Extended proximity sensor device with electrostatic discharge protection

• US 8,232,810 B2
• Filed: 05/12/2009
• Issued: 07/31/2012
• Est. Priority Date: 05/12/2009
• Status: Expired due to Fees

• Current Assignee: Synaptics Incorporated
• Original Assignee: Synaptics Incorporated
• Inventors: Reynolds, Joseph Kurth, Dattalo, Tracy Scott
• Primary Examiner(s): Dole, Timothy J
• Application Number:
  US12/464,743
• Publication Number:
  US 20100289503A1
• Time in Patent Office: 1,176 Days
• Field of Search: 345/174, 345/658
• US Class Current: 324/662
• CPC Class Codes: G06F 3/0443 using a single layer of sensing electrodes
• CPC Class Codes: H03K 17/955 using a capacitive detector
• CPC Class Codes: H03K 2217/960705 Safety of capacitive touch and proximity switches, e.g. increasing reliability, fail-safe

Abstract

An input device is provided with improved electrostatic discharge protection. Specifically, the input device includes a plurality of capacitive sensing electrodes configured for object detection. An electrostatic discharge (ESD) shunt is disposed near the capacitive sensing electrodes and configured to provide ESD protection to the capacitive sensing electrodes. The input device also includes an extended-proximity capacitive sensing electrode configured to for object detection of relatively distant objects. The ESD shunt has an associated first resistance, and the extended-proximity capacitive sensing electrode has an associated second resistance. The second resistance is greater than the first resistance such that an electrostatic discharge at a first exposed location would be attracted to the ESD shunt via a first potential discharge path instead of being attracted to the extended-proximity capacitive sensing electrode via a second potential discharge path, where the first discharge path is longer than the second discharge path.

Claims

1. A sensing device comprising:

a substrate;

a plurality of capacitive sensing electrodes disposed on the substrate, the plurality of capacitive sensing electrodes configured to detect objects that are relatively near a surface;

an electrostatic discharge (ESD) shunt disposed on the substrate, the ESD shunt having an associated first resistance, the ESD shunt shaped to at least partially surround the plurality of capacitive sensing electrodes; and

an extended-proximity capacitive sensing electrode formed outside the at least partially surrounded plurality of capacitive sensing electrodes, the extended-proximity capacitive sensing electrode configured to provide a relatively long range electrode field to detect objects that are relatively far from the surface, the extended-proximity capacitive sensing electrode having an associated second resistance, the second resistance substantially greater than the first resistance such that an electrostatic discharge at a first exposed location would be attracted to the ESD shunt via a first potential discharge path to the ESD shunt instead of the extended-proximity capacitive sensing electrode via a second potential discharge path to the extended-proximity capacitive sensing electrode, where the first potential discharge path is longer than the second potential discharge path.

2. The sensing device of claim 1 wherein the extended-proximity capacitive sensing electrode is configured to couple to a processor through a routing trace, and wherein the second resistance comprises a resistance between a location on the extended-proximity capacitive sensing electrode near the first exposed location and the processor.

3. The sensing device of claim 2 further comprising a discrete resistor ohmically in series with the routing trace such that the discrete resistor contributes to the second resistance.

4. The sensing device of claim 1 wherein the first resistance comprises a resistance between a location on the ESD shunt and a system ground.

5. The sensing device of claim 1 wherein the second resistance is at least one order of magnitude larger than the first resistance.

6. The sensing device of claim 1 wherein the extended-proximity capacitive sensing electrode has a linear resistance of at least 20 ohms/mm.

7. The sensing device of claim 6 wherein the ESD shunt has a linear resistance of less than 10 ohms/mm.

8. The sensing device of claim 1 wherein the extended-proximity capacitive sensing electrode comprises carbon ink.

9. The sensing device of claim 1 wherein the extended-proximity capacitive sensing electrode has a length, a width, and a thickness, and wherein the length is at least an order of magnitude greater than the width and the thickness.

10. The sensing device of claim 1 wherein the ESD shunt surrounds at least a portion of the plurality of capacitive sensing electrodes, and wherein the extended-proximity capacitive sensing electrode is disposed on the substrate and farther from a center of the plurality of capacitive sensing electrodes than the ESD shunt.

11. The sensing device of claim 1 wherein the extended-proximity capacitive sensing electrode is disposed on the substrate, and wherein at least a portion of the ESD shunt is between the plurality of capacitive sensing electrodes and the extended-proximity capacitive sensing electrode.

12. A sensing device configured to be in an assembly comprising:

a substrate;

a plurality of capacitive sensing electrodes disposed on the substrate, the plurality of capacitive sensing electrodes configured to detect objects that are relatively near a surface;

an electrostatic discharge (ESD) shunt disposed on the substrate, the ESD shunt shaped to at least partially surround the plurality of capacitive sensing electrodes, the ESD shunt having an associated first resistance, where the first resistance comprises a resistance between a location on the ESD shunt and a system ground;

a first exposed location, the first exposed location being a location that would be exposed after assembly, the first exposed location having an associated first discharge path to the ESD shunt; and

an extended-proximity capacitive sensing electrode formed outside the at least partially surrounded plurality of capacitive sensing electrodes, the extended-proximity capacitive sensing electrode configured to provide a relatively long range electrode field to detect objects that are relatively far from the surface, the extended-proximity capacitive sensing electrode having an associated second discharge path from the first exposed location, the first discharge path longer than the second discharge path, the extended-proximity capacitive sensing electrode having an associated second resistance, where the second resistance comprises a resistance between a location on the extended-proximity capacitive sensing electrode and a processor, the second resistance greater than the first resistance such that an electrostatic discharge at the first exposed location would be more attracted to the ESD shunt via the first discharge path than to the extended-proximity capacitive sensing electrode via the second discharge path.

13. The sensing device of claim 12 further comprising a discrete resistor and a routing trace, the discrete resistor ohmically in series with the routing trace, the discrete resistor and the routing trace configured to couple the extended-proximity capacitive sensing electrode with the processor such that the discrete resistor and the routing trace contribute to the second resistance.

14. The sensing device of claim 12 wherein the second resistance is at least one order of magnitude larger than the first resistance.

15. The sensing device of claim 12 wherein the extended-proximity capacitive sensing electrode has a linear resistance of at least 100 ohms/mm and the ESD shunt has a linear resistance less than 10 ohms/mm.

16. The sensing device of claim 12 wherein the extended-proximity capacitive sensing electrode comprises a patterned resistive material.

17. The sensing device of claim 12 wherein the ESD shunt surrounds at least majority of the plurality of capacitive sensing electrodes, and wherein the extended-proximity capacitive sensing electrode is farther from a center of the plurality of capacitive sensing electrodes than the ESD shunt.

18. The sensing device of claim 12 wherein the extended-proximity capacitive sensing electrode is disposed on the substrate, and at least a portion of the ESD shunt is between the plurality of capacitive sensing electrodes and the extended-proximity capacitive sensing electrode, and wherein the ESD shunt includes a protrusion extending towards the extended-proximity capacitive sensing electrode.

19. The sensing device of claim 12 wherein the assembly comprises a display system or device.

20. An electronic system comprising:

a system housing;

a substrate, the substrate configured to be physically coupled with the system housing;

a plurality of capacitive sensing electrodes disposed on the substrate, the plurality of capacitive sensing electrodes configured to detect objects that are relatively near a surface;

an electrostatic discharge (ESD) shunt disposed on the substrate, the ESD shunt shaped to at least partially surround the plurality of capacitive sensing electrodes, the ESD shunt having an associated first resistance;

a first exposed location, the first exposed location corresponding to a vulnerability in the system housing such that the first exposed location is subject to electrostatic discharge, the first exposed location having an associated first discharge path to the ESD shunt;

an extended-proximity capacitive sensing electrode formed outside the at least partially surrounded plurality of capacitive sensing electrodes, the extended-proximity capacitive sensing electrode configured to provide a relatively long range electrode field to detect objects that are relatively far from the surface, the extended-proximity capacitive sensing electrode having an associated second discharge path from the first exposed location, wherein the first discharge path is longer than the second discharge path, and wherein the extended-proximity capacitive sensing electrode has an associated second resistance, the second resistance greater than the first resistance such that an electrostatic discharge at the first exposed location would be attracted to the ESD shunt via the first discharge path instead of the extended-proximity capacitive sensing electrode via the second discharge path; and

a processor physically coupled to the substrate, coupled to the plurality of capacitive sensing electrodes, and coupled to the extended-proximity capacitive sensing electrode, the processor configured to detect capacitances using the plurality of capacitive sensing electrodes and the extended-proximity capacitive sensing electrode.