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| United States Patent | 5576737 |
| Link to this page | http://www.wikipatents.com/5576737.html |
| Inventor(s) | Isozaki; Shingo (Suwa, JP) |
| Abstract | The objectives of this invention are to improve the method of supplying
power from an operating power source and thus implement a liquid crystal
drive device with an internal display data storage device that consumes
less power and is also larger. A signal electrode drive circuit (X driver)
is made up of a low-voltage-amplitude operating portion that operates on
the supply of a first power voltage group, and a high-voltage-amplitude
operating portion that operates on the supply of a second power voltage
group. A frame memory that stores display data is provided in the
high-voltage-amplitude operating portion, with the configuration being
such that the operating power source for the frame memory is supplied from
the second power voltage group. The power source of the frame memory could
also be supplied through a constant-voltage circuit that regulates these
second power voltages, and the supply of the first and second power
voltages could be switched in accordance with the state of the second
power voltage supply by a power monitoring device that monitors the second
power voltage group. The configuration of the present invention is
particularly effective for the multiple line selection drive method. |
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Title Information  |
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Drawing from US Patent 5576737 |
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Liquid crystal drive device, liquid crystal display device, and liquid
crystal drive method |
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| Publication Date |
November 19, 1996 |
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| Filing Date |
December 19, 1994 |
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| Priority Data |
Dec 22, 1993[JP]5-325169 |
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Title Information |
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References |
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| Market Size |
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Market Review |
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Technical Review |
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Claims |
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What is claimed is:
1. A liquid crystal drive device comprising:
a low-voltage amplitude operating portion having at least a control logic
unit and operating on the supply of a first power voltage group; and
a high-voltage-amplitude operating portion operating on the supply of a
second power voltage group, said second power voltage group having a
voltage difference between at least one pair of power voltages included
within said second power voltage group, one on a high-potential side and
one on a low-potential side, said voltage difference being greater than a
voltage difference between a power voltage on a high-potential side and a
power voltage on a low-potential side within said first power voltage
group, said second power voltage group being used to drive liquid crystal
elements of a liquid crystal panel;
said liquid crystal drive device further comprising:
data storage means for storing image data for driving the liquid crystal
elements of said liquid crystal panel; and
means for supplying an operating power source to said data storage means,
said operating power source being a voltage group that is one of said
second power voltage group and a third power voltage group which is
obtained by converting said second power voltage group.
2. A liquid crystal drive device according to claim 1, wherein:
said data storage means comprises a plurality of memory cells capable of
being temporarily written to and read from, and each of said memory cells
comprises at least one pair of transistors for holding data, with a
high-resistance element connected to each of said transistors in series.
3. A liquid crystal drive device according to claim 1, further comprising:
latch means for latching image data that has been read out from said data
storage means;
level-shifting means for converting the voltage levels of said latched
image data; and
voltage selection means for a) selecting from said second power voltage
group a liquid crystal drive voltage on the basis of said image data whose
voltage level has been converted, and for b) outputting said liquid
crystal drive voltage to signal electrodes of said liquid crystal panel;
said latch means, said level-shifting means, and said voltage selection
means being located in said high-voltage amplitude operating portion.
4. A liquid crystal drive device according to claim 1, further comprising:
drive signal determination means for determining drive voltage information
for signal electrodes of said liquid crystal panel based on image data
read out from said data storage means and based on the voltage states of a
plurality of simultaneously selected scan electrodes of said liquid
crystal panel;
latch means for latching said drive voltage information that is output from
said drive signal determination means; and
voltage selection means for a) selecting from said second power voltage
group a liquid crystal drive voltage on the basis of said latched drive
voltage information and for b) outputting said liquid crystal drive
voltage to said signal electrodes;
said drive signal determination means, said latch means, and said voltage
selection means being located in said high-voltage-amplitude operating
portion.
5. A liquid crystal drive device according to claim 1, further comprising:
constant-voltage generation means that yields a regulated voltage from said
second power voltage group, said data storage means operating on the
supply of said regulated voltage.
6. A liquid crystal drive device according to claim 4, further comprising:
constant-voltage generation means that yields a regulated voltage from said
second power voltage group, said data storage means operating on the
supply of said regulated voltage.
7. A liquid crystal drive device according to claim 1, further comprising:
power monitoring means for monitoring the voltage state of said second
power voltage group or said third power voltage group, said power
monitoring means comprising switching means for switching the operating
power source supplied to said data storage means from a voltage within one
of said second power voltage group and said third power voltage group to a
voltage within said first power voltage group.
8. A liquid crystal drive device according to claim 4, further comprising:
power monitoring means for monitoring the voltage state of said second
power voltage group or said third power voltage group, said power
monitoring means comprising switching means for switching the operating
power source supplied to said data storage means from a voltage within one
of said second power voltage group and said third power voltage group to a
voltage within said first power voltage group.
9. A liquid crystal drive device according to claim 5, further comprising:
power monitoring means for monitoring the voltage state of said second
power voltage group or said third power voltage group, said power
monitoring means comprising switching means for switching the operating
power source voltage supplied to said data storage means from a voltage
within one of said second power voltage group and said third power voltage
group to a voltage within said first power voltage group.
10. A liquid crystal drive device according to claim 6, further comprising:
power monitoring means for monitoring the voltage state of said second
power voltage group or said third power voltage group, said power
monitoring means comprising switching means for switching the operating
power source voltage supplied to said data storage means from a voltage
within one of said second power voltage group and said third power voltage
group to a voltage within said first power voltage group.
11. A liquid crystal drive device according to claim 7, wherein said power
monitoring means comprises output means for supplying a result signal
indicative of the voltage state of said second power voltage group to an
external device.
12. A liquid crystal drive device according to claim 7, wherein said power
monitoring means comprises:
means for dividing the voltage difference existing between a pair of power
voltages within one of said second power voltage group and said third
power voltage group, one of said pair of power voltages being on a
high-potential side and the other of said pair of power voltages being on
a low-potential side, to generate a divided voltage;
comparison means for comparing said divided voltage with a reference
voltage selected from said first power voltage group to yield a comparison
result; and
switching means for a) performing an on/off operation on the basis of said
comparison result and for b) switching the power voltage supplied to said
data storage means from a voltage within one of said second power voltage
group and said third power voltage group to a voltage within said first
power voltage group.
13. A liquid crystal drive device according to claim 8, wherein said power
monitoring means comprises:
means for dividing the voltage difference existing between a pair of power
voltages within one of said second power voltage group and said third
power voltage group, one of said pair of power voltages being on a
high-potential side and the other of said pair of power voltages being on
a low-potential side, to generate a divided voltage;
comparison means for comparing said divided voltage with a reference
voltage selected from said first power voltage group to yield a comparison
result; and
switching means for a) performing an on/off operation on the basis of said
comparison result and for b) switching the power voltage supplied to said
data storage means from a voltage within one of said second power voltage
group and said third power voltage group to a voltage within said first
power voltage group.
14. A liquid crystal drive device according to claim 9, wherein said power
monitoring means comprises:
means for dividing the voltage difference existing between a pair of power
voltages within one of said second power voltage group and said third
power voltage group, one of said pair of power voltages being on a
high-potential side and the other of said pair of power voltages being on
a low-potential side, to generate a divided voltage;
comparison means for comparing said divided voltage with a reference
voltage selected from said first power voltage group to yield a comparison
result; and
switching means for a) performing an on/off operation on the basis of said
comparison result and for b) switching the power voltage supplied to said
data storage means from a voltage within one of said second power voltage
group and said third power voltage group to a voltage within said first
power voltage group.
15. A liquid crystal drive device according to claim 10, wherein said power
monitoring means comprises:
means for dividing the voltage difference existing between a pair of power
voltages within one of said second power voltage group and said third
power voltage group, one of said pair of power voltages being on a
high-potential side and the other of said pair of power voltages being on
a low-potential side, to generate a divided voltage;
comparison means for comparing said divided voltage with a reference
voltage selected from said first power voltage group to yield a comparison
result; and
switching means for a) performing an on/off operation on the basis of said
comparison result and for b) switching the power voltage supplied to said
data storage means from a voltage within one of said second power voltage
group and said third power voltage group to a voltage within said first
power voltage group.
16. A liquid crystal display device comprising at least the liquid crystal
drive device of claim 1 and a liquid crystal panel in which liquid crystal
elements are arranged in matrix form.
17. A liquid crystal display device comprising at least the liquid crystal
drive device of claim 4 and a liquid crystal panel in which liquid crystal
elements are arranged in matrix form.
18. A liquid crystal display device comprising at least the liquid crystal
drive device of claim 5 and a liquid crystal panel in which liquid crystal
elements are arranged in matrix form.
19. A liquid crystal display device comprising at least the liquid crystal
drive device of claim 7 and a liquid crystal panel in which liquid crystal
elements are arranged in matrix form.
20. A liquid crystal drive method used in a liquid crystal drive device,
said liquid crystal drive device comprising a low-voltage-amplitude
operating portion having at least a control logic unit and operating on
the supply of a first power voltage group, said liquid crystal drive
device further comprising a high-voltage-amplitude operating portion
operating on the supply of a second power voltage group, said second power
voltage group being used to drive liquid crystal elements arranged in
matrix form on a liquid crystal panel, said method comprising:
setting a voltage difference between at least one pair of power voltages
included within said second power voltage group, one on a high-potential
side and one on a low-potential side, to be greater than a voltage
difference between a power voltage on a high-potential side and a power
voltage on a low-potential side within said first power voltage group;
storing data for driving the liquid crystal elements of said liquid crystal
panel in a data storage means; and
supplying an operating power source to said data storage means, said
operating power source being a voltage group that is one of said second
power voltage group and a third power voltage group which is obtained by
converting said second power voltage group.
21. A liquid crystal device, comprising:
a liquid crystal panel having a plurality of scan electrodes, a plurality
of signal electrodes intersecting said scan electrodes, and a plurality of
liquid crystal elements arranged in matrix form; and
a drive device for driving said liquid crystal panel, said drive device
comprising:
a first circuit portion operating on the supply of a first power voltage
group and including a control circuit;
a second circuit portion operating on the supply of a second voltage group
and including a voltage selector;
data storage means for storing data controlled by said control circuit,
said voltage selector selecting a drive voltage that is applied to said
signal electrodes based on said stored data; and
power supplying means for supplying an operating power source to said data
storage means, said operating power source being a voltage group that is
one of said second power voltage group and a third power voltage group
which is obtained by converting said second power voltage group, a voltage
difference between a power voltage on a high-potential side and a power
voltage on a low-potential side within said second power voltage group
being greater than a voltage difference between a power voltage on a
high-potential side and a low-potential side within said first power
voltage group.
22. The liquid crystal device according to claim 21, wherein said control
circuit is a data input circuit.
23. The liquid crystal device according to claim 21, wherein said control
circuit is a timing circuit.
24. The liquid crystal device according to claim 21, wherein said control
circuit is an address register of said data storage means.
25. The liquid crystal device according to claim 21, wherein said control
circuit is an input register for storing said data.
26. A liquid crystal device according to claim 21, wherein:
said data storage means comprises a plurality of memory cells capable of
being temporarily written to and read from, each of said memory cells
comprising at least one pair of transistors for holding data with a
high-resistance element connected to each of said transistors in series.
27. A liquid crystal device according to claim 21, wherein said drive
device further comprises:
latch means for latching data that has been read out from said data storage
means;
level-shifting means for converting the voltage levels of said latched
data; and
voltage selection means for a) selecting from said second power voltage
group a liquid crystal drive voltage on the basis of said data whose
voltage level has been converted, and for b) outputting said liquid
crystal drive voltage to signal electrodes of said liquid crystal panel;
said latch means, said level-shifting means, and said voltage selection
means being located in said second circuit portion.
28. A liquid crystal device according to claim 21, wherein said drive
device further comprises:
drive signal determination means for determining drive voltage information
for said signal electrodes based on data read out from said data storage
means and based on the voltage states of a plurality of simultaneously
selected scan electrodes;
latch means for latching said drive voltage information that is output from
said drive signal determination means; and
voltage selection means for a) selecting from said second power voltage
group a liquid crystal drive voltage on the basis of said latched drive
voltage information and for b) outputting said liquid crystal drive
voltage to signal electrodes of said liquid crystal panel;
said drive signal determination means, said latch means, and said voltage
selection means being located in said second circuit portion.
29. A liquid crystal device according to claim 21, wherein said drive
device further comprises:
constant-voltage generation means that yields a regulated voltage from said
second power voltage group, said data storage means operating on the
supply of said regulated voltage.
30. A liquid crystal device according to claim 28, wherein said drive
device further comprises:
constant-voltage generation means that yields a regulated voltage from said
second power voltage group, said data storage means operating on the
supply of said regulated voltage.
31. A liquid crystal device according to claim 21, wherein said drive
device further comprises:
power monitoring means for monitoring the voltage state of one of said
second power voltage group and said third power voltage group, said power
monitoring means comprising switching means for switching the operating
power source supplied to said data storage means from a voltage within one
of said second power voltage group and said third power voltage group to a
voltage within said first power voltage group.
32. A liquid crystal device according to claim 28, wherein said drive
device further comprises:
power monitoring means for monitoring the voltage state of one of said
second power voltage group and said third power voltage group, said power
monitoring means comprising switching means for switching the operating
power source supplied to said data storage means from a voltage within one
of said second power voltage group and said third power voltage group to a
voltage within said first power voltage group.
33. A liquid crystal device according to claim 29, wherein said drive
device further comprises:
power monitoring means for monitoring the voltage state of one of said
second power voltage group and said third power voltage group, said power
monitoring means comprising switching means for switching the operating
power voltage supplied to said data storage means from a voltage within
one of said second power voltage group and said third power voltage group
to a voltage within said first power voltage group.
34. A liquid crystal device according to claim 30, wherein said drive
device further comprises:
power monitoring means for monitoring the voltage state of one of said
second power voltage group and said third power voltage group, said power
monitoring means comprising switching means for switching the operating
power voltage supplied to said data storage means from a voltage within
one of said second and said third power voltage group to a voltage within
said first power voltage group.
35. A liquid crystal device according to claim 31, wherein:
said power monitoring means comprises output means for supplying a result
signal indicative of the voltage state of said second power voltage group
to an external device.
36. A liquid crystal device according to claim 31, wherein said power
monitoring means comprises:
means for dividing the voltage difference existing between a pair of power
voltages within one of said second power voltage group and said third
power voltage group, one of said pair of power voltages being on a
high-potential side and the other of said pair of power voltages being on
low-potential side, to generate a divided voltage;
comparison means for comparing said divided voltage with a reference
voltage selected from said first power voltage group to yield a comparison
result; and
switching means for a) performing an on/off operation on the basis of said
comparison result and for b) switching the power voltage supplied to said
data storage means from a voltage within one of said second power voltage
group and said third power voltage group to a voltage within said first
power voltage group.
37. A liquid crystal device according to claim 32, wherein said power
monitoring means comprises:
means for dividing the voltage difference existing between a pair of power
voltages within one of said second power voltage group and said third
power voltage group, one of said pair of power voltages being on a
high-potential side and the other of said pair of power voltages being on
a low-potential side, to generate a divided voltage;
comparison means for comparing said divided voltage with a reference
voltage selected from said first power voltage group to yield a comparison
result; and
switching means for a) performing an on/off operation on the basis of said
comparison result and for b) switching the power voltage supplied to said
data storage means from a voltage within one of said second power voltage
group and said third power voltage group to a voltage within said first
power voltage group.
38. A liquid crystal device according to claim 33, wherein said power
monitoring means comprises:
means for dividing the voltage difference existing between a pair of power
voltages within one of said second power voltage group and said third
power voltage group, one of said pair of power voltages being on a
high-potential side and the other of said pair of power voltages being on
a low-potential side, to generate a divided voltage;
comparison means for comparing said divided voltage with a reference
voltage selected from said first power voltage group to yield a comparison
result; and
switching means for a) performing an on/off operation on the basis of said
comparison result and for b) switching the power voltage supplied to said
data storage means from a voltage within one of said second power voltage
group and said third power voltage group to a voltage within said first
power voltage group.
39. A liquid crystal device according to claim 34, wherein said power
monitoring means comprises:
means for dividing the voltage difference existing between a pair of power
voltages within one of said second power voltage group and said third
power voltage group, one of said pair of power voltages being on a
high-potential side and the other of said pair of power voltages being on
a low-potential side, to generate a divided voltage;
comparison means for comparing said divided voltage with a reference
voltage selected from said first power voltage group to yield a comparison
result; and
switching means for a) performing an on/off operation on the basis of said
comparison result and for b) switching the power voltage supplied to said
data storage means from a voltage within one of said second power voltage
group and said third power voltage group to a voltage within said first
power voltage group. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to improvements in a signal electrode driver with
internal RAM that is used in a liquid crystal display device.
2. Background Art
A known prior art method of transferring display data from a microprocessor
unit (MPU) to a single electrode drive circuit (X driver) in a liquid
crystal display module (liquid crystal panel or LCD panel) in a simple
matrix type of liquid crystal display device uses an X driver with
internal RAM. With this method, the display data is sequentially
transferred to the X driver by a shift clock, and this display data is
temporarily written to the internal RAM. The display operation is
performed by simultaneously reading out the display data for one scan
line. With this method, display data is stored in the internal RAM of the
X driver. Therefore, if there are no changes in the display, the display
can be refreshed by reading out the display data from the internal RAM
without having to transfer new display data to the X driver. This makes it
unnecessary to transfer display data by the shift clock when there are no
changes in the display, enabling low-power operation.
An example of the configuration of a prior art X driver with internal RAM
is shown in FIG. 14. This X driver comprises a row address counter decoder
904, a timing circuit 906, a data input control circuit 908, a chip enable
control circuit 910, a bidirectional shift register 912, data register
914, a frame memory (internal RAM) 916, a latch circuit 918, a level
shifter 920, and a voltage selector 922. The row address counter decoder
904 functions to sequentially select one line at a time from the frame
memory 916. Initialization of the selection address is based on a YD
signal, and the selection address is incremented when data write to the
frame memory 916 ends after the falling edge of an LP signal. The timing
circuit 906 has various functions, such as control of the row address
counter decoder 904 on the basis of a shift clock XSCL. The data input
control circuit 908 fetches display data D.sub.0 to D.sub.n from the MPU
and transfers the fetched data to the data register 914. The chip enable
control circuit 910 implements automatic power-saving for individual
chips, when a plurality of chips are used, on the basis of enable signals
CEI and CEO. The bidirectional shift register 912 outputs a control signal
to the data register 914 for writing display data D.sub.0 to D.sub.n to
the data register 914. The order in which the display data is fetched to
the data register 914 is inverted by an SHL signal. The data register 914
controls the writing of the display data to the frame memory 916, and data
is written to the frame memory 916 at the falling edge of the LP signal.
The latch circuit 918 reads from the frame memory 916 display data for the
row address selected by the row address counter decoder 904 at the falling
edge of the LP signal, and outputs it to the level shifter 920. The level
shifter 920 is a circuit for converting the voltage levels of signals from
a logical power voltage level (V.sub.DD or V.sub.SS) to a power voltage
level for the liquid crystal drive (V.sub.o to V.sub.s). The voltage
selector 922 functions to select from voltages V.sub.o to V.sub.s for
driving signal electrodes X.sub.1 to X.sub.m. The selection of one of
V.sub.o to V.sub.s is determined by the display data and the FR signal
which acts as a signal for alternating liquid crystal drive.
In the above described example of the prior art, the row address counter
decoder 904, the timing circuit 906, the data input control circuit 908,
the chip enable control circuit 910, the bidirectional shift register 912,
the data register 914, the frame memory (internal RAM) 916, and the latch
circuit 918 are located in a low-voltage-amplitude operating portion 901,
as shown in FIG. 14, and the level shifter 920 and the voltage selector
922 are located in a high-voltage-amplitude operating portion 902. A
voltage difference between a power voltage on a high-potential side and a
power voltage on a low-potential side within the low-voltage-amplitude
operating portion 901 is small, but a voltage difference between a power
voltage on a high-potent | | |
