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US 2010/0073405 A1Published application
Unipolar gray scale drive scheme for cholesteric liquid crystal displays
Assignee3M Innovative Properties Company
InventorPatrick M. Campbell
Life of this patent
Estimating the term…
Abstract
A unipolar gray scale drive scheme for passive matrix displays, more specifically, cholesteric liquid crystal displays, capable of creating any number of desired levels of gray scale. The drive scheme is single stage and can use either an amplitude modulation or a pulse width modulation column voltage signal in combination with a selecting row voltage signal to drive a pixel receiving the two intersecting signals to a desired level of gray scale.
Claims22
A method for driving at least a portion of a passive matrix display system having rows and columns forming pixels, comprising steps of:
- (a) initially driving the portion of the passive matrix display system to a uniform state;
- (b) outputting to the columns a column voltage signal, oscillating between two non-negative voltages, wherein the column voltage signal comprises at least three different sets of non-negative voltages causing three different states of the gray scale reflectivity of the pixels;
- (c) outputting to the rows a first row voltage signal oscillating between a non-planar voltage and a planar voltage, wherein the first row voltage signal is applied to a row of the matrix being written;
- and
- (d) outputting to the rows a second row voltage signal oscillating between a first voltage and a second voltage, wherein the difference between the second row voltage signal and the column voltage signal at any time is sufficiently low that a state of a pixel receiving the second row voltage signal and the column voltage signal will remain substantially unchanged, and wherein the second row voltage signal is applied to all of the rows of the matrix not being written.
2 more elements
A system for driving a display having rows and columns forming pixels, comprising:
- (a) a column driver outputting to the columns a column voltage signal oscillating between two non-negative voltages, wherein the column voltage signal comprises at least three different sets of non-negative voltages causing three different states of a gray scale reflectivity of the pixels;
- and
- (b) a row driver outputting to the rows a first row voltage signal and a second row voltage signal, wherein the first row voltage signal oscillates between a non-planar voltage and a planar voltage and is applied to a row of the matrix being written, and the second row voltage signal oscillates between a first voltage and a second voltage, the difference between the second row voltage signal and column voltage signal at any time being sufficiently low that a state of a pixel receiving the second row voltage signal and the column voltage signal will remain substantially unchanged, and wherein the second row voltage signal is applied to all of the rows of the matrix not being written.
A system for driving a display comprising:
- (a) a passive matrix display having rows and columns forming pixels;
- (b) a column driver outputting to the columns a column voltage signal oscillating between two non-negative voltages, wherein the column voltage signal comprises at least three different sets of non-negative voltages causing three different states of the gray scale reflectivity of the pixels;
- (c) a row driver outputting to the rows a first row voltage signal and a second row voltage signal, wherein the first row voltage signal oscillates between a non-planar voltage and a planar voltage and is applied to a row of the matrix being written, and the second row voltage signal oscillates between a first voltage and a second voltage, the difference between the second row voltage signal and column voltage signal being sufficiently low that a state of a pixel receiving the second row voltage signal and the column voltage signal will remain substantially unchanged, and wherein the second row voltage signal is applied to all of the rows of the matrix not being written;
- and
- (d) a controller electrically coupled to the passive matrix display, the row driver, and the column driver, wherein the controller controls the first row voltage signal, the second row voltage signal, and the column voltage signal.
2 more elements
A method for driving at least a portion of a passive matrix display system having rows and columns forming pixels, comprising steps of:
- (a) initially driving the portion of the passive matrix display system to a uniform state;
- (b) outputting to the columns a column voltage signal, cycling through four non-negative voltage levels, wherein the first voltage level is sufficiently high to change the pixel state to a planar reflective state, the second voltage will put the pixel into a weakly scattering focal conic state, the third voltage is sufficiently low that it cannot substantially change the pixel state, and the fourth voltage is the difference between the first voltage and the second voltage, and wherein a time period for the first and third voltages is proportional to t1 and a time period for the second and fourth voltages is proportional to t2, wherein
- t
-
-
- 1
- =
- n
- ×
- driveperiod
- 2
-
- (
- N
- -
- 1
- )
- t
-
-
- 2
- =
- (
- N
- -
- 1
- -
- n
- )
-
- (
- driveperiod
- )
- 2
-
- (
- N
- -
- 1
- )
- wherein N is a total number of desired levels of gray scale;
- n is a number representing a particular desired level of gray scale within the range of 0 to N−1;
- and
- drive period is a length of time inversely proportional to a frequency of oscillation of the row voltages;
- (c) outputting to the rows a first row voltage signal oscillating between a non-planar voltage and a planar voltage, wherein the first row voltage signal is applied to a row of the matrix being written;
- and
- (d) outputting to the rows a second row voltage signal oscillating between a first voltage and a second voltage, wherein the difference between the second row voltage signal and column voltage signal at any time is sufficiently low that a state of a pixel receiving the second row voltage signal and the column voltage signal will remain substantially unchanged, and wherein the second row voltage signal is applied to all rows of the matrix not being written.
44 more elements
A system for driving a display having rows and columns forming pixels comprising:
- (a) a passive matrix display having rows and columns forming pixels;
- (b) a column driver outputting to the columns a column voltage signal, cycling through four non-negative voltage levels, wherein the first voltage level is sufficiently high to change the pixel state to a planar reflective state, the second voltage will put the pixel into a weakly scattering focal conic state, the third voltage is sufficiently low that it cannot substantially change the pixel state, and the fourth voltage is the difference between the first voltage and the second voltage, and wherein a time period for the first and third voltages is proportional to t1 and a time period for the second and fourth voltages is proportional to t2, wherein
- t
-
-
- 1
- =
- n
- ×
- driveperiod
- 2
-
- (
- N
- -
- 1
- )
- t
-
-
- 2
- =
- (
- N
- -
- 1
- -
- n
- )
-
- (
- driveperiod
- )
- 2
-
- (
- N
- -
- 1
- )
- wherein N is the total number of desired levels of gray scale;
- n is a number representing a particular desired level of gray scale within the range of 0 to N−1;
- and
- drive period is a length of time inversely proportional to a frequency of oscillation of the row voltages;
- (c) a row driver outputting to the rows a first row voltage signal and a second row voltage signal, wherein the first row voltage signal oscillates between a non-planar voltage and a planar voltage, and is applied to a row of the matrix being written;
- and the second row voltage signal oscillates between a first voltage and a second voltage, the difference between the second row voltage signal and column voltage signal at any time being sufficiently low that a state of a pixel receiving the second row voltage signal and the column voltage signal will remain substantially unchanged, and is applied to all of the rows of the matrix not being written;
- and
- (d) a controller electrically coupled to the passive matrix display, the row driver, and the column driver, wherein the controller controls the first row voltage signal, the second row voltage signal, and the column voltage signal.
45 more elements
Dependencies are inferred from the claim text.