System for freeing stuck accelerometers

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.

TECHNICAL FIELD

The present description relates generally to sensor technology, and, more particularly, but not exclusively, to a system for freeing stuck accelerometers.

BACKGROUND

An accelerometer is an electromechanical device used to measure acceleration forces. Such forces may be static, like the continuous force of gravity, or, as is the case with many mobile devices, dynamic in order to sense movement or vibrations. Acceleration is the measurement of the change in velocity, or speed divided by time. Portable electronic devices such as smartphones and smartwatches include microelectromechanical system (MEMS) capacitive accelerometers for perceiving device orientation. The accelerometer monitors the motion of the device in order to enable various motion-based features.

A user reliability issue with a MEMS capacitive accelerometer device is the stiction of the device after high acceleration shock events. Stiction is when the accelerometer becomes stuck to a contact surface and remains even after cessation of the high acceleration input, which renders the accelerometer inoperable. A subsequent high acceleration shock or vibration input may unstick the part from the contact surface, but there are no methods for achieving this in a controlled fashion in the system.

DETAILED DESCRIPTION

In some aspects, the subject disclosure provides a system for freeing stuck accelerometers. The disclosed solution implements a controlled vibration system for purposes of unsticking a stuck part of the accelerometer such as a microelectromechanical system (MEMS) capacitive accelerometer. The subject technology comprises both a means for implementing the vibration as well as a means for stiction detection that controls initiation of the vibration. Methods of vibration input include piezoelectric exciters and/or capacitors located outside the accelerometer package. The disclosed method of detection of the saturation (stiction) includes in-situ circuitry for detection of saturation due to contact and hosts digital implementation for detecting clipping of the output, as described in more detail herein.

FIGS. 1A and 1Bare schematic diagrams illustrating a stuck state100A and a free state100B of an example of a MEMS capacitive accelerometer102, in accordance with various aspects of the subject technology. The MEMS capacitive accelerometer102(hereinafter, the accelerometer102) includes a cantilever110, an anchor112, a weight114, a substrate120, an over-range stop pad122(hereinafter, the stop pad122), a sense electrode124, an unstick electrode126and a control voltage Vc. The stop pad122limits the travel of the cantilever110during high accelerations. In the stuck state100A, the cantilever110gets stuck due to surface adhesion forces (e.g., van der Waals forces) to the contact surface of the stop pad122after a high acceleration input and remains in that state after cessation of the high acceleration input. The sense electrode124is used to sense and measure the input acceleration applied to the accelerometer102.

The unstick electrode126is a feature of the subject technology that enables freeing the stuck cantilever by applying high energy vibrations115. The high energy vibrations115are created by an electrostatic force generated by activation of the control voltage Vc, which is applied between an unstick electrode126and the anchor112that is electrically connected to the cantilever110.FIG. 1B shows the free state100B when the applied high energy vibrations115have released the cantilever110and the accelerometer102is ready for normal operation, and the sense electrode124can detect input accelerations.

FIGS. 2A and 2Bare schematic diagrams illustrating example structures200A and200B of MEMS capacitive accelerometers202and204with provisions for freeing from the stuck state (stiction), in accordance with various aspects of the subject technology. The MEMS capacitive accelerometer202(hereinafter, the accelerometer202) is a pendulous type of accelerometer that has a different structure from the accelerometer102and includes a cantilever210supported by a fulcrum212. The fulcrum212includes a torsion spring213and a middle anchor215. The accelerometer202further includes a substrate220, a stop pad222, sense electrodes224(224-1and224-2), an unstick electrode226and a weight214. The unstick electrode226can be used to release the accelerometer202from a stuck state by applying an attractive electrostatic force to an opposite end of the cantilever210. The electronic circuitry that creates the electrostatic force will be discussed below.

The MEMS capacitive accelerometer204(hereinafter, the accelerometer204) is a pendulous type of accelerometer similar to the accelerometer202ofFIG. 2A, except that it is enclosed in a housing, including walls230and a lid240. Additionally, the accelerometer204includes an unstick electrode242that is attached to the lid240and can be used to further assist with freeing the accelerometer204from a stuck state by applying a repulsive electrostatic force to the opposite end of the cantilever210. The electronic circuitry that creates the repulsive electrostatic force will be discussed below. In one or more aspects, the lid240can be used as a giant unstick electrode. The additional repulsive electrostatic force exerted by the unstick electrode242or the lid240can enhance the release mechanism of the accelerometer204and make it a more reliable accelerometer device.

FIGS. 3A, 3B and 3Care schematic diagrams illustrating examples of MEMS capacitive accelerometer systems300A,300B and300C with electronic circuitry for freeing from the stuck state (stiction), in accordance with various aspects of the subject technology. The MEMS capacitive accelerometer system300A (hereinafter, the accelerometer system300A) includes an accelerometer device302and an associated electronic circuitry (e.g., an ASIC) including a charge-to-voltage (C2V) converter310, an analog-to-digital converter (ADC)320, a clip-detection circuit330, a switch S1and a wave generator350. The accelerometer device302is the same as the accelerometer102ofFIG. 1A, including a sense electrode326and an unstick electrode324similar to the sense electrode126and unstick electrode124ofFIG. 1A. The C2V converter310receives a charge signal that represents a measure of the input acceleration from the sense electrode326and generates an analog voltage signal proportional to the charge signal. The analog voltage signal generated by the C2V converter310is converted to a digital signal by the ADC320. The digital signal is the normal output of the accelerometer system300A.

The normal state of the switch S1is open and isolates the unstick electrode324from the control voltage Vc. The clip-detection circuit330can detect a stuck state of the accelerometer device302based on the digital signal received from the ADC320. When a stuck state is detected, the clip-detection circuit330causes the wave generator350to generate the control voltage Vc and the switch S1to close to allow the control voltage Vc to be applied to the unstick electrode324. The unstick electrode324, in response to receiving the control voltage Vc, generates an electrostatic force, which creates a high vibrational energy that frees the accelerometer device from a stuck state. In one or more implementations, the clip-detection circuit330may receive an interrupt signal from a host processor indicating stiction of the accelerometer device302. The host processor may execute a clip-detection algorithm by comparing the digital signal received from the ADC320with a threshold value and generating the interrupt signal when the digital signal exceeds the threshold value.

The MEMS capacitive accelerometer system300B (hereinafter, the accelerometer system300B) includes an accelerometer device304and an associated electronic circuitry, including the C2V converter310, a comparator312, a stiction qualifier314, the ADC320, an analog stiction-release circuit332, the switch S1and a wave generator350. The accelerometer system300B is similar to the accelerometer system300A except that the accelerometer system300B is enclosed in a housing, including walls303and a lid305and includes an additional unstick electrode340. The output of the ADC320is the normal output signal of the accelerometer device304. The comparator312compares the analog voltage signal of the C2V converter310with an analog threshold voltage (Athreshold) and, when the amplitude of the analog voltage signal of the C2V converter310exceeds Athreshold, sends a pulse (output of the comparator312) to the stiction qualifier314, which, when qualifies the stiction event, sends a stiction indictor signal to the analog stiction-release circuit332as an indication of a stiction state. In response, the analog stiction-release circuit332triggers the wave generator350to generate the control voltages Vc1and Vc2and the switch S1to close to allow the control voltages Vc1and Vc2to be applied to the unstick electrode324and the additional unstick electrode340. The unstick electrode324and the additional unstick electrode340, in response to receiving the control voltage Vc, generate an electrostatic force, which creates a high vibrational energy that frees the accelerometer device from a stuck state.

The MEMS capacitive accelerometer system300C (hereinafter, the accelerometer system300C) includes the accelerometer device304and an associated electronic circuitry, including the C2V converter310, the ADC320, a first digital filter360-1, a second digital filter360-2, the comparator312, the stiction qualifier314, a digital clip-detection circuit330, the switch S1and the wave generator350. The accelerometer system300C is similar to the accelerometer system300B except for the addition of the first digital filter360-1and the second digital filter360-2. The output of the ADC320is filtered by the first digital filter360-1and the second digital filter360-2to generate the normal output signal of the accelerometer device304. The comparator312compares the filtered digital signal of the first digital filter360-1with a digital threshold voltage (Dthreshold) and, when the filtered digital signal exceeds Dthreshold, sends a pulse to the stiction qualifier314, which, when qualifies the stiction event, sends a stiction indictor signal to the digital clip-detection circuit330as an indication of a stiction state. In response, the analog stiction-release circuit332triggers the wave generator350to generate the control voltages Vc1and Vc2and the switch S1to close to allow the control voltages Vc1and Vc2to be applied to the unstick electrode324and the additional unstick electrode340. The unstick electrode324and the additional unstick electrode340, in response to receiving the control voltage Vc, generate an electrostatic force, which creates a high vibrational energy that frees the accelerometer device from a stuck state.

FIG. 4is a schematic diagram illustrating an example of a MEMS capacitive accelerometer system400with an external vibrational stimulation, in accordance with various aspects of the subject technology. The MEMS capacitive accelerometer system400(hereinafter, system400) includes a MEMS capacitive accelerometer device402(hereinafter, accelerometer device402), a housing420, an external vibrational stimulator404and an in-system wave generator450. The accelerometer device402is similar to the accelerometer device304ofFIG. 3Bexcept that the unstick electrode324and the additional unstick electrode340are replaced with the external vibrational stimulator404. The accelerometer device402is disposed on a substrate432, which in turn is placed on a system main logic board (MLB)430and is electronically connected to it through a number of vias.

The external vibrational stimulator404includes a piezoelectric material440attached to electrodes442, which are connected through the system MLB430to the in-system wave generator450. In response to signals (e.g., sine wave signals) from the in-system wave generator450, a control voltage Vc is generated that causes vibration (e.g., at a few KHz) of the piezoelectric material440. Vibrational waves445generated by the piezoelectric material440can couple to the cantilever410of the accelerometer device402and free it from a stuck state. The in-system wave generator450responds to an interrupt signal from an analog or digital clip detection, as discussed in more detail below.

FIGS. 5A, 5B and 5Care schematic diagrams illustrating examples of various packaging schemes500A,500B and500C for the MEMS capacitive accelerometer ofFIG. 4, in accordance with various aspects of the subject technology. In the packaging scheme500A, the packaged accelerometer device510includes the accelerometer device, a C2V converter (e.g.,310ofFIG. 3A), an ADC (e.g.,320ofFIG. 3A) and generates an accelerometer digital output512, which is processed by a host processor (e.g., a processor of a host device such as a smartphone or a smartwatch). The host processor may use a clipping detection algorithm520to detect whether the digital output512corresponds to a stuck or normal state of the accelerometer device, and, when a stuck accelerometer situation is detected, cause a wave generator algorithm530to generate a chirp or a sine wave (e.g., a frequency of a few KHz) that can be used by a piezo exciter540to excite an external vibrational stimulator (e.g.,404ofFIG. 4).

In the packaging scheme500B, the packaged accelerometer device550includes the accelerometer device, a C2V converter (e.g.,310ofFIG. 3A), an ADC (e.g.,320ofFIG. 3A) and an onboard clipping detection circuit that generates an interrupt552when a stuck accelerometer situation is detected. The interrupt552causes an in-system wave generator560to generate a chirp or a sine wave (e.g., a frequency of a few KHz) that can be used by the piezo exciter540to excite the external vibrational stimulator (e.g.,404ofFIG. 4).

In the packaging scheme500C, the packaged accelerometer device570includes the accelerometer device, a C2V converter (e.g.,310ofFIG. 3A), an ADC (e.g.,320ofFIG. 3A) and an onboard clipping detection circuit that generates an internal interrupt for an onboard sine wave generator. When a stuck accelerometer situation is detected, the packaged accelerometer device570generates sine waves (or chirp waves) at a general-purpose input-output (GPIO) port. The GPIO port is connected to the piezo exciter540that can use the generated waves to excite the external vibrational stimulator (e.g.,404ofFIG. 4).

FIG. 6illustrates a wireless communication device in which aspects of the subject technology are implemented. In one or more implementations, the wireless communication device600can be a smartphone or a smartwatch that hosts the accelerometer of the subject technology, including a system for freeing the accelerometer when it is stuck due to a high acceleration input. The wireless communication device600may comprise a radio-frequency (RF) antenna610, a duplexer612, a receiver620, a transmitter630, a baseband processing module640, a memory650, a processor660, a local oscillator generator (LOGEN)670and one or more transducers680. In various embodiments of the subject technology, one or more of the blocks represented inFIG. 6may be integrated on one or more semiconductor substrates. For example, the blocks620-670may be realized in a single chip or a single system on a chip, or may be realized in a multichip chipset.

The receiver620may comprise suitable logic circuitry and/or code that may be operable to receive and process signals from the RF antenna610. The receiver620may, for example, be operable to amplify and/or down-convert received wireless signals. In various embodiments of the subject technology, the receiver620may be operable to cancel noise in received signals and may be linear over a wide range of frequencies. In this manner, the receiver620may be suitable for receiving signals in accordance with a variety of wireless standards, Wi-Fi, WiMAX, Bluetooth, and various cellular standards.

The transmitter630may comprise suitable logic circuitry and/or code that may be operable to process and transmit signals from the RF antenna610. The transmitter630may, for example, be operable to up-convert baseband signals to RF signals and amplify RF signals. In various embodiments of the subject technology, the transmitter630may be operable to up-convert and amplify baseband signals processed in accordance with a variety of wireless standards. Examples of such standards may include Wi-Fi, WiMAX, Bluetooth, and various cellular standards. In various embodiments of the subject technology, the transmitter630may be operable to provide signals for further amplification by one or more power amplifiers.

The duplexer612may provide isolation in the transmit band to avoid saturation of the receiver620or damaging parts of the receiver620, and to relax one or more design requirements of the receiver620. Furthermore, the duplexer612may attenuate the noise in the receiver band. The duplexer612may be operable in multiple frequency bands of various wireless standards.

The baseband processing module640may comprise suitable logic, circuitry, interfaces, and/or code that may be operable to perform processing of baseband signals. The baseband processing module640may, for example, analyze received signals and generate control and/or feedback signals for configuring various components of the wireless communication device600, such as the receiver620. The baseband processing module640may be operable to encode, decode, transcode, modulate, demodulate, encrypt, decrypt, scramble, descramble, and/or otherwise process data in accordance with one or more wireless standards.

The processor660may comprise suitable logic, circuitry, and/or code that may enable processing data and/or controlling operations of the wireless communication device600. In this regard, the processor660may be enabled to provide control signals to various other portions of the wireless communication device600. The processor660may also control transfer of data between various portions of the wireless communication device600. Additionally, the processor660may enable implementation of an operating system or otherwise execute code to manage operations of the wireless communication device600.

In operation, the processor660may configure the various components of the wireless communication device600based on a wireless standard according to which it is desired to receive signals. Wireless signals may be received via the RF antenna610, amplified, and down-converted by the receiver620. The baseband processing module640may perform noise estimation and/or noise cancellation, decoding, and/or demodulation of the baseband signals. In this manner, information in the received signal may be recovered and utilized appropriately. For example, the information may be audio and/or video to be presented to a user of the wireless communication device, data to be stored to the memory650, and/or information affecting and/or enabling operation of the wireless communication device600. The baseband processing module640may modulate, encode, and perform other processing on audio, video, and/or control signals to be transmitted by the transmitter630in accordance with various wireless standards.

In some implementations, the processor660may perform the functionalities of the host processor ofFIG. 5Ato execute the clipping detection algorithm520ofFIG. 5Aand/or to generate chip and/or sine waves.

The memory650may comprise suitable logic, circuitry, and/or code that may enable storage of various types of information such as received data, generated data, code, and/or configuration information. The memory650may comprise, for example, RAM, ROM, flash, and/or magnetic storage. In various embodiments of the subject technology, information stored in the memory650may be utilized for configuring the receiver620and/or the baseband processing module640.

The LOGEN670may comprise suitable logic, circuitry, interfaces, and/or code that may be operable to generate one or more oscillating signals of one or more frequencies. The LOGEN670may be operable to generate digital and/or analog signals. In this manner, the LOGEN670may be operable to generate one or more clock signals and/or sinusoidal signals. Characteristics of the oscillating signals such as the frequency and duty cycle may be determined based on one or more control signals from, for example, the processor660and/or the baseband processing module640.

The one or more transducers680may include miniature transducers such as the accelerometer of the subject technology including a system for freeing the accelerometer when it is stuck due to a high acceleration input.

In accordance with various aspects of the subject disclosure, 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.

In accordance with other aspects of the subject disclosure, a wireless communication system includes a processor and an accelerometer apparatus to measure an input acceleration. The accelerometer apparatus comprises an accelerometer and an unstick device. The accelerometer includes a cantilever and at least one sense electrode to sense the input acceleration and to generate a current signal based on the input acceleration. The unstick device includes one or more unstick electrodes and a control circuitry that causes the unstick electrode to generate vibrational energy to release the cantilever from stiction to a stop pad due to a saturating acceleration input.

In accordance with other aspects of the subject disclosure, an apparatus includes an accelerometer device and an external vibrational stimulator. The accelerometer device consists of a cantilever that moves toward a stop pad in response to an input acceleration and at least one sense electrode that can sense the input acceleration. The external vibrational stimulator generates vibrational energy to cause vibration of the cantilever when the cantilever is stuck to the stop pad.

While the above discussion primarily refers to microprocessor or multicore processors that execute software, some implementations are performed by one or more integrated circuits, such as ASICs or field-programmable gate arrays (FPGAs). In some implementations, such integrated circuits execute instructions that are stored on the circuit itself.

Many of the above-described features and applications are implemented as software processes that are specified as a set of instructions recorded on a computer-readable storage medium (also referred to as a computer-readable medium). When these instructions are executed by one or more processing unit(s) (e.g., one or more processors, cores of processors, or other processing units), they cause the processing unit(s) to perform the actions indicated in the instructions.