Display apparatus with a display device and method of driving the display device
View Patent ↗A display apparatus ( 1 ) comprises a matrix display device (DD) with pixels ( 10 ) wherein particles ( 14 ) move in a fluid ( 13 ) between electrodes ( 6, 6′, 7 ). An optical state of the pixels ( 10 ) is defined by a value of a drive voltage (VDi) and a duration (Di) of a drive period (TDi) during which the drive voltage (VDi) is present across the pixel ( 10 ). A DC-balancing circuit ( 3 ) controls the amplitudes of the drive voltages (VDi) and/or durations (Di) of drive periods (TDi) to obtain a substantially zero time-average value (N) across each pixel ( 10 ) or across each sub-group of pixels. This control of the amplitude of the drive voltages (VDi) and/or the duration (Di) of the drive periods (TDi) allows minimizing the image retention, without requiring reset pulses causing all pixels ( 10 ) to become temporarily white or black. In a preferred embodiment in accordance with the invention, a display device (DD) is used in which a drive voltage (VDi) is supplied to the pixel ( 10 ) with a level such that the grey level (or the amount of colorization) does not change anymore after an initial period of time. Now, if applicable, the DC-balancing can be performed by making the duration (Di) of the drive periods (TDi) longer than the initial period of time.
1. An electrophoretic display apparatus comprising:
at least a pixel comprising:
a plurality of electrodes; and
a plurality of particles disposed in a fluid between the electrodes;
a driver configured to supply first and second drive voltages for first and second durations, respectively, to the electrodes to control the movement of the particles to display a desired gray scale; and
a controller configured to:
control at least one of the second drive voltage or the second duration such that a sum of a first product of the first voltage multiplied by the first duration and a second product of the second voltage multiplied by the second duration becomes substantially zero;
compare an absolute value of the sum with a pre-determined threshold value; and
control the driver to supply a reset pulse to the electrodes when the sum is greater than the pre-determined threshold value.
2. The electrophoretic display device of claim 1 , wherein the first product and the second product have opposite polarities.
3. The electrophoretic display device of claim 1 , wherein the controller is configured to control the driver such that the desired gray scale is displayed before the end of the second duration.
4. The electrophoretic display device of claim 3 , wherein the second duration is equal to the first duration.
5. The electrophoretic display device of claim 1 , further comprising a memory storing the sum.
6. The electrophoretic display device of claim 1 , wherein the value of the sum is zero.
7. An electrophoretic display device comprising:
at least a pixel comprising:
a plurality of electrodes;
a plurality of particles disposed in a fluid between the electrodes;
a driver configured to supply a plurality of first drive voltages during corresponding first durations to the electrodes to control the movement of the particles;
a controller configured to:
calculate a sum of products of the first drive voltages multiplied by the corresponding first durations;
store the sum in a memory;
determine a second drive voltage having a polarity opposite to a polarity of the sum and second duration in response to an input image signal, wherein an absolute value of a product of the second voltage multiplied by the second duration is substantially equal to an absolute value of the sum;
control the driver to display a desired gray scale based on the second drive voltage and the second duration;
add the product of the second voltage multiplied by the second duration to the sum and store the updated sum in the memory;
compare the absolute value of the updated sum with a pre-determined threshold value; and
control the driver to supply a reset pulse to the electrodes when the updated sum is greater than the pre-determined threshold value.
8. The electrophoretic display device of claim 7 , wherein the controller is configured to control the driver such that the desired gray scale is displayed before the end of the second duration.
9. A method of displaying an image by driving an electrophoretic display device comprising at least a pixel having a plurality of electrodes, an optical state of the pixel being defined by particles moving in a fluid between the electrodes, the method comprising:
supplying first and second drive voltages for first and second durations, respectively, to the electrodes to control the movement of the particles to display a desired gray scale;
controlling at least one of the second drive voltage or the second duration such that a sum of a first product of the first voltage multiplied by the first duration and a second product of the second voltage multiplied by the second duration becomes substantially zero;
comparing an absolute value of the sum with a pre-determined threshold value; and
supplying a reset pulse to the electrodes when the absolute value of the sum is greater than the pre-determined threshold value.
10. The method of claim 9 , further comprising displaying the desired gray scale before the end of the second duration.
11. The method of claim 9 , wherein the second drive voltage or the second duration is controlled so that the value of the sum is zero.