Ratiometric biasing for high impedance capacitive sensing
AssigneesAkustica, Inc., Robert Bosch GmbH
InventorsMatthew A. Zeleznik, Anthony T. Zisko
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Abstract
A biasing circuit for a capacitive sensor includes a capacitive sensor element configured to produce a sensor voltage at a sense node, and a preamplifier connected to the sense node and configured to amplify the sensor voltage. The biasing circuit has an auxiliary amplifier connected between an output of the preamplifier and the sense node and configured to set a DC component of an input voltage for the preamplifier to a ratiometric DC bias voltage.
Claims10
A biasing circuit for a capacitive sensor, the biasing circuit comprising:
- a capacitive sensor element configured to produce a sensor voltage at a sense node;
- a preamplifier connected to the sense node and configured to amplify the sensor voltage;
- and
- an auxiliary amplifier connected between an output of the preamplifier and the sense node and configured to set a DC component of an input voltage for the preamplifier to a ratiometric DC bias voltage,
- wherein the auxiliary amplifier has a first input and a second input, the first input being connected to the output of the preamplifer, and
- wherein the second input receives a ratiometric reference voltage, wherein the ratiometric reference voltage is proportional to a power supply voltage of the biasing circuit while the power supply voltage changes.
A biasing circuit for a capacitive sensor, the biasing circuit comprising:
- a capacitive sensor element configured to produce a sensor voltage at a sense node;
- a preamplifier connected to the sense node and configured to amplify the sensor voltage;
- a feedback loop that branches off from an output of the preamplifier to a supply line between the sense node and an input of the preamplifier, the feedback loop including:
- an auxiliary amplifier configured to generate a ratiometric DC bias voltage, the auxiliary amplifier having a first input and a second input, the first input being connected to the output of the preamplifer, the second input receiving a ratiometric reference voltage, wherein the ratiometric reference voltage is proportional to a power supply voltage of the biasing circuit while the power supply voltage changes;
- and
- a high impedance diode network that receives the ratiometric DC bias voltage and sets an input DC bias voltage level for the preamplifier based on the ratiometric DC bias voltage.
Dependencies are inferred from the claim text.