LINEARITY ENHANCEMENT OF CAPACITIVE TRANSDUCERS BY AUTO-CALIBRATION USING ON-CHIP NEUTRALIZATION CAPACITORS AND LINEAR ACTUATION
First Claim
1. A method for automatically calibrating a capacitive transducer to neutralize feed-through capacitance starting from an initial value for a neutralization capacitance, the method comprising:
- applying no electrostatic force to a proof mass of the capacitive transducer;
recording a base output value of the capacitive transducer while no electrostatic force is applied to the proof mass;
applying an electrostatic force F0 to the proof mass of the capacitive transducer;
recording a first change in the output value of the capacitive transducer between the base output value and a first output value when the electrostatic force F0 is applied to the proof mass;
applying an electrostatic force n*F0 to the proof mass of the capacitive transducer, where F0 is a fraction of n*F0;
recording a second change in the output value of the capacitive transducer between the first output value and a second output value when the electrostatic force n*F0 is applied to the proof mass;
increasing, decreasing or maintaining the neutralization capacitance based on the recorded first and second changes in the output value of the capacitive transducer; and
repeating the method until a final value for the neutralization capacitance is reached.
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Abstract
A system and method are disclosed for automatically calibrating capacitive transducers to neutralize feed-through capacitance using linear actuation. The method includes starting with an initial neutralization capacitance, applying no electrostatic force and two known electrostatic forces to a proof mass of the transducer, recording the transducer output changes due to the applied forces; and determining how to revise neutralization capacitance based on the changes. The method can use a binary search to find a final neutralization capacitance providing the best linearity. The method can include comparing the final linearity to a threshold linearity. The electrostatic forces can be applied using a charge control method where the electrostatic force is a linear function of the actuation duration. The linear actuation can be used for continuous self-test of capacitive sensors.
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Citations
20 Claims
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1. A method for automatically calibrating a capacitive transducer to neutralize feed-through capacitance starting from an initial value for a neutralization capacitance, the method comprising:
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applying no electrostatic force to a proof mass of the capacitive transducer; recording a base output value of the capacitive transducer while no electrostatic force is applied to the proof mass; applying an electrostatic force F0 to the proof mass of the capacitive transducer; recording a first change in the output value of the capacitive transducer between the base output value and a first output value when the electrostatic force F0 is applied to the proof mass; applying an electrostatic force n*F0 to the proof mass of the capacitive transducer, where F0 is a fraction of n*F0; recording a second change in the output value of the capacitive transducer between the first output value and a second output value when the electrostatic force n*F0 is applied to the proof mass; increasing, decreasing or maintaining the neutralization capacitance based on the recorded first and second changes in the output value of the capacitive transducer; and repeating the method until a final value for the neutralization capacitance is reached. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. An apparatus for linearly actuating a sensor using a charge control method, the apparatus comprising:
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a capacitive core comprising a first sense node, a second sense node and a proof mass, a first variable capacitor being formed between the first sense node and the proof mass, and a second variable capacitor being formed between the second sense node and the proof mass; an operational amplifier including an inverting input, a non-inverting input, an output, and a first feedback path coupling the output to the inverting input, the capacitive core being in the first feedback path; a conductive path short circuiting the second variable capacitor; and an actuation source for placing an actuation force on the proof mass of the capacitive core for a duty cycle, the actuation force being a linear function of the duty cycle. - View Dependent Claims (16, 17)
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18. A continuous self-test method for a capacitive sensor of a transducer system, the capacitive sensor comprising a first sense node, a second sense node and a proof mass, a first variable capacitor formed between the first sense node and the proof mass, and a second variable capacitor formed between the second sense node and the proof mass, the method comprising:
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continuously using linear actuation to apply an electrostatic force to the proof mass of the capacitive sensor; measuring the displacement of the proof mass caused by the electrostatic force; reading an output signal of the transducer system due to the displacement of the proof mass; determining whether the output signal is within an operational range; and assuming the transducer system is malfunctioning if the output signal is not within the operational range. - View Dependent Claims (19, 20)
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Specification