Capacitive field sensor with sigma-delta modulator
AssigneeCypress Semiconductor Corporation
InventorsAndriy Ryshtun, Victor Kremin
Life of this patent
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Abstract
A capacitive sensor includes a switching capacitor circuit, a comparator, and a charge dissipation circuit. The switching capacitor circuit reciprocally couples a sensing capacitor in series with a modulation capacitor during a first switching phase and discharges the sensing capacitor during a second switching phase. The comparator is coupled to compare a voltage potential on the modulation capacitor to a reference and to generate a modulation signal in response. The charge dissipation circuit is coupled to the modulation capacitor to selectively discharge the modulation capacitor in response to the modulation signal.
Claims20
A method comprising:
- generating a pulse signal based on a pseudorandom signal;
- responsive to a first level of the pulse signal, charging a sensing capacitor and a modulation capacitor;
- responsive to a second level of the pulse signal, discharging the sensing capacitor;
- generating a modulating signal based on an amount of charge stored on the modulation capacitor;
- and
- determining, based on a duty cycle of the modulating signal, whether an object is proximate to the sensing capacitor.
A method comprising:
- responsive to a pseudorandom signal, charging a modulation capacitor based on a capacitance of a sensing capacitor;
- generating a modulating signal having a duty cycle that changes in a first direction in response to a change in capacitance of the sensing capacitor and changes in a second direction in response to noise.
An apparatus comprising:
- a pseudorandom signal generator configured to generate a pseudorandom pulse signal;
- a switch configured to couple a first capacitor with a second capacitor responsive to a first value of the pseudorandom pulse signal and to couple the first capacitor to a reference voltage responsive to a second value of the pseudorandom pulse signal;
- a modulator circuit configured to generate a modulating signal based on a charge of the second capacitor;
- a measurement circuit configured to determine, based on a duty cycle of the modulating signal, whether an object is proximate to the first capacitor.
Dependencies are inferred from the claim text.