Advanced analog cells for low-power/low-voltage sensor interfaces

This thesis has investigated the development of a novel general-purpose multi-sensor sensor interface that performs System on Chip functionalities and is capable of using both external and integrated sensors. This interface is called Sensiplus, born from a collaboration with the start-up Sensichips s.r.l. Considering the low voltage scenario that could be the future for some Sensiplus’ applications, some new low-voltage IPs have been designed and their performances estimated by means of accurate electrical measurements. In the first Chapter of this work, a brief state-of-art of sensor interfaces has been provided, focusing on pros and cons of latest sensor interfaces. A large part of this analysis has been dedicated on chemical sensors. In the second Chapter, the Sensiplus interface is introduced. From a schematic block-view, each block is described, and its functionalities analysed. Thus, for each block, main issues are highlighted, and possible causes explained. In particular, the revised blocks are: Programmable Voltage Reference, 12 bits DAC, Programmable Switch Matrix for 2 and 4 contact measures. The third Chapter is completely dedicated to the Sensiplus’ Bandgap Voltage Reference. After a brief recap on its behaviour, the main issues are investigated. To solve the issues, we re-designed this IP, from the schematic to layout. Finally, a deep experimental characterization has been carried out. In Chapter 4, some new sensing features introduced in the Sensiplus R7 platform are presented and discussed. In Section 4.1, the ability of Sensiplus R7 to measure the chip temperature has been evaluated. Then, in Section 4.2 an innovative IDE, capable of measuring the pH of a liquid solution, was presented and all the required new electronic circuits discussed. In Section 4.3, was investigated how to increase the number of supported external sensors that can be connected to the Sensiplus R7 platform at the same time. Finally, in Section 4.4 a new 12-bits DAC for DAS block was presented, overcoming the issues showed in the previous prototype and discussed in Chapter 2. Chapter 5 can be considered "a window towards the future" for the Sensiplus interface. In particular, a Low Voltage scenario for electrochemical impedance measurement is investigated. Two different Low-Voltage All-MOSFET BVRs are presented: from the idea to the experimental measurements. The first Low Voltage BVR shows an output voltage of 0.462V@VDD=0.9V and a spread of 37mV in the temperature range 0°C, +80°C. The second one presents an output voltage close to 220mV@VDD=0.5V and a TC of 92.8 ppm. The last Chapter is dedicated to a side-activity performed during the Ph.D. program. This is concerning the design and testing of an innovative solid state 3D printed anemometer. It was fabricated with a stereolithography technique. It is capable of measuring the direction and the magnitude of wind speed with a reduce angle error.