Methods and apparatus for a capacitive sensor
Various embodiments of the present technology may comprise methods and apparatus for increased sensitivity of a capacitive proximity sensor. The method and apparatus may comprise additional external capacitors coupled in parallel with internal variable capacitors to increase the effective capacitance of a detection circuit allowing for a larger sensing element, and therefore a stronger sensing field, without increasing the applied voltage or the internal capacitance of the proximity sensor. In alternative embodiments, the methods and apparatus may be configured to operate as one of a transmission electrode and a reception electrode to increase the strength of the sensing field.
1. A capacitive proximity sensor, comprising:
a sensing element, comprising:
a first and second electrode, wherein the first and second electrodes form a first sensing capacitor;
a first reference capacitor;
a first external capacitor coupled in series with the first sensing capacitor at a first node; and
a second external capacitor coupled in series with the reference capacitor at a second node;
an integrated circuit electrically connected to the sensing element, comprising:
a first variable capacitor coupled in parallel with the first external capacitor;
a second variable capacitor coupled in parallel with the second external capacitor; and
a differential amplifier; and
a voltage source coupled to the first external capacitor, the second external capacitor, the first variable capacitor and the second variable capacitor.
2. The capacitive proximity sensor according to claim 1 , wherein the integrated circuit further comprises:
a first feedback capacitor electrically coupled between a first input terminal and a first output terminal of the differential amplifier, and
a second feedback capacitor electrically coupled between a second input terminal and a second output terminal of the differential amplifier.
3. The capacitive proximity sensor according to claim 1 , wherein the voltage source is an inverted voltage source.
4. The capacitive proximity sensor according to claim 1 , wherein:
the first sensing capacitor and the first external capacitor are coupled at the first node; and
the first reference capacitor and the second external capacitor are coupled at the second node.
5. The capacitive proximity sensor according to claim 4 , wherein:
the first node is electrically connected to a first input terminal of the differential amplifier; and
the second node is electrically connected to a second input terminal of the differential amplifier.
6. The capacitive proximity sensor according to claim 1 , wherein the first and second electrodes are coplanar along a surface of the sensing element.
7. The capacitive proximity sensor according to claim 1 , wherein:
the first electrode comprises a transmission electrode;
the second electrode comprises a reception electrode; and
the first electrode surrounds the second electrode.
8. The capacitive proximity sensor according to claim 1 , further comprising a control unit configured to transmit a control signal.
9. The capacitive proximity sensor according to claim 8 , further comprising a first multiplexer electrically coupled to and responsive to the control unit.
10. The capacitive proximity sensor according to claim 9 , further comprising a third electrode, wherein the first and third electrodes form a second sensing capacitor.
11. The capacitive proximity sensor according to claim 10 , further comprising a second multiplexer responsive to the control unit.
12. The capacitive proximity sensor according to claim 11 , further comprising:
a second reference capacitor coupled to the second multiplexer, and
a third external capacitor and fourth external capacitor coupled to the first multiplexer.
13. A method for increasing the sensitivity of a capacitive proximity sensor, comprising:
forming a first sensing capacitor by applying a first voltage to a first and second electrode;
forming a reference capacitor;
forming a first internal capacitor and a second internal capacitor within an integrated circuit;
forming a first external capacitor and a second external capacitor outside of the integrated circuit;
applying a second voltage to the first external capacitor, the second external capacitor, the first internal capacitor, and the second internal capacitor;
forming a first equivalent capacitance by coupling the first external capacitor and the first internal capacitor in parallel;
coupling the first sensing capacitor in series with the first external capacitor and the first internal capacitor;
forming a second equivalent capacitance by coupling the second internal capacitor and the second external capacitor in parallel; and
coupling the first reference capacitor in series with the second external capacitor and the second internal capacitor.
14. The method according to claim 11 , further comprising forming a second sensing capacitor and selectively outputting capacitance data from one of the first sensing capacitor or the second sensing capacitor.
15. A proximity sensor system, comprising:
a sensing element, comprising:
a transmission electrode and a reception electrode, wherein:
the transmission and reception electrodes form a first sensing capacitor, and
the transmission and reception electrodes are coplanar along a surface of the sensing element;
a first reference capacitor;
a first external capacitor coupled in series with the first capacitor; and
a second external capacitor coupled in series with the reference capacitor;
a detection circuit comprising:
an integrated circuit electrically connected to the sensing element, comprising:
a first variable capacitor coupled in parallel with the first external capacitor;
a second variable capacitor coupled in parallel with the second external capacitor; and
a differential amplifier; and
a voltage source coupled to the first external capacitor, the second external capacitor, the first variable capacitor and the second variable capacitor; and
an analog to digital converter coupled to an output of the differential amplifier.
16. The proximity sensor system according to claim 15 , wherein:
the first capacitor and the first external capacitor are coupled at a first node; and
the reference capacitor and the second external capacitor are coupled at a second node.
17. The proximity sensor system according to claim 16 , further comprising a control unit and a first multiplexer responsive to the control unit.
18. The proximity sensor system according to claim 17 , further comprising a second reception electrode, wherein the transmission electrode and the second reception electrode form a second sensing capacitor.
19. The proximity sensor system according to claim 18 , further comprising a second multiplexer responsive to the control unit.
20. The proximity sensor system according to claim 18 , further comprising:
a second reference capacitor coupled to the second multiplexer, and
a third external capacitor and fourth external capacitor coupled to the first multiplexer.