Active matrix EWOD device and method of driving thereof

1. An AM-EWOD device comprising:

a plurality of array element electrodes disposed on a first substrate and defining respective array elements in the AM-EWOD device;

a reference electrode disposed on the first substrate;

a sensor;

a reference electrode drive circuit; and

a second reference electrode disposed on a second substrate opposed to the first substrate;

wherein the reference electrode drive circuit is configured to drive the reference electrode with any one of a first voltage waveform for actuating an array element and a second voltage waveform different from the first voltage waveform when performing a sensing operation using the sensor.

2. A device as claimed in claim 1 wherein at least a part of the reference electrode is disposed between a first array element electrode of the plurality of array element electrodes and a second array element electrode of the plurality of array element electrodes, and

wherein the second voltage waveform is configured to cause the reference electrode to provide electro-magnetic shielding between the first array element electrode and the second array element electrode.

3. A device as claimed in claim 1 wherein the second voltage waveform is a DC voltage waveform.

4. A device as claimed in claim 1 and further comprising an array element electrode drive circuit configured to, when the reference electrode drive circuit is driving the reference electrode with the first voltage waveform, drive an array element electrode with a third voltage waveform for actuating the array element, the third voltage waveform being out of phase with the first voltage waveform.

5. A device as claimed in claim 1 wherein the reference electrode comprises a plurality of independently addressable electrode segments.

6. A device as claimed in any claim 5 wherein the reference electrode drive circuit is configured to drive one electrode segment of the reference electrode with the first voltage waveform and simultaneously to drive another electrode segment of the reference electrode with the second voltage waveform.

7. A device as claimed in claim 1 wherein the array element electrodes are arranged in a matrix of rows and columns, and

wherein the reference electrode is provided between at least a column of array element electrodes including the first array element electrode and a column of array element electrodes including the second array element electrode, or is provided between at least a row of array element electrodes including the first array element electrode and a row of array element electrodes including the second array element electrode.

8. A device as claimed in claim 1 wherein the second reference electrode is electrically connected to the reference electrode, and wherein the reference electrode drive circuit drives the second reference electrode in common with the reference electrode.

9. A device as claimed in claim 1 wherein the second reference electrode is addressable independently from the reference electrode.

10. A device as claimed in claim 1 and comprising an insulator layer disposed over the array element electrodes but not over the reference electrode.

11. A device as claimed in claim 1 wherein the first and second array element electrodes and the reference electrode are co-planar with one another.

12. A device as claimed in claim 10 wherein the reference electrode is disposed over the insulator layer.

13. A device as claimed in claim 1 and comprising a hydrophobic layer disposed over the array element electrodes but not over the reference electrode.

14. An AM-EWOD device comprising:

a plurality of array element electrodes disposed on a first substrate and defining respective array elements in the AM-EWOD device;

a reference electrode disposed on the first substrate;

a sensor; and

a reference electrode drive circuit;

wherein the reference electrode drive circuit is configured to drive the reference electrode with any one of a first voltage waveform for actuating an array element and a second voltage waveform different from the first voltage waveform when performing a sensing operation using the sensor;

the device further comprising an insulator layer disposed over the array element electrodes but not over the reference electrode, wherein the reference electrode is disposed over the insulator layer.