Digital Temperature Compensation Research Articles

An Interface ASIC Design of MEMS Gyroscope with Analog Closed Loop Driving.

This paper introduces a digital interface application-specific integrated circuit (ASIC) for a micro-electromechanical systems (MEMS) vibratory gyroscope. The driving circuit of the interface ASIC uses an automatic gain circuit (AGC) module instead of a phase-locked loop to realize a self-excited vibration, which gives the gyroscope system good robustness. In order to realize the co-simulation of the mechanically sensitive structure and interface circuit of the gyroscope, the equivalent electrical model analysis and modeling of the mechanically sensitive structure of the gyro are carried out by Verilog-A. According to the design scheme of the MEMS gyroscope interface circuit, a system-level simulation model including mechanically sensitive structure and measurement and control circuit is established by SIMULINK. A digital-to-analog converter (ADC) is designed for the digital processing and temperature compensation of the angular velocity in the MEMS gyroscope digital circuit system. Using the positive and negative diode temperature characteristics, the function of the on-chip temperature sensor is realized, and the temperature compensation and zero bias correction are carried out simultaneously. The MEMS interface ASIC is designed using a standard 0.18 μM CMOS BCD process. The experimental results show that the signal-to-noise ratio (SNR) of sigma-delta (ΣΔ) ADC is 111.56 dB. The nonlinearity of the MEMS gyroscope system is 0.03% over the full-scale range.

A 2MHz, low temperature coefficient relaxation oscillator with hybrid temperature compensation and real-time calibration

An RC relaxation oscillator (ROSC) with hybrid temperature compensation as well as the frequency of 2 MHz is proposed in this paper. Frequency stability is enhanced with analog compensation by replicating the path of comparator and level determination logic (LDL), the compensation approach removes the temperature-dependent delay of the comparator and LDL. Since frequency is undesirable at low temperatures (below 0 °C) due to non-zero-temperature-coefficient current and voltage references, as well as weak carrier mobility, digital low temperature compensation is presented to extend the oscillator’s operating temperature range to −40 °C–125 °C. The digital compensation module, after hybrid compensation, is then utilized for real-time oscillator calibration by the same operating principle. The presented oscillator with hybrid compensation and real-time calibration is developed in a standard 0.18-μm CMOS process with the active area of 0.04 mm2, and post-simulation results reveal that after hybrid compensation, the temperature coefficient (TC) of this oscillator is 43.97 ppm/°C in the temperature range of −40 °C–125 °C. The power of this ROSC is 185 μW when the supply voltage is 1.8V.

A 16 MHz CMOS RC Frequency Reference With ±90 ppm Inaccuracy From −45 °C to 85 °C

This article presents a 16-MHz <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> frequency reference implemented in a standard 180-nm CMOS process. It consists of a frequency-locked loop (FLL) in which the output frequency of a digitally controlled oscillator (DCO) is locked to the frequency-phase characteristic of a Wien bridge <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> filter. Since it is made from on-chip resistors and capacitors, the filter’s characteristic is temperature dependent. To compensate for this, the control signal of the DCO is derived by digitizing the filter’s output phase and combining it with the digital output of a Wheatstone bridge temperature sensor. After a two-point trim, this digital temperature compensation scheme achieves an inaccuracy of ±90 ppm from −45 °C to 85 °C. The frequency reference draws 220 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{A}$ </tex-math></inline-formula> from a 1.8-V supply, with a supply sensitivity of 0.12%/V and a 320-ppb Allan Deviation floor for a 10-s stride.

A portable NMR platform with arbitrary phase control and temperature compensation.

In this paper, we present a custom-designed nuclear magnetic resonance (NMR) platform based on a broadband complementary metal-oxide-semiconductor (CMOS) NMR-on-a-chip transceiver and a synchronous reference signal generator, which features arbitrary phase control of the excitation pulse in combination with phase-coherent detection at a non-zero intermediate frequency (IF). Moreover, the presented direct digital synthesis (DDS)-based frequency generator enables a digital temperature compensation scheme similar to classical fieldlocking without the need for additional hardware. NMR spectroscopy and relaxometry measurements verify the functionality of the proposed frequency reference and temperature compensation scheme as well as the overall state-of-the-art performance of the presented system.

Temperature Compensated Wide-Range Micro Pressure Sensor with Polyimide Anticorrosive Coating for Harsh Environment Applications

In this work, a MEMS piezoresistive micro pressure sensor (1.5 × 1.5 × 0.82 mm) is designed and fabricated with SOI-based micromachining technology and assembled using anodic bonding technology. In order to optimize the linearity and sensitivity over a wide effective pressure range (0–5 MPa) and temperature range (25–125 °C), the diaphragm thickness and the insulation of piezoresistors are precisely controlled by an optimized micromachining process. The consistency of the four piezoresistors is greatly improved by optimizing the structure of the ohmic contact pads. Furthermore, the probability of piezoresistive breakdown during anodic bonding is greatly reduced by conducting the top and bottom silicon of the SOI. At room temperature, the pressure sensor with 40 µm diaphragm demonstrates reliable linearity (0.48% F.S.) and sensitivity (33.04 mV/MPa) over a wide pressure range of 0–5.0 MPa. In addition, a polyimide protection layer is fabricated on the top surface of the sensor to prevent it from corrosion by a moist marine environment. To overcome the linearity drift due to temperature variation in practice, a digital temperature compensation system is developed for the pressure sensor, which shows a maximum error of 0.43% F.S. in a temperature range of 25–125 °C.

Improved Stability and Performance of Surface Acoustic Wave Nanosensors Using a Digital Temperature Compensation

Surface Acoustic Waves (SAW) sensors are known to be an excellent choice for the measurement of a small concentration of analytes in gas mixtures. The use of this type of sensor has been limited until now in the industrial environment due to the sensitivity of its response to temperature variations. To overcome this problem, thermal stabilization of equipment is normally used. We propose here a simple procedure of compensation of thermal drift in SAW sensors, allowing the measurements to be performed in temperature intervals of up to 20 degrees without any thermal stabilization of the sensitive element of a sensor. By monitoring the temperature of the key points of the sensor and applying the proposed polynomial compensation, it is possible to reduce the influence of thermal instabilities of the ambient temperature to the response more than four times. The method is illustrated by a temperature compensated SAW humidity sensor with a graphene oxide nanofilm as water molecules’ sensitive element. The results show enhanced performance of the sensor over a large temperature interval.

A Highly Accurate, Polynomial-Based Digital Temperature Compensation for Piezoresistive Pressure Sensor in 180 nm CMOS Technology.

Recently, piezoresistive-type (PRT) pressure sensors have been gaining attention in variety of applications due to their simplicity, low cost, miniature size and ruggedness. The electrical behavior of a pressure sensor is highly dependent on the temperature gradient which seriously degrades its reliability and reduces measurement accuracy. In this paper, polynomial-based adaptive digital temperature compensation is presented for automotive piezoresistive pressure sensor applications. The non-linear temperature dependency of a pressure sensor is accurately compensated for by incorporating opposite characteristics of the pressure sensor as a function of temperature. The compensation polynomial is fully implemented in a digital system and a scaling technique is introduced to enhance its accuracy. The resource sharing technique is adopted for minimizing controller area and power consumption. The negative temperature coefficient (NTC) instead of proportional to absolute temperature (PTAT) or complementary to absolute temperature (CTAT) is used as the temperature-sensing element since it offers the best temperature characteristics for grade 0 ambient temperature operating range according to the automotive electronics council (AEC) test qualification ACE-Q100. The shared structure approach uses an existing analog signal conditioning path, composed of a programmable gain amplifier (PGA) and an analog-to-digital converter (ADC). For improving the accuracy over wide range of temperature, a high-resolution sigma-delta ADC is integrated. The measured temperature compensation accuracy is within ±0.068% with full scale when temperature varies from −40 °C to 150 °C according to ACE-Q100. It takes 37 µs to compute the temperature compensation with a clock frequency of 10 MHz. The proposed technique is integrated in an automotive pressure sensor signal conditioning chip using a 180 nm complementary metal–oxide–semiconductor (CMOS) process.

A $192\times128$ Time Correlated SPAD Image Sensor in 40-nm CMOS Technology

A <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$192 \times 128$ </tex-math></inline-formula> pixel single photon avalanche diode (SPAD) time-resolved single photon counting (TCSPC) image sensor is implemented in STMicroelectronics 40-nm CMOS technology. The 13% fill factor, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$18.4\,\,\mu \text {m} \times 9.2\,\,\mu \text{m}$ </tex-math></inline-formula> pixel contains a 33-ps resolution, 135-ns full scale, 12-bit time-to-digital converter (TDC) with 0.9-LSB differential and 5.64-LSB integral nonlinearity (DNL/INL). The sensor achieves a mean 219-ps full-width half-maximum (FWHM) impulse response function (IRF) and is operable at up to 18.6 kframes/s through 64 parallelized serial outputs. Cylindrical microlenses with a concentration factor of 3.25 increase the fill factor to 42%. The median dark count rate (DCR) is 25 Hz at 1.5-V excess bias. A digital calibration scheme integrated into a column of the imager allows off-chip digital process, voltage, and temperature (PVT) compensation of every frame on the fly. Fluorescence lifetime imaging microscopy (FLIM) results are presented.

Adaptive digital temperature compensation of inductor DCR current measurement

Inductor DC resistance (DCR) measurement is the standard technique used to measure the current in a single- or multi-phase voltage regulators in computing applications. It is well noted that variations in operating conditions such as temperature cause a mismatch of time constants of the inductor and its DCR, and the RC sensing network. This mismatch affects everything from transient response to safety by affecting the performance of peak current protection features. A digital filter with temperature-adaptive coefficients is presented to correct the DCR measurement across the operating temperature range. Experimental results of a 12 V/1.8 V converter validate the analysis and prove the feasibility of the approach.

Intelligent thermal vacuum sensors based on multipurpose thermopile MEMS chips

Realization of intelligent thermal vacuum sensors based on multipurpose thermopile microelectromechanical (MEMS) chips is presented in this work. These vacuum sensors satisfy the main requirements for contemporary sensors, they are cost-effective in both fabrication and operation, and simple to use. Intelligent devices based on two types of thermal sensors, A-type with Al heater, and P-type with p+Si heater, were developed. Both types have two thermopiles with 30 p+Si/Al thermocouples each. Thermal and electrical isolation is provided by a sandwich membrane (residual n-Si and sputtered oxide). The intelligent functionality is achieved by using a signal processing unit the authors developed earlier for pressure sensing based on their proprietary Si piezoresistive pressure sensing elements. The main issues which were of key importance for realization of intelligent vacuum sensors are addressed in this work: design and fabrication of the intelligent vacuum sensors, adaptation of the software module, linearization of the input signal using digital signal processing and temperature compensation. A three-stage test procedure is presented. The A-type sensor, with a thinner membrane, achieved 19 times better thermopile voltage-pressure sensitivity compared with the P-type sensor, with a thicker membrane. Since the estimated noise level of the measuring system is comparable with the useful signal of the P-type device, the improved voltage-pressure sensitivity provides a better resolution and signal to noise ratio of the intelligent vacuum measuring system.

Smart Electrochemical Oxygen Sensor for Personal Protective Equipment

Self contained closed circuit rebreathers are life supporting breathing systems, where the exhaled gas is recycled by filtering CO2 and replacing metabolized O2. For the O2 injection control galvanic O2 sensors are used to measure the partial pressure of O2. A malfunction of the sensors can lead to a gas mixture beyond life supporting limits which is life threatening. Galvanic O2 sensors are often used in anaesthetic machines in hospitals. Also in this case, a malfunction of the sensors can cause severe injury to a person. It is obvious that such sensors are key elements in life supporting equipment and as such must be designed in order to achieve high functional safety. However these sensors are consuming sensors, and with that, will fail at a certain time. Failure modes include current limitation, non linearity, electrolyte evaporation or leakage, etc. Within this paper a novel low cost read out electronic circuit for galvanic O2 sensors is presented, which allows not only digital readout, digital temperature compensation, on board storage of calibration and manufacturing data, but also can be used for performing voltammetry cycles to test the Pb anode for exhaustion. First measurements are presented and compared to data from a Solartron SI 1287 impedance analyzer, which is state-of-the-art in electrochemical sensor characterization.

Focus on sensors and detectors

Focus on sensors and detectors

Digital self-learning calibration system for smart sensors

Design and realization of a digitally controlled closed loop calibration system for smart sensors, capable of self-learning, is reported. Closed loop design enables analysis of sensor properties and optimization of calibration procedure. Dedicated software was developed, enabling control of acquired data and calibration procedure. Resulting statistical data provide closed loop feedback variable for failure analysis. Calibration system enables digital temperature compensation by acquisition of calibration points, calculation of sensor polynomial coefficients and storing the calculated data in the sensor memory. Due to the proposed digital temperature compensation method, temperature output error of pressure sensors was significantly reduced (typically from 0.15% FSO/°C to 0.05% FSO/°C, based on calibration of 29482 manifold absolute pressure sensors). Modular approach results in reduction of calibration time (typically down to 42 s/sensor), thus enabling mass calibration.

The cheap air data computer for aviation applications

PurposeTo present both the construction and sample applications of the small, low‐cost air data computer (ADC) with CAN interface, which has been designed at Avionics Department of Rzeszow Technical University.Design/methodology/approachThe ADC has been developed as a partial task during realization of few aviation projects. It uses cheap piesoresistive pressure sensors with digital temperature compensation to calculate following flight data: altitude, airspeed computed in two ways as instrumental airspeed and true airspeed, altitude rate, and atmosphere parameters: pressure, temperature and air density. This device is small and lightweight then it can be used on boards of both small aircraft and unmanned flying vehicles.FindingsThis paper provides information about designed ADC's measurements accuracy. Also it informs about possibilities of the presented device uses.Practical implicationsThe lightweight low‐cost ADC can reduce both price and weight of complete control systems different types of flying vehicles are equipped with.Originality/valueThis paper presets original the construction of the ADC equipped with CAN 2B interface and working with CAN Aerospace protocol.

Dynamic temperature model and dynamic temperature compensation of crystal oscillators

In temperature-compensated crystal oscillators (TCXO), the compensating action is commonly estimated as a function of one variable-environmental temperature, At the same time, experimental data show that TCXO frequency stability is also dependent on the dynamics of the temperature process. The greater the temperature variation, the more pronounced Is the loss of temperature compensation. In this paper, the origins of this phenomenon are analyzed, and a method for reducing its effects is presented. A new approach is suggested according to which the compensating action is formed as a function of two variables: the temperature and the rate of its variation. A theoretical basis for this method is given. A functional model of the devices performing the dynamic temperature compensation is suggested. Experimental investigations of a TCXO with a microprocessor-based dynamic temperature compensation system confirmed the possibility of TCXO frequency stability improvement in nonstationary thermal conditions. In a system using an AT cut resonator and a separate Y-cut thermosensor, the application of dynamic temperature compensation resulted in an order of magnitude improvement as compared to conventional digital temperature compensation procedures. Even with dual-mode SC-cut resonators, the application of dynamic temperature compensation is shown to be useful. >

An electronically switched flowmeter and temperature sensor employing a single thermistor probe

The design of an electronically switched flowmeter and temperature sensor employing a single thermistor probe is described. Digital temperature compensation is incorporated in the design. The concept is applicable to geophysical flows; in this case, design criteria for a tidal channel were used. The flowmeter is designed for use in the 0.05 to 0.5 m s4-1 range with a fluid temperature variation of 2 degrees C. A frequency response of 0.25 Hz is obtained.

Digital temperature compensation of a thermistor flowmeter

The temperature compensation of a thermistor flowmeter is accomplished digitally, thus simplifying the compensation problem by replacing required hardware with software. The resistance-temperature curve of the thermistor is a least-squares fit to a logarithmic function whose coefficients are stored in computer memory. Signals representing the temperature of the heated thermistor and the ambient temperature are digitised and converted to temperature values based on the stored resistance-temperature curve. In this case the signals are obtained from a single thermistor switched between the high and low overheat modes. The thermistor temperature T, the ambient temperature Ta, and the electrical power input are used to form the dissipation factor (K=P/(T-Ta)) which calibrates the flowmeter when plotted against velocity. Results from calibration experiments on a thermistor flowmeter designed for use in human coronary arteries are presented to demonstrate the viability of the method.

Evaluation of digital temperature compensation of crystal oscillators

There are two ways to eliminate the effect of temperature on the frequency drift of a crystal oscillator (CO): precision thermostatic control and temperature compensation. Temperature compensation makes it possible to create highly stable, economical, and compact crystal oscillators with fast response. Temperature compensation of a CO consists of controlling frequency as a function of temperature such that the temperature instability of the CO frequency is reduced. Analog and digital methods of temperature compensation are distinguished.