Temperature compensated sensor system for high temperature applications in rugged environment
Date of Issue2016
School of Electrical and Electronic Engineering
Institute of Microelectronics, A*STAR
Sensor systems operating over wide temperature ranges are found in many applications such as the wireless sensor nodes, food/chemical analysis and automotive electronics. Silicon technologies have been employed in these areas to help reduce product cost and system volume. However, temperature dependences of both sensors and silicon circuits limit sensing accuracies and even fault on measurements in harsh environments. Such limitations have led researchers to identify new sensor technologies and also interface circuits that can operate and survive in high temperature and high pressure environment while still achieving fine accuracies. Progress in these technologies can very well change the practice of using bulky sensors for sensing automotive engines, industrial gas turbines, aircrafts and well-bore systems, such as the geothermal and oil and gas explorations. In the design of the abovementioned sensor systems, the temperature effects of the sensor devices, the clock reference, and interfacing circuits have significant influence on the sensing accuracies. Such temperature effects are widely found in the reference circuitries, the sensor devices, the readout circuits, etc. Thus, suitable temperature compensation techniques must be applied before the circuits can be used in rugged environments. The sensing accuracy and temperature coefficient are the two key factors for evaluating the efficiency of the temperature compensation techniques. Moreover, the stability of a circuit is another important factor to ensure system survival under various conditions. Consequently, the technique to minimize the temperature coefficient of the sensor is explored through device physics—a pressure sensor device based on acoustic wave microelectromechanical technology that depends on the temperature characteristics of both the Rayleigh wave and the Lamb wave is proposed in this research. An accurate model of the Lamb wave resonator is also developed to allow circuit simulations. An adaptive technique deployed in the resonator oscillator has helped provide stable oscillations to the different resonators, whereby different resonant sensors can use the same oscillator chip. The proposed method has greatly reduced the number of circuit designs and fabrication cycles since a traditional oscillator circuit is only suitable for resonators of the same features. A CMOS dual-mode oscillator using cascaded tuned-amplifier technique has been developed in this research, which presents superior stability. A constant biased varactor technique is proposed to compensate the frequency drift of a LC oscillator by directly nullifying the temperature coefficients of the LC-tank. The compensated temperature coefficient of the LC oscillator, implemented in standard 0.18-μm CMOS technology, outperformed the state-of-the-arts by tens of times. A combination of both the biased varactor temperature nullifying technique and the temperature coherent quantization technique enable the capacitive sensor readout to resist the temperature effects to enhance the accuracies. The proposed works will certainly add value to the silicon technologies in sensor applications across wide temperature ranges.