Active matrix device and method of driving

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

a plurality of array elements arranged in an array of rows and columns, each of the array elements including array element circuitry, an element electrode, and a reference electrode;

wherein the array element circuitry comprises:

an actuation circuit configured to apply actuation voltages to the element and reference electrodes for actuating the array element; and

an impedance sensor circuit configured to sense impedance at the array element electrode to determine a droplet property at the array element, and wherein the impedance sensor circuit is configured to be operated by perturbing a potential applied to the reference electrode.

2. The AM-EWOD device of claim 1 , further comprising a common addressing line, and whereby the impedance sensor circuit is configured to be operated by supplying voltage signals over the common addressing line to effect both a reset operation and an operation for selecting a row in the array to be sensed.

3. The AM-EWOD device of claim 2 , wherein the impedance sensor circuit is configured to be operated by perturbing a potential applied to the reference electrode and by perturbing a potential applied to the common addressing line.

4. The AM-EWOD device of claim 1 , wherein the common addressing line is common to all elements in the same row of the array.

5. The AM-EWOD device of claim 1 , wherein the impedance sensor circuit further comprises a capacitor connected between the element electrode and the gate of a sensing transistor, and the impedance at the array element is sensed based on a change in a sensing voltage coupled across the capacitor.

6. The AM-EWOD device of claim 5 , wherein the impedance sensor circuit further comprises a transistor for setting the voltage at the gate of the sensing transistor.

7. The AM-EWOD device of claim 6 , wherein the sensing transistor and the transistor for setting the voltage at the gate of the sensing transistor are n-type transistors.

8. The AM-EWOD device of claim 1 , wherein the actuator circuit comprises isolating elements configured to isolate the element electrode from the actuation voltage during operation of the impedance sensor circuit.

9. The AM-EWOD device of claim 8 , further comprising a sensor input line for actuating the impedance sensor circuit, wherein the isolating elements include a transistor between the actuation circuit and the impedance sensor circuit that receives an input from the sensor input line.

10. The AM-EWOD device of claim 8 , wherein the isolating elements include an isolating capacitor that is connected to a row addressing line.

11. The AM-EWOD device of claim 1 , further comprising:

a sensor input line for actuating the impedance sensor circuit; and

an isolating transistor between the actuation circuit and the impedance sensor circuit that receives an input from the sensor input line, wherein the isolating transistor isolates the actuation circuit from the impedance sensor circuit during operation of the impedance sensor circuit.

12. The AM-EWOD device of claim 1 , wherein the actuation circuit comprises:

a memory part for storing data corresponding to either an actuated state or an unactuated state of the array element; and

an actuation part for supplying the actuation voltages to the element electrode and the reference electrode.

13. The AM-EWOD device of claim 12 wherein the actuation circuit is comprised of a single transistor and a single capacitor configured as a Dynamic RAM element.

14. A method of operating an active matrix electro-wetting on dielectric (AM-EWOD) device comprising the steps of:

arranging a plurality of array elements in an array of rows and columns, each of the array elements including array element circuitry, an element electrode, and a reference electrode, and the array element circuitry comprises an actuation circuit and an impedance sensor circuit;

applying actuation voltages with the actuation circuit to the element and reference electrodes to actuate the array element;

perturbing a potential applied to the reference electrode;

sensing impedance at the array element electrode with the impedance sensor circuit; and

determining a droplet property at the array element based on the sensed impedance.

15. The operating method of claim 14 , wherein the AM-EWOD device further comprises a common addressing line,

the operating method further comprising supplying voltage signals over the common addressing line to effect both a reset operation and an operation for selecting a row in the array to be sensed.

16. The operating method of claim 15 , further comprising operating the impedance sensor circuit by perturbing a potential applied to the reference electrode and by perturbing a potential applied to the common addressing line.

17. The operating method of claim 14 , wherein the impedance sensor circuit includes a capacitor connected between the element electrode and a gate of a sensing transistor;

the operating method further comprising sensing the impedance at the array element based on a change in a sensing voltage coupled across the capacitor.

18. The operating method of claim 14 , further comprising isolating the array element from the actuation voltage during operating of the impedance sensor circuit.

19. The operating method of claim 18 , wherein the isolating step comprises applying an input to a sensor input line to actuate the impedance sensor circuit.

20. The operating method of claim 14 , wherein applying the actuation voltages comprises:

storing data in a memory part of the actuation circuit corresponding to either an actuated state or an unactuated state of the array element; and

supplying the actuation voltages with an actuation part of the actuation circuit to the element electrode and the reference electrode.