Capacitive sensing device
First Claim
1. A capacitive sensing device, comprisingan antenna electrode for emitting an alternating electric field in response to an alternating voltage caused in the antenna electrodeand a control and evaluation circuit that includesa transimpedance amplifier arrangement configured to maintain the alternating voltage in the antenna electrode 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 first multiplexer configured and arranged to switch said antenna electrode alternately to an input node of the transimpedance amplifier arrangement and to the alternating reference voltage node,wherein said transimpedance amplifier arrangement comprises a differential transimpedance amplifier with an inverting input and a non-inverting input and a second multiplexer, said second multiplexer configured and arranged to switch a signal on the input node of the transimpedance amplifier arrangement alternately to the inverting input and a non-inverting input of said transimpedance amplifier, wherein the microcontroller is configured to control the second multiplexer with a digital control signal, wherein the second multiplexer and the differential transimpedance amplifier and a first low-pass filter operatively connected to the transimpedance amplifier form together a synchronous rectifier arrangement.
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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
12 Claims
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1. A capacitive sensing device, comprising
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 that includes a transimpedance amplifier arrangement configured to maintain the alternating voltage in the antenna electrode 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 first multiplexer configured and arranged to switch said antenna electrode alternately to an input node of the transimpedance amplifier arrangement and to the alternating reference voltage node, wherein said transimpedance amplifier arrangement comprises a differential transimpedance amplifier with an inverting input and a non-inverting input and a second multiplexer, said second multiplexer configured and arranged to switch a signal on the input node of the transimpedance amplifier arrangement alternately to the inverting input and a non-inverting input of said transimpedance amplifier, wherein the microcontroller is configured to control the second multiplexer with a digital control signal, wherein the second multiplexer and the differential transimpedance amplifier and a first low-pass filter operatively connected to the transimpedance amplifier form together a synchronous rectifier arrangement.
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12. A combined capacitive sensing and heating system, comprising a heating circuit and a capacitive sensing device wherein said capacitive sensing device comprises
an antenna electrode for emitting an alternating electric field in response to an alternating voltage caused in the antenna electrode, said antenna electrode being part of said heating circuit and a control and evaluation circuit that includes a transimpedance amplifier arrangement configured to maintain the alternating voltage in the antenna electrode 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 first multiplexer configured and arranged to switch said antenna electrode alternately to an input node of the transimpedance amplifier arrangement and to the alternating reference voltage node, wherein said transimpedance amplifier arrangement comprises a differential transimpedance amplifier with an inverting input and a non-inverting input and a second multiplexer, said second multiplexer configured and arranged to switch a signal on the input node of the transimpedance amplifier arrangement alternately to the inverting input and a non-inverting input of said transimpedance amplifier, wherein the microcontroller is configured to control the second multiplexer with a digital control signal, wherein the second multiplexer and the differential transimpedance amplifier and a first low-pass filter operatively connected to the transimpedance amplifier form together a synchronous rectifier arrangement.
Specification