Capacitance to code converter with sigma-delta modulator
View Patent ↗Apparatuses and methods of converting a capacitance measured on a sense element to a digital value are described. One apparatus includes a modulator having a modulator capacitor, a sense element selectively coupled in a feedback loop of the modulator to operate as a switching capacitor. The apparatus also includes a first switch coupled between a voltage source and a first node of the switching capacitor and a second switch coupled between the first node of the switching capacitor and a first node of the modulator capacitor. The switching capacitor provides a charge current to the modulator capacitor via the second switch. The modulator measures a capacitance of the sense element and converts the measured capacitance to a digital code representing the capacitance.
1. A capacitance-to-code converter comprising:
an input selectively couplable to a first sensing electrode;
an integrating circuit to integrate a signal on the input;
a first conversion circuit to convert the integrated signal to a first digital value, wherein the first digital value is representative of a self capacitance of the first sensing electrode; and
a second conversion circuit to convert the integrated signal to a second digital value, wherein the second digital value is representative of a mutual capacitance between the first sensing electrode and a second sensing electrode.
2. The capacitance-to-code converter of claim 1 , wherein the signal is a voltage.
3. The capacitance-to-code converter of claim 2 , wherein the voltage is applied to the first sensing electrode in a first phase of a switched-capacitor operation.
4. The capacitance-to-code converter of claim 1 , wherein the signal is a current.
5. The capacitance-to-code converter of claim 4 , wherein the current is induced on the first sensing electrode by a transmit signal on the second sensing electrode.
6. The capacitance-to-code converter of claim 1 , wherein the first sensing electrode is substantially orthogonal to the second sensing electrode.
7. The capacitance-to-code converter of claim 1 , wherein the first conversion circuit and the second conversion circuit share at least one component.
8. The capacitance-to-code converter of claim 1 , wherein the first conversion circuit and the second conversion circuit operate at a first time and a second time, respectively.
9. The capacitance-to-code converter of claim 8 , wherein the first conversion circuit and the second conversion circuit comprise substantially the same circuit elements, and wherein the circuit elements are configured to convert a self capacitance and a mutual capacitance in a first mode and a second mode, respectively.
10. A method comprising:
receiving a first signal on a first input coupled to a first sensing electrode;
integrating the first signal to generate a first integrated signal;
converting the first integrated signal to a first digital value, wherein the first digital value is representative of a self capacitance of the first sensing electrode; and
converting the first integrated signal to a second digital value, wherein the second digital value is representative of a mutual capacitance between the first sensing electrode and a second sensing electrode coupled to a second input.
11. The method of claim 10 , further comprising:
providing a second signal on the second input.
12. The method of claim 11 , wherein the first signal received on the first input is a current induced by the second signal on the second input.
13. The method of claim 10 , wherein the first signal is a voltage.
14. The method of claim 10 , wherein converting the first integrated signal to the second digital value comprises:
reconfiguring at least one component of a conversion circuit for converting the first integrated signal to the first digital value.
15. A capacitance sensing device comprising:
a first capacitance sensing electrode;
a second capacitance sensing electrode;
an integrating circuit coupled to the first capacitance sensing electrode;
a first conversion circuit to convert an integrated signal from the first capacitance sensing electrode to a first digital value, wherein the first digital value is representative of a self capacitance of the first sensing electrode; and
a second conversion circuit to convert the integrated signal from the first capacitance sensing electrode to a second digital value, wherein the second digital value is representative of a mutual capacitance between the first capacitance sensing electrode and the second capacitance sensing electrode.
16. The capacitance sensing device of claim 15 , wherein the first capacitance sensing electrode is substantially orthogonal to the second capacitance sensing electrode.
17. The capacitance sensing device of claim 15 , wherein the first capacitance sensing electrode is substantially adjacent to the second capacitance sensing electrode.
18. The capacitance sensing device of claim 15 , wherein the first conversion circuit and the second conversion circuit share at least one component.
19. The capacitance sensing device of claim 15 , wherein the first conversion circuit and the second conversion circuit operate at a first time and a second time, respectively.
20. The capacitance sensing device of claim 19 , wherein the first conversion circuit and the second conversion circuit comprise substantially the same circuit elements, and wherein the circuit elements are configured to convert a self capacitance and a mutual capacitance in a first mode and a second mode, respectively.