Measuring Capacitance of a Capacitive Sensor with a Microcontroller Having Digital Outputs for Driving a Guard Ring
First Claim
Patent Images
1. A microcontroller comprising:
- a digital processor with memory;
a plurality of external input/output nodes that can be programmed to function as analog nodes,a multiplexer controlled by the digital processor for selecting one of said analog nodes and coupling the analog node to an analog bus;
an analog-to-digital converter (ADC) coupled with the analog bus for converting an analog voltage on the analog bus to a digital representation thereof and having a digital output coupled to the digital processor for conveying the digital representation; and
an external node coupled to the analog bus.
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Abstract
A guard ring is provided around each capacitive sensor plate and charged to substantially the same voltage as a voltage on the capacitive sensor plate. The guard ring reduces parasitic capacitances of the capacitive sensor plate caused by differences in voltage potentials between the capacitive sensor plate, and adjacent circuit conductors, ground planes and power planes. Two digital outputs and associated voltage divider resistors are used to drive the guard ring voltage to substantially the same voltage as the voltage on the capacitive sensor plate.
48 Citations
27 Claims
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1. A microcontroller comprising:
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a digital processor with memory; a plurality of external input/output nodes that can be programmed to function as analog nodes, a multiplexer controlled by the digital processor for selecting one of said analog nodes and coupling the analog node to an analog bus; an analog-to-digital converter (ADC) coupled with the analog bus for converting an analog voltage on the analog bus to a digital representation thereof and having a digital output coupled to the digital processor for conveying the digital representation; and an external node coupled to the analog bus. - View Dependent Claims (2, 3)
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4. A microcontroller comprising:
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a digital processor with memory; a plurality of digital output drivers controlled by the digital processor; a sample and hold capacitor; an analog-to-digital converter (ADC) having a digital output coupled to the digital processor; at least two digital output nodes of the microcontroller coupled to respective ones of the plurality of digital output drivers; a first analog node coupled to a first analog bus in the microcontroller; the first analog bus is switchably coupled to a power supply common, a power supply voltage, the sample and hold capacitor, or a second analog bus; the second analog bus is switchably coupled to the power supply common, the power supply voltage, the sample and hold capacitor, or the first analog bus; and the sample and hold capacitor is switchably coupled to either the first analog bus or an input of the ADC. - View Dependent Claims (5, 6, 7, 8, 9, 10, 11, 12)
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13. A capacitive sensor system, said system comprising:
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a capacitive sensor; a guard ring associated with the capacitive sensor; a first resistor coupled to the guard ring; a second resistor coupled to the guard ring; and a microcontroller, comprising; a digital processor with memory; a plurality of digital output drivers controlled by the digital processor; a sample and hold capacitor; an analog-to-digital converter (ADC) having a digital output coupled to the digital processor; at least two digital output nodes of the microcontroller coupled to respective ones of the plurality of digital output drivers, wherein one of the at least two digital output nodes is coupled to the first resistor and the other one of the at least two digital output nodes is coupled to the second resistor; a first analog node is coupled to a first analog bus in the microcontroller and the capacitive sensor; the first analog bus is switchably coupled to a power supply common, a power supply voltage, the sample and hold capacitor, or a second analog bus; the second analog bus is switchably coupled to the power supply common, the power supply voltage, the sample and hold capacitor, or the first analog bus; and the sample and hold capacitor is switchably coupled to either the first analog bus or an input of the ADC. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20)
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21. A method for measuring capacitance of a capacitive sensor and controlling a voltage on a guard ring associated with the capacitive sensor, said method comprising the steps of:
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providing a capacitive sensor; providing a guard ring associated with the capacitive sensor; providing a first resistor coupled to the guard ring; providing a second resistor coupled to the guard ring; and providing a microcontroller, comprising; a digital processor with memory; a plurality of digital output drivers controlled by the digital processor; a sample and hold capacitor; an analog-to-digital converter (ADC) having a digital output coupled to the digital processor; at least two digital output nodes of the microcontroller coupled to respective ones of the plurality of digital output drivers, wherein one of the at least two digital output nodes is coupled to the first resistor and the other one of the at least two digital output nodes is coupled to the second resistor; a first analog node is coupled to a first analog bus in the microcontroller and the capacitive sensor; the first analog bus is switchably coupled to a power supply common, a power supply voltage, the sample and hold capacitor, or a second analog bus; the second analog bus is switchably coupled to the power supply common, the power supply voltage, the sample and hold capacitor, or the first analog bus; and the sample and hold capacitor is switchably coupled to either the first analog bus or an input of the ADC; and performing the steps of; coupling the sample and hold capacitor to the first analog bus; coupling the first analog bus to a power supply voltage; coupling the second analog bus to a power supply common; driving respective ones of the at least two digital output nodes to substantially the power supply common with outputs from the first and second output drivers; driving a one of the at least two digital output nodes to substantially the power supply voltage; driving an other one of the at least two digital output nodes to substantially the power supply common; coupling the first and second analog buses together long enough for a first charge to settle therebetween; decoupling the sample and hold capacitor from the first analog bus; coupling the second analog bus to the power supply common; coupling the second analog bus to the power supply voltage; driving the third and fourth analog buses to substantially the power supply voltage; converting the settled first charge on the sample and hold capacitor to a first digital representation thereof with the ADC; reading the first digital representation from the ADC with the digital processor; coupling the first analog bus to the power supply common; driving the one of the at least two digital output nodes to substantially the power supply common; driving the other one of the at least two digital output nodes to substantially the power supply voltage; coupling the first and second analog buses together long enough for a second charge to settle therebetween; decoupling the sample and hold capacitor from the first analog bus; coupling the second analog bus to the power supply voltage; coupling the second analog bus to the power supply common; driving the third and fourth analog buses to substantially the power supply common; converting the settled second charge on the sample and hold capacitor to a second digital representation thereof with the ADC; and reading the second digital representation from the ADC with the digital processor. - View Dependent Claims (22, 23)
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24. A method for measuring capacitance of a capacitive sensor and controlling a voltage on a guard ring associated with the capacitive sensor, said method comprising the steps of:
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a) charging a sample and hold capacitor to a first voltage; b) charging a capacitive sensor to a second voltage; c) charging a guard ring associated with the capacitive sensor to the second voltage; d) charging the guard ring to a third voltage; e) coupling together the sample and hold capacitor and the capacitive sensor long enough for a first charge to settle therebetween; f) decoupling the sample and hold capacitor from the capacitive sensor; g) converting the settled first charge on the sample and hold capacitor to a first digital representation thereof with an analog-to-digital converter (ADC); h) charging the capacitive sensor to the second voltage; i) charging the capacitive sensor to the first voltage; j) charging the guard ring to the first voltage; k) reading the first digital representation of the first charge from the ADC with a digital processor; l) charging the guard ring to a fourth voltage; m) coupling together the sample and hold capacitor and the capacitive sensor long enough for a second charge to settle therebetween; n) decoupling the sample and hold capacitor from the capacitive sensor; o) converting the settled second charge on the sample and hold capacitor to a second digital representation thereof with the analog-to-digital converter (ADC); p) charging the capacitive sensor to the first voltage; q) charging the capacitive sensor to the second voltage; r) charging the guard ring to the second voltage; s) reading the second digital representation of the second charge from the ADC with the digital processor; and t) returning to step d). - View Dependent Claims (25, 26, 27)
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Specification