Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2000-04-04
2003-10-21
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S089000, C345S090000, C345S091000, C345S092000, C345S097000, C345S100000, C345S104000, C345S173000, C345S205000, C345S206000, C345S207000, C349S159000
Reexamination Certificate
active
06636194
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electro-optic device that has a driving circuit which may consist of a memory circuit and a pixel driver that is provided for each pixel and that controls pixel display according to a data signal held in the memory circuit, and to electronic equipment, such as office automation equipment and portable equipment in which the electro-optic device is installed.
2. Description of Related Art
In recent years, as an information display device of portable equipments or the like, including a portable telephone and a portable information terminal, a liquid crystal device, which is an example of an electro-optic device, has been in use. The contents of displayed information have been conventionally displayed in characters. These days, however, dot-matrix liquid crystal panels have been used to display more information at a time, and the number of pixels is gradually increasing with a consequent higher duty.
Hitherto, for the above portable equipment, a passive matrix liquid crystal device has been used as a display device. However, a passive matrix liquid crystal device requires a higher voltage with an increasing duty for a selection signal of a scanning line when performing multiplex drive, posing a serious problem in battery-driven portable equipment that is strongly required to minimize power consumption.
To solve such a problem, there has been proposed a static drive liquid crystal device in which one of a pair of substrates constituting a liquid crystal panel is formed of a semiconductor substrate, and a memory circuit shown in
FIG. 12
is formed on the semiconductor substrate for each pixel to conduct display control based on data held in the memory circuit. In conjunction with
FIG. 12
, an operation of a conventional static drive liquid crystal device will now be described.
A scanning line drive circuit
410
is controlled by a scanning line drive circuit control signal
418
, and a selection signal (scanning signal) is output to a selected scanning line
409
-n (“n” is a natural number denoting a number of scanning lines). Likewise, a data line drive circuit
413
is controlled by a data line drive circuit control signal
419
, and data signals are supplied to a selected pair of data lines
411
-m and
412
-m (“m” is a natural number denoting a number of data lines) so that they have mutually opposite phases (complementary signals).
At an intersection of the scanning line
409
-n and the pair of data lines
411
-m and
412
-m, a circuit connected to those lines constitutes a pixel. n-channel MOS switching circuits
401
and
402
connected to the scanning line
409
-n and the pair of data lines
411
-m and
412
-m are set to a conducting state when the scanning line
409
-n is selected and a selection signal is supplied, and write complementary data signals of the pair of data lines
411
-n and
412
-m to a memory circuit
403
. The memory circuit
403
has two inverters in feedback connection. Then, the scanning line
409
-n is set at a nonselective potential and the pair of data lines
411
-m and
412
-m are set at a high impedance to thereby place the switching circuits
401
and
402
in a nonconducting state, and the data signals written to the memory circuit
403
are retained.
A liquid crystal pixel driver
404
composed of two transmission gate circuits is controlled by potential levels of a first node in the memory circuit
403
and a second node at an inverted level of a potential level at a point of connection of the first node. A first transmission gate circuit is connected to a first voltage signal line
416
and conducts according to a level of a data signal held by the memory circuit
403
, and applies a first voltage
414
to a pixel electrode
406
. On the other hand, a second transmission gate circuit is connected to a second voltage signal line
417
and conducts according to a level of a data signal held by the memory circuit
403
, and applies a second voltage
415
to the pixel electrode
406
. To be more specific, if the held data signal is at an H-level, then the first voltage signal line
416
that sets a liquid crystal layer
407
of a liquid crystal pixel driver
404
to an ON state in the case of a normally white display mode conducts, causing the first voltage
414
to be supplied to the pixel electrode
406
via the first transmission gate circuit of the liquid crystal driver
404
, so that the liquid crystal pixel
405
is set to in a black display mode by a potential difference from a reference voltage
420
supplied to a common electrode
408
. Similarly, if the held data signal is at an L-level, then the second voltage signal line
417
that sets the liquid crystal layer
407
in an OFF state conducts, causing the second voltage
415
to be supplied to the liquid crystal pixel
405
via the second transmission gate circuit of the liquid crystal driver
404
, so that the liquid crystal pixel
405
is placed in a white display mode.
The foregoing structure allows a line voltage, the first and second voltage signals, and a reference voltage to be driven by a logic voltage alone. Also, little current exept leakage current flow, because it is able to hold display screen by a data hold function of a memory circuit, in the case that the rewriting of a screen display is not necessary. Accordingly, consumption electric power can be reduced.
However, in the conventional static drive liquid crystal device, the data signals for the pair of data lines must be complementary signals having phases opposite to each other for writing data, and must be controlled to a high impedance for holding data. Thus, control of the data lines has been extremely complicated, and a circuit configuration has also been complicated.
SUMMARY OF THE INVENTION
The present invention has been made to solve the problem described above, and it is an object of the present invention to provide an electro-optic device that consumes less power, and features a simple control method and a simple control circuit configuration.
An electro-optic device in accordance with the present invention has, on a substrate, a plurality of row scanning lines and a plurality of column scanning lines that intersect with each other, a plurality of data lines provided along the column scanning lines, voltage signal lines that supplies voltage signals, and a plurality of pixel drive circuits disposed, corresponding to intersections of the row scanning lines and the column scanning lines, wherein each of the pixel drive circuits has a switching circuit that is set to a conducting mode when the row scanning lines and the column scanning lines are selected, while it is set to a nonconducting mode when at least either the row scanning lines or the column scanning lines are not selected, a memory circuit that captures data signals of the data lines when the switching circuit is in the conducting mode, while it holds data signals when the switching circuit is in the nonconducting mode, and a pixel driver that outputs a first voltage signal to the pixel from the voltage signal line when a data signal held in the memory circuit is at a first level, while it outputs a second voltage signal to the pixel from the voltage signal line when the data signal is at a second level.
The configuration in accordance with the present invention enables a line voltage, the first and second voltage signals, and a reference voltage to be driven at a level of a logic voltage. Furthermore, little current flows, because when there is no need to rewrite screen display, a display state can be held by a data holding function of the memory circuit. With this arrangement, comparison as a liquid crystal device indicates that power consumption is cmarkedly reduced as compared with the conventional passive matrix liquid crystal device. Moreover, unlike the conventional static drive liquid crystal device, it is no longer necessary to carry out the complicated control wherein data signals for a pair of data lines are set to have opposite phases for writing da
Hjerpe Richard
Nguyen Jennifer T.
Seiko Epson Corporation
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