Interface Circuits for Sensors and Actuators

Experimental measurements showed that the worst-case measurement for the capacitor pair matching is around 0.98% error at 500fF. This value is compliant to the feasibility of A/D converters for sensor readout with resolution better than 10 bits. It is clear from the results that matching performance is comparable to previous technologies, making the 28nm technology eligible for analog signal processing in front-end circuits for physical experiments and related data converters. Samples have been sent to irradiation facility to be exposed to different radiation doses in order to be re-measured and compared in terms of matching and absolute capacitance values with respect to the measurements done before. Based on the results obtained on the basic devices in 28nm technology, we designed a 14-bit 1MS/s extended range incremental A/D converter composed by the cascade of two resettable second-order sigma-delta modulators. The system is designed for reading out detector arrays in particle physics experiments. The two stages, ideally targeting 9 and 6 bits, respectively, are both based on a cascade of integrators with feed-forward (CIFF) architecture to maximize linearity. If necessary, they can work in pipeline to minimize conversion time. When the conversion of each sample by the two stages is completed, a digital recombination filter produces the overall ADC output word with the required resolution (ENOB) of at least 13 bits and a throughput of 1MS/s at the very low over sampling ratio (OSR) of 16. Each stage, implemented with the switched capacitor technique, consists of two integrators followed by a multi-bit quantizer and a capacitive DAC for the feedback. At the start of each conversion cycle, both analog integrators and the digital filter memory elements are reset. The ADC has been sent for fabrication in 28nm technology. Driving circuit for the piezoelectric actuators in ultrasonic washing machines The third project deals with the design of the driving circuit for the piezoelectric actuators in ultrasonic washing machines. The object of this project concerns the study and design of a driving and control system for an ultrasonic cleaning machine, or more commonly called ultrasonic washing machine. These devices are used in several industrial applications. Ultrasonic washing machines consist of a tank filled with a detergent solvent, an electronic interface circuit and one or more piezoelectric transducers, which are mechanically connected to the tank and electrically to the driving circuit. The driving system is connected from the AC mains and consists of three cascaded stages: a rectifier followed by a boost converter, to regulate the power factor and produce an intermediate DC voltage; a buck converter, to adjust the amplitude of the supply voltage for the piezoelectric transducers; an inverter, to drive the actuators with a square wave at their resonance frequency between 30kHz and 40kHz. A flyback converter has also been designed for generating the auxiliary power supply voltage for all the integrated components in the system. A control system based on an Arduino microcontroller has been developed to adjust the frequency of the square wave to the resonance frequency of the transducer, control the output voltage of the buck converter and read data from a current sensor. The system is designed and implemented on a PCB board of 10cm×15cm. The system has been tested on machined with two different tank sizes.

The research activity described in this Thesis is the result of three different projects, all dealing with interface circuits for sensors and actuators. 1) Capacitive Humidity sensor with temperature controller and heater integrated in CMOS technology The first project deals with the design of the integrated interface circuit for accurately controlling the temperature of a CMOS capacitive humidity sensor, with the final goal of allowing self-dignostics and self-calibration of the sensor. The humidity sensor used is equipped with an integrated resistor and a temperature sensor which allow changing and measuring the actual sensor temperature. This activity concentrated initially on the characterization of the humidity sensor provided by Texas Instruments, with the goal of determining the features and the behavior of the device and identifying the specifications of the integrated interface circuit. A measurement setup based on LabView has been developed to allow controlling the temperature of the sensor with an accuracy of 0.005˚C and measuring both the relative humidity and the temperature. Based on the sensor measurement results we developed a model of the humidity sensor with built-in heater and thermometer in the Cadence framework, to allow the simulation of the complete system. In this sensor model, all the dynamic effects of the heater and relative humidity variation have been considered, to guarantee proper design of the temperature controller integrated circuit. The temperature controller is designed in CMOS technology; it allows a precise adjustment of the temperature with an accuracy better than 0.1˚C. The circuit is based on an analog control loop with PWM modulator. The circuit has been fabricated using a 0.35µm CMOS technology. 2) Scaltech28 (test structures in CMOS 28nm) The second project deals with the design of test structures in CMOS 28nm technology, to evaluate it potential for the implementation of sensor interface circuits in future high-energy physics experiments. This work has been carried out in the frame of project, SCALTECH28, which continues the tradition of other similar studies carried out in previous technology generations for achieving optimal results in IC design for various detectors. This investigation within the selected 28nm technology had to address basic analysis on the single MOS devices (n-MOS and p-MOS), on passive elements like resistors and capacitors, and finally on basic circuits and system building blocks, among the most critical in the sensor interface circuits for different physics experiments. The main purpose of the work is to investigate the performance of the 28nm technology in terms of signal processing quality, power consumption, and radiation hardness with respect to previous technological generations. An additional target is to experimentally evaluate radiation damage effects on single devices and on full circuits to develop rad-models for simulations. A test chip including elementary device arrays and dedicated read-out circuits has been developed and fully characterized. In particular, a capacitance to frequency converter has been integrated to measure the matching between different capacitors of a programmable array.