Electrophoretic display with reduction of remnant voltages by selection of characteristics of inter-picture potential differences
An electrophoretic display panel ( 1 ), comprising a plurality of picture elements ( 2 ), an electrophoretic medium ( 5 ) having charged particles ( 6 ), and first and second electrodes ( 3,4 ) associated with each picture element ( 2 ) for receiving a potential difference. As the display ( 1 ) is addressed, for each picture element ( 2 ), the product of voltage and duration of picture voltages is read from a controller ( 102 ). After one or more image update periods, there will be a history generated of the total energy seen by each picture element ( 2 ). DC balancing is achieved by introducing feedback loop into the controller ( 102 ) which attempts to reduce the number stored in the memory ( 104 ) to zero, for each picture element ( 2 ) by applying one or more high voltage short pulses with a polarity opposite to the number stored in the memory ( 104 ).
1 . A display apparatus ( 1 ) comprising:
an electrophoretic medium ( 5 ) comprising charged particles ( 6 ) in a fluid;
a plurality of picture elements ( 2 );
a first and second electrode ( 8 , 9 ) associated with each picture element ( 2 ) for receiving a potential difference; and
drive means ( 100 ) arranged to:
a) supply a sequence of picture potential differences to each of said picture elements ( 2 ), each of said picture potential differences having a picture value and an associated picture duration, the product of which represents a picture energy for enabling the particles to occupy one of the positions for displaying a picture; and
b) supply one or more inter-picture potential differences between at least two consecutive picture potential differences, said one or more inter-picture potential differences having an inter-picture value and an associated inter-picture duration, the product of which represents an inter-picture energy which is insufficient to substantially change the positions of the particles;
the apparatus ( 1 ) further comprising memory means ( 104 ) for receiving data representative of the picture energy and inter-picture energy of all potential differences applied to each picture element ( 2 ), and providing a running total thereof for each picture element ( 2 ), the drive means ( 100 ) being arranged to select the polarity of said one or more inter-picture potential differences such that the magnitude of said running total for a respective picture element ( 2 ) is reduced.
2 . Apparatus ( 1 ) according to claim 1 , wherein a time interval is provided between each inter-picture potential difference applied to a picture element ( 2 ).
3 . Apparatus ( 1 ) according to claim 2 , wherein said time interval is of the order of 0.5.
4 . Apparatus ( 1 ) according to any one of the preceding claims, wherein the pulse time-period of each inter-picture potential difference is 2-8 ms.
5 . Apparatus ( 1 ) according to any one of the preceding claims, wherein the value of said inter-picture potential differences is substantially the maximum voltage available on the drive means ( 100 ).
6 . Apparatus ( 1 ) according to any one of the preceding claims, wherein one or more of said inter-picture potential differences have an inter-picture value below the threshold voltage of the ink materials used in said display apparatus.
7 . Apparatus ( 1 ) according to any one of the preceding claims, wherein the number and polarity of said inter-picture potential differences are stored in the memory means ( 104 ).