Atlantic Inertial Systems, Inc.

Silicon Sensing Systems Limited

Michael Terence Durston

Kevin Townsend

Douglas Sitch

Christopher Paul Fell

Takafumi Moriguchi

Ryuta Araki

David M Beasley

Luke Greep

A signal processing system for a sensor. The system comprises a digital signal processing system configured to set a drive signal frequency for the primary drive transducer, a voltage controlled oscillator configured to receive an input indicative of the resonant frequency and to generate a first periodic signal at a first multiple of the resonant frequency, and a first phase locked loop, configured to receive the first periodic signal, and to generate a second periodic signal at a second multiple of the resonant frequency. The first and second periodic signals are used to control the operation of an analog-to-digital converter (ADC) configured to sample the primary pick off signal and a digital-to-analog converter (DAC) configured to generate a drive signal waveform applied to the primary drive transducer.

Synchronous timing to MEMS resonant frequency

A method of manufacturing an inertial measurement unit (IMU) comprises fabricating a plurality of individual MEMS inertial sensor packages at a package level as sealed packages containing a MEMS inertial sensor chip and an integrated circuit electrically connected together. Fabricating the individual MEMS inertial sensor packages comprises forming mechanical interconnect features in each package and assembling the IMU by mechanically interconnecting each individual MEMS inertial sensor package with another individual MEMS inertial sensor package in a mutually orthogonal orientation.

Inertial measurement units

An micro electro mechanical sensor comprising: a substrate; and a sensor element movably mounted to a first side of said substrate; wherein a second side of said substrate has a pattern formed in relief thereon. The pattern formed in relief on the second side of the substrate provides a reduced surface area for contact with the die bond layer. The reduced surface area reduces the amount of stress that is transmitted from the die bond layer to the substrate (and hence reduces the amount of transmitted stress reaching the MEMS sensor element). Because the substrate relief pattern provides a certain amount of stress decoupling, the die bond layer does not need to decouple the stress to the same extent as in previous designs. Therefore a thinner die bond layer can be used, which in turn allows the whole package to be slightly thinner.

Micro electromechanical systems (MEMS)inertial sensor

A method for closed loop operation of a capacitive accelerometer uses a single current source () and a single current sink () to apply an in-phase drive signal V' to a first set of fixed capacitive electrode fingers and a corresponding anti-phase drive signal V&#x2032; to a second set of fixed capacitive electrode fingers. This provides a net electrostatic restoring force on the proof mass for balancing the inertial force of the applied acceleration and maintains the proof mass at a null position.

Accelerometers

A digitally controlled voltage controlled oscillator comprising an Nbit digital to analogue convertor arranged to receive a frequency change demand signal as a digital Nbit word, and having an output provided via an integrator to a voltage controlled oscillator configured to provide a frequency output.

Digital controlled VCO for vibrating structure gyroscope

In a method for open loop operation of a capacitive accelerometer, a first mode of operation comprises electrically measuring a deflection of a proof mass () from the null position under an applied acceleration using a pickoff amplifier () set to a reference voltage Vcm. A second mode of operation comprises applying electrostatic forces in order to cause the proof mass () to deflect from the null position, and electrically measuring the forced deflection so caused. In the second mode of operation the pickoff amplifier () has its input () switched from Vcm to Vss, using a reference control circuit (), so that drive amplifiers () can apply different voltages Vdd to the proof mass () and associated fixed electrodes ().

A sensor device includes at least two transducers, a sensor signal processing circuit, and a transducer to sensor signal processing circuit electrical connections, each connecting a respective one of the transducers to the sensor signal processing circuit. The device also includes a differential amplifier connected with two bond wires, the bond wires connected to the differential inputs of the differential amplifier and the amplifier output connected to the sensor signal processing circuit.

Pickoff transducer wire bond bit detection

A method for closed loop operation of a capacitive accelerometer comprising: a proof mass; first and second sets of both fixed and moveable capacitive electrode fingers, interdigitated with each other; the method comprising: applying PWM drive signals to the fixed fingers; sensing displacement of the proof mass and changing the mark:space ratio of the PWM drive signals, to provide a restoring force on the proof mass that balances the inertial force of the applied acceleration and maintains the proof mass at a null position; detecting when the mark:space ratio for the null position is beyond a predetermined upper or lower threshold; and further modulating the PWM drive signals by extending or reducing x pulses in every y cycles, where x&#x3e;1 and y&#x3e;1, to provide an average mark:space ratio beyond the upper or lower threshold without further increasing or decreasing the mark length of the other pulses.

A successive approximation Analog to Digital Converter (ADC), comprising: a sample and hold device arranged to sample and hold an input signal at the beginning of a conversion cycle; a successive approximation register that sequentially builds up a digital output from its most significant bit to its least significant bit; a digital to analog converter that outputs a signal based on the output of the successive approximation register; a comparator that compares the output of the digital to analog converter with an output of the sample and hold device and supplies its output to the successive approximation register; and a residual signal storage device arranged to store the residual signal at the end of a conversion cycle; and wherein the successive approximation ADC is arranged to add the stored residual signal from the residual signal storage device to the input signal stored on the sample and hold device at the start of each conversion cycle. After each ADC full conversion by the SAR, the analog conversion of the digital output is as close to the original input signal as the resolution will allow. However there remains the residual part of the input signal that is smaller than what can be represented by the least significant bit of the digital output of the SAR. In normal operation, successive outputs of a SAR for the same input will result in the same digital value output and the same residual. By storing the residual at the end of each conversion and adding the residual onto the input signal of the next conversion the residuals are accumulated over time so that they may affect the output digital value. After a number of conversions, the accumulated residuals add up to more than the value represented by the LSB of the register and the digital value will be one higher than if a conversion had been performed on the input signal alone. In this way, the residual signal affects the output value in time and thus can be taken into account by processing the digital output in the time domain.

Oversampling noise-shaping successive approximation ADC

A vibratory gyroscope is provided comprising a plurality of secondary pickoff transducers which are each sensitive to the secondary response mode, wherein: at least two of the secondary pickoff transducers comprise skew transducers designed to be sensitive to the primary mode which produce an induced quadrature signal in response thereto. A method of using the gyroscope is provided comprising the steps of arranging electrical connections between the secondary pickoff transducers and a pickoff amplifier so that in use the induced quadrature signal is substantially rejected by the amplifier in the absence of a fault condition, and the amplifier outputs an induced quadrature signal when a fault condition disconnects one of the skew transducers from the amplifier, and a comparator compares the quadrature output from the pickoff amplifier with a predetermined threshold value and provides a fault indication when the predetermined threshold is exceeded.

Fault detection using skewed transducers

An electronic circuit and method for carrying out built in test of a capacitor connected to, and arranged to suppress noise at, an input of an electrical circuit is disclosed. The electronic circuit causes current pulses at the input, and monitors the voltage at the input by comparing the voltage at the input with high and/or low reference voltages, outputting a fault signal if the voltage at the input is greater than a high reference voltage or lower than a low reference voltage.

Critical capacitor built in test

An inertial sensor is described that has means for improving quadrature rejection The sensor is of a ring type, driven by a driver circuit, the sensor further comprising primary and secondary portions having corresponding signal pickoffs. The primary pickoff signal amplitude is controlled via an automatic gain control, the primary phase lock loop and VCO locks to the resonant frequency to provide the clocks for the synchronous detectors, the primary pickoff signals via the primary phase shift circuit is provided to the primary driver, the secondary pickoff signal being input into a detector circuit capable of detecting motion in the sensor. The secondary channel comprises a series of circuits that when operable in series significantly improve the quadrature rejection ability of the sensor. The circuits include a synchronous detector, passive and active filters and a decimator.

Rate sensor with quadrature rejection

An angular velocity sensor is described with improved ageing and hysteresis properties. The sensor may be of a ring type driven by a driver circuit, the sensor further comprising primary and secondary portions having corresponding signal pickoffs. The gain of the primary pickoff signal and the capacitance of the primary portions of the sensor are controlled relative to the gain of the secondary pickoff and the capacitance of the secondary portions of the sensor. Control electronics is provided that enables matching of the relative signals from the respective channels. In this way, temperature hysteresis and ageing effects of materials used in forming the sensor are overcome.

Angular rate sensor with improved aging properties

An inertial sensor is described that has a commanded test function. The sensor is of a ring type driven by a driver circuit, the sensor further includes primary and secondary portions having corresponding signal pickoffs. The primary pickoff signal amplitude is controlled via an automatic gain control, the primary phase lock loop and VCO locks to the resonant frequency to provide the clocks for the synchronous detectors, the primary pickoff signals via the primary phase shift circuit is provided to the primary driver, the secondary pickoff signal being input into a detector circuit capable of detecting motion in the sensor. The commanded test function includes a signal derived from the primary portion of the circuit and input into the two inputs of a differential amplifier in the secondary pickoff detector circuit.

Sensor

An inertial sensor is described in which a resonant element is driven by control electronics into resonance. The control electronics includes an oscillator. A circuit is provided for matching the frequency of the oscillator with the frequency of the output of the resonant element such that the time to operation from start up of the sensor is minimized and the requirement of frequency matching a given sensor to the control electronics is removed.

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Plymouth, United Kingdom

Michael Terence Durston