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The in-phase error caused by misalignment of comb fingers leads to bias drift of silicon microgyroscopes which is also susceptible to stress. By periodically making the drive loop close and open and sampling the sense mode output while it’s open, the in-phase error term can be canceled. The calibrated bias of gyro is greatly improved and is no longer susceptible to stress. This method is also applicable to silicon accelerometer and provides a solution for enhancing the long-term stability of MEMS inertial devices.

This paper presents a modified pierce oscillator based ultra-low power CMOS readout circuit for a MEMS resonant accelerometer. Differential topology is adopted to make the readout circuit compatible with the MEMS sensing element and depress the common mode noise from amplitude control circuit and bias current source. A g m regulated amplitude control strategy is proposed to avoid the MEMS resonator from strong nonlinear region without deteriorating its noise performance. Simulation results indicate the proposed readout circuit only consumes 1.8μW with a supply of 1.8V. Interfaced with a MEMS resonant accelerometer, it could realize a noise floor of 2μg/Hz1/2 but with 1000~10,000x lower power than published works.

A phase noise model is proposed for silicon oscillating accelerometers (SOAs), which can be used to estimate the frequency noise from the accelerometer. This model treats the SOA as a time-varying system and employs a unified approach to decompose the physical system into phase and amplitude modulation paths to predict the phase noise in SOA. Furthermore, the model also reveals the relationship between mechanical displacement amplitude and design specifications, which can serve as a guideline for performance optimization. The soundness of this model has been validated against both time-domain numerical simulations and experimental results. This model is also applicative in microelectromechanical-system (MEMS) oscillators and MEMS oscillator-based sensors.

This paper describes a compact and low-power oscillating circuit for silicon oscillating accelerometer (SOA). The influence of oscillation amplitude control strategy on accelerometer performance is analyzed. A rail to rail comparator replaces the traditional AGC (automatic gain control) circuit for oscillation amplitude control. It makes the circuit more compact, lower power consumption, and reduces the flicker noise introduced by amplitude control greatly. The experiment shows the bias stability is 13.3µg from 22.9µg, the bias-instability is 4.3µg from 9.3µg, and the system power consumption is reduced to 200mW from 1.2W.

This paper reports a method of measuring the on-chip thermal stress for silicon resonant accelerometer (SRA). This method could be used to evaluate the stress-temperature characteristic of SRA, and that would help to focus the problems exist in SRA. Clamp-clamp Double Ended Turning Fork resonator is used as a basic measurement unit. Analysis of the accuracy and noise in stress measurement is given. An implementation of this method on a silicon resonant accelerometer is detail described. The Experiment shows that the on-chip thermal stress could be precisely measured, and the test result shows a more clear view of the state of the individual SRA.

This paper demonstrates a silicon resonant accelerometer which consists of a MEMS structure and an ASIC readout circuit. The MEMS sensor is fabricated in an 80-µm thick SOI process with a wafer level vacuum package. For noise reduction, several techniques are employed during the circuit design. And in order to reduce the temperature drift due to self heating, the power consumption is carefully limited. Finally, the prototype with these two chips is implemented, and the testing results show it can achieve sub-µg bias instability and equation velocity random walk within ±30g full scale. Moreover, this prototype consumes 3.5mW under 1.5V single supply.

In this paper we present the recent improvement of a silicon micro-mechanical vibrating beam accelerometer (SVBA) which combine the advantage of low cost of silicon MEMS fabrication technology, small size vacuum wafer level package, low noise low power application-specific integrated oscillation circuit and digital frequency demodulation technology. Under room temperature, it has achieved bias instability 1µg (Allan variance), stability 10µg (1σ, one hour), resolution 13µg (direct test result, including all drift and noise), non-linearity 11.4ppm in full-range of ±20g. And the stability of scale factor is 1.5ppm which is tested for seven times during 70mins where temperature be controlled within 0.1°C.

In order to improve the bias stabilities in different temperature for silicon resonant accelerometer (SRA), a temperature measurement method, which measure Temperature in package cavity, was proposed based on chip integrated temperature resonator. Firstly, the frequency-temperature characteristics of the resonators in SRA is analyzed. Afterwards, the heat transfer model for SRA based on chip integrated temperature resonator is established, and the temperature measurement error is analyzed. Then, the hysteresis errors of the two temperature measurement methods based on the external temperature sensor and integrated temperature resonator are contrasted. At last, the first-order linear temperature compensation model is established after several tests of accelerometer bias and the temperature related bias is compensated. Experiment results indicate that using integrated temperature measurement resonator, hysteresis error decreases from 200 Hz to 10 Hz and the bias instability from 283.3 ug to 28 ug after temperature compensation. The results exposed that integrated temperature measurement resonator can accurately reflect the cavity temperature of SRA and increase accuracy of temperature compensation.

This paper gives a detail description of a silicon vibration beam accelerometer which was fabricated by SOI technology and encapsulated in a wafer level vacuum package. The wafer level package gives advantage of small size and low cost, but also produce additional residual stresses that increased the temperature coefficient of the vibration beams. To solve this problem, the sensing structure was redesigned and reduce the temperature coefficient from 50Hz/℃ to 10Hz/℃. Moreover, with carefully assembly, control and measure technology, the accelerometer system achieved reliable performance. Experiment result shows that the scale factor was 120Hz/g, measurement rang was ±50g with non-linearity coefficients of 19μg/g2 and 0.06μg/g3, resolution was 10μg/sqrt(Hz), bias Allan variance was 10μg.

This paper describes a silicon resonant accelerometer implemented in SOI technology. With fully differential design and micro-lever system, the accelerometer achieves a sensitivity of 82Hz/g with a nominal frequency of 30 kHz. The MEMS device is placed in a ceramic vacuum package, so gets a quality factor nearly 1e5. Readout circuit is also introduced which includes two differential oscillators and a double channel frequency measure circuit. A novel differential capacitance sense circuit employing high frequency carrier and diodes ring is used to avoid driving signal feed through. And a 90° phase shifter and AAC (automatic amplitude control) are also used to maintain phase and amplitude balance. The frequency measurement circuit is based on all digital multi-bit PLL (phase lock loop) technology, which is implemented by 18bit ADC and FPGA, the accuracy of each channel is better than 1mHz. The complete resonant accelerometer achieves 13.5μg/ √ Hz resolution and 3.6μg bias stability.