1,721,037 research outputs found
Temperature Sensing for MEMS Sensors: A Review, and Chances for the Frequency-Control Community
No full textWith an increasing demand of higher and higher performance for several microelectromechanical system (MEMS) based sensors, accurate temperature calibration and real-time compensation become a key enabling factor. Approaches to temperature (T) sensing operated directly on the MEMS die have inherent advantages over T-sensing implemented on the integrated or board level electronics. This work provides a review of temperature sensing approaches, with a special focus on those implemented through resonant operation of microstructures, providing the latest results for MEMS-based T sensors
Can LSE Reduce Noise in Sensing Applications?
No full textThis work reports an experimental investigation of Large Scale Excitation (LSE) in sensing applications. This technique aims at mitigating flicker noise by suppressing its originating, signal-dependent, phenomena. Differently from modulation/chopping, which is not effective in these situations (flicker noise is modulated just as the signal is), LSE aims at switching on/off the source of signal generation without leaving enough time for carrier trapping or mobility changing, so blocking random telegraph noise phenomena which build up 1/f noise. As 1/f noise appears both in transistors and thin-film resistors, which are both key elements in the front-end of various sensors types, this work, after providing a simplified model for the scenario, experimentally verifies LSE. Results confirm the possibility of consistent flicker noise reduction in MOS transistors, by as much as a factor 3.3, whereas no flicker noise reduction is observed on piezoresistors, hinting that the source of 1/f is here a different process
A MEMS Real-Time Clock with Single-Temperature Calibration and Deterministic Jitter Cancellation
Full text linkThis article presents a real-time clock (RTC) system based on a microelectromechanical system (MEMS) resonator coupled to an integrated circuit (IC) that implements a frequency-compensating machine. The MEMS resonator is built with a standard, industrial-grade polysilicon process characterized by a -30-ppm/K linear temperature coefficient of frequency ( ) and the frequency-drift compensation is entirely carried out within the IC using a fractional frequency division. The large, but deterministic, output jitter (≈1 ) is then suppressed down to less than 40 with a low-power digital-to-time converter (DTC), whose usefulness in this kind of application is then analyzed. With a single-point temperature calibration, a ±8-ppm output frequency stability is demonstrated at ≈800-nA current consumption from a 1.2-V supply
State-Space Modeling of a Novel 2-output, single-L Driver for PZT Actuators with Charge Recovery
No full textThe growing need for larger transduction forces to be applied by piezoelectric actuators leads to the increase of their footprint, capacitance and voltage level. This is in trade-off with low power dissipation needs, and thus new driving circuits shall be conceived. In this work a novel architecture based on a two-output, single-inductor, DC-AC converter is presented, which exploits a charge-recovery technique. It is of utmost importance to derive a linear time-invariant (LTI) model for such a switching circuit, so that a target driving waveform can be obtained on the piezoelectric actuators, depending on the duty cycle applied to the circuit switches. A state-space averaging technique and linearization is used to extract the LTI model of the proposed driver. The so computed equations are then exploited to predict the required duty cycles to generate, as a real-case scenario, a 56-V, 120-Hz sawtooth signal, typically used to drive MEMS micromirrors. The entire circuit model is finally validated by an open-loop behavioral simulation, showing a relative error deviation between the target and the obtained voltage waveforms smaller than 2.7%, with zero power dissipation in the assumption of ideal switches
Challenges in Implementing Pitch/Roll Rate Integrating Gyroscopes: A Case Study on a New Dynamically Balanced Dual-Mass Resonator
No full textA case study on a new dynamically balanced dual-mass resonator, for implementation in pitch/roll rate integrating gyroscopes (RIGs), is reported in this article. Proper measures have been taken during structural design to minimize the mismatch of both the resonant frequencies and the -factors between in-plane (IP) and out-of-plane (OOP) modes. To improve the -factor of OOP mode, which is generally significantly lower than that of IP mode, a dual-mass structure reduces the torque applied to the supporting substrate in the OOP mode. Thus, dominant loss mechanisms are thermoelastic dissipation (TED) and squeeze film damping (SFD). After optimizing design parameters, -factor machining can be achieved by tuning SFD by operation pressure. The designed microelectromechanical systems (MEMS) resonator was fabricated using two layers of Si substrate combined with Au-Au thermocompression bonding technology. The experimental characterization revealed that the mismatches of resonant frequencies and -factors were as small as 1.3% and 32%, respectively
MEMS real-time clocks based on epitaxial polysilicon: System-level requirements and experimental characterization
No full textThe purpose of this paper is to assess the feasibility of MEMS-based real-time clocks (RTCs) using conventional polysilicon, without correcting the temperature coefficient of frequency (TCf) through dedicated technological steps. The paper first shows how such a large TCf (-30 ppm/K) is not an issue in terms of maximum frequency correction to achieve with a dedicated electronics: indeed, whatever the TCf, the dominant part of the frequency correction, required to match the 32-kHz RTC target value, is always demanded by the native frequency offset due to etching nonuniformities, and not by temperature changes. This sets the required number of bits of the modulator used to drive a fractional frequency divider that performs the compensation. Instead, requirements in the bit number and refresh rate of the temperature sensor are affected by a large TCf. Nevertheless, the paper shows the possibility to achieve few ppm frequency stability using a 9-bit temperature sensor with a 4-Hz refresh rate. This makes the approach quite competitive against more sophisticated MEMS processes, especially in terms of final cost. Experimental measurements on a MEMS-based resonator coupled to a dedicated integrated circuit are used to support the discussion
Piezoresistive Versus Piezoelectric Position Sensing in MEMS Micromirrors: A Noise and Temperature Drift Comparison
No full textThis letter presents a comparative study concerning the characterization of piezoresistive (PZR) and piezoelectric (PZT) tilt-angle sensing in MEMS micromirrors. Position tracking is mandatory in such devices, so to achieve high-resolution displays, and the control system must be accurate against noise sources and stable against drifts of physical parameters, such as ambient temperature. This letter presents the performance results achieved on PZR and PZT sensors integrated on the same micromirror, showing that, at the cost of a larger area occupation, the latter achieves ten times larger sensitivity (with improvements in the signal-to-noise ratio and thus in position accuracy), and a five times lower overall transduction variation under temperature changes
Two-axis multiple masses resonator with frequency and Q-factor matching
No full textThis paper reports a design and experimental results of a two-axis symmetric dynamically balanced resonator based on a triple mass system, whose frequency and Q-factor can be independently tuned. Two dynamically equivalent proof masses are connected by four coupling springs, and four coupling proof masses are implemented between them. The frequency and Q-factor of the anti-phase modes can be tuned independently of each other. The frequency is tuned by electrostatically softening the suspensions stiffness, and the Q-factor is adjusted by controlling the squeeze film damping through the mode coupling between the anti-phase and in-phase modes. The changes of frequency and mode coupling under different DC bias tunings are studied by FEA, which reveals the modification of the suspension stiffness only decreases the frequency and the modification of the inner stiffness of the coupling proof masses exerts a large effect on the mode shape, i.e. Q-factor, while a minor effect on the frequency. The as-fabricated frequency and Q-factor mismatches were evaluated as 5% and 7.7% in a fabricated device, respectively. A large adjustment of the Q-factor by 21% was observed by adding a 27 V DC voltage on the tuning electrodes inside the coupling proof masses, while the frequency was only decreased by as small as 810 ppm. A mode matching was achieved by electrostatic softening the suspensions of both main proof masses. Thanks to the decoupling between frequency and Q-factor, a frequency matching under 10 ppm and a Q-factor matching under 650 ppm were experimentally proved
Modeling and First Characterization of Broad-Spectrum Vibration Rejection of Frequency Modulated Gyroscopes
Full text linkThe work presents a detailed modeling and the first-ever characterization of a frequency modulated (FM) yaw gyroscope in presence of vibrations from low frequency (30 Hz), through the main modes, and up to 40 kHz. The gyroscope two in-plane axes (around 25 kHz) are operated under a Lissajous trajectory (70 Hz period) by an integrated circuit (IC) including oscillators, frequency digitization, and digital demodulation stages. In presence of 2-gpk-pk vibrations, no effects are visible across the spectrum apart from the region including the modes. In this range, as predicted by theory, for each axis no effect is observed for accelerations at the axis resonance (< 0.1 dps/g), but a huge effect (tens of dps/g) is visible for accelerations at an offset frequency from resonance corresponding to the mode split
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