CAPACITIVE KEY TOUCH SENSING USING ANALOG INPUTS AND DIGITAL OUTPUTS
First Claim
1. An integrated circuit device that senses actuation of a capacitive touch key, comprising:
- an analog-to-digital converter (ADC) having a sampling capacitor, wherein the ADC converts an analog voltage on the sampling capacitor to a digital representation thereof;
a digital processor coupled to a digital output of the ADC;
a switch matrix controlled by the digital processor;
a digital driver controlled by the digital processor;
a first node adapted for coupling to a capacitive touch key, the first node is coupled to the sampling capacitor through the switch matrix;
a second node adapted for coupling to the capacitive touch key, the second node is coupled to the digital driver through the switch matrix;
wherein a voltage pulse from the digital driver and through the capacitive touch key charges the sampling capacitor to a first voltage in proportion to a capacitance ratio thereof,wherein when an object having a capacitance to a common potential is in close proximity to the capacitive touch sensor some of the voltage pulse through the capacitive touch sensor is diverted from the sampling capacitor to the common potential, andwhereby the sampling capacitor is charged to a second voltage when the object is in close proximity to the capacitive touch key, were the second voltage is less than the first voltage.
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Accused Products
Abstract
A pulse is applied through a capacitive touch key sensor to a sampling capacitor of an analog-to-digital converter (ADC). The voltage charge arriving at the sampling capacitor will be maximum when there is substantially no shunt capacitance between the capacitive touch key sensor and the sampling capacitor. However, a object such as an operator'"'"'s finger when in close proximity to the capacitive touch key sensor will create a capacitive shunt to ground that diverts some of the charge that is supposed to go to the sampling capacitor and thereby reduces the voltage charge on the sampling capacitor. This change in charge voltage when the capacitive touch key sensor is activated (touched) may be easily detected with the ADC. In addition, light emitting diodes (LEDs) may be integrated with the capacitive touch key sensors and use the same connections on an integrated circuit device in a time division multiplexed manor.
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Citations
20 Claims
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1. An integrated circuit device that senses actuation of a capacitive touch key, comprising:
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an analog-to-digital converter (ADC) having a sampling capacitor, wherein the ADC converts an analog voltage on the sampling capacitor to a digital representation thereof; a digital processor coupled to a digital output of the ADC; a switch matrix controlled by the digital processor; a digital driver controlled by the digital processor; a first node adapted for coupling to a capacitive touch key, the first node is coupled to the sampling capacitor through the switch matrix; a second node adapted for coupling to the capacitive touch key, the second node is coupled to the digital driver through the switch matrix; wherein a voltage pulse from the digital driver and through the capacitive touch key charges the sampling capacitor to a first voltage in proportion to a capacitance ratio thereof, wherein when an object having a capacitance to a common potential is in close proximity to the capacitive touch sensor some of the voltage pulse through the capacitive touch sensor is diverted from the sampling capacitor to the common potential, and whereby the sampling capacitor is charged to a second voltage when the object is in close proximity to the capacitive touch key, were the second voltage is less than the first voltage. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A system for sensing actuation of one or more of a plurality of capacitive touch keys, said system comprising:
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a plurality of capacitive touch keys, an integrated circuit device having a plurality of external connections coupled to the plurality of capacitive touch keys, the integrated circuit device comprising; an analog-to-digital converter (ADC) having a sampling capacitor, wherein the ADC converts an analog voltage on the sampling capacitor to a digital representation thereof; a digital processor coupled to a digital output of the ADC; a switch matrix controlled by the digital processor, wherein the plurality of external connections are coupled to the switch matrix; a digital driver controlled by the digital processor, wherein the digital driver is coupled to the switch matrix; wherein a voltage pulse from the digital driver is coupled to a selected one of the plurality of capacitive touch keys through the switch matrix and a resulting voltage from the selected one of the plurality of capacitive touch keys charges the sampling capacitor to a first voltage in proportion to a capacitance ratio thereof, wherein when an object having a capacitance to a common potential is in close proximity to the selected one of the plurality of capacitive touch keys some of the voltage pulse through the selected one of the plurality of capacitive touch keys is diverted from the sampling capacitor to the common potential, and whereby the sampling capacitor is charged to a second voltage when the object is in close proximity to the capacitive touch key, were the second voltage is less than the first voltage. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16)
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17. A method for sensing actuation of any one of a plurality of capacitive touch keys arranged in P(x) rows and A(y) columns, said method comprising the steps of:
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setting P(x) rows and A(y) columns to a logic low for discharging any residual charges on a plurality of capacitive touch keys; coupling each of the A(y) columns to an analog input; generating a pulse on each of the P(x) rows for each of the A(y) columns; measuring an analog voltage associated with each of the plurality of capacitive touch keys that are generated by each of the pulses; storing the measured analog voltages associated with each of the plurality of capacitive touch keys; determining when any one of the stored measured analog voltages is below a certain voltage threshold; and indicating which one of the plurality of capacitive touch keys has the associated stored analog voltage below the certain voltage threshold. - View Dependent Claims (18, 19, 20)
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Specification