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US 12,000,876 B2Granted
Capacitive sensing
AssigneeTexas Instruments Incorporated
InventorsKrishnasawamy Nagaraj, Paul Kimelman, Abhijit Kumar Das
Life of this patent
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Abstract
A capacitive sensing system includes a controller, a node connected to one side of a capacitance, the controller configured to measure the capacitance by measuring a time for a voltage across the capacitance to reach a predetermined reference voltage, a noise measurement circuit configured to measure electrical noise on the node, and the controller receiving the measurement of noise from the noise measurement circuit.
Claims21
A circuit comprising:
- a variable capacitance device that includes a plate;
- a node coupled to the plate of the variable capacitance device;
- a first current source;
- a first charging switch coupled between the first current source and the node;
- a second current source;
- a second charging switch coupled between the second current source and the node, such that the first current source and the first charging switch are coupled in parallel with the second current source and the second charging switch;
- a discharge switch coupled between the node and a ground node;
- a first comparator coupled to the node;
- a noise measurement circuit comprising:
- a rectifier having an input coupled to the node, and an output;
- and
- an integrator having an input coupled to the output of the rectifier and having an output coupled to provide a noise measurement;
- and
- a controller coupled to the first comparator and coupled to control the first charging switch, the second charging switch, and the discharge switch, the controller configured to:
- receive the noise measurement of the node;
- determine a range for a capacitance measurement of the variable capacitance device based on the noise measurement;
- determine whether the capacitance measurement of the variable capacitance device is within the range;
- and
- determine whether to reject the capacitance measurement based on whether the capacitance measurement is outside the range.
16 more elements
A circuit comprising:
- a variable capacitance device that includes a plate;
- a node coupled to the plate of the variable capacitance device;
- a charging circuit coupled to the node;
- a discharge switch coupled between the node and a ground node;
- a noise measurement circuit comprising:
- a rectifier having an input coupled to the node, and an output;
- and
- an integrator having an input coupled to the output of the rectifier and having an output coupled to a controller;
- and
- the controller coupled to the charging circuit and the discharge switch, the controller configured to:
- measure a capacitance of the variable capacitance device by:
- causing the charging circuit to charge the variable capacitance device using a first current;
- thereafter, causing the discharge switch to discharge the variable capacitance device;
- causing the charging circuit to charge the variable capacitance device using a second current that is different from the first current;
- and
- thereafter, causing the discharge switch to discharge the variable capacitance device;
- receive a noise measurement of the node provided by the noise measurement circuit;
- determine a range for the measurement of the capacitance of the variable capacitance device based on the noise measurement;
- and
- determine whether to reject the measurement of the variable capacitance device based on whether the measurement of the capacitance is outside the range.
17 more elements
A method comprising:
- determining a capacitance measurement of a variable capacitance device, the variable capacitance device coupled to a node, the node coupled between a first switch circuit and a second switch circuit, the second switch circuit coupled to ground, wherein the determining includes:
- charging the variable capacitance device using a first current from a first current source;
- in response to the charging using the first current, discharging the variable capacitance device;
- charging the variable capacitance device using a second current from a second current source, wherein the first current and the second current are different in magnitude;
- and
- in response to the charging using the second current, discharging the variable capacitance device;
- receiving a noise measurement of a node coupled to the variable capacitance device, the noise measurement of the node received from a noise measurement circuit coupled to the node, the noise measurement circuit comprising a rectifier having an input coupled to the node and an integrator having an input coupled to an output of the rectifier and having an output coupled to provide the noise measurement;
- determine a range for the capacitance measurement of the variable capacitance device based on the noise measurement;
- determining whether the capacitance measurement is outside the range;
- and
- rejecting the capacitance measurement in response to determining the capacitance measurement is outside the range.
8 more elements
Dependencies are inferred from the claim text.