METHOD AND DEVICE FOR CAPACITIVE DETECTION OF OBJECTS
First Claim
1. A device for capacitively detecting an object, said device comprising:
- a capacitive sensor having a sensor capacitor formed between at least one first capacitive element and at least one second capacitive element such that a presence of said object can change a capacitance of said sensor capacitor,a voltage supply,a first switch to couple said sensor capacitor to said voltage supply in order to charge said sensor capacitor,a tank capacitor,a second switch to couple said sensor capacitor to said tank capacitor in order to transfer charge from said sensor capacitor to said tank capacitor and to change the voltage of said tank capacitor,at least one switch driver unit to control said charging and charge transfer by opening and closing said switches several times such that said switches are not in the closed state simultaneously,a voltage monitoring unit to monitor the voltage of said tank capacitor, anda controller to determine at least one measurement value which depends on the rate of change of the voltage of said tank capacitor.
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Accused Products
Abstract
Proximity of a person causes a change in a capacitance value of a sensor capacitor having a pair of capacitive plates. The change is detected by charging the sensor capacitor by coupling the sensor to a voltage supply. The voltage supply is disconnected from a tank capacitor during the charging. The charge is transferred from the sensor capacitor to a tank capacitor. The voltage supply is disconnected from the tank capacitor during the charge transfer. The charging and charge transfer are repeated several times. The voltage of the tank capacitor is monitored. At least one value is determined which depends on the rate of change of the voltage of the tank capacitor. The capacitance of the capacitive sensor is typically low, typically in the order of 100 pF to 1 nF. The capacitance of the tank capacitor may be several orders of magnitude higher than the capacitance of the sensor capacitor. The large tank capacitor acts as a part of a low-pass filter which effectively filters out signal noise.
46 Citations
16 Claims
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1. A device for capacitively detecting an object, said device comprising:
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a capacitive sensor having a sensor capacitor formed between at least one first capacitive element and at least one second capacitive element such that a presence of said object can change a capacitance of said sensor capacitor, a voltage supply, a first switch to couple said sensor capacitor to said voltage supply in order to charge said sensor capacitor, a tank capacitor, a second switch to couple said sensor capacitor to said tank capacitor in order to transfer charge from said sensor capacitor to said tank capacitor and to change the voltage of said tank capacitor, at least one switch driver unit to control said charging and charge transfer by opening and closing said switches several times such that said switches are not in the closed state simultaneously, a voltage monitoring unit to monitor the voltage of said tank capacitor, and a controller to determine at least one measurement value which depends on the rate of change of the voltage of said tank capacitor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 16)
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14. A method for capacitively detecting an object by using a capacitive sensor having a sensor capacitor formed between at least one first capacitive element and at least one second capacitive element such that a presence of said object can change the capacitance value of said sensor capacitor, said method comprising:
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charging said sensor capacitor by coupling the sensor capacitor to a voltage supply, wherein said voltage supply is disconnected from a tank capacitor during said charging, transferring charge from said sensor capacitor to a tank capacitor, wherein said voltage supply is disconnected from said tank capacitor during said charge transfer, repeating said charging and charge transferring several times, monitoring the voltage of said tank capacitor, and determining at least one measurement value which depends on a rate of change of the voltage of said tank capacitor. - View Dependent Claims (15)
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Specification