A sigma–delta interface ASIC for force-feedback micromachined capacitive accelerometer

A single-loop fourth-order sigma?Cdelta (????) interface circuit for micromachined accelerometer is presented in this study. Two additional electronic integrators are cascaded with the micromachine sensing element to form a fourth-order loop filter to eliminate quantization noise. A precise model for the overall system is set up based on nonlinear model of 1-bit quantizer. Three main noise sources affecting the overall system resolution of a ???? accelerometer: mechanical noise, electronic noise and quantization noise are analyzed in more detail. A switched-capacitor charge integrator and correlated double sampling are applied to reduce input-referred electronic noise. The ASIC is fabricated in 0.5???m two-metal two-poly n-well CMOS process, and test results show that the noise density floors of the open-loop and closed-loop modes are 12 and 80???g/Hz^1/2, respectively, the sensitivity is 1.25?V/g, the full measurement range can be achieved from ?2 to +2?g, and the power dissipation is 40?mW.     

A fourth-order /spl Sigma//spl Delta/ interface for micromachined inertial sensors

This paper presents the design and implementation of a high-order /spl Sigma//spl Delta/ interface for micromachined inertial sensors, which employs an electronic filter in series with the mechanical sensor element to reject the excessive in-band quantization noise inherently present in state-of-the-art second-order solutions. A fourth-order prototype was fabricated in a standard 0.5-/spl mu/m CMOS process. The active circuit area measures 0.9 mm/sup 2/, and the interface consumes 13 mW from a 5-V supply and achieves resolution of 1/spl deg//s//spl radic/Hz with a gyroscope and 150/spl mu/g//spl radic/Hz with an accelerometer. Comparison between the measured and simulated behavior of the system shows that the contribution of the quantization error to the total noise is negligible.     

减小交叉耦合的三维微加速度计的设计

介绍了一种减小交叉耦合的三维微加速度计的设计,该设计采用全差分电容式结构,X轴和Y轴采用梳齿电容式加速度计,Z轴采用扭摆电容式加速度计,三个轴向各自具有不同的敏感质量块,能够有效减小交叉耦合度。通过公式计算得到三个轴向的机械噪声,X轴为-60μg/Hz,Y轴为-66μg/Hz,Z轴为-53μg/Hz。从计算结果来看,三个维度的噪声系数较低,在电路噪声保证足够小的情况下,该三维微加速度计能够达到较高的精度。最后,采用COMSOL MULTIPHYSICS软件对该结构三个维度进行了模态仿真,仿真结果表明该设计能够有效减小三个维度的交叉耦合度。     

A monolithic surface micromachined accelerometer with digitaloutput

A surface micromachined accelerometer with on-chip electronics realized in a 3 μm BiCMOS technology is described. The sensing element consists of a thin film of polysilicon that is deposited after fabrication of the electronic circuitry. Acceleration is measured by capacitively sensing sub-angstrom displacements of a mechanical proof-mass weighing 0.5 μgrams. The sensor uses force-feedback and achieves a resolution of 1.6 mg/√(Hz) (1 g=9.8 m/s²). The limitations arising from the small size and mass of the sensing element and means for improvement are discussed. The small active die area of less than 3 mm² including the sensor along with the possibility to combine several different sensors on a single chip make this approach particularly attractive for applications demanding very small form factors     

电容式z轴微机械陀螺的噪声抑制

将z轴微机械陀螺两个模态的机械噪声效应等效为各自在单位噪声力作用下的振动,根据陀螺的工作原理得到两个噪声力作用下陀螺敏感模态的机械输出噪声。建立了包含运放和电路板非理想因素在内的接口电路的噪声模型。结合机械噪声模型和接口电路模型噪声,建立了包括结构参数和电路最小检测电容量在内的陀螺的噪声等效输入角速度模型,为陀螺的设计优化提供了参考。分析了结构参数对陀螺等效输入角速度噪声影响,并采用两个参数不同的电容式z轴微机械陀螺进行了实验。结果表明,通过结构参数的调整,将电容式z轴微机械陀螺的输出噪声从414μV/Hz降低至235μV/Hz。     

Surface micromachined accelerometers

Surface micromachining has enabled the cofabrication of thin-film micromechanical structures and CMOS or bipolar/MOS integrated circuits. Using linear, single-axis accelerometers as a motivating example, this paper discusses the fundamental mechanical as well as the electronic noise floors for representative capacitive position-sensing interface circuits. Operation in vacuum lowers the Brownian noise of a polysilicon accelerometer to below 1 μg/√(Hz). For improved sensor performance, the position of the microstructure should be controlled using electrostatic force-feedback. Both analog and digital closed-loop accelerometers are described and contrasted, with the latter using high-frequency voltage pulses to apply force quanta to the microstructure and achieve a very linear response     

一种微机械压阻式加速度传感器及其设计优化

给出了一种新型的微梁直拉直压的微机械压阻式加速度传感器的工作原理。该设计能同时提高传感器的灵敏度和自由振动频率。基于分析模型 ,本文还给出了传感器的结构优化和各种量程的设计规则。采用SOI硅片和深反应离子刻蚀 (DRIE)工艺给出了传感器的制造和测试结果     

A Ka-band micromachined low-phase-noise oscillator

A low-phase-noise 28.65 GHz oscillator has been demonstrated using a planar resonator. The resonator is micromachined close to the transistor and has an unloaded Q of 460. The oscillator uses a commercially available high electron mobility transistor (HEMT) for the active device, and results in an output power of 0.6 dBm with a 5.7% DC-RF efficiency. The measured phase noise is -92 dBc/Hz at a 100 kHz offset frequency and -122 dBc/Hz at 1 MHz offset frequency. This is compared with a low-Q planar design showing a 10 dB improvement in phase noise. The micromachined resonator is competitive with other hybrid nonplanar technologies, such as dielectric resonators     

微电容超声换能器的前端专用集成电路设计

针对微电容超声换能器(CMUT)微弱电流信号检测的要求,设计了一种用于CMUT的前端专用集成电路——运算放大器(OPA)电路。运算放大器电路采用两级放大结构,第一级采用全差分折叠-共源共栅结构,输出级采用AB类控制的轨到轨输出级,在运算放大器电路反相输入端和输出端通过一个反馈电阻实现CMUT电流信号到电压信号的转换。采用GlobalFoundries 0.18μm的标准CMOS工艺进行了仿真设计和流片,芯片尺寸为226μm×75μm。仿真结果表明,运算放大器的开环增益为62 dB,单位增益带宽为30 MHz,在3 MHz处的输入参考噪声电压为2.9μV/Hz^1/2,电路采用±3.3 V供电,静态功耗为11 mW。测试结果表明仿真与实测结果相符,该运算放大器电路能够实现CMUT微弱电流信号检测功能。     

Noise analysis and characterization of a sigma-delta capacitive microaccelerometer

This paper reports a high-sensitivity low-noise capacitive accelerometer system with one micro-g//spl radic/Hz resolution. The accelerometer and interface electronics together operate as a second-order electromechanical sigma-delta modulator. A detailed noise analysis of electromechanical sigma-delta capacitive accelerometers with a final goal of achieving sub-/spl mu/g resolution is also presented. The analysis and test results have shown that amplifier thermal and sensor charging reference voltage noises are dominant in open-loop mode of operation. For closed-loop mode of operation, mass-residual motion is the dominant noise source at low sampling frequencies. By increasing the sampling frequency, both open-loop and closed-loop overall noise can be reduced significantly. The interface circuit has more than 120 dB dynamic range and can resolve better than 10 aF. The complete module operates from a single 5-V supply and has a measured sensitivity of 960 mV/g with a noise floor of 1.08 /spl mu/g//spl radic/Hz in open-loop. This system can resolve better than 10 /spl mu/g//spl radic/Hz in closed-loop.     

A 22-GHz push-push CMOS oscillator using micromachined inductors

This letter presents a low phase noise 0.35-/spl mu/m CMOS push-push oscillator utilizing micromachined inductors. This oscillator results in an improvement in phase noise compared with the previously published Si-based voltage-controlled oscillators (VCOs) around 20GHz. With the high-Q inductors introduced by the micromachined structure, the oscillator achieves an oscillating frequency of 22.2GHz while exhibiting an output power of -7.5dBm with a phase noise of -110.1dBc/Hz at 1-MHz offset. This work also demonstrates the highest operating frequency among previously published Si-based VCOs using micromachined structures.     

Architecture, design, and test of continuous-time tunableintermediate-frequency bandpass delta-sigma modulators

This paper examines the architecture, design, and test of continuous-time tunable intermediate-frequency (IF) fourth-order bandpass delta-sigma (BP ΔΣ) modulators. Bandpass modulators sampling at high IFs (~100 MHz) allow direct sampling of the RF signal-reducing analog hardware and make it easier to realize completely software programmable receivers. This paper presents circuit design of and test results from continuous-time fourth-order BP ΔΣ modulators fabricated in AlInAs/GaInAs heterojunction bipolar technology with a peak unity current gain cutoff frequency (f_T) of 80 GHz and a maximum frequency of oscillation (f_MAX) of about 130 GHz. Operating from ±5-V power supplies, a fabricated 180-MHz IF fourth-order ΔΣ modulator sampling at 4 GS/s demonstrates stable behavior and achieves 75.8 dB of signal-to-(noise+distortion)-ratio (SNDR) over a 1-MHz bandwidth. Narrowband performance (~1 MHz) performance of these modulators is limited by thermal/device noise while broadband performance (~60 MHz), is limited by quantization noise. The high sampling frequency (4 GS/s) in this converter is dictated by broadband (60 MHz) performance requirements     

MEMS陀螺仪ΣΔ闭环系统优化设计

为解决传统ΣΔ闭环控制系统存在的量化增益不可控问题,设计了基于3-level量化技术的改进系统;针对此系统应用于微电子机械系统(MEMS)陀螺仪时引入的非线性反馈误差,提出了一种调整反馈脉冲宽度的矫正技术;并基于课题组研制的新型类蛛网环式谐振陀螺仪验证了改进系统的实用性。首先采用Simulink建立了四阶机电耦合ΣΔ系统等效模型,理论分析与仿真结果表明,3-level量化技术在降低量化噪声的同时解决了量化增益不可控问题,进而有效提高了陀螺仪量程和噪声水平性能。然后基于现场可编程逻辑门阵列(FPGA)设计制作了相应的数字测控电路,实验结果显示,陀螺仪的角度随机游走由0.094°/√h降低为0.062°/√h,量程由100°/s提高到130°/s,系统性能得到了有效提升。     

A ΣΔ micro accelerometer with 6 µg/√Hz resolution and 130 dB dynamic range

This paper reports the implementation of a low noise, high dynamic-range ΣΔ readout for low cost capacitive Micro-Electro-Mechanical Systems (MEMS) accelerometers. The readout circuit sets the bandwidth of the ΣΔ loop through an extra feedback path, and hence allows the closed loop system to operate with the low noise characteristics similar to a second-order ΣΔ analog-to-digital converter. A thorough noise analysis of the proposed accelerometer shows that the mechanical noise is the most significant source and quantization noise is mostly eliminated. Dynamic range (DR) of the system is improved by minimizing the circuit noise and increasing the full scale range (FSR) by high-voltage pulse feedback. Utilization of these techniques allows the implementation of low cost, low noise, and high DR navigation-grade accelerometers, by eliminating the need for large proof mass, large area MEMS sensors. The proposed system can achieve a minimum of 6.0 µg/√Hz noise floor, 3.2 µg bias instability, and a maximum of 130 dB DR at 1 Hz. A FSR of ±20 g is reported for 6.2 µg/√Hz noise floor. This range can be increased up to ±40 g at the cost of noise performance and DR.     

Static characterization of bulk micromachined accelerometer structure using a nanoindenter

This paper presents the static characterization of the bulk micromachined quad beam accelerometer structure using a nanoindenter as a loading tool. The paper reveals how a nanoindenter, an instrument designed to measure mechanical properties of the films or objects, can be used in a non-traditional fashion to characterize MEMS accelerometer structure. The stiffness and breaking load of the mechanical structures of this device were experimentally measured and compared with the predictions based on FEM simulations.     

High-performance micromachined gyroscope with a slanted suspension cantilever

This paper presents a novel structure for improving the stability and the mechanical noise of micromachined gyroscopes.Only one slanted cantilever is used for suspension in this gyroscope,so the asymmetry spring and the thermal stress,which most micromachined gyroscopes suffer from,are reduced.In order to reduce the mechanical noise,the proof masses are designed to be much larger than in most micromachined gyroscopes.The gyroscope chip is sealed at 0.00 1 Pa vacuum.A gyroscope sample and its read-out circuit are fabricated.The scale factor of this gyroscope is measured as 57.6 mV/(deg/sec) with a nonlinearity better than 0.12%in a measurement range of ±100 deg/sec.The short-term bias stability in 20 min is 60 deg/h.     

Monolithic folded pendulum accelerometers for seismic monitoring and active isolation systems

A new class of very low noise low-frequency force-balance accelerometers is presented. The device has been designed for advanced mirror isolation systems of interferometric gravitational wave detectors. The accelerometer consists of a small monolithic folded pendulum with 2 s of natural period and an in-vacuum mechanical quality factor of 3000. The folded pendulum geometry, combined with the monolithic design, allows a unique 0.01% cross-axis residual coupling. Equipped with a high-resolution capacitance position sensor, it is capable of a noise-equivalent inertial displacement of 1-nm root mean square integrated over all the frequencies above 0.01 Hz. The main features of this new accelerometer are here reviewed. New possible applications of monolithic folded pendula in geophysical instrumentation are discussed.     

Robust CMOS Micromachined Inductors With Structure Supports for Gilbert Mixer Matching Circuits

In this brief, three novel structure supports for on-chip CMOS-based micromachined inductors are proposed to improve mechanical stability. The inductors are fabricated using a two-step maskless post-CMOS process. A 3-D electromagnetic inductor simulation model is established for performance analysis of the inductors before fabrication. The proposed inductors are applied in the matching network of the double-balanced Gilbert mixer to improve the performance and mechanical reliability for mobile communication. The mixers with and without micromachined process inductors are fabricated in a 0.5-mum CMOS process. The measurement results show an 18.6% increase in the conversion gain, a 31.7% improvement in the third intercept point (IIP3), and a 25.3% reduction in the noise figure.     

Design and Optimization of a Low-Noise Voltage Reference Using Chopper Stabilization Technique

A low-noise voltage reference is presented to enhance resolution of MEMS capacitive accelerometer and reduce system noise,in which the circuit uses Chopper stabilization (CHS) technique for the suppression of low-frequency noise.A 3.7V voltage reference chip is fabricated in a 0.5-μm CMOS process.Compared with the voltage reference without using CHS,the proposed design is much more superior in low-noise performance.Experimental results indicate that the output noise of reference voltage VRP can reach 0.121μV/sqrt(Hz) at the vicinity of 3Hz.     

微机械气流式加速度计敏感机理的有限元分析

揭示了微机械气流式加速度计的敏感机理。采用有限元方法,分析了在不同加速度输入时敏感元件内的流场分布。结果表明,无加速度输入时,两热敏电阻处的气流速度相等,两热敏电阻上的电流相等,电桥输出为0;有加速度输入时,两热敏电阻处的气流速度之差随加速度变化而变化,引起两热敏电阻上电流之差也随之变化,电桥输出一个对应于加速度的电压。所述的方法为微机械气流式加速度计的结构优化设计提供了简单有效的途径。