Apple Inc.

Christopher C Painter

Gregory B Arndt

See-Ho Tsang

Wesley Scott Smith

Qinghung Lee

Te Hsi Lee

According to some aspects of the subject technology, an apparatus includes an accelerometer including one or more sense electrodes to sense an input acceleration, and an unstick device to free the accelerometer from a stuck state due to a saturating acceleration input. The unstick device includes at least one unstick electrode and a control circuitry to cause the unstick electrode to generate vibrational energy to free the accelerometer.

System for freeing stuck accelerometers

An in-situ test calibration system and method are disclosed where a perpetual out-of-band electrostatic force induced excitation is used to dither the proof-mass of a MEMS based accelerometer where the amount of deflection change is proportional to sensitivity changes. The supplier of the accelerometer would exercise the accelerometer in a calibration station to determine initial sensitivity values. After the calibration and before removing the accelerometer from the calibration station, the supplier would start the dither and calibrate the acceleration equivalent force (F) to drive voltage transfer function (F/V). After installation of the accelerometer into a system or sometime later in the field, any changes in the F/V transfer function due to changes in the sensitivity are observable and can be used for re-calibrating the accelerometer.

Continuous calibration of accelerometer sensitivity by proof-mass dithering

An in-situ calibration system, method and apparatus is disclosed that uses test electrodes to stimulate a proof-mass of a MEMS based gyroscope at a drive frequency as quasi-Coriolis forces to extract the electromechanical gain, and uses a non-resonant carrier signal on the proof-mass to extract the additional changes in the sense and drive capacitance. Additionally, an in-situ calibration system, method and apparatus is disclosed that uses quadrature electrodes to apply a known force stimulus to the proof-mass as part of a calibration procedure, where the known force is applied again after installation into a system or further into the life of the gyroscope. Differences in the proof-mass response to the force are proportional to changes in sensitivity, which allows the sensitivity to be corrected in-field.

Gyroscope sensitivity calibration

A quadrature ADC feedback compensation system and method for MEMS gyroscope is disclosed. In an embodiment, a MEMS gyroscope comprises an analog processing chain including a drive circuit for generating an analog drive signal and a sense circuit that is configured to generate an analog rate signal and an analog quadrature signal in response to a change in capacitance output by the MEMS gyroscope. A compensation circuit coupled to the sense circuit is configured to null the analog quadrature signal using the analog drive signal and a compensation value, and to adaptively compensate, in a digital processing chain, a quadrature-induced rate offset of a digital rate signal over temperature using a digital quadrature signal, the compensation value and temperature data.

Quadrature ADC feedback compensation for capacitive-based MEMS gyroscope

A MEMS sensor is disclosed that includes dual pendulous proof masses comprised of sections of different thickness to allow simultaneous suppression of vertical and lateral thermal gradient-induced offsets in a MEMS sensor while still allowing for the normal operation of the accelerometer. In an embodiment, the structure and different sections of the MEMS sensor is realized using multiple polysilicon layers. In other embodiments, the structure and different thickness sections may be realized with other materials and processes. For example, plating, etching, or silicon-on-nothing (SON) processing.

MEMS sensor with dual pendulous proof masses

A multi-stage MEMS accelerometer is disclosed that includes a MEMS sensor that has two suspended structures (proof masses) suspended by suspension members. The suspended structures move together in response to input acceleration when less the acceleration is less than a threshold value. When the input acceleration is greater than the threshold value, one of the suspended structures makes contact with a mechanical stop while the other suspended structure continues to move with increased stiffness due to the combined stiffness of the suspension members. The contact with the mechanical stop contributes a nonlinear mechanical stiffening effect that counteracts the nonlinear capacitive effect inherent in capacitive based MEMS accelerometers. In some embodiments, more than two suspended structures can be used to allow for optimization of sensitivity for multiple full-scale ranges, and for higher fidelity tuning of mechanical sensitivity with nonlinear capacitance. In some embodiments, compliant mechanical stops are used.

Multi-stage MEMS accelerometer for mixed g-level operation

An architecture is disclosed for an angular rate sensor that includes a duty-cycled phase shifter for generating a clock with high resolution delay for use in synchronized demodulation of a sensor output signal. In an embodiment, a sensor comprises: a mechanical resonator; a drive circuit coupled to the mechanical resonator and operable to actuate the mechanical resonator into resonant vibration; a sense circuit mechanically coupled to the mechanical resonator, the sense circuit operable to generate a sense signal having an in-phase signal component and a quadrature signal component; a demodulator circuit operable to receive the sense signal and a first clock for demodulating the sense signal to separate the in-phase signal component from the quadrature signal component; and a duty-cycled phase shifter coupled to the demodulator, the duty-cycled phase shifter operable to generate the first clock.

Duty-cycled phase shifter for angular rate sensor

In some implementations, a control system for a resonating element comprises: a resonating element being driven by an oscillating drive signal and configured to generate a sense signal proportional to an amplitude of motion; a phase comparator coupled to the resonating element and to an oscillating drive signal, the phase comparator configured to compare the sense signal and the oscillating drive signal and to generate an error signal proportional to the phase difference; an oscillator coupled to the phase comparator and configured for generating the oscillating drive signal, the oscillator configured to receive the error signal and to adjust a phase of the oscillating signal based on the error signal; and an automatic gain control coupled to the resonating element and the oscillator, the automatic gain control configured to adjust the gain of the oscillating drive signal based on the signal generated by the resonating element.

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Dublin, CA, United States of America

Christopher C Painter