Display device with proximity detection and method of using said device

1. An electronic display device comprising means of detection of proximity of a conducting element situated in proximity to a display zone of the device, the device comprising:

two insulating plates;

a layer of material exhibiting electro-optical properties configured to render at least a portion of its surface visible under the effect of an electrical control signal, the layer being disposed between the two plates;

at least one first electrode disposed on a face of one of the insulating plates;

a second electrode disposed on a face of the other insulating plate opposite at least one first electrode;

means for generating an image display zone control signal and outputting the image display zone control signal to the second electrode as a function of an image to be displayed on the display zone;

means for generating a high frequency signal applied to the second electrode;

means for detecting a modification of the high frequency signal independent of applying the image display zone control signal to the second electrode; and

means of mixing the high frequency signal and the image display zone control signal, the mixing means operable to add the high frequency signal and the image display zone control signal, whereby the image display zone control signal and the high frequency signal are applied simultaneously to the second electrode.

2. The device as claimed in claim 1 , wherein the means for generating the image display zone control signal comprise a low frequency voltage source ( 30 ) whose first terminal is linked to the first electrode and a second terminal of which is linked to the second electrode, in that the means for generating the high frequency signal are linked to the second electrode, in that the mixing means comprise a first resistor (Rscb) connected in series with the low frequency voltage source.

3. The device as claimed in claim 2 , wherein the means for detecting a modification, if any, of the high frequency signal are linked to the second electrode.

4. The device as claimed in claim 2 , wherein the value of the first resistor (Rscb) lies between 1 kilo-ohm and 100 kilo-ohms.

5. The device as claimed in claim 2 , wherein the means for generating the high frequency signal ( 31 ) are linked to the second electrode ( 7 ) by way of an injection capacitor (Cinj), and in that the value of the first resistor (Rscb) is at least of the order of magnitude of the impedance of the injection capacitor (Cinj) at the frequency of the high frequency signal.

6. The device as claimed in claim 1 , wherein the second electrode is linked to the means for generating the image display zone control signal and to the means for generating the high frequency signal by a feed pad whose resistance value (Rlsb) is less than 5 k ohms.

7. The device as claimed in claim 1 , wherein the first electrode and the second electrode form a capacitor (Cpsb), in that the first electrode is linked to the means for generating the image display zone control signal by way of a second resistor (Rlss+Rscs) whose value is adapted so that a time constant (τ) formed by the capacitor (Cpsb) and the second resistor (Rlss+Rscs) is at least of an order of magnitude smaller than a period of the image display zone control signal.

8. The device as claimed in claim 7 , wherein the value of the time constant (τ) is greater than or equal to a period of the high frequency signal.

9. The device as claimed in claim 7 , wherein the value of the second resistor (Rlss+Rscs) is adapted by etching of a feed pad ( 9 , Rlss) of the first electrode.

10. The device as claimed in claim 9 , wherein the value of the second resistor (Rlss+Rscs) is adapted by modifying the length and/or the width and/or the thickness of the feed pad ( 9 , Rlss) of the first electrode.

11. The device as claimed in claim 7 , wherein the second resistor (Rlss+Rscs) comprises an additional resistor (Rscs) connected in series with the feed pad ( 9 , Rlss) of the first electrode.

12. The device as claimed in claim 7 , wherein it comprises at least two first electrodes of different area disposed opposite a second electrode, in that the value of the second resistor (Rlss+Rscs) of each first electrode increases with the inverse of the area of the first electrode considered.

13. The device as claimed in claim 1 , wherein the second electrode comprises two distinct connection pads each linked by distinct lugs.

14. The device as claimed in claim 13 , wherein the first of the lugs is linked to the means for generating a high frequency signal, and the second of the lugs is linked to the means for generating an image display zone control signal.

15. The device as claimed in claim 14 , wherein a value of the mixing means (Rscb) is adapted by etching of the pad linked to the second of the lugs.

16. A method of using a device as claimed in claim 1 , wherein the means for generating an image display zone control signal ( 30 ) provide a periodic signal comprising positive and negative alternations, in that the means for generating a high frequency signal ( 31 ) inject a high frequency signal at substantially equal quantity during as many positive alternations as negative alternations of the image display zone control signal ( 30 ).

17. The method as claimed in claim 16 , wherein the high frequency signal is interrupted during switchings between the positive and negative alternations of the image display zone control signal ( 30 ).

18. The method as claimed in claim 16 , wherein the duration and/or the amplitude of the high frequency signal delivered by the means for generating a high frequency signal are such that the effective value of the high frequency signal is less than a threshold voltage of the layer.