Projected capacitive touch sensor circuit
View Patent ↗A method for measuring a mutual capacitance between electrodes of a touch sensitive device includes generating a periodic pulse, communicating the pulse to a drive electrode, and measuring a mutual capacitance between the drive electrode and a sense electrode at a point of intersection between the drive electrode and the sense electrode. Measuring further includes continuously integrating a sense signal from the sense electrode to thereby generate an integrated sense signal, periodically sampling the integrated sense signal at a first time that is prior to a falling edge of the pulse, and at a second time that is prior to a rising edge of the pulse to thereby sample a maximum value and a minimum value of the integrated sense signal, digitizing the maximum value and the minimum value, and determining a difference between the maximum value and the minimum value to thereby determine a mutual capacitance between the drive electrode and the sense electrode.
1. A circuit for measuring a mutual capacitance between electrodes disposed on a substrate, comprising:
a drive circuit configured to generate a periodic pulse and to communicate the pulse to a drive electrode; and
a sense circuit configured to measure a mutual capacitance between the drive electrode and a sense electrode at a point of intersection between the drive electrode and the sense electrode, wherein the sense circuit comprises:
an integrator circuit with an input section that is in continuous electrical communication with the sense electrode for an amount of time required for measuring the mutual capacitance;
a switch circuit with an input in electrical communication with an output of the integrator circuit and an output in electrical communication with a analog-to-digital converter, wherein the switch operates to momentarily communicate an output signal of the integrator circuit to the analog-to-digital converter at a first time that is prior to a falling edge of the pulse, and at a second time that is prior to a rising edge of the pulse to thereby sample a maximum value and a minimum value of the output signal; and
computational logic configured to determine a difference between the maximum value and the minimum value to thereby determine a mutual capacitance between the drive electrode and the sense electrode.
2. The circuit of claim 1 , further comprising averaging the difference between the maximum value and the minimum value for a plurality of pulses.
3. The circuit of claim 2 , wherein the average is a weighted average.
4. The circuit of claim 3 , wherein the weighted average is obtained via a 1-2-1 filter that filters the maximum value and the minimum value of the plurality of pulses.
5. The circuit of claim 2 , wherein for each intersection of a sense electrode and a drive electrode, sixteen or fewer pairs of maximum values and minimum values are measured to determine a mutual capacitance at the intersection.
6. The circuit of claim 1 , wherein a frequency of the pulse is between about 50 kHz and 500 kHz.
7. The circuit of claim 1 , further comprising a plurality of sense circuits, each being configured to measure a mutual capacitance between one or more drive electrodes and sense electrodes.
8. The circuit of claim 7 , wherein each sense electrode is coupled to a different sense circuit.
9. A method for measuring a mutual capacitance between electrodes disposed on a substrate, comprising:
generating a periodic pulse;
communicating the pulse to a drive electrode; and
measuring a mutual capacitance between the drive electrode and a sense electrode at a point of intersection between the drive electrode and the sense electrode, wherein measuring further comprises:
continuously integrating a sense signal from the sense electrode during a time required for determining the mutual capacitance to thereby generate an integrated sense signal;
periodically sampling the integrated sense signal at a first time that is just prior to a falling edge of the pulse, and at a second time that is just prior to a rising edge of the pulse to thereby sample a maximum value and a minimum value of the integrated sense signal;
digitizing the maximum value and the minimum value; and
determining a difference between the maximum value and the minimum value to thereby determine a mutual capacitance between the drive electrode and the sense electrode.
10. The method of claim 9 , further comprising averaging the difference between the maximum value and the minimum value for a plurality of pulses.
11. The method of claim 10 , wherein the average is a weighted average.
12. The method of claim 11 , further comprising filtering the maximum value and the minimum value of the plurality of pulses with a 1-2-1 filter to obtain the weighted average.
13. The method of claim 9 , wherein a frequency of the pulse is between about 50 kHz and 500 kHz.
14. A touch sensitive system, comprising:
a substrate having disposed thereon a plurality of drive electrodes and a plurality of sense electrodes; and
a circuit for determining a location of a touch, the circuit comprising:
a drive circuit configured to generate a periodic pulse and to communicate the pulse to a drive electrode; and
a sense circuit configured to measure a mutual capacitance between the drive electrode and a sense electrode at a point of intersection between the drive electrode and the sense electrode, wherein the sense circuit comprises:
an integrator circuit with an input section that is in continuous electrical communication with the sense electrode;
a switch circuit with an input in electrical communication with an output of the integrator circuit and an output in electrical communication with an analog-to-digital converter, wherein the switch operates to momentarily communicate an output signal of the integrator circuit to the analog-to-digital at a first time that is prior to a falling edge of the pulse, and at a second time that is prior to a rising edge of the pulse to thereby sample a maximum value and a minimum value of the output signal; and
computational logic configured to determine a difference between the maximum value and the minimum value to thereby determine a mutual capacitance between the drive electrode and the sense electrode.
15. The touch sensitive system of claim 14 , further comprising averaging the difference between the maximum value and the minimum value for a plurality of pulses.
16. The touch sensitive system of claim 15 , wherein the average is a weighted average.
17. The touch sensitive system of claim 16 , wherein the weighted average is obtained via a 1-2-1 filter that filters the maximum value and the minimum value of the plurality of pulses.
18. The touch sensitive system of claim 14 , wherein a frequency of the pulse is about between about 50 kHz and 500 kHz.
19. The touch sensitive system of claim 14 , further comprising a plurality of sense circuits, each being configured to measure a mutual capacitance between one or more drive electrodes and sense electrodes.
20. The touch sensitive system of claim 19 , wherein each sense electrode is coupled to a different sense circuit.