Noise handling in capacitive touch sensors
View Patent ↗In a capacitive sensor of the type having X electrodes which are driven and Y electrodes that are used as sense channels connected to charge measurement capacitors, signal measurements are made conventionally by driving the X electrodes to transfer successive packets of charge to the charge measurement capacitors. However, an additional noise measurement is made by emulating or mimicking the signal measurement, but without driving the X electrodes. The packets of charge transferred to the charge accumulation capacitor are then indicative of noise induced on the XY sensing nodes. These noise measurements can be used to configure post-processing of the signal measurements.
1. A method comprising:
grounding a first plate of a charge-accumulation capacitor;
injecting, through a resistor coupled to a voltage source, a predetermined amount of charge onto a charge-measurement capacitor;
transferring an amount of charge accumulated on a second plate of the charge-accumulation capacitor to a first plate of the charge-measurement capacitor, the charge having accumulated on the second plate of the charge-accumulation capacitor due at least in part to noise; and
determining, through a measured voltage across the charge-measurement capacitor, the amount of charge.
2. The method of claim 1 , further comprising calculating a noise factor to configure a filter based on the determined amount of charge.
3. The method of claim 1 , further comprising if the calculated noise factor is above a specified threshold value, then applying the configured filter to perform a numerical process on a measured signal.
4. An apparatus comprising:
a charge-measurement capacitor having a second plate coupled to a first plate of a charge-accumulation capacitor; and
one or more non-transitory computer-readable storage media embodying logic that is operable when executed to:
ground the first plate of the charge-accumulation capacitor;
inject a predetermined amount of charge onto the charge-measurement capacitor through a resistor coupled to a voltage source;
transfer an amount of charge accumulated on a second plate of the charge-accumulation capacitor to a first plate of the charge-measurement-capacitor, the charge having accumulated on the second plate of the charge-accumulations capacitor due at least in part to noise; and
determine, through a measured voltage across the charge-measurement capacitor, the amount of charge.
5. The apparatus of claim 4 , wherein the logic is further operable when executed to calculate a noise factor to configure a filter based on the determined amount of charge due to noise.
6. The apparatus of claim 5 , wherein the logic when executed is further operable to apply the configured filter to perform a numerical process on a measured signal, if the calculated noise factor is above a specified value.
7. The apparatus of claim 4 , wherein injecting the predetermined amount of charge further comprises coupling the second plate of the charge-measurement capacitor to the voltage source for a predetermined amount of time.
8. The apparatus of claim 4 , wherein the logic is further operable when executed to determine the amount of charge by measuring an amount of time to reduce the measured voltage across the charge-measurement capacitor to ground.
9. The apparatus of claim 8 , wherein the logic is further operable when executed to determine the amount of time by counting a number of clock periods for the measured voltage across the charge-measurement capacitor to become ground.
10. A non-transitory computer-readable storage media embodying logic that is operable when executed to:
ground a first plate of a charge-accumulation capacitor;
inject, through a resistor coupled to a voltage source, a predetermined amount of charge onto a charge-measurement capacitor;
transfer an amount of charge on a second plate of the charge-accumulation capacitor to a first plate of the charge-measurement capacitor, the charge having accumulated on the second plate of the charge-accumulation capacitor at least in part due to noise; and
determine, through a measured voltage across the charge-measurement capacitor, the amount of charge.
11. The media of claim 10 , wherein the logic is further operable when executed to calculate a noise factor to configure a filter based on the determined amount of charge.
12. The media of claim 11 , wherein the logic is further operable when executed to apply the configured filter to a numerical process on a measured signal, if the calculated noise factor is above a specified value.
13. The media of claim 10 , wherein injecting the predetermined amount of charge further comprises coupling the second plate of the charge-measurement capacitor to the voltage source for a predetermined amount of time.
14. The media of claim 10 , wherein the logic is further operable when executed to determine the amount of charge by measuring an amount of time to reduce the measured voltage across the charge-measurement capacitor to ground.
15. The media of claim 14 , wherein the logic is further operable when executed to determine the amount of time by counting a number of clock periods for the measured voltage across the charge-measurement capacitor to become ground.
16. The method of claim 1 , wherein injecting the predetermined amount of charge further comprises coupling the second plate of the charge-measurement capacitor to the voltage source for a predetermined amount of time.
17. The method of claim 1 , wherein determining the amount of charge further comprises measuring an amount of time to reduce the measured voltage across the charge-measurement capacitor to ground.
18. The method of claim 17 , wherein determining the amount of time further comprises counting a number of clock periods for the measured voltage across the charge-measurement capacitor to become ground.