DYNAMIC CAPACITIVE SENSING

Abstract

A capacitive sensing circuit which uses the same electrodes or conductive structure or structures to perform both self-capacitance and mutual-capacitance measurements during a self-capacitance mode and a mutual-capacitance mode respectively, wherein the mutual-capacitance measurements are used to detect user proximity and the self-capacitance measurements are used to detect user touch.

Claims

1.-10. (canceled)

11. A capacitive sensing circuit comprising first and second sensing electrodes, self-capacitance measurement circuitry and mutual-capacitance measurement circuitry, wherein said sensing circuit utilize both self-capacitance sensing and mutual-capacitance sensing to optimally detect an engaging object via said electrodes, said detection comprising use of mutual-capacitance measurements, using both the first and second electrodes, for proximity detection over a first distance and use of self-capacitance measurements, using said first sensing electrode(s), said second sensing electrode(s) or both said first and second sensing electrodes, for detection over a second distance, wherein said first distance is substantially larger than said second distance.

12. The circuit of claim 11, wherein grounded structures close to said electrode(s) in a mobile electronic product containing said circuit substantially limit proximity detection distance with self-capacitance measurements.

13. The circuit of claim 11 wherein said object is a human body part.

14. The circuit of claim 12 wherein said mobile electronic product is at least one product selected from the group consisting of an activity band or watch, a mobile phone, a tablet computer and a headphone or earphone.

15. The circuit of claim 12, wherein said grounded structures comprise at least one of a battery of said mobile product, a screen of said mobile product, a printed circuit board conductor or other grounded conductive structures in said product.

16. The circuit of claim 11, wherein said mutual-capacitance measurements are used to detect object proximity over the first distance, wherein said self-capacitance measurements are used to detect object proximity or touch over the second distance and wherein a combination of said mutual-capacitance and self-capacitance measurements are used to detect object proximity or touch over a third distance, with said third distance less than said second distance.

17. The circuit of claim 14, wherein said product is a mobile phone and wherein mutual-capacitance measurements are used to detect user proximity to the mobile phone, facilitating a decision when to switch a screen of the mobile phone off, with said self-capacitance measurements used to detect when the mobile phone is on-ear.

18. The circuit of claim 17, wherein the sensing electrodes are also used as radio frequency antennas for communication.

19. The circuit of claim 14, wherein said product is an activity band or watch, wherein the mutual-capacitance measurements are used to detect proximity when a band of the activity band or watch is fastened loosely, and wherein the self-capacitance measurements are used to detect user touch or proximity when said band is fastened tightly.

20. The circuit of claim 11 comprising an additional sensing channel used for reference measurements to compensate for at least one of temperature, noise and time, wherein the additional reference channel is not substantially influenced by said engaging object.

21. The circuit of claim 11, wherein a decrease in said first proximity detection distance is used to either trigger or release a proximity detection event based on the self-capacitance measurements.

22. The circuit of claim 11, wherein both the mutual-capacitance and self-capacitance measurements are used to identify when a device comprising said circuit is picked up from a surface.

23. The circuit of claim 14, wherein said product is a headphone or an earphone, and wherein detection of a user proximity event via both said mutual-capacitance and self-capacitance measurements is used to determine that the product is picked up by said user.

24. The circuit of claim 23, wherein detection of a user proximity or touch event via said mutual-capacitance measurements but not via said self-capacitance measurements is used to determine that the product is placed on or in ears of said user.

25. The circuit of claim 24, wherein detection of a user proximity event via both said mutual-capacitance and said self-capacitance measurements without detecting a user touch event via said measurements is used to determine that the product has been removed from or out of the ears of said user.

26. The circuit of claim 11, wherein values obtained during said self-capacitance measurements are used to determine when to change a reference value used during said mutual-capacitance measurements and wherein said change uses subsequent mutual-capacitance measured values.

27. The circuit of claim 11, wherein said self-capacitance measurement values are used to determine the baseline of reference values for subsequent mutual-capacitance measurements.

28. The circuit of claim 11, wherein said self-capacitance measurement values are used to determine thresholds for proximity or touch events discerned during subsequent mutual-capacitance measurements.

29. The circuit of claim 11, wherein mutual-capacitance measurement values are used to reseed, adjust and/or reset subsequent self-capacitance measurements.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The invention is further described by way of examples with reference to the accompanying drawings in which:

[0024] FIG. 1 shows an exemplary capacitive sensing circuit which embodies the present invention;

[0025] FIG. 2 shows a typical mobile phone with dual capacitive sensing electrodes;

[0026] FIG. 3 has plan and side views of an activity band or watch which embodies the present invention;

[0027] FIG. 4 shows two personal audio device embodiments of the invention; and

[0028] FIG. 5 shows a state diagram used to determine device state in a personal audio device.

DETAILED DESCRIPTION OF EMBODIMENTS

[0029] Disclosure of the present invention may be further aided by a detailed description of exemplary embodiments depicted in the appended drawings. It should be understood that both the drawings and the following description are not meant to limit the present invention, but merely to clarify its disclosure.

[0030] FIG. 1 presents an exemplary embodiment of the present invention at 1.1, wherein an integrated capacitive sensing circuit 1.2 may perform both self-C and mutual-C measurements using electrodes 1.5 and 1.6, with mutual-C values which may be used to detect proximity of a user 1.7 and self-C values to detect user touch. The circuit 1.2 is powered from a positive supply 1.3 and is connected to circuit ground 1.4. Various connections 1.8 to 1.10 are made to the circuit 1.2, for example communication lines, control lines, digital input/output pins and so forth.

[0031] The circuit 1.2 may automatically switch between a mutual-C sensing mode and a self-C sensing mode in a time-divisional manner, or it may switch modes based on the one or other stimulus or input. Self-C measurements may utilize either or both of the electrodes 1.5 and 1.6 to measure capacitance between said electrodes and a local electrical earth 1.10. There may be a varying amount of capacitive coupling between the electrical earth 1.10 and the local circuit ground 1.4.

[0032] Mutual-C measurements may be performed by using the electrode 1.5 as a transmitter electrode and the electrode 1.6 as a receiver electrode, or vice versa. According to the present invention, when the electrodes 1.5 and/or 1.6 are located close to ground 1.4, self-C based proximity detection of the user 1.7 may be severely limited in distance, in which case the circuit 1.2, or another circuit, may utilize measured values from either or both self-C and mutual-C measurements to decide to switch to a mutual-C mode and to use mutual-C measurement values for said proximity detection.

[0033] FIG. 2 presents an exemplary mobile phone application of the present invention at 2.1, wherein a phone 2.2 comprises capacitive sensing circuitry, not shown, but of the kind depicted in FIG. 1, which embodies the present invention, and which may make both self-C and mutual-C measurements in a time-divisional or other manner using capacitive sensing electrodes Cx1 and Cx2. A screen 2.3 of the phone is located quite close to said electrodes, as shown, and may be viewed as a grounded structure in terms of capacitive sensing. Either or both of the electrodes Cx1 and Cx2 may be used for self-C measurements. For mutual-C measurements, the electrode Cx1 is used a transmitter electrode and Cx2 as a receiver electrode, or vice versa. Typical applications of the capacitive sensing in said phone may include on-ear detection, Specific Absorption Rate (SAR) related measurements or left/right hand grip detection. In some embodiments, the electrode Cx1 may also function as an LTE antenna, with a high parasitic capacitance, and the electrode Cx2 may function as a Wi-Fi or GPS antenna.

[0034] Due to the nearness of screen or grounded structure 2.3, mutual-C measurements with the electrodes Cx1 and Cx2 may be used by said capacitive sensing circuit (not shown) to detect proximity of a user, as self-C capacitance based proximity detection distance may be limited. The capacitive sensing circuit (not shown) may use self-C measurements with either or both of the electrodes Cx1 and Cx2 to detect when the phone is located very close to the user's body, for example for on-ear detection. The sensing circuit may also utilize measurement values obtained with the electrodes Cx1 and Cx2 during a self-C mode to determine when and how to reseed, reset or adjust a reference value or decision thresholds used for mutual-C measurements with said electrodes, or vice versa.

[0035] In wearable consumer electronic products, for example in a watch or activity band 3.2 as shown at 3.1 in FIG. 3, grounded structures 3.3 are located very close to electrodes Cx1 and Cx2 used for capacitive sensing. This may adversely influence self-C measurements performed with the electrodes, especially in terms of proximity detection distance. Due to the nature of watches and activity bands, these are often worn loosely around a user's wrist using straps 3.4 and 3.5 (for example), necessitating the use of proximity measurements. According to the present invention, a combination of mutual-C and self-C measurements by a capacitive sensing circuit 1.2, not shown in FIG. 3 but included in a case of the watch or band 3.2 may be used to determine the wear case, and to decide when to utilize mutual-C measurements with the electrodes Cx1 and Cx2 to detect user proximity over a longer distance than what may be possible via self-C measurements with either or both of the electrodes Cx1 and Cx2. As before, self-C measurement values can be used to determine when to reseed, restart or adjust a reference value or decision thresholds used for mutual-C measurements, or vice versa.

[0036] FIG. 4 depicts yet another exemplary consumer electronic embodiment of the present invention, for personal audio devices. Over-ear headphones 4.3 for a user 4.2 is shown at 4.1, with said headphones 4.3 comprising a capacitive sensing circuit 1.2 (not shown) which embodies the present invention, and which performs both self-C and mutual-C measurements with electrodes Cx1 and Cx2 in a time-divisional, alternating or other manner. Due to the nature of over-ear headphones usage, the headphones often shift position. This may necessitate the use of proximity sensing. However, as space is at a premium in such products, a grounded structure, as shown in exemplary manner at 4.5 is often located quite close to the sensing electrodes Cx1 and Cx2, making the use of self-C based proximity detection, as is conventionally used in the art, impractical. Accordingly, the present invention teaches that said capacitive sensing circuit 1.2 (not shown) or another circuit, may perform proximity measurements based on mutual-C values, and may use measurements from either or both self-C and mutual-C modes to determine when to switch modes, or how and when to adjust the present capacitive sensing mode or the other capacitive sensing mode, or both.

[0037] A related embodiment is shown at 4.6, wherein in-ear headphones or earphones 4.7 utilize a capacitive sensing circuit 1.2, not shown, as well as capacitive sensing electrodes Cx1 and Cx2, to perform both self-C and mutual-C measurements in a time-divisional, alternating or other manner, similar to that taught elsewhere in the present disclosure. In such devices, space is severely limited, leading to very small capacitive sensing electrodes Cx1 and Cx2 as well as small ground reference conducting structures, as shown at 4.8. To ensure reliable user proximity, touch, pick-up, insertion and release detection, the apparatus and methods as taught by the present invention may need to be utilized.

[0038] For example, a state-diagram for ear- or headphone detection is presented in FIG. 5. The diagram is largely self-explanatory, but will be explained briefly. When earphones are off-ear, as at state 5.2, a low power mode switch may cause a transition 5.6 to a reseed state 5.1 and a return 5.8 to the off-ear state 5.2 when the reseeding is complete. When both mutual-C and self-C measurements detect a user's proximity, as at 5.7, the capacitive sensing circuit, or another circuit, may discern that reseeding is required, for example due to a pick-up event, resulting in transition to and from the reseed state 5.1.

[0039] When the earphones are in the off-ear state 5.2, and both proximity and touch are detected via mutual-C measurements, but not via self-C measurements, a transition 5.9 is made to an on-ear state 5.3. The state diagram returns from the on-ear state 5.3 to the off-ear state 5.2 via a transition 5.10 when no proximity or touch is detected via mutual-C and no proximity or touch is detected via self-C measurements.

[0040] When the earphones are in the off-ear state 5.2, and proximity is detected via mutual-C and self-C measurements, a transition 5.14 to a second off-ear state 5.4 with a lower mutual-C touch threshold is made. Once proximity is not detected via mutual-C measurements any more, the system returns via a transition 5.13 to the off-ear state 5.2.

[0041] From the second off-ear state 5.4, a touch detected via mutual-C or self-C may cause the system to transition via 5.12 to the on-ear state 5.3, with a return to the second off-ear state 5.4 via a transition 5.11 if only proximity and not touch is detected via mutual-C and self-C measurements. As is evident, the system may also return from the on-ear state 5.3 to the off-ear state 5.2 via the transition 5.10 after moving from the state 5.4 to the state 5.3.