Method of driving an active matrix electro-wetting on dielectric device and an active matrix electro-wetting on dielectric device

1. A method of driving an active matrix electro-wetting on dielectric (AM-EWOD) device with an alternating sign of actuation voltage, the AM-EWOD device comprising a plurality of array element electrodes defining respective array elements and a reference electrode, the method comprising:

(i) setting the reference electrode to a first reference voltage;

(ii) writing a set of data to array element electrodes of array elements of the device, whereby an array element is put into an actuated state if a first data voltage is written to the corresponding array element electrode to define a voltage difference of magnitude equal to or greater than an actuation voltage and having a first sign across the array element and is put into a non-actuated state if a second, different data voltage is written to the corresponding array element electrode;

(iii) either:

(a) maintaining the voltages written to the array element electrodes in feature (ii) until a time t 0

or

(b) re-writing N−1 times (where N≥2) the set of data to the array element electrodes of the array elements;

(iv) setting the reference electrode to a second reference voltage different from the first reference voltage, wherein the second reference voltage is of opposite sign to the first reference voltage;

(v) writing another set of data to array element electrodes of at least some array elements of the device whereby an array element is put into the actuated state if a third data voltage is written to the corresponding array element electrode to define a voltage difference of magnitude equal to or greater than the actuation voltage and having a second sign opposite to the first sign across the array element and is put into the non-actuated state if a fourth, different data voltage is written to the corresponding array element electrode; and

(vi) either:

(a) maintaining the voltages written to the array element electrodes element in feature (v) until a time t 1

or

(b) re-writing M−1 times (where M≥2) the another set of data to the array element electrodes of the at least some array elements.

2. A method as claimed in claim 1 in which the first and second reference voltages are of equal magnitude to one another.

3. A method as claimed in claim 2 in which the magnitude of the first and second reference voltages is approximately half the magnitude of the actuation voltage.

4. A method as claimed in claim 3 , in which the first data voltage has the same magnitude as and is of opposite sign to the second data voltage, and in which the magnitude of the first to fourth data voltages is approximately half the magnitude of the actuation voltage.

5. A method as claimed in claim 1 in which the first data voltage has the same magnitude as and is of opposite sign to the second data voltage.

6. A method as claimed in claim 1 in which the first data voltage has the same magnitude as and is of opposite sign to the third data voltage.

7. A method as claimed in claim 1 in which the first data voltage has the same magnitude and sign as the fourth data voltage.

8. A method as claimed in claim 1 wherein the set of data corresponds to a first data frame and the another set of data corresponds to an inverse of the first data frame.

9. A method as claimed in claim 1 wherein the set of data corresponds to a first data frame for a portion of the device and the another set of data corresponds to an inverse of the first data frame for the portion of the device.

10. A method as claimed in claim 1 wherein the set of data corresponds to an Nth data frame and the another set of data corresponds to an (N+1)th data frame or to an inverse of an (N+1)th data frame.

11. A method as claimed in claim 10 wherein writing the another set of data comprising writing data only to array elements with data values that change between the Nth data frame and the (N+1)th data frame.

12. A method as claimed in claim 1 and further comprising setting all array elements into the actuated state before (iv) setting the reference electrode to the second reference voltage or further comprising setting all array elements into the non-actuated state before (iv) setting the reference electrode to the second reference voltage.

13. An active matrix electro-wetting on dielectric (AM- EWOD) device comprising:

a plurality of array element electrodes defining respective array elements;

a reference electrode;

array element electrode drive circuits for driving respective array elements;

a reference electrode drive circuit; and

a controller programmed to, in accordance with input data, control the array element electrode drive circuits and the reference electrode drive circuit to perform the method as defined in claim 1 .

14. An AM-EWOD device as claimed in claim 13 wherein the array element drive circuits comprise:

a capacitor connected to the array element electrode; and

a switch connected between a data voltage input and the array element electrode, the switch having a control terminal connected to a control input.

15. An AM-EWOD device as claimed in claim 13 wherein the array element drive circuits comprise a static random access memory connected between a data voltage input and the array element electrode, the static random access memory having a control terminal connected to a control input.