Capacitive sensing interface for proximity detection
AssigneeSemtech Corporation
InventorsOlivier Nys, Pascal Monney, Daniel Aebischer
Life of this patent
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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.
Claims18
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.
Dependencies are inferred from the claim text.