Computer graphics processing and selective visual display system – Display driving control circuitry – Waveform generator coupled to display elements
Reexamination Certificate
2001-01-16
2003-07-15
Saras, Steven (Department: 2675)
Computer graphics processing and selective visual display system
Display driving control circuitry
Waveform generator coupled to display elements
C345S094000, C345S087000, C348S184000, C324S701000
Reexamination Certificate
active
06593921
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a system and method for adjusting the image quality of a liquid crystal display by adjusting the potential on the common electrode in such a way as to reduce flicker (i.e., fluctuation of brightness) produced on the viewing screen of the liquid crystal display.
2. Description of the Related Art
FIG. 10
is a block diagram of the prior art driver circuit for a liquid crystal display. Shown in this figure are a liquid crystal panel
1
consisting of two glass substrates and a liquid crystal material sandwiched between the glass substrates, a signal-side driver IC
2
for driving the liquid crystal panel
1
, a scanning-side driver IC
3
for driving the liquid crystal panel
1
, and a control circuit
4
for supplying control signals to the signal-side driver IC
2
and to the scanning-side driver IC
3
. The control circuit
4
also supplies a scanning signal
5
and a display signal
6
. A large number of pixels for making up an image are arranged in rows and columns on the liquid crystal panel
1
.
FIG. 11
is an enlarged view of some pixels.
FIG. 11
is a diagram illustrating the configuration of pixels of the prior art liquid crystal panel. Shown in this figure are scanning signal lines
7
connected with the scanning-side driver IC
3
, display signal lines
8
connected with the signal-side driver IC
2
, switching elements
9
such as TFTs placed at the intersections of the scanning signal lines
7
and the display signal lines
8
, and pixel electrodes
10
connected with the switching elements
9
.
FIG. 12
is a cross-sectional view of the prior art liquid crystal panel, illustrating the cross-sectional structure of pixels. Shown in this figure are an array substrate
11
that is a first substrate, a counter substrate
12
that is a second substrate and located opposite to the array substrate
11
, a common electrode
14
formed over the whole surface of the counter substrate
12
, and a liquid crystal material
15
sealingly sandwiched between the array substrate
11
and the counter substrate
12
. The first and second substrates
11
and
12
are made of glass. The pixel electrodes
10
are formed at individual pixels on the array substrate
11
. The scanning signal lines
7
, the display signal lines
8
, and the switching elements
9
are also formed on the array substrate
11
.
FIG. 13
is a diagram illustrating the waveforms of the display signal on each display electrode and of the potential on the common electrode of the prior art liquid crystal display. The display signal on the pixel electrode
10
is indicated by
6
. The potential Vcom applied to the common electrode
14
is indicated by
16
. The display signal
6
and the potential Vcom
16
shown in
FIG. 13
are waveforms associated with one pixel. In
FIG. 13
, FO is an odd frame and FE is an even frame.
In the liquid crystal display of the construction as described above, the display signal is generally inverted in polarity every frame period at about 60 Hz to prevent the liquid crystal material from deteriorating due to aging. If the voltage applied to the liquid crystal material agrees with the center about which the polarity is inverted like the potential Vcom
16
a
shown in
FIG. 13
, the voltage applied to the liquid crystal material is constant with time. However, if the voltage deviates like potential Vcom
16
b
, and if the voltage value of an AC signal applied to the layer of the liquid-crystal material differs between when the polarity is positive and when it is negative, flicker (i.e., fluctuation of brightness) occurs at about 30 Hz.
To eliminate this flicker, it is necessary to adjust the level of the potential Vcom so that the voltage applied to the liquid crystal material does not differ between when the polarity is positive and when it is negative. In particular, an image producing easily discernible flicker is displayed on the viewing screen. Then, the operator adjusts the Vcom-adjusting knob mounted on the liquid crystal display, whereby the degree of flicker observed with the naked eye is minimized.
With this method, human factors vary the adjusted value of the potential Vcom. Accordingly, as shown in
FIG. 14
, another method uses an optical sensor in a certain location on the viewing screen. The resulting electrical signal waveform is observed. An adjustment is made to minimize the amplitude.
FIG. 14
is a block diagram showing the prior art image quality-adjusting system. The aforementioned optical sensor, indicated by numeral
17
, is positioned opposite to a liquid crystal panel
1
and produces an electrical signal corresponding to the amount of light that the sensor receives. The output signal from the optical sensor
17
is amplified by an amplifier
18
. A band-pass filter
19
is located on the output side of the amplifier
18
and detects a flicker signal component. The flicker signal from the band-pass filter
19
is indicated by
20
. An oscilloscope
21
is used to observe the flicker signal
20
. An image signal generator
22
produces an image display signal
23
to the liquid crystal panel
1
.
A method disclosed in Japanese Patent Laid-Open No. 269991/1989 uses an optical sensor mounted opposite to a liquid crystal panel, a rectifier circuit for rectifying the output signal from the sensor that is in proportion to the light impinging on the sensor, and a low-pass filter for smoothing the rectifier output from the rectifier circuit and producing an output signal indicating the deviation from the optimum value of the potential on the common electrode. This method enables accurate adjustment.
In the above-described method using operator's visual observation to make an adjustment for minimizing flicker, human factors vary the adjusted value of the potential Vcom. Especially, where the display screen is large, an optimum value of the potential Vcom at which flicker is minimized differs from location to location on the viewing screen. It is highly likely that the position at which an adjustment is made to minimize flicker varies, depending on the worker. As a result, fabricated products differ in performance.
Furthermore, the worker must watch flicker of high optical intensity for a long time. This may adversely affect the human body psychologically and physically.
In one of the above-described methods, the optical sensor located at some location on the viewing screen is used, the resulting electrical signal waveform is observed, and an adjustment is made to minimize the amplitude. In this method, the magnitude of the observed waveform differs according to the magnitude of the brightness of backlight and so it is difficult to detect the minimum value of the amplitude. Especially, immediately after the backlight is turned on, the brightness varies violently, thus deteriorating the efficiency of operation greatly.
Furthermore, the method disclosed in the above-cited Japanese Patent Laid-Open No. 269991/1989 makes use of the principle that the magnitude of a signal corresponding to the brightness is minimized. Therefore, the adjustment is directly affected by the brightness of backlight in the same way as in the above-described method.
In a further method, an adjustment is made with a frequency analyzer to minimize the frequency component corresponding to flicker. This method needs expensive apparatus. In addition, the response of the observed signal is slow. Hence, the efficiency of operation is poor.
SUMMARY OF THE INVENTION
The present invention has been made to solve the foregoing problems.
It is an object of the present invention to provide an image quality-adjusting system for a liquid crystal display, the system permitting one to adjust potential Vcom with high accuracy and high reproducibility for minimizing flicker.
An image quality-adjusting system for a liquid crystal display in accordance with the present invention comprises at least one optical sensor located opposite to a given location on a liquid crystal panel and an oscilloscope synchronized to a vertical synchro
Ikuta Yoshikazu
Kinoshita Yoshimi
Miyaoka Akitoshi
Nakanishi Kunifumi
Nishizaki Shuji
Alphonse Fritz
Kabushiki Kaisha Advanced Display
Saras Steven
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