Drivers providing DC-balanced refresh sequences for color electrophoretic displays
A method for driving an electro-optic display having a front electrode, a backplane, and a display medium including at least three differently-colored particles, wherein the medium is positioned between the front electrode and the backplane. The method includes applying a reset phase and a color transition phase to the display such that the sum of all impulses results in an offset that maintains a DC-balance across the display medium. The invention additionally includes controllers for executing the method.
1. A method for driving an electrophoretic display having a front electrode, a backplane, and a display medium positioned between the front electrode and the backplane, the display medium comprising three sets of differently-colored particles, the method comprising:
applying a reset phase and a color transition phase to the display, the reset phase comprising:
applying a first signal having a first polarity, a first amplitude as a function of time, and a first duration on the front electrode;
applying a second signal having a second polarity opposite the first polarity, a second amplitude as a function of time, during the first duration on the backplane;
applying a third signal having the second polarity opposite the first polarity, a third amplitude as a function of time, during a second duration on the front electrode;
applying a fourth signal having the first polarity and the first amplitude as a function of time plus an impulse offset proportional to a kickback voltage experienced by the display medium, during the second duration on the backplane;
the color transition phase comprising:
applying a fifth signal having the second polarity, a fourth amplitude as a function of time, and a third duration preceded by the first and second durations on the front electrode;
applying a sixth signal having the first polarity, a fifth amplitude as a function of time, and a fourth duration preceded by the first and second durations on the backplane;
wherein the sum of the first and second amplitudes as a function of time integrated over the first duration, and the sum of the first, second, and third amplitudes as a function of time integrated over the second duration, and the fourth amplitude as a function of time integrated over the third duration, and the fifth amplitude as a function of time integrated over the fourth duration produces the impulse offset proportional to a kickback voltage experienced by the display medium and designed to maintain a DC-balance on the display medium over the reset phase and the color transition phase.
2. The method of claim 1 , wherein the reset phase erases previous optical properties rendered on the display.
3. The method of claim 1 , wherein the color transition phase substantially changes the optical property displayed by the display.
4. The method of claim 1 , wherein the first polarity is a negative voltage.
5. The method of claim 1 , wherein the first polarity is a positive voltage.
6. The method of claim 1 , wherein the fourth duration occurs during the third duration.
7. The method of claim 6 , wherein the third duration and the fourth duration initiate at the same time.
8. A controller for an electrophoretic display comprising a front electrode, a backplane, and a display medium positioned between the front electrode and the backplane, the display medium comprising three sets of differently-colored particles, the controller being operatively coupled to the front electrode and the backplane, and configured to apply a reset phase and a color transition phase to the display,
the reset phase comprising:
applying a first signal having a first polarity, a first amplitude as a function of time, and a first duration on the front electrode;
applying a second signal having a second polarity opposite the first polarity, a second amplitude as a function of time, during the first duration on the backplane;
applying a third signal having the second polarity opposite the first polarity, a third amplitude as a function of time, during a second duration on the front electrode;
applying a fourth signal having the first polarity and the first amplitude as a function of time plus an impulse offset proportional to a kickback voltage experienced by the display medium, during the second duration on the backplane;
the color transition phase comprising:
applying a fifth signal having the second polarity, a fourth amplitude as a function of time, and a third duration preceded by the first and second durations on the front electrode;
applying a sixth signal having the first polarity, a fifth amplitude as a function of time, and a fourth duration preceded by the first and second durations on the backplane;
wherein the sum of the first and second amplitudes as a function of time integrated over the first duration, and the sum of the first, second, and third amplitudes as a function of time integrated over the second duration, and the fourth amplitude as a function of time integrated over the third duration, and the fifth amplitude as a function of time integrated over the fourth duration produces an impulse offset proportional to a kickback voltage experienced by the display medium and designed to maintain a DC-balance on the display medium over the reset phase and the color transition phase.
9. The controller of claim 8 , wherein the controller applies a different reset phase depending upon the color to be displayed by the electrophoretic display.
10. The controller of claim 8 , wherein the display medium comprises white, cyan, yellow, and magenta particles.
11. The controller of claim 8 , wherein the display medium comprises white, red, blue, and green particles.