A sensor interface device is essential for sensor data collection of industrial wireless sensor networks (WSN) in IoT environments. However, the current connect number, sampling rate, and signal types of sensors are generally restricted by the device. Meanwhile, in the Internet of Things (IoT) environment, each sensor connected to the device is required to write complicated and cumbersome data collection program code. In this paper, to solve these problems, a new method is proposed to design a reconfigurable smart sensor interface for industrial WSN in IoT environment, in which complex programmable logic device (CPLD) is adopted as the core controller. Thus, it can read data in parallel and in real time with high speed on multiple different sensor data. The standard of IEEE1451.2 intelligent sensor interface specification is adopted for this design. It comprehensively stipulates the smart sensor hardware and software design framework and relevant interface protocol to realize the intelligent acquisition for common sensors. A new solution is provided for the traditional sensor data acquisitions. The device is combined with the newest CPLD programmable technology and the standard of IEEE1451.2 intelligent sensor specification. Performance of the proposed system is verified and good effects are achieved in practical application of IoT to water environment monitoring.

A Reconfigurable Smart Sensor Interface for Industrial WSN in IoT Environment

A novel fully-analog lock-in amplifier for the accurate measurements of low quantities of gas in sensor applications is here presented. When compared with commercial lock-in and other solutions available in the literature, the proposed system implements an automatic alignment of the relative phase between input and reference signals, both at power-on and for any variation of the input signal phase and amplitude during the working time, so allowing to detect, accurately and in a continuous way, the mean value of the input signal coming from sensors (typically buried into noise). The circuit has been optimized to operate at a specified reference frequency, in particular 77 Hz; this value is suitable for gas sensor applications, since it avoids also any kind of interferences at 50 Hz net frequency and its harmonics. Experimental results have confirmed the correct functionality of the system, also tested for both carbon monoxide (CO) and ethylene glycol detections. With respect to the simpler resistive gas sensor interface, implemented by a resistive voltage divider, the improvement experimentally given by the proposed automatic lock-in amplifier, in terms of resolution, has been of a factor of about 100 for the CO and 230 for the ethylene glycol measurements, so allowing a theoretical gas detection in the order of ppb.

A Fully-Analog Lock-In Amplifier With Automatic Phase Alignment for Accurate Measurements of ppb Gas Concentrations

A compact, low power interface for capacitive sensors, is described. The output signal is a pulse width modulated (PWM) signal, where the pulse duration is linearly proportional to the sensor differential capacitance. The original conversion approach consists in stimulating the sensor capacitor with a triangular-like voltage waveform in order to obtain a square-like current waveform, which is subsequently demodulated and integrated over a clock period. The charge obtained in this way is then converted into the output pulse duration by an approach that includes an intrinsic tunable low pass function. The main non idealities are thoroughly investigated in order to provide useful design indications and evaluate the actual potentialities of the proposed circuit. The theoretical predictions are compared with experimental results obtained with a prototype, designed and fabricated using 0.32 μm CMOS devices from the BCD6s process of STMicroelectroncs. The prototype occupies a total area of 1025× 515 mm2 and is marked by a power consuption of 84 μW. The input capacitance range is 0-256 fF, with a resolution of 0.8 fF and a temperature sensitivity of 300 ppm/°C.

A Low-Power Interface for Capacitive Sensors With PWM Output and Intrinsic Low Pass Characteristic

In this paper, we propose novel fully analog uncalibrated readout circuits for wide-range capacitance estimation. The working principle is based on a modified De-Sauty ac bridge configuration where two capacitances and two resistances are employed. Through the use of a voltage controlled resistor and of a suitable feedback loop, an accurate estimation over a wide range of the sensor capacitance variation is possible, also without the knowledge of the other bridge component values. The first two proposed solutions are able to estimate, experimentally, ~1.5 decades (optimized range: [25-840 nF]) and more than 3 decades [900 pF-1.1 μF] of capacitive variations, respectively, ensuring, continuously, the bridge equilibrium condition; the third interface allows the evaluation of the sensor capacitance also outside this condition, increasing the capacitive variation decades to more than 4 [81 pF-1.1 μF]. The proposed topologies have been also modified to detect the capacitive sensor parasitic resistance. In this case, experimental results on PCB have demonstrated the capability to simultaneously estimate ~ 1.7 capacitive [2-100 nF] and 1.5 resistive variation decades [33 kΩ-1.2 MΩ]. Finally, a suitable optimization of the operating range of the first proposed solution, obtained through a proper passive components sizing, has been performed with the aim to employ the commercial humidity sensor HCH-1000 in a high accuracy (11.4 bits) RH% detection.

Novel Modified De-Sauty Autobalancing Bridge-Based Analog Interfaces for Wide-Range Capacitive Sensor Applications

We report the design of a two-degree-of-freedom microelectromechanical systems nanopositioner for on-chip atomic force microscopy (AFM). The device is fabricated using a silicon-on-insulator-based process to function as the scanning stage of a miniaturized AFM. It is a highly resonant system with its lateral resonance frequency at ${\sim}{\rm 850}~{\rm Hz}$ . The incorporated electrostatic actuators achieve a travel range of 16 $\mu{\rm m}$ in each direction. Lateral displacements of the scan table are measured using a pair of electrothermal position sensors. These sensors are used, together with a positive position feedback controller, in a feedback loop, to damp the highly resonant dynamics of the stage. The feedback controlled nanopositioner is used, successfully, to generate high-quality AFM images at scan rates as fast as 100 Hz. $\hfill[2013\hbox{--}0063]$

A Feedback Controlled MEMS Nanopositioner for On-Chip High-Speed AFM

We present a low-power, low complexity, and wide-dynamic-range universal sensor readout circuit that converts the sensing capacitance or resistance changes to digital duty cycles based on pulsewidth modulation (PWM). The readout circuit utilizes a RC-controlled pulse generator and produces pulse signals whose duration width is proportional to the charging time. The circuit is comprised of complementary CMOS circuit that enables the proposed design to consume significantly less power compared with traditional designs. The proposed design is universal and can be configured according to the application requirements. The sensor interface chip is designed and fabricated in TSMC 0.13-μm CMOS technology. The proposed interface achieves 13-aF to 10.7-nF capacitance and 5-Ω to 11.5-MΩ resistance sensing ranges with 60- μW power consumption. The functionality of the full circuit, including circuit analysis, noise analysis and measurement results, has been demonstrated.

A Low-Power, Wide-Dynamic-Range Semi-Digital Universal Sensor Readout Circuit Using Pulsewidth Modulation

The proposed sensor interface minimizes the optical detection system size while maximizing its overall efficiency (both power and sensitivity) of a multi-stage microfluidic cell sorter system. The proposed ΣΔ sensor interface achieves at least one order of magnitude higher sensitivity while consuming less power (2mW) as compared to the traditional operational amplifier based transimpedance amplifier sensor interface. The proposed ΣΔ sensor interface will be used to complete a full implementation of the developed multi-stage microfluidic system that would prove to be a great advancement in microfluidic cell sorting technology.

Jong-Kee Kwon

Papers

A Low-Power, Wide-Dynamic-Range Semi-Digital Universal Sensor Readout Circuit Using Pulsewidth Modulation

Low-noise wide dynamic range readout circuit for multi-stage microfluidic cell sorting systems