CAPACITIVE SENSOR WITH ACTIVE SHIELD ELECTRODE

• US 20120074961A1
• Filed: 09/27/2011
• Published: 03/29/2012
• Est. Priority Date: 09/29/2010
• Status: Abandoned Application

• Current Assignee: Kopin Corporation
• Original Assignee: Kopin Corporation
• Inventors: HERRMANN, FREDERICK P.
• Application Number:
  US13/246,394
• Publication Number:
  US 20120074961A1
• Time in Patent Office: Days
• US Class Current: 324/658
• CPC Class Codes: G06F 2203/04107 Shielding in digitiser, i.e. guard or shielding arrangements, mostly for capacitive touchscreens, e.g. driven shields, driven grounds
• CPC Class Codes: G06F 3/044 by capacitive means
• CPC Class Codes: G06F 3/0443 using a single layer of sensing electrodes
• CPC Class Codes: H03K 17/962 Capacitive touch switches
• CPC Class Codes: H03K 2217/960765 Details of shielding arrangements

Abstract

A capacitive sensor having an active shield electrode driven by a unity gain amplifier. Various arrangements using multiplexors or switch arrays may allow single shield with multiple sense electrodes.

Claims

1. A capacitive sensor circuit comprising:

a capacitive sense electrode;

an active shield electrode, spaced apart from the capacitive sense electrode; and

an amplifier, connected between the sense electrode and the active shield electrode.

2. The sensor circuit of claim 1 in which the amplifier is an operational amplifier.

3. The sensor circuit of claim 1 in which the amplifier is an MOS source follower.

4. The sensor circuit of claim 1 wherein the amplifier is a unity gain amplifier.

5. The sensor circuit of claim 1 in which the active shield electrode is disposed on a side of a printed circuit board or flexible printed circuit opposite the sense electrode.

6. The sensor circuit of claim 1 in which the active shield electrode is on a same side of a printed circuit board or flexible printed circuit as, and in a position surrounding, the sense electrode.

7. The sensor circuit of claim 1 in which one or more active shield electrode is placed between multiple sense electrodes.

8. The sensor circuit of claim 1 in which the active shield electrodes(s) are placed on an internal layer of a multi-layer printed circuit board (PCB) or flexible printed circuit (FPC).

9. The sensor circuit of claim 8 in which the active shield electrode is disposed between the sense electrode and a ground shield electrode on a third conductive layer.

10. The sensor circuit of claim 8 in which a back side of the PCB or FPC is used to support additional circuitry.

11. The sensor circuit of claim 1 with multiple sense electrodes, and multiple active shield electrodes with the active shield electrodes driven by respective independent unity gain amplifiers.

12. The sensor circuit of claim 1 with multiple sense electrodes and a shared active shield electrode, the shared active shield electrode driven by a single amplifier, with the amplifier input connected to the active sense electrode via a multiplexor.

13. The sensor circuit of claim 1 with multiple sense electrodes and a shared active shield electrode driven by a single unity gain amplifier, with a single multiplexor connecting the shared active sense electrode to the unity gain amplifier input.

14. The sensor circuit of claim 1 with multiple sense electrodes and a shared active shield electrode driven by a single unity gain amplifier, with a switch network connecting the shaped active sense electrode to the unity gain amplifier input, and connecting the inactive sense electrodes to the unity gain amplifier output.

15. The sensor circuit of claim 1 with multiple sense electrodes and a multiplexor and sense circuit for selecting one of the multiple capacitive sense electrodes as a selected sense electrode, and also integrating an amplifier on a common substrate to drive the active shield electrode while maintaining a constant potential difference between the active shield electrode and the selected sense electrode.