Full-scale Output Research Articles

Nuevo algoritmo de compensación térmica para sensores de presión piezorresistivos basado en la aproximación lineal por segmentos

The piezoresistive pressure sensors are widely used in monitoring and control applications within the industrial sector. These sensors have problems of temperature dependence, and non-linearities that affect the measurement accuracy. For this reason, it is necessary to use signal conditioning circuits for to obtain high accuracy outputs. One of the most common techniques currently used to conditioning the signals from the sensors is based on the use of digital signal processors and compensation algorithms.This paper proposes a new calibration and compensation algorithm for piezoresistive pressure sensors based on the linear segment approximation with thermal compensation. The algorithm was simulated using the mathematical software MathCAD and using data from a piezoresistive pressure dummy sensor. The algorithm has been validated experimentally implementing it into two digital signal processors using vented piezoresistives pressure sensors of 10bar in the range of temperatures from 0°C to 80°C. The result was that the maximum error in the sensor output due to the temperature dependence of the offset was 0,081% of full scale output. The maximum error obtained at the output caused by the temperature dependence of the sensitivity was 0,106% of full scale output. The effectiveness of the algorithm is demonstrated in the thermal compensation of piezoresistive pressure sensors. This algorithm can be applied to other types of sensors having thermal dependencies and incorporating a microprocessor or digital signal processor.

Development of high sensitivity, large frequency bandwidth ZnO-based accelerometers

ZnO has excellent capability in micromachining process for the fabrication of miniaturized accelerometer but its sensitivity is lower because the piezoelectric effect of ZnO is poor. In this paper, a novel accelerometer was made by ZnO and the real part of electrical impedance of ZnO accelerometer at its electrical port was employed to improve its sensitivity. The proposed method is able to obtain active, time varying real part of electrical impedance which correlates with the measured acceleration, usually experienced at the mechanical port of ZnO accelerometer. By comparing with the conventional approach which relies on the output voltage of ZnO accelerometer, the sensitivity is improved almost double with relatively low linearity error and large full scale output. Furthermore, the frequency bandwidth of ZnO accelerometer is extended up to its resonance frequency because the measurement of acceleration is done at the resonance frequency of ZnO accelerometer. Therefore, it allows the ZnO accelerometer to operate at its full frequency bandwidth since the unity response of ZnO accelerometer is no longer limited by the frequency response function of ZnO accelerometer.

A contact stress sensor based on strain gauge

In this paper a sensor with flexible strain gauge is proposed. The sensor can monitor the contact stress between two surfaces in some extreme environments such as thin slits. The force sensitive element inside the sensor is made up of film grid, supporting layer with holes and deforming layer for smoothing load. The device with this structure can easily convert the positive pressure into pulling stress of film grid. The sensor performance related to the number of holes, thickness of layers and elastic constant of layers is investigated. The response of the sensor is simulated and analyzed with finite element analysis software. Based on simulation results, several parameters are optimized and the corresponding sensor is manufactured. The whole sensor thickness is less than 300 μm. Based on the load test in 0–4 MPa, the results show that the linearity error is ±1.77% of full-scale output (FSO), the average deviation is ±0.98% FSO and the hysteresis is ±0.92% FSO. The proposed sensor has advantages of simple structure, easy package, excellent performance and great practicality.

High Overload Pressure Sensor Construct With Polysilicon Nanofilm

A high overload pressure sensor is prepared by surface micromachined technology, and its full scale pressure is 2.5 MPa. The structure of the proposed sensor is based on a seal cavity made by sacrificial layer, a deposition of polysilicon nanofilm acts as piezoresistors on the diaphragm. The stress distribution of the diaphragm of the sensor is simulated by the large displacement static analysis and the nonlinear contact analysis. Due to polysilicon high tensile strength and appropriate cavity height, the sensor full scale output voltage and overload capacity is greatly improved. The measured results indicate that the overpressure of the sensor sample is seven times higher than its full-scale pressure, and its full scale output voltage is 362 mV with a supply voltage of 5 V.

4H-SiC Piezoresistive Pressure Sensors at 800 °C With Observed Sensitivity Recovery

Uncooled MEMS-based 4H-SiC Wheatstone bridge configured piezoresistive pressure sensors were demonstrated from 23 °C to 800 °C. The full-scale output (FSO) voltage exhibited gradual decrease with increasing temperature from 23 °C to 400 °C, then swung upward as temperature increased further to where the values measured at 800 °C were nearly equal to or higher than the room temperature values. This newly observed FSO behavior in 4H-SiC contrasts sharply with the FSO behavior of silicon piezoresistive sensors that decrease continuously with increasing temperature. The increase in the sensor output sensitivity at 800 °C implies higher signal to noise ratio and improved fidelity, thereby offering promise of further insertion into >600 °C environments without the need for cooling and complex signal conditioning.

Toward a Novel Digital Electronic Conditioning for the GMI Magnetic Sensors: The Software Defined Radio

A new high frequency and fully digital electronics was implemented for the conditioning of giant magnetoimpedance (GMI) sensors. The electronics are based on the use of a direct digital synthesizer as a high frequency source for the excitation of the sensing element and a software defined radio (SDR) that performs a direct analog-to-digital conversion, with over-sampling, and quadrature digital down conversion (DDC) of GMI voltage. This DDC includes digital mixers and digital decimation filters that ensure a low-pass filtering and a processing gain. The DDC outputs the in-phase and quadrature baseband digital signals. Except for an optional preamplifier and a voltage-to-current converter, the whole system is digital and fully programmable in real time using a high performance digital signal processor. The architecture of the developed electronics is given and the various aspects of the design are addressed. The performance and potential of the SDR are discussed throughout this paper. The dynamic range for the digital full scale output was between 95 and 120 dB. The out-of-band noise rejection was beyond our measurement instruments. The concept has been successfully applied and used for a GMI sensor and the first measurements were conducted.

Vertical-plate-type microaccelerometer with high linearity and low cross-axis sensitivity

This paper reports the development of a microaccelerometer with high performance in linearity and cross-axis sensitivity. The accelerometer consisted of a vertical, double-ended flexural beam, a proof mass integrated at the middle section of the beam, and four suspended piezoresistors fixed at the mass block and across the trenches to the anchor pads. The mass block had maximum displacements of the dynamic structure which would activate the sensors to deliver maximal output. The sensing chip was fabricated on a silicon-on-insulator wafer through MEMS processes. The accelerometer was placed on a rate table that provided stable centrifugal acceleration up to approximately 3000×G for testing. The output voltage of the accelerometer was digitized and radio-frequency transmitted for remote data acquisition. The correlations for the individual runs showed that the accelerometer had a sensitivity of 3.0015μV/Vexc/G with extraordinary performance. The linearity of the sensing output was only 0.11% of full scale output (FS, or 59dB), as deduced from the average standard deviation of all test runs. The average of the maximum reading deviations from the corresponding correlated curves was approximately 0.26% FS. Moreover, the cross-axis sensitivity for the two orthogonal directions nearly vanished in the test range. With the high rigidity of the microstructure, the accelerometer exhibited an ultra high performance factor of 25.8×106MHz2. The accelerometer possessed exceptional sensitivity, linearity, and repeatability, and extremely low cross-axis interference and noise.

An IP-oriented 11-bit 160 MS/s 2-channel current-steering DAC

This paper presents an 11-bit 160 MS/s 2-channel current-steering digital-to-analog converter (DAC) IP. The circuit and layout are carefully designed to optimize its performance and area. A 6-2-3 segmented structure is used for the trade-off among linearity, area and layout complexity. The sizes of current source transistors are calculated out according to the process matching parameter. The unary current cells are placed in a one-dimension distribution to simplify the layout routing, spare area and wiring layer. Their sequences are also carefully designed to reduce integral nonlinearity. The test result presents an SFDR of 72 dBc at 4.88 MHz input signal with DNL ⩽ 0.25 LSB, INL ⩽ 0.8 LSB. The full-scale output current is 5 mA with a 2.5 V analog power supply. The core of each channel occupies 0.08 mm2 in a 1P-8M 55 nm CMOS process.

Pixel-level A/D conversion using voltage reset technique

This paper presents a 50 Hz 15-bit analog-to-digital converter (ADC) for pixel-level implementation in CMOS image sensors. The ADC is based on charge packets counting and adopts a voltage reset technique to inject charge packets. The core circuit for charge/pulse conversion is specially optimized for low power, low noise and small area. An experimental chip with ten pixel-level ADCs has been fabricated and tested for verification. The measurement result shows a standard deviation of 1.8 LSB for full-scale output. The ADC has an area of 45 × 45 μm2 and consumes less than 2 μW in a standard 1P-6M 0.18 μm CMOS process.

Structured diaphragm with a centre boss and four peninsulas for high sensitivity and high linearity pressure sensors

Using the structured diaphragm with a centre boss and four peninsulas (CBP structure), a high sensitivity and high linearity pressure sensor for low pressure ranges was demonstrated. The finite element analysis indicated that the CBP structure could achieve a far better performance than other typical structures for low pressure applications. In accordance with the simulation, the fabricated pressure sensor showed a sensitivity of 21.0 mV/V full-scale output and a nonlinearity error of 0.15% full-scale span in the pressure range of 0–5 kPa. The sensors with the CBP structure are potentially a better choice for measuring low pressures.

A high sensitivity and high linearity pressure sensor based on a peninsula-structured diaphragm for low-pressure ranges

The trade-off between sensitivity and linearity has been the major problem in designing the piezoresistive pressure sensors for low pressure ranges. To resolve the problem, a novel peninsula-structured diaphragm with specially designed piezoresistors was proposed. Finite element method (FEM) was adopted for analyzing the sensor performance as well as comparisons with other sensor structures. In comparison to flat diaphragm, the proposed sensor design could achieve a sensitivity increase by 11.4%, nonlinearity reduction of 60% and resonance frequency increase of 41.8%. In addition, the modified peninsula-structured diaphragms featuring a center boss have been optimized to achieve ultra-low nonlinearities of 0.018%FFS and 0.07%FFS for the 5kPa and 3kPa pressure ranges respectively with higher sensitivities as compared to the CBM (cross beam membrane) and hollow stiffening structures. In accordance with the FEM results, the fabricated pressure sensor with the peninsula-structured diaphragm showed a sensitivity of 18.4mV/V full-scale output and a nonlinearity error of 0.36%FSS in the pressure range 0–5kPa. The proposed sensor structure is potentially a better choice for designing low pressure sensors.

Characterization of Differentially Measured Strain Using Passive Wireless Surface Acoustic Wave (SAW) Strain Sensors

This paper presents characterization results from surface acoustic wave resonator (SAWR) strain sensors used to carry out wireless passive differential strain measurement. An elevated temperature SAWR strain sensor characterization data set is presented and the results used to demonstrate temperature compensation strategies and overall measurement channel signal sensitivity improvements with a differential SAW sensing element pair. The results are generated by a new wide bandwidth wireless interrogator capable of interrogating two SAWR sensors at high sample rates. Cross axis sensitivity caused by loading conditions generating strains in different directions to the desired strain condition is shown and a compensation strategy presented. The compensation method has reduced the cross axis sensitivity from 24% to 4% of full scale output (FSO). The elevated temperature characterization performance between 20 °C and 100 °C demonstrated a maximum hysteresis level of 0.49% of FSO between 400 με in compression and tension and an overall reduction in the apparent strain due to temperature from approximately 5.5% to 2.7% of FSO.

New Architecture for Intelligent Pressure Sensors with Analog and Digital Outputs

This article proposes a new architecture for intelligent pressure sensors based on the interconnection of a Digital Signal Processor (DSP) and a microcontroller. This configuration allows to obtain a highly accurate output using a reduced number of electronic components. Additionally, very low response times are obtained and different protocols for digital communication are implemented. This paper also discusses the compensation algorithm used to correct the sensitivity and offset dependence on temperature, as well as non-linearity of the pressure sensor response. Hardware and tests performed to verify the proposed architecture operation are described. The total error band obtained in the digital output was 0.07% of full scale output for a relative pressure sensor in a temperature range of 0 to 50 °C. The obtained results demonstrate the advantages of the new architecture proposed.

A Complete 256-Electrode Retinal Prosthesis Chip

This paper presents a complete 256-electrode retinal prosthesis chip, which is small and ready for packaging and implantation. It contains 256 separate programmable drivers dedicated to 256 electrodes for flexible stimulation. A 4-wire interface is employed for power and data transmission between the chip and a driving unit. Power and forward data are recovered from a 600 kHz differential signal, while backward data are sent at 100 kbps rate simultaneously. The stimulator possesses many stimulation features, supporting various stimulation strategies. Many safety features are included such as real-time monitoring of voltage compliance and temperature, electrode self-locking in the event of out-of-compliance, and ESD protection circuit at every electrode. The chip is fabricated in a 65 nm CMOS process. The electrode driver pitch is 150 μm, and total chip area is 8 mm 2 . The chip has been extensively tested and all the requirements have been successfully verified. The measured DC current error for single driver stimulation without electrode shorting is 20 nA. The average power consumption per electrode with typical stimulus pulse parameters and full-scale output current is 129 μW, inclusive of all standby power. The chip overall power efficiency is 70% with 23 mW of power delivered to load.

Cross-validation of a portable, six-degree-of-freedom load cell for use in lower-limb prosthetics research

The iPecs™ load cell is a lightweight, six-degree-of-freedom force transducer designed to fit easily into an endoskeletal prosthesis via a universal mounting interface. Unlike earlier tethered systems, it is capable of wireless data transmission and on-board memory storage, which facilitate its use in both clinical and real-world settings. To date, however, the validity of the iPecs™ load cell has not been rigorously established, particularly for loading conditions that represent typical prosthesis use. The aim of this study was to assess the accuracy of an iPecs™ load cell during in situ human subject testing by cross-validating its force and moment measurements with those of a typical gait analysis laboratory. Specifically, the gait mechanics of a single person with transtibial amputation were simultaneously measured using an iPecs™ load cell, multiple floor-mounted force platforms, and a three-dimensional motion capture system. Overall, the forces and moments measured by the iPecs™ were highly correlated with those measured by the gait analysis laboratory (r>0.86) and RMSEs were less than 3.4% and 5.2% full scale output across all force and moment channels, respectively. Despite this favorable comparison, however, the results of a sensitivity analysis suggest that care should be taken to accurately identify the axes and instrumentation center of the load cell in situations where iPecs™ data will be interpreted in a coordinate system other than its own (e.g., inverse dynamics analysis).

A high precision SOI MEMS–CMOS ±4g piezoresistive accelerometer

System development and characterization of a low noise low offset SOI MEMS–CMOS PCB-integrated multi-chip ±4g piezoresistive accelerometer sensor comprising a coupled multi-bandwidth variable-gain amplifier block and a thermal sensitivity and offset compensation block is presented in this work. Custom design and fabrication has been carried out for both the SOI MEMS sensor and the analog front-end for high precision and operational reliability. The system is shown to have a scale factor of ∼4mV/g and an output nonlinearity <1% of full-scale output with a cross-axis sensitivity <1%. Cyclic loading experiments exhibit distortionless operation over ∼1000,000 cycles without failure indicative of an extremely robust system.

Demonstration of SiC Pressure Sensors at 750 °C

We report the first demonstration of MEMS-based 4H-SiC piezoresistive pressure sensors tested at 750 °C and in the process confirmed the existence of strain sensitivity recovery with increasing temperature above 400 °C, eventually achieving near or up to 100 % of the room temperature values at 750 °C. This strain sensitivity recovery phenomenon in 4H-SiC is uncharacteristic of the well-known monotonic decrease in strain sensitivity with increasing temperature in silicon piezoresistors. For the three sensors tested, the room temperature full-scale output (FSO) at 200 psig ranged between 29 and 36 mV. Although the FSO at 400 °C dropped by about 60 %, full recovery was achieved at 750 °C. This result will allow the operation of SiC pressure sensors at higher temperatures, thereby permitting deeper insertion into the engine combustion chamber to improve the accurate quantification of combustor dynamics.

High Sensitive and Linear Pressure Sensor for Ultra-low Pressure Measurement

A novel peninsula-structured diaphragm with specially designed piezoresistors was proposed in our present pressure sensor for ultra-low pressure measurement. Finite element method (FEM) was adopted for analyzing the sensor performance. In comparison to typical sensors with flat and center-bossed diaphragms, the optimized sensor design could achieve excellent sensitivity and linearity. In accordance with the FEM results, the fabricated pressure sensor showed a sensitivity of 18.4 mV/V full-scale output and a nonlinearity error of 0.36%FSS in the pressure range 0-5 kPa. The proposed sensor structure is potentially a better choice for measuring low pressures.

An I/Q DAC with gain matching circuit for a wireless transmitter

This paper presents a two-channel 12-bit current-steering digital-to-analog converter (DAC) for I and Q signal paths in a wireless transmitter. The proposed DAC has a full-scale output current with an adjusting range of 2 to 10 mA. A gain matching circuit is proposed to reduce gain mismatch between the I and Q channels. The tuning range is ±24% of full scale and the minimum resolution is 1/16 LSB. To further improve its dynamic performance, the switch driver and current cell are optimized to minimize glitch energy. The chip has been processed in a standard 0.13 μm CMOS technology. Gain mismatch between a I-channel DAC and a Q-channel DAC is measured to be approximately 0.13%. At 120-MSPS sample rate for 1 MHz sinusoidal signal, the spurious free dynamic range (SFDR) is 75 dB. The total power dissipation is 62 mW and has an active area of 1.08 mm2.

A Sensor for the Measurement of the Moisture of Undisturbed Soil Samples

This paper presents a very accurate sensor for the measurement of the moisture of undisturbed soil samples. The sensor relies on accurate estimation of the permittivity which is performed independently of the soil type, and a subsequent calibration. The sensor is designed as an upgrade of the conventional soil sampling equipment used in agriculture—the Kopecky cylinder. The detailed description of the device is given, and the method for determining soil moisture is explained in detail. Soil moisture of unknown test samples was measured with an absolute error below 0.0057 g/g, which is only 2.24% of the full scale output, illustrating the high accuracy of the sensor.