Measuring voltage

1. A method comprising:

receiving one of a plurality of first voltages, each of the first voltages resulting at least in part from a signal applied to an electrode of each of one or more nodes of a capacitive touch sensor;

receiving a second voltage across a measurement capacitor, the second voltage resulting at least in part on charging the measurement capacitor through application of a pre-determined voltage;

monitoring an output voltage during the charging of the measurement capacitor, the output voltage changing state based at least in part on a comparison of the second voltage relative to the one of the first voltages; and

determining whether a touch input has occurred based at least in part on an amount of time from a start of the charging of the measurement capacitor to a change in the state of the output voltage.

2. The method of claim 1 , wherein:

one of the first voltages is coupled to a first input of a comparator;

the second voltage across the measurement capacitor is coupled to a second input of the comparator; and

the output voltage is provided by an output terminal of the comparator.

3. The method of claim 2 , wherein charging the measurement capacitor comprises:

applying the pre-determined voltage to the measurement capacitor through a first resistor coupled to the second input of a comparator for a pre-determined amount of time; and

applying the pre-determined voltage to the measurement capacitor through a second resistor coupled to the second input of the comparator, wherein a resistance of the first resistor is lower than a resistance of the second resistor.

4. The method of claim 2 , wherein charging the measurement capacitor comprises:

applying the pre-determined amount of charge to the measurement capacitor through application of the pre-determined voltage to a charging capacitor coupled to the second input of a comparator; and

applying the pre-determined voltage to the measurement capacitor through a resistor coupled to the second input of a comparator.

5. The method of claim 1 , wherein charging the measurement capacitor comprises:

applying a pre-determined amount of charge to the measurement capacitor through one or more charge transfers, each charge transfer comprising:

transferring a pre-determined amount of charge to the measurement capacitor through application of the pre-determined voltage to a charging capacitor coupled to the measurement capacitor; and

discharging the charging capacitor through application of a high-impedance state to terminals of the charging capacitor.

6. The method of claim 1 , wherein monitoring the output voltage comprises determining whether the second voltage is substantially equal to the one of the first voltages.

7. The method of claim 1 , wherein each of the first voltages is across one of a plurality of sampling capacitors, each of the sampling capacitors being coupled to one of a plurality of inputs of a multiplexer.

8. A circuit configured to:

receive one of a plurality of first voltages, each of the first voltages resulting at least in part from a signal applied to an electrode of each of one or more nodes of a capacitive touch sensor;

receive a second voltage across a measurement capacitor, the second voltage resulting at least in part on charging the measurement capacitor through application of a pre-determined voltage;

monitor an output voltage during the charging of the measurement capacitor, the output voltage changing state based at least in part on a comparison of the second voltage relative to the one of the first voltages; and

determining whether a touch input has occurred based at least in part on an amount of time from a start of the charging of the measurement capacitor to a change in the state of the output voltage.

9. The circuit of claim 8 , wherein:

one of the first voltages is coupled to a first input of a comparator;

the second voltage across the measurement capacitor is coupled to a second input of the comparator; and

the output voltage is provided by an output terminal of the comparator.

10. The circuit of claim 9 , wherein the circuit is further configured to:

apply the pre-determined voltage to the measurement capacitor through a first resistor coupled to the second input of a comparator for a pre-determined amount of time; and

apply the pre-determined voltage to the measurement capacitor through a second resistor coupled to the second input of the comparator, wherein a resistance of the first resistor is lower than a resistance of the second resistor.

11. The circuit of claim 9 , wherein the circuit is further configured to:

apply the pre-determined amount of charge to the measurement capacitor through application of the pre-determined voltage to a charging capacitor coupled to the second input of a comparator; and

apply the pre-determined voltage to the measurement capacitor through a resistor coupled to the second input of a comparator.

12. The circuit of claim 8 , wherein the circuit is further configured to:

apply a pre-determined amount of charge to the measurement capacitor through one or more charge transfers, each charge transfer comprising:

transfer a pre-determined amount of charge to the measurement capacitor through application of the pre-determined voltage to a charging capacitor coupled to the measurement capacitor; and

discharge the charging capacitor through application of a high-impedance state to terminals of the charging capacitor.

13. The circuit of claim 8 , wherein the circuit is further configured to determine whether the second voltage is substantially equal to the one of the first voltages.

14. The circuit of claim 8 , wherein each of the first voltages is across one of a plurality of sampling capacitors, each of the sampling capacitors being coupled to one of a plurality of inputs of a multiplexer.

15. An apparatus comprising:

a capacitive touch sensor having a plurality of nodes; and

a computer-readable non-transitory storage medium coupled to the capacitive touch sensor that embodies logic that is configured when executed to:

receive one of a plurality of first voltages, each of the first voltages resulting at least in part from a signal applied to an electrode of each of the nodes of the capacitive touch sensor;

receive a second voltage across a measurement capacitor, the second voltage resulting at least in part on charging the measurement capacitor through application of a pre-determined voltage;

monitor an output voltage during the charging of the measurement capacitor, the output voltage changing state based at least in part on a comparison of the second voltage relative to the one of the first voltages; and

determine whether a touch input has occurred based at least in part on an amount of time from a start of the charging of the measurement capacitor to a change in the state of the output voltage.

16. The apparatus of claim 15 , wherein:

one of the first voltages is coupled to a first input of a comparator;

the second voltage across the measurement capacitor is coupled to a second input of the comparator; and

the output voltage is provided by an output terminal of the comparator.

17. The apparatus of claim 16 , wherein the logic is further configured to:

apply the pre-determined voltage to the measurement capacitor through a first resistor coupled to the second input of a comparator for a pre-determined amount of time; and

apply the pre-determined voltage to the measurement capacitor through a second resistor coupled to the second input of the comparator, wherein a resistance of the first resistor is lower than a resistance of the second resistor.

18. The apparatus of claim 16 , wherein the logic is further configured to:

apply the pre-determined amount of charge to the measurement capacitor through application of the pre-determined voltage to a charging capacitor coupled to the second input of a comparator; and

apply the pre-determined voltage to the measurement capacitor through a resistor coupled to the second input of a comparator.

19. The apparatus of claim 15 , wherein the logic is further configured to:

apply a pre-determined amount of charge to the measurement capacitor through one or more charge transfers, each charge transfer comprising:

transfer a pre-determined amount of charge to the measurement capacitor through application of the pre-determined voltage to a charging capacitor coupled to the measurement capacitor; and

discharge the charging capacitor through application of a high-impedance state to terminals of the charging capacitor.

20. The apparatus of claim 15 , wherein the logic is further configured to determine whether the second voltage is substantially equal to the one of the first voltages.