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US 2014/0368222 A1Published application
Capacitive Proximity Detection Using Delta-Sigma Conversion
AssigneeMicrochip Technology Incorporated
InventorKeith Curtis
Life of this patent
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Abstract
Capacitive proximity detection is provided by combining a delta-sigma modulator and a capacitive voltage divider circuit to create a high resolution capacitive-to-digital converter. Period and duty cycle counters provide duty cycle ratios from the delta-sigma modulator for comparison of changes in capacitance values of a capacitive sensor when an object is in proximity thereto.
Claims30
A proximity detection system, said system comprising:
- a comparator having first and second inputs and an output, wherein the second input is coupled with a reference voltage and the first input is coupled with a holding capacitor;
- a capacitive sensor;
- a switch for coupling the capacitive sensor alternately to a voltage and the holding capacitor;
- a clock having an output;
- a flip-flop having an input coupled with the output of the comparator, a clock input coupled to the output of the clock and an output;
- a feedback resistor coupled between the output of the flip-flop and the first input of the comparator;
- a duty cycle counter having a clock input coupled to the output of the clock, a reset input, an enable input coupled to the output of the flip-flop, and an output for providing a number of clock outputs counted, wherein the duty cycle counter only counts the clock outputs when the enable input thereof is at a first logic level;
- and
- a circuit for controlling the switch whenever the output of the flip-flop goes from a second logic level to the first logic level;
- wherein the number of clock outputs counted are used in determining proximity of an object to the capacitive sensor.
7 more elements
A method for detecting an object proximate to a capacitive sensor, said method comprising the steps of:
- charging a capacitive sensor to a first voltage;
- coupling the charged capacitive sensor in parallel with a holding capacitor;
- comparing a resulting voltage on the parallel connected capacitive sensor and holding capacitor to a reference voltage with a voltage comparator, wherein:
- if the resulting voltage is greater than the reference voltage then partially discharge the holding capacitor to a lower voltage, and
- if the resulting voltage is less than the reference voltage then partially charge the holding capacitor to a higher voltage and add one count to a duty cycle counter;
- add one count to a period counter;
- return to the step of charging the capacitive sensor to the first voltage.
4 more elements
A method for detecting an object proximate to a capacitive sensor, said method comprising the steps of:
- discharging a capacitive;
- coupling the discharged capacitive sensor in parallel with a holding capacitor;
- comparing a resulting voltage on the parallel connected capacitive sensor and holding capacitor to a reference voltage with a voltage comparator, wherein:
- if the resulting voltage is less than the reference voltage then partially charge the holding capacitor to a higher voltage, and
- if the resulting voltage is greater than the reference voltage then partially discharge the holding capacitor to a higher voltage and add one count to a duty cycle counter;
- add one count to a period counter;
- return to the step of charging the capacitive sensor to the first voltage.
4 more elements
An apparatus for proximity detection, comprising:
- a comparator having first and second inputs and an output, wherein the second input is coupled with a reference voltage and the first input is coupled with a holding capacitor;
- a switch adapted for coupling a capacitive sensor alternately to a voltage and the holding capacitor;
- a clock having an output;
- a flip-flop having an input coupled with the output of the comparator, a clock input coupled to the output of the clock and an output;
- a feedback resistor coupled between the output of the flip-flop and the first input of the comparator;
- a duty cycle counter having a clock input coupled to the output of the clock, a reset input, an enable input coupled to the output of the flip-flop, and an output for providing a number of clock outputs counted, wherein the duty cycle counter only counts the clock outputs when the enable input thereof is at a first logic level;
- and
- a circuit for controlling the switch whenever the output of the flip-flop goes from a second logic level to the first logic level.
5 more elements
An apparatus for proximity detection, comprising:
- a voltage summer having first and second inputs and an output;
- a switch adapted for coupling a capacitive sensor alternately to a voltage and the first input of the voltage summer;
- a clock having an output, wherein at each clock pulse the switch briefly couples the capacitive sensor to the voltage then back to the first input of the voltage summer;
- a voltage reference having a reference voltage output;
- an operational amplifier having a first input coupled to an output of the voltage summer and a second input coupled to the output of the voltage reference;
- an integrating capacitor coupled between the first input of the operational amplifier and an output thereof;
- an analog-to-digital converter (ADC) having an input coupled to the output of the, wherein the ADC converts the operational amplifier output to a multi-bit digital representation thereof;
- a digital-to-analog converter (DAC) having inputs coupled to the ADC and converting the multi-bit digital representation from the ADC into an analog feedback voltage coupled to the second input of the voltage summer;
- a decimating filter having inputs coupled to the multi-bit digital representation from the ADC;
- and
- a digital signal processor (DSP) coupled to the decimating filter, wherein the DSP determines when an object is proximate to the capacitive sensor.
8 more elements
Dependencies are inferred from the claim text.