Dual touch sensor architecture with XY-position and Z-force sensing for touch-on-surface button

1. A device, comprising

a touch surface that is deflectable with touch pressure applied to the touch surface having a button area defined on the touch surface;

a touch sensor assembly including:

a capacitive sensor attached to a backside of the touch surface, having a co-planar touch button and a differential reference capacitive ring providing a reference capacitance, wherein the capacitive sensor includes an XY-position sensor including an XY electrode to define an XY sensing area corresponding to the button area, the XY-position sensor configured to sense a touch within the XY sensing area as a button-touch event;

a first compressible elastic insulator attached to the capacitive sensor on a first surface opposite the touch surface;

a Z-force sensor attached to the first compressible elastic insulator on a surface opposite the first surface, and including a Z-electrode, with a Z-target, to sense touch-pressure deflection of the touch surface that exceeds a button-press threshold as a button-press event;

the Z-electrode comprising one of a Z inductor coil and a Z capacitive electrode;

the Z-force sensor comprising either:

the Z-target disposed between the Z inductor coil and the XY electrode, the Z-target separated from the XY electrode and the Z inductor coil by the first compressible elastic insulator, such that the touch-pressure deflection of the touch surface causes a corresponding movement of the Z target toward the Z inductor coil, or

the Z capacitive electrode disposed between the Z-target and the XY electrode, the Z capacitive electrode separated from the XY electrode and the Z-target by the first compressible elastic insulator, such that the touch-pressure deflection of the touch surface causes a corresponding movement of the Z capacitive electrode toward the Z-target;

a second elastic insulator separating the X-Y position sensor from the Z-force sensor;

sensor electronics coupled to the XY-position sensor and the Z-force sensor to detect, as a button touch-press condition, the XY-position sensor sensing a button-touch event, substantially contemporaneous with the Z-force sensor sensing a button-press event.

2. The device of claim 1 , wherein the XY sensor comprises one of:

a capacitive XY sensor, including an XY capacitive electrode disposed at the touch surface opposite the button area to define an XY capacitive sensing area corresponding to the button area; and

a fingerprint sensor to detect a finger touch at the button area, with or without fingerprint verification.

3. The device of claim 1 , wherein

the XY sensor comprises a capacitive XY sensor, including an XY capacitive electrode disposed at the touch surface opposite the button area to define an XY capacitive sensing area corresponding to the button area; and

further comprising a differential reference capacitive electrode, co-planar with and adjacent to the XY-position capacitive electrode;

the sensor electronics coupled to the XY capacitive electrode and the differential reference capacitive electrode.

4. The device of claim 3 , wherein the differential reference capacitive electrode is ring-shaped around a substantial portion of the circumference of the XY capacitive electrode.

5. The device of claim 1 , wherein the surface is a glass display panel.

6. A device, comprising:

a case; including

a touch surface deflectable based on touch pressure applied to the touch surface;

a button area defined on the touch surface;

a touch sensor assembly within the case, including:

a capacitive sensor having a co-planar touch button and a differential reference capacitive ring providing a reference capacitance, the capacitive sensor attached to a backside of the touch surface, wherein the capacitive sensor includes an XY-Position sensor, including:

an XY capacitive electrode to define a projected capacitance XY sensing area substantially coextensive with the button area; and

capacitive sensor electronics coupled to the XY capacitive electrode and the differential reference capacitive ring to capture differential capacitance measurements, including sensing human body capacitance within the XY capacitive sensing area as a button-touch event; and

an inductive Z-Force sensor, including

a Z inductor coil spaced from the XY capacitive electrode,

a conductive target disposed between the Z inductor coil and the XY capacitive electrode, and

inductive sensor electronics coupled to the Z inductor coil to capture inductance measurements, and

a first elastic insulator disposed between the XY capacitive electrode and the conductive target, and between the conductive target and the Z inductor coil, such that the touch-pressure deflection of the touch surface causes a corresponding movement of the Z conductive target toward the inductor coil,

the inductive sensor electronics to capture changes in inductance caused by touch-pressure deflection of the touch surface that causes movement of the Z conductive target toward the Z inductor coil, including sensing touch-pressure deflection that exceeds a button-press threshold as a button-press event;

a second elastic insulator separating the X-Y position sensor from the Z-force sensor;

such that a button touch-press condition corresponds to the capacitive sensor electronics sensing a button-touch event, and the inductive sensor electronics substantially contemporaneously sensing a button-press event.

7. The device of claim 6 , further comprising:

a differential reference capacitive electrode, co-planar with and adjacent to the XY capacitive electrode;

the capacitive sensor electronics coupled to the XY capacitive electrode and the differential reference capacitive electrode.

8. The device of claim 7 , wherein the differential reference capacitive electrode is ring-shaped around a substantial portion of the circumference of the XY capacitive electrode.

9. The device of claim 6 , wherein the surface is a glass display panel.

10. A method of touch force sensing suitable for implementing a button defined on a surface of a device, comprising:

attaching a capacitive sensor having a co-planar touch button and a differential reference capacitive ring providing a reference capacitance, and including an XY sensor to a device touch surface structure opposite a button area corresponding to a button, to define an XY sensing area corresponding to the button area,

sensing a human body touch at the XY sensing area as a button-touch event;

sensing a touch-pressure deflection of the device surface with a Z-force sensor, including sensing a touch-pressure deflection that exceeds a button-press threshold as a button-press event;

the Z-force sensor including a Z-electrode, with a Z-target, the Z-electrode comprising one of a Z inductor coil and a Z capacitive electrode, the Z-force sensor comprising either:

the Z-target disposed between the Z inductor coil and the XY electrode, the Z-target separated from the XY electrode and the Z inductor coil by the first compressible elastic insulator, such that the touch-pressure deflection of the touch surface causes a corresponding movement of the Z target toward the Z inductor coil, or

the Z capacitive electrode disposed between the Z-target and the XY electrode, the Z capacitive electrode separated from the XY electrode and the Z-target by the first compressible elastic insulator, such that the touch-pressure deflection of the touch surface causes a corresponding movement of the Z capacitive electrode toward the Z-target;

a second elastic insulator separating the X-Y position sensor from the Z-force sensor; and

signaling the button-press event.

11. The method of claim 10 , wherein the XY sensor comprises one of:

a capacitive XY sensor, including an XY capacitive electrode disposed at the surface opposite the button area to define an XY capacitive sensing area corresponding to the button area; and

a fingerprint sensor to detect a finger touch at the button area, with or without fingerprint verification.

12. The method of claim 10 :

wherein the XY sensor comprises a capacitive XY sensor, including an XY capacitive electrode disposed at the touch surface opposite the button area to define an XY capacitive sensing area corresponding to the button area; and

further comprising a differential reference capacitive electrode, co-planar with and adjacent to the XY-position capacitive electrode.

13. The method of claim 10 , wherein the surface is a glass display panel.