective of the claimed invention to provide a light source adjusting mechanism that applies to a back light source and a front light source. 
     According to the claimed invention, a thin film transistor liquid crystal display (TFT-LCD) capable of adjusting its light source includes a liquid crystal sealed between a first substrate and a second substrate, with the second substrate having an active region and a peripheral region. The TFT-LCD also includes a pixel matrix array disposed in the active region of the second substrate, and at least one thin film transistor (TFT) functioning as a photo sensor disposed in the peripheral region of the second substrate, with the TFT having an amorphous silicon layer. The TFT-LCD further includes a feedback circuit, and a light source module that includes the light source and a light source modulator. When ambient light enters the first substrate and passes through the amorphous silicon layer of the TFT, the TFT generates a current in the feedback circuit. Then a feedback signal is sent from the feedback circuit to the light source modulator to adjust the light source of the TFT-LCD to an optimal brightness level that depends on ambient illumination. 
     It is an advantage that the claimed invention uses the TFT disposed in the peripheral region of the second substrate as the photo sensor to detect the ambient illumination and that the light source modulator can enhance, weaken, open, or close the light source of the TFT. Therefore, manufacturing costs are reduced, without consuming power and causing eyestrains. 
     These and other objectives of the claimed invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a circuit diagram of a prior art back light adjusting circuit. 
     FIG. 2 is a block diagram of a light source adjusting circuit according to the present invention. 
     FIG. 3 is a circuit diagram of the light source adjusting circuit according to the present invention. 
     FIG. 4 is a schematic diagram of a thin film transistor liquid crystal display (TFT-LCD) capable of adjusting its light source according to the present invention. 
     FIG. 5 is a top view illustrating a second substrate of the TFT-LCD according to the present invention. 
     FIG. 6 is a cross-sectional view of the second substrate of the TFT-LCD. 
    
    
     DETAILED DESCRIPTION 
     FIG. 2 is a block diagram of a light source adjusting circuit  30  according to the present invention. FIG. 3 is a circuit diagram of the light source adjusting circuit  30  according to the present invention. FIG. 4 is a schematic diagram of a thin film transistor liquid crystal display (TFT-LCD)  60  capable of adjusting its light source according to the present invention. FIG. 5 is a top view illustrating a second substrate  64  of the TFT-LCD  60  according to the present invention. FIG. 6 is a cross-sectional view of the second substrate  64  of the TFT-LCD  60  along a line AA shown in FIG.  4 . In a preferred embodiment of the present invention, the light source adjusting circuit  30  and the TFT-LCD  60  utilize a back light source  38  as an example. However, the present invention is not limited in the back light source  38 , but also applies to a TFT-LCD having a front light source. 
     Please refer to FIG.  2  and FIG.  3 . The light source adjusting circuit  30  includes a light source module  32 , a photo sensor  34 , and a feedback circuit  36 . The light source module  32  includes the back light source  38  and a light source modulator  42 . The feedback circuit  36  includes an amplified circuit  44  and a decisive circuit  46 . The decisive circuit  46  comprises a processor, such as a photo diode D 2  and a memory (not shown), and the memory includes a database (not shown). The photo sensor  34  is a thin film transistor (TFT) having an amorphous silicon layer  40  as shown in FIG.  6 . 
     When an ambient light source  48  generates ambient light  50  passing through the amorphous silicon layer  40  of the TFT  34 , the TFT  34  generates a photocurrent  52  that depends on the illumination of the ambient light  50 . Since the photocurrent  52  is very weak, the amplified circuit  44  is used to amplify the photocurrent  52  to perform the subsequent signal processes conveniently. When a base of a transistor Q 3  of the amplified circuit  44  receives a voltage signal converted from the photocurrent  52  by a resistance R 3 , an amplified signal  54  is sent from a collector of the transistor Q 3  to the processor D 2  of the decisive circuit  46  to calculate the illumination of the ambient light  50 . After comparing the ambient illumination with the database of the memory, a feedback signal  56  is produced and transferred to the light source modulator  42 , i.e. an inverter. Then, a pulse width modulation (PWM) controller  58  generates a PWM signal  59  corresponding to a pulse width to modulate a voltage pulse value, i.e. a voltage pulse frequency. After that, the voltage pulse value is transferred to a base of a transistor Q 4 , and a voltage source V M  is indirectly connected to a transformer T 2  by turning on and off the transistor Q 4 . Thereafter, a corresponding driving current, i.e. a lamp current is produced so that the back light source  38  generates a corresponding back light that depends on the lamp current. The light source modulator  42  can also utilize a voltage input device (not shown) to modulate the voltage pulse value to generate the corresponding driving current in order to adjust the back light source  38  of the TFT-LCD  60 . 
     Please refer to FIG.  4  and FIG.  5 . The light source adjusting circuit  30  is applied to the TFT-LCD  60  that is capable of adjusting its light source. The TFT-LCD  60  includes a first substrate  62 , a second substrate  64  parallel to the first substrate  62 , a color filter layer  66  and a transparent electrode  68  disposed on an underside of the first substrate  62  respectively, a polarizer  72  disposed on an above of the first substrate  62 , a polarizer  74  disposed on an underside of the second substrate  64 , and a liquid crystal  76  sealed between the first substrate  62  and the second substrate  64 . The second substrate  64  includes an active region I and a peripheral region II, and a pixel matrix array  78  is disposed in the active region I of the second substrate  64 . The pixel matrix array  78  includes a plurality of adjacent pixels  80 , and each of the pixels  80  includes a thin film transistor  82 . The first substrate  62  and the second substrate  64  are transparent glass substrates. The color filter layer  66  includes a R/G/B color filter array (CFA)(not shown) and a black filter array (not shown). The black filter array is used to prevent the TFT  82  from generating the photocurrent and cover light oblique leaks of the TFT-LCD  60 . 
     The back light source  32  of the light source adjusting circuit  30  is disposed under the second substrate  64  of the TFT-LCD  60 . The TFT  34  of the light source adjusting circuit  30  is disposed in the peripheral region  11  of the second substrate  64 . Since the TFT  34  is utilized as the photo sensor, an upper side of the TFT  34  cannothold the black filter array. Instead, the TFT  34  must be exposed to the ambient light. The feedback circuit  36  of the light source adjusting circuit  30  is disposed outside the second substrate  64 . The TFT  82  disposed in the active region I of the second substrate  64  and the TFT  34  disposed in the peripheral region II are formed simultaneously and have the same structure, as shown in FIG.  6 . 
     When ambient light (not shown) enters the first substrate  62  of the TFT-LCD  60  and passes through the amorphous silicon layer  60  of the TFT  34 , the TFT  34  generates and transfers a photocurrent to the feedback circuit  36 . And a feedback signal is sent from the feedback circuit  36  to the light source modulator  42  of the light source module  32  to adjust the back light source  38  of the TFT-LCD  60  to an optimal brightness level that depends on ambient illumination. Similarly, a front light source (not shown) can be applied to the TFT-LCD of the present invention. Since the upper side of the TFT  34  does not hold the black filter array, the front light irradiates the amorphous silicon layer  40  of the TFT  34  directly to generate a photocurrent. 
     Please refer to FIG. 2 again, a signal trigger circuit (not shown) can be located between the photo sensor  34  and the decisive circuit  46 . When the ambient illumination reaches an advanced set brightness level, which is a dark enough level to turn on the back light source  38 , the signal trigger circuit outputs a signal to turn on the back light source  38  spontaneously. While the back light source  38  turned on, the feedback signal  56  sent from the decisive circuit  46  varies a lamp current output of the inverter according to variations of the ambient illumination to adjust the back light source  38  to an optimal brightness level. 
     In a word, the TFT-LCD capable of adjusting its light source of the present invention utilizes the TFT disposed in the peripheral region of the second substrate as the photo sensor. Therefore the back light source or the front light source of the TFT-LCD can be adjusted to an optimal brightness level that depends on ambient illumination spontaneously without causing eyestrain. When the ambient illumination is too bright or dark, the back light source or the front light source can be turned off or turned on spontaneously to save power. 
     In contrast to the prior art technology, the present invention utilizes the TFT disposed in the peripheral region of the second substrate as the photo sensor. Since the photo sensor and the TFT disposed inside the active region I are formed simultaneously, no additional photo sensor is required, simplifying manufacturing processes and reducing costs. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.