Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2002-06-12
2004-10-26
Chang, Kent (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S207000, C348S602000
Reexamination Certificate
active
06809718
ABSTRACT:
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.
REFERENCES:
patent: 4760389 (1988-07-01), Aoki et al.
patent: 5270818 (1993-12-01), Ottenstein
patent: 5717422 (1998-02-01), Fergason
patent: 5952992 (1999-09-01), Helms
patent: 6078302 (2000-06-01), Suzuki
patent: 6094185 (2000-07-01), Shirriff
patent: 6664744 (2003-12-01), Dietz
Wei Chung-Kuang
Wu Chao-Wen
Chang Kent
Chi Mei Optoelectronics Corporation
Hsu Winston
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