CAPACITIVE SENSING INTERFACE FOR PROXIMITY DETECTION
First Claim
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1. A measuring circuit for a proximity sensor, comprising a measure terminal connectable to a capacity that is variable in response to proximity to conductive bodies;
- a charge amplifier having an input connected to the measure terminal and a reference node connected to a variable reference voltage, a variable voltage source (Vin), connected between a ground voltage and said variable reference voltage and generating a variable voltage (VP) comprising voltage steps such that the charge amplifier is floating with respect to the ground by a voltage (VF) equal to the output of the variable voltage source, and a measurement circuit comprising a sampling unit arranged for sampling the output of the charge amplifier at time instants (T1, T2, T3, T4) synchronised with the variable voltage source (Vin), in such a manner that the output of the charge amplifier is sampled before and after a voltage step, the measuring circuit being arranged for determining an estimation of the capacity connected to the measure terminal based on said sampled output of the charge amplifier.
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Abstract
A measuring circuit for a proximity sensor, comprising a charge amplifier in a floating voltage domain that is driven by a square waveform. The output signal is sampled synchronously with the voltage of the floating domain, and demodulated by measuring the voltage steps amplitude. This approach is compatible with a switched capacitor implementation and allows discriminating the capacity signal from the ambient noise; the latter can be evaluated independently.
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Citations
18 Claims
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1. A measuring circuit for a proximity sensor, comprising a measure terminal connectable to a capacity that is variable in response to proximity to conductive bodies;
- a charge amplifier having an input connected to the measure terminal and a reference node connected to a variable reference voltage, a variable voltage source (Vin), connected between a ground voltage and said variable reference voltage and generating a variable voltage (VP) comprising voltage steps such that the charge amplifier is floating with respect to the ground by a voltage (VF) equal to the output of the variable voltage source, and a measurement circuit comprising a sampling unit arranged for sampling the output of the charge amplifier at time instants (T1, T2, T3, T4) synchronised with the variable voltage source (Vin), in such a manner that the output of the charge amplifier is sampled before and after a voltage step, the measuring circuit being arranged for determining an estimation of the capacity connected to the measure terminal based on said sampled output of the charge amplifier.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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