Inductive sensing methods, devices and systems
A method can include in a first phase of a sensing operation, controlling at least a first switch to energize a sensor inductance; in a second phase of the sensing operation that follows the first phase, controlling at least a second switch to couple the sensor inductance to a first modulator capacitance to induce a first fly-back current from the sensor inductance, the first fly-back current generating a first modulator voltage at the first modulator capacitance, and in response to the first modulator voltage, controlling at least a third switch to generate a balance current that flows in an opposite direction to the fly-back current at the first modulator node. The first and second phases can be repeated to generate a first modulator voltage at the first modulator capacitance. the modulator voltage can be converted into a digital value representing the sensor inductance. Related devices and systems are also disclosed.
1. A method comprising:
coupling a sense current to a modulator node, the sense current formed by an inductive sensor cell and a first switching matrix;
coupling a balance current to the modulator node;
generating, with a comparator coupled to the modulator voltage, a bitstream, the modulator voltage formed by a modulator capacitance, the sense current, and the balance current.
2. The method of claim 1 further comprising:
coupling a compensation current to the modulator node, the compensation current formed by a compensation capacitance cell and a third switching matrix.
3. The method of claim 1 , further comprising:
converting the bitstream to a digital value, the digital value corresponding to an inductance of the inductive sensor cell.
4. The method of claim 1 , wherein the first sense current is formed by:
in a first phase, coupling a first node of the inductive sensor cell to a first voltage potential and a second node of the inductive sensor cell to a second voltage potential;
in a second phase, coupling the first node of the inductive sensor cell to the second voltage potential and the second node of the inductive sensor cell to the first voltage potential;
in a third phase, coupling the first node of the inductive sensor cell to the second voltage potential and the second node of the inductive sensor cell to the modulator node; and
in a fourth phase, coupling the first node and second nodes of the inductive sensor cell to the second voltage potential.
5. The method of claim 4 , wherein the first voltage potential is a supply voltage and the second voltage potential is ground.
6. The method of claim 4 , wherein the first voltage potential is ground and the second voltage potential is a supply voltage.
7. The method of claim 1 , wherein the balance current formed by a reference capacitance cell and a second switching matrix.
8. The method of claim 1 , wherein the balance current formed by current digital to analog converter (IDAC).
9. A device comprising:
a comparator having a first input, a second input, and an output;
a first modulation node coupled to the first input of the comparator;
a inductive sensor cell coupled to at least the first modulation node, the inductive sensor cell providing a sense current to the at least first modulation node;
a reference cell coupled to the at least first modulation node, the reference cell providing a balance current to the at least first modulation node; and
a modulation capacitor coupled to the first input of the comparator, wherein the output of the comparator is converted into a bitstream by a circuit, the bitstream corresponding to an inductance of the inductive sensor cell.
10. The device of claim 9 , further comprising a compensation cell coupled to the at least first modulation node, the compensation cell comprising a compensation capacitor.
11. The device of claim 9 , further comprising a digital section, the digital section for converting the bitstream to a digital value.
12. The device of claim 9 , wherein the inductive sensor cell is coupled to a switch matrix, the switch matrix for:
in a first phase, coupling a first node of the inductive sensor cell to a first voltage potential and a second node of the inductive sensor cell to a second voltage potential;
in a second phase, coupling the first node of the inductive sensor cell to the second voltage potential and the second node of the inductive sensor cell to the first voltage potential;
in a third phase, coupling the first node of the inductive sensor cell to the second voltage potential and the second node of the inductive sensor cell to the modulator node; and
in a fourth phase, coupling the first node and second nodes of the inductive sensor cell to the second voltage potential.
13. The device of claim 12 , wherein the first voltage potential is a supply voltage and the second voltage potential is ground.
14. The device of claim 12 , wherein the first voltage potential is ground and the second voltage potential is a supply voltage.
15. A system comprising:
a sensor cell having a sensor inductance; a reference cell; and
an integrated circuit comprising:
an analog front end for converting a sense current from the sensor cell and a switch matrix to a bitstream, and
a digital section for converting the bitstream to a digital value; wherein
the reference cell is providing a balancing current to a modulation circuit of the integrated circuit, the modulation circuit for receiving the sense current.
16. The system of claim 15 , further comprising a compensation cell comprising a capacitance, the compensation cell for providing a compensation current to the modulation circuit.
17. The system of claim 15 , wherein the sense current is provided by:
in a first phase, coupling a first node of the sensor cell to a first voltage potential and a second node of the sensor cell to a second voltage potential;
in a second phase, coupling the first node of the sensor cell to the second voltage potential and the second node of the sensor cell to the first voltage potential;
in a third phase, coupling the first node of the sensor cell to the second voltage potential and the second node of the sensor cell to the modulator node; and
in a fourth phase, coupling the first node and second nodes of the sensor cell to the second voltage potential.
18. The system of claim 15 , wherein the digital value is representative of an inductance of the sensor inductance of the sensor cell.
19. The system of claim 15 , wherein the reference cell comprises a capacitance, the capacitance disposed within the integrated circuit.