Method for calibrating accelerometer sensitivity
AssigneeAnalog Devices, Inc.
InventorsKevin H.-L. Chau, Howard R. Samuels
Life of this patent
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Abstract
A method for calibrating the sensitivity of a micromachined differential-capacitor accelerometer without applying mechanical stimulation, such as shaking. The accelerometer is fabricated with dimensional control structures so that a dimensional relationship is set-up among operational features of the device. The method includes measuring the resonant frequency of a movable mass and measuring the change in the output signal of the accelerometer as the mass is displaced by electrostatic means. The sensitivity of the accelerometer is then calculated.
Claims17
A method of calibrating an accelerometer comprising:
- a. providing the accelerometer comprising:
- i. a substrate;
- ii. a mass suspended over the substrate and movable relative to the substrate, the mass including a movable electrode;
- iii. a first fixed electrode suspended over the substrate and not movable relative to the substrate;
- iv. a second fixed electrode suspended over the substrate and not movable relative to the substrate, the movable electrode and the first and second fixed electrode forming a differential capacitor;
- v. an excitation and readout circuit coupled to the movable electrode and to the fixed electrodes to provide an amplified signal;
- vi. an actuator, the actuator suspended over the substrate, the actuator displacing the mass by electrical means when activated;
- and
- vii. a spring suspended over the substrate connected to the mass, the spring and the actuator laid out such that a dimensional relationship is established between the actuator and the spring;
- b. measuring the resonant frequency of the mass;
- c. displacing the mass with the actuator;
- d. measuring the change in the amplified signal;
- and
- e. calculating the sensitivity of the accelerometer including calculating an acceleration equivalent to displacing the mass with the actuator wherein calculating the acceleration includes calculating a function of the resonant frequency, the form of the function determined by the dimensional relationship between the actuator and the spring.
A self-calibrating accelerometer comprising:
- a. a substrate;
- b. a mass suspended over the substrate and laterally movable relative to the substrate, the mass including a movable electrode;
- c. a first fixed electrode suspended over the substrate and not movable relative to the substrate;
- d. a second fixed electrode suspended over the substrate and not movable relative to the substrate, the movable electrode and the first and second fixed electrode forming a differential capacitor;
- e. an excitation and readout circuit coupled to the movable electrode and to the fixed electrodes to provide an amplified signal;
- f. an actuator, the actuator suspended over the substrate, the actuator displacing the mass by electrical means when activated;
- and
- g. a spring suspended over the substrate connected to the mass, the spring and the actuator laid out such that a dimensional relationship is established between the actuator and the spring;
- h. logic for
- i. measuring the resonant frequency of the mass,
- ii. displacing the mass with the actuator,
- iii. measuring the change in the amplified signal, and
- iv. calculating the sensitivity of the accelerometer, including calculating an acceleration equivalent to displacing the mass with the actuator wherein calculating the acceleration includes calculating a function of the resonant frequency, the form of the function determined by the dimensional relationship between the actuator and the spring.
Dependencies are inferred from the claim text.