CAPACITIVE SENSING WITH HIGH-FREQUENCY NOISE REDUCTION
First Claim
1. A method of sensing the presence of a body from a change in an amount of charge present on a capacitively charged key, the method comprisingperforming a measurement burst which generates a plurality of signal sample values from a plurality of measurement cycles, each of the measurement cycles including,inducing charge onto the key during a drive part of the measurement cycle,measuring during a signal measurement part of the measurement cycle the charge induced on the key during the drive part of the measurement cycle,generating a signal sample value representing the charge measured from the key during the signal measurement part of the measurement cycle,comparing the value of the plurality of the signal sample values of the measurement burst with a determined range of accepted values between a determined maximum and a determined minimum value, andprocessing any of the plurality of signal sample values, which are outside the determined accepted range to the effect that the presence of a body can be determined only from a change in the value of one or more of the plurality of signal samples which are within the determined accepted range.
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Abstract
A method and apparatus for sensing the presence of a body from a change in an amount of charge present on a capacitively charged key includes performing a measurement burst which generates a plurality of signal sample values from a plurality of measurement cycles. Each of the measurement cycle includes inducing charge onto the key during a drive part of the measurement cycle, measuring during a signal measurement part of the measurement cycle the charge induced on the key during the drive part of the measurement cycle, and generating a signal sample value to represent of the charge measured from the key during the signal measurement part of the measurement cycle. The method includes comparing the value of the plurality of the signal sample values of the measurement burst with a determined range of accepted values between a determined maximum and a determined minimum value, and processing any of the plurality of signal sample values, which are outside the determined accepted range to the effect that the presence of the body can be determined only from a change in the value of one or more of the plurality of signal samples which are within the determined accepted range. By removing the effects of signal sample values, which are outside the determined accepted range of values, then the effects of noise, such as rectangular noise, which might otherwise cause a body to be erroneously detected can be substantially reduced.
51 Citations
22 Claims
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1. A method of sensing the presence of a body from a change in an amount of charge present on a capacitively charged key, the method comprising
performing a measurement burst which generates a plurality of signal sample values from a plurality of measurement cycles, each of the measurement cycles including, inducing charge onto the key during a drive part of the measurement cycle, measuring during a signal measurement part of the measurement cycle the charge induced on the key during the drive part of the measurement cycle, generating a signal sample value representing the charge measured from the key during the signal measurement part of the measurement cycle, comparing the value of the plurality of the signal sample values of the measurement burst with a determined range of accepted values between a determined maximum and a determined minimum value, and processing any of the plurality of signal sample values, which are outside the determined accepted range to the effect that the presence of a body can be determined only from a change in the value of one or more of the plurality of signal samples which are within the determined accepted range.
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8. An apparatus for sensing the presence of a body from a change in an amount of charge present on a capacitively charged key, the apparatus comprising
a driving circuit coupled to the key and operable to induce charge onto the key, a charge sensing circuit which includes a signal measurement capacitor, and a controller, the controller being operable to control the driving circuit and the charge sensing circuit to generate a signal sample value for each of a plurality of measurement cycles forming a measurement burst by inducing charge onto the key during a drive part of the measurement cycle, measuring during a signal measurement part of the measurement cycle the charge induced on the key during the drive part of the measurement cycle, and generating a signal sample value to represent of the charge measured from the key during the signal measurement part of the measurement cycle, to compare the value of the plurality of the signal sample values of the measurement burst with a determined range of accepted values between a determined maximum and a determined minimum value, and to process any of the plurality of signal sample values, which are outside the determined accepted range to the effect that the presence of the body can be determined only from a change in the value of one or more of the plurality of signal samples which are within the determined accepted range.
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15. A touch sensitive control panel including a key matrix comprising a first plurality, N of input lines, a second plurality, M, of output lines and N times M keys, each of the N times M keys being arranged to sense the presence of a body and each of the N times M keys is disposed adjacent a respective intersection of an input line and an output line and comprises a driven plate (X) connected to one of the N input lines and a receiving plate (Y) connected to one of the M output lines,
each of the N input lines being connected to a respective drive circuit, and each of the M output lines being connected to a respective charge sensing circuit, each of the charge sensing circuits including a signal measurement capacitor, wherein the key matrix includes a controller, the controller being operable to control the driving circuits and the charge sensing circuits to generate, for each of the N times M keys, a signal sample value for each of a plurality of measurement cycles forming a measurement burst by inducing charge onto the drive plate of each of the keys during a drive part of the measurement cycle, measuring during a signal measurement part of the measurement cycle the charge induced on the sensing plate of each of the keys during the drive part of the measurement cycle, and generating the signal sample value to represent the charge measured from each of the keys during the signal measurement part of the measurement cycle, to compare the value of the plurality of the signal sample values of the measurement burst with a determined range of accepted values between a pre-determined maximum and a determined minimum value, and to process any of the plurality of signal sample values, which are outside the determined accepted range to the effect that the presence of the body can be determined only from a change in the value of one or more of the plurality of signal samples which are within the determined accepted range.
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22. A method of sensing the presence of a body proximate a touch sensitive control panel, the touch sensitive control panel including a key matrix comprising a first plurality, N of input lines, a second plurality, M, of output lines and N times M keys, each of the N times M keys being disposed adjacent a respective intersection of an input line and an output line and comprises a driven plate (X) connected to one of the N input lines and a receiving plate (Y) connected to one of the M output lines,
each of the N input lines being connected to a respective drive circuit, and each of the M output lines being connected to a respective charge sensing circuit, each of the charge sensing circuits including a signal measurement capacitor, the method comprising controlling the driving circuits and the charge sensing circuits to generate, for each of the N times M keys, a signal sample value for each of a plurality of measurement cycles forming a measurement burst by inducing charge onto the drive plate of each of the keys during a drive part of the measurement cycle, measuring during a signal measurement part of the measurement cycle the charge induced on the sensing plate of each of the keys during the drive part of the measurement cycle, and generating a signal sample value to represent of the charge measured from each of the keys during the signal measurement part of the measurement cycle, comparing the value of the plurality of the signal sample values of the measurement burst with a determined range of accepted values between a determined maximum and a determined minimum value, and processing any of the plurality of signal sample values, which are outside the determined accepted range to the effect that the presence of a body can be determined only from a change in the value of one or more of the plurality of signal samples which are within the determined accepted range.
Specification