Array element circuit and active matrix device

1. An array element circuit with an integrated impedance sensor, comprising:

an array element which is controlled by application of a drive voltage by a drive element;

writing circuitry for writing the drive voltage to the drive element; and

sense circuitry for sensing an impedance presented at the drive element;

wherein:

the array element is a hydrophobic cell having a surface of which the hydrophobicity is controlled by the application of the drive voltage by the drive element, and the sense circuitry senses the impedance presented at the drive element by the hydrophobic cell,

and the writing circuitry writes the drive voltage to the drive element independently of the sense circuitry sensing the impedance at the drive element.

2. The array element circuit according to claim 1 , wherein:

the writing circuitry is configured to perturb the drive voltage written to the drive element;

the sense circuitry is configured to sense a result of the perturbation of the drive voltage written to the drive element, the result of the perturbation being dependent upon the impedance presented at the drive element; and

the sense circuitry includes an output for producing an output signal a value of which represents the impedance presented at the drive element.

3. The array element circuit according to claim 1 , wherein the sense circuitry is AC coupled to the drive element.

4. The array element circuit according to claim 1 , wherein:

the drive element includes a node between the hydrophobic cell and a capacitor which stores the written drive voltage; and

the sense circuitry includes a sensor row select line connected to the capacitor, the sensor row select line serving to provide at least one pulse to the node via the capacitor in order to sense the impedance presented at the drive element.

5. The array element circuit according to claim 4 , wherein the capacitor is formed by a gated diode.

6. The array element circuit according to claim 1 , wherein:

the sense circuitry comprises a sense node AC coupled to the drive element; and

the sense circuitry further comprises reset circuitry for resetting a voltage at the sense node prior to sensing the impedance presented at the drive element.

7. The array element circuit according to claim 6 , wherein:

the reset circuitry comprises a pair of diodes connected in series with the sense node therebetween and connected at opposite ends to corresponding reset lines.

8. The array element circuit according to claim 6 , wherein:

the reset circuitry comprises at least one transistor having a gate coupled to a reset line for selectively coupling the sense node to a reset potential.

9. The array element circuit according to claim 1 , the array element circuit comprising a counter-substrate and the impedance presented at the drive element representing the impedance between the drive element and the counter-substrate.

10. The array element circuit according to claim 1 , wherein the array element comprises a display element, and application of the drive voltage by the drive element controls an optical property of the display element.

11. An active-matrix device, comprising:

a plurality of array element circuits arranged in rows and columns;

a plurality of source addressing lines each shared between the array element circuits in corresponding same columns;

a plurality of gate addressing lines each shared between the array element circuits in corresponding same rows; and

a plurality of sensor row select lines each shared between the array element circuits in corresponding same rows,

wherein each of the plurality of array element circuits comprises:

an array element which is controlled by application of a drive voltage by a drive element;

writing circuitry for writing the drive voltage to the drive element, the writing circuitry being coupled to a corresponding source addressing line and gate addressing line among the plurality of source addressing lines and gate addressing lines; and

sense circuitry for sensing an impedance presented at the drive element, the sense circuitry being coupled to a corresponding sensor row select line, and

wherein:

the array elements are hydrophobic cells having a surface of which the hydrophobicity is controlled by the application of the drive voltage by a corresponding drive element, and the sense circuitry senses the impedance presented at the drive element by the hydrophobic cell,

and for each of the plurality of array element circuits, the writing circuitry writes the drive voltage to the drive element independently of the sense circuitry sensing the impedance at the drive element.

12. The device according to claim 11 , wherein with respect to each of the plurality of array element circuits:

the writing circuitry is configured to perturb the drive voltage written to the drive element;

the sense circuitry is configured sense a result of the perturbation of the drive voltage written to the drive element, the result of the perturbation being dependent upon the impedance presented at the drive element; and

the sense circuitry includes an output for producing an output signal a value of which represents the impedance presented at the drive element.

13. The device according to claim 11 , wherein:

the device includes a plurality of sensor output lines each shared between the array element circuits in corresponding same columns, and the outputs of the plurality of array element circuits are coupled to a corresponding sensor output line.

14. The device according to claim 11 , wherein in each of the plurality of array element circuits the sense circuitry is AC coupled to the drive element.

15. The device according to claim 11 , wherein with respect to each of the plurality of array element circuits:

the drive element includes a node between the hydrophobic cell and a capacitor which stores the written drive voltage; and

the corresponding row select line is connected to the capacitor, the sensor row select line serving to provide at least one pulse to the node via the capacitor in order to sense the impedance presented at the drive element.

16. The device according to claim 11 , wherein with respect to each of the plurality of array element circuits:

the sense circuitry comprises a sense node AC coupled to the drive element; and

the sense circuitry further comprises reset circuitry for resetting a voltage at the sense node prior to sensing the impedance presented at the drive element.

17. The device according to claim 11 , the device comprising a counter-substrate shared by the array element circuits, and the impedance presented at the corresponding drive element representing the impedance between the corresponding drive element and the counter-substrate.

18. The array element circuit according to claim 11 , wherein the array element comprises a display element, and application of the drive voltage by the drive element controls an optical property of the display element.