Capacitive sensing device
First Claim
1. A capacitive sensing device, comprisingan antenna electrode configured for emitting an alternating electric field in response to an alternating voltage caused in said antenna electrode;
- a control and evaluation circuit configured to maintain said alternating voltage equal to an alternating reference voltage by injecting a current into said antenna electrode and to measure said current;
wherein said control and evaluation circuit includesa microcontroller with a digital output for providing a digital signal;
and a low-pass filter operatively connected to said digital output for generating said alternating reference voltage by low-pass-filtering said digital signal, andwherein said control and evaluation circuit comprises a transimpedance amplifier having a current input operatively connected to said antenna electrode, a reference voltage input operatively connected to said low-pass-filter for receiving said alternating reference voltage and an output operatively connected with said current input via a feedback network, said transimpedance amplifier being configured for preventing a difference in potential between said current input and said reference voltage input by causing a current to flow across said reference network and into said antenna electrode, said output being configured to output a measurement voltage indicative of said current.
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Accused Products
Abstract
A capacitive sensing device includes an antenna electrode for emitting an alternating electric field in response to an alternating voltage caused in the antenna electrode and a control and evaluation circuit configured to maintain the alternating voltage equal to an alternating reference voltage by injecting a current into the antenna electrode and to measure the current. The control and evaluation circuit includes a microcontroller with a digital output for providing a digital signal and a low-pass filter operatively connected to the digital output for generating the alternating reference voltage by low-pass-filtering the digital signal.
13 Citations
14 Claims
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1. A capacitive sensing device, comprising
an antenna electrode configured for emitting an alternating electric field in response to an alternating voltage caused in said antenna electrode; -
a control and evaluation circuit configured to maintain said alternating voltage equal to an alternating reference voltage by injecting a current into said antenna electrode and to measure said current; wherein said control and evaluation circuit includes a microcontroller with a digital output for providing a digital signal; and a low-pass filter operatively connected to said digital output for generating said alternating reference voltage by low-pass-filtering said digital signal, and wherein said control and evaluation circuit comprises a transimpedance amplifier having a current input operatively connected to said antenna electrode, a reference voltage input operatively connected to said low-pass-filter for receiving said alternating reference voltage and an output operatively connected with said current input via a feedback network, said transimpedance amplifier being configured for preventing a difference in potential between said current input and said reference voltage input by causing a current to flow across said reference network and into said antenna electrode, said output being configured to output a measurement voltage indicative of said current. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A capacitive sensing device, comprising
an antenna electrode configured for emitting an alternating electric field in response to an alternating voltage caused in the antenna electrode and a control and evaluation circuit that includes a transimpedance amplifier configured to maintain the alternating voltage equal to an alternating reference voltage on a reference voltage node by injecting a current into the antenna electrode and to measure the current, a microcontroller, and a multiplexer configured and arranged to switch said antenna electrode alternately to a current input of the transimpedance amplifier and to the alternating reference voltage node, wherein the microcontroller is configured to control the multiplexer with a digital control signal, wherein the multiplexer and the transimpedance amplifier and a low-pass filter operatively connected to the transimpedance amplifier form together a synchronous rectifier arrangement, and wherein the current input node of the transimpedance amplifier is AC-coupled to the reference voltage node by a protection capacitor.
Specification