Driving methods for color display devices
The present invention provides driving methods for electrophoretic color display devices. The backplane system used for the driving methods is found to be simpler which renders color display devices more cost effective. More specifically, the driving method comprises first driving all pixels towards a color state by modulating only the common electrode, followed by driving all pixels towards their desired color states by maintaining the common electrode grounded and applying different voltages to the pixel electrodes.
1. A method of driving a display layer having a plurality of pixels and a first, viewing surface and a second surface on the opposed side of the display layer from the first surface, the display layer being provided with means for applying an electric field between the first and second surfaces, the display layer further comprising an electrophoretic fluid comprising a fluid and first, second, third and fourth types of particles dispersed in the fluid, the first, second, third and fourth types of particles having respectively first, second, third and fourth optical characteristics differing from one another, the first and third types of particles bear charges of one polarity and the second and fourth types of particles bear charges of the opposite polarity, the method comprising:
a) applying to all pixels a first electric field having a high magnitude, thereby driving the first type of particles towards the viewing surface and causing the display layer to display the first optical characteristic at the viewing surface;
b) thereafter applying to all pixels a second electric field having a lower magnitude than, and a polarity opposite to, the first electric field, thereby driving the fourth type of particles towards the viewing surface and causing the display layer to display the fourth optical characteristic at the viewing surface; and
c) thereafter applying to at least one pixel of the display an electric field to cause the pixel to display an optical characteristic different from the optical characteristic displayed at the end of step b).
2. The method of claim 1 wherein step c) is effected by at least one of the following:
(i) applying to at least one pixel of the display a high electric field having the same polarity as the first electric field, thereby causing the pixel to display the first optical characteristic;
(ii) applying to at least one pixel of the display a high electric field having the opposite polarity from the first electric field, thereby causing the pixel to display the second optical characteristic; and
(iii) applying to at least one pixel of the display a high electric field having from the opposite polarity from the first electric field, followed by applying to the pixel a low electric field of the same polarity as the first electric field, thereby causing the pixel to display the third optical characteristic.
3. The method of claim 1 , further comprising applying a shaking waveform prior to step (a).
4. A method of driving a display layer having a plurality of pixels and a first, viewing surface and a second surface on the opposed side of the display layer from the first surface, the display layer being provided with means for applying an electric field between the first and second surfaces, the display layer further comprising an electrophoretic fluid comprising a fluid and first, second and third types of particles dispersed in the fluid, the first, second and third types of particles having respectively first, second and third optical characteristics differing from one another, the first type of particles bear charges of one polarity and the second and third types of particles bear charges of the opposite polarity, the method comprising:
a) applying to all pixels a first electric field having a high magnitude, thereby driving the first type of particles towards the viewing surface and causing the display layer to display the first optical characteristic at the viewing surface;
b) thereafter applying to all pixels a second electric field having a lower magnitude than, and a polarity opposite to, the first electric field, thereby driving the third type of particles towards the viewing surface and causing the display layer to display the third optical characteristic at the viewing surface; and
c) thereafter applying to at least one pixel of the display an electric field to cause the pixel to display an optical characteristic different from the optical characteristic displayed at the end of step b).
5. The method of claim 4 wherein step c) is effected by at least one of the following:
(i) applying to at least one pixel of the display a high electric field having the same polarity as the first electric field, thereby causing the pixel to display the first optical characteristic; and
(ii) applying to at least one pixel of the display a high electric field having the opposite polarity from the first electric field, thereby causing the pixel to display the second optical characteristic.
6. The method of claim 4 , further comprising applying a shaking waveform prior to step (a).
7. A method of driving a display layer having a plurality of pixels and a first, viewing surface and a second surface on the opposed side of the display layer from the first surface, the display layer being provided with means for applying an electric field between the first and second surfaces, the display layer further comprising an electrophoretic fluid comprising a fluid and first, second, third and fourth types of particles dispersed in the fluid, the first, second, third and fourth types of particles having respectively first, second, third and fourth optical characteristics differing from one another, the first and third types of particles bear charges of one polarity and the second and fourth types of particles bear charges of the opposite polarity, the method comprising:
a) applying to all pixels a first electric field having a high magnitude, thereby driving the second type of particles towards the viewing surface and causing the display layer to display the second optical characteristic at the viewing surface;
b) thereafter applying to all pixels a second electric field having a lower magnitude than, and a polarity opposite to, the first electric field, thereby driving the third type of particles towards the viewing surface and causing the display layer to display the third optical characteristic at the viewing surface; and
c) thereafter applying to at least one pixel of the display an electric field to cause the pixel to display an optical characteristic different from the optical characteristic displayed at the end of step b).
8. The method of claim 7 wherein step c) is effected by at least one of the following:
(i) applying to at least one pixel of the display a high electric field having the same polarity as the first electric field, thereby causing the pixel to display the second optical characteristic;
(ii) applying to at least one pixel of the display a high electric field having the opposite polarity from the first electric field, thereby causing the pixel to display the first optical characteristic; and
(iii) applying to at least one pixel of the display a high electric field having from the opposite polarity from the first electric field, followed by applying to the pixel a low electric field of the same polarity as the first electric field, thereby causing the pixel to display the fourth optical characteristic.
9. The method of claim 7 , further comprising applying a shaking waveform prior to step (a).