Computer graphics processing and selective visual display system – Display driving control circuitry – Display power source
Reexamination Certificate
2000-06-28
2004-01-13
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Display driving control circuitry
Display power source
C345S087000, C345S092000, C345S098000, C345S100000, C345S211000, C345S214000, C345S093000, C345S094000
Reexamination Certificate
active
06677937
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a driving method for an active-matrix-type display using switching elements, and also concerns a liquid crystal display driven by such a driving method.
BACKGROUND OF THE INVENTION
Recently, along with the development of the information-dependent society, mobile information terminals, in particular, personal data asistances (PDA), have received much attention. One of objectives with these personal data assistances is to achieve low power consumption, and liquid crystal displays have been mainly used as the display device thereof.
Liquid crystal displays are mainly classified into two types, that is, the passive-matrix type and the active matrix type, and the latter type has superior features in the display quality. The active-matrix-type displays are classified into two types, that is, those using three-terminal elements such as TFTs (Thin Film Transistors) and those using two-terminal elements such as MIM (Metal-Insulator-Metal) devices, as the switching elements thereof. The latter type is advantageous in that the manufacturing process is simpler as compared with the former, making it possible to achieve low costs, and in that the two-terminal construction makes the electrode wiring simpler and the device smaller, resulting in a higher aperture ratio in pixels.
FIG. 6
shows the construction of a conventional active-matrix-type liquid crystal display
51
using two-terminal elements. The liquid crystal display
51
is provided with a display panel section
60
having a structure in which a liquid crystal layer is sandwiched by a pair of substrates. More specifically, as indicated by an equivalent circuit in
FIG. 7
, the display panel section
60
has an arrangement in which two-terminal elements
72
and liquid crystal display elements
71
(display elements) are series-connected for each unit area between a plurality of scanning electrodes Yi (i=1, 2, . . . , m) and a plurality of data electrodes Xj (j=1, 2, . . . , n) that are arranged in directions so as to intersect each other, and areas corresponding the respective liquid crystal display elements
71
are arranged in a matrix format as pixels.
A driver
64
for scanning-electrode signals selects the respective scanning electrodes Yi in a line-sequential manner for each frame period and applies a predetermined selection voltage thereto, and is normally constituted by a control section, shift registers, analog switches, etc. A driver
62
for data-electrode signals applies a predetermined data signal voltage corresponding to display data to respective data electrodes Xj that are in the selection period. Thus, the selection voltage and the data signal voltage are applied to the respective pixels during the selection period. A voltage difference between the selection voltage and the data signal voltage allows a charge corresponding to the display data to be accumulated. This charge is maintained by the two-terminal elements
72
until the next selection period so that the display state is maintained during one frame period. In other words, the display state is desirably controlled on the display panel section
60
by applying predetermined voltages to the respective ends of each pixel.
In order to display external input information on the display panel
60
, a control section
65
sends control signals to a voltage-forming circuit
61
for forming a voltage to be applied to the driver
62
for data-electrode signals as well as to a voltage-forming circuit
63
for forming a voltage to be applied to the driver
64
for scanning-electrode signals. Input signals to the control section
65
consist of a scanning start signal S, a scanning clock LP, a clock CLK, a display data signal DATA, a data enable signal ENAB, a power-supply signal DISP, etc. Among these, the scanning clock LP, the clock CLK, the display data signal DATA and the data enable signal ENAB are outputted to the voltage-forming circuit
61
and the driver
62
for data-electrode signals, while the scanning start signal S and the scanning clock LP are outputted to the voltage-forming circuit
63
and the driver
64
for scanning-electrode signals.
A power-supply voltage for driving the liquid crystal display
51
, not shown, is sent to the voltage-forming circuits
61
and
63
. Thus, the power-supply voltage and the respective signals sent from the control section
65
are used to form voltage waveforms to be applied to the data electrode Xj and the scanning electrodes Yi.
FIG. 8
shows one example of a timing chart of the above-mentioned input signal. When a selection voltage, not shown, is applied to the respective scanning electrodes Yi during a selection period corresponding to the frequency of the scanning clock LP, the display data signal DATA (a signal corresponding to the “HIGH” period of the data enable signal ENAB), which has a data signal voltage sent in synchronism with the clock CLK, is outputted to the respective data electrodes Xj so that a voltage corresponding to a difference between the selection voltage and the data signal voltage is applied to the respective pixels. The signal indicating the scanning start of one frame is the scanning start signal S, and the scanning clocks LP the number of which is not less than the number of scanning electrodes are present within one period of the scanning start signal S. These signals are generated and supplied while the power-supply signal DISP goes high, from the application of the power until the liquid crystal display
51
to the cut-off thereof.
The active-matrix type liquid crystal display
51
using two-terminal elements
72
has a problem in which a sticking phenomenon occurs due to variations in the voltage-current characteristics of the two-terminal elements
72
. In order to solve this problem, U.S. Pat. No. 5,760,758 (published on Jun. 2, 1998) and U.S. Pat. No. 5,663,744 (published on Sep. 2, 1997) have disclosed a driving method in which, during the selection period of the respective scanning electrodes, a voltage is switched to a plurality of levels and applied to the scanning electrodes.
FIGS. 9 and 10
show examples of waveforms to be applied to the display panel in the above-mentioned method.
FIG. 9
shows the construction of U.S. Pat. No. 5,760,758 in which a voltage to be applied to the scanning electrodes for one selection period is switched to two levels. Supposing that the liquid crystal display to which this driving method is applied has the same structure as the liquid crystal display
51
of
FIG. 6
, signals, sent from the control section
65
and the voltage-forming section
63
to the driver
64
for scanning-electrode signals, allow signals
85
and
86
having voltage waveforms as respectively shown in the Figure to the scanning electrodes Yi and Yi+1, respectively. In the same manner, the signals, sent from the control section
65
and the voltage-forming section
61
to the driver
62
for data-electrode signals, and the display data signal DATA allow a signal
87
having a voltage waveform indicated by a solid line or a broken line in accordance with the display data to be supplied to the data electrodes Xj. Signals
81
to
84
are part of signals generated in the control section
65
; and signal
81
is a scanning start signal S for determining the scanning start for one frame, signal
82
is a scanning clock LP for deciding one selection period, signal
83
is a signal for controlling the pulse width with respect to the voltage levels to be applied to the scanning electrodes Yi during one selection period, and signal
84
is a signal for determining the polarity of the respective voltage levels.
FIG. 10
shows the construction of U.S. Pat. No. 5,663,744 in which a voltage to be applied to the scanning electrodes for one selection period is switched to three levels. Similarly, supposing that the same structure as the liquid crystal display
51
of
FIG. 6
is used, signals, sent from the control section
65
and the voltage-forming section
63
to the driver
64
for scanning-electrode signals,
Kokuhata Yoshiyuki
Takahashi Masahiro
Birch & Stewart Kolasch & Birch, LLP
Hjerpe Richard
Nguyen Jennifer T.
Sharp Kabushiki Kaisha
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