This thesis reports the description and results of the doctoral research programme in Information Engineering (University of Pisa), carried out in the three years from 2008 to 2010. The doctoral research programme has been originated by the European project ProeTEX aimed at developing a new generation of equipments for the market of emergency operators, like fire-fighters and Civil Protection rescuers.
In this context, the multidisciplinary research group originated by the international cooperation of the research groups led by Prof. Danilo De Rossi (University of Pisa, Italy) as for Bio-engineering and Dr. Domenico Zito (University College Cork and Tyndall National Institute, Cork, Ireland) as for Microelectronics, has focused on the implementation of an innovative ultra-wide-band (UWB) pulse radar sensor fully integrated on a single silicon die for non-invasive and contact-less cardio-pulmonary monitoring within a wearable textile sensor platform. The radar sensor is designed to detect the heart and respiratory rates, which can be transmitted to a personal server that coordinates the entire Wireless Body Area Network (WBAN). Such radar sensor should sense the mechanical activity instead of the electrical activity of the heart. UWB bio-sensing allows low risk preliminary monitoring without discomfort since the radar system permits continuous monitoring without requiring any contact with the skin of the patient unlike the traditional technologies (i.e. ultrasounds).
In detail, the radar transmits a sequence of extremely short electromagnetic pulses towards the heart and, due to the capability of microwaves to penetrate body tissues, detects the heart wall movement by correlating the echoes reflected with local replicas of the transmitted pulses properly delayed (i.e. time of flight).
The specific aim of the doctoral research program has been the design and experimental characterization of the CMOS UWB analog multiplier, which is a crucial circuit in the receiver chain that implements the correlation between the received and amplified echo and the local replica, generated on-chip, of the transmitted pulse.
The fully-differential circuit consists of a p-MOSFET common-gate differential pair as input stage for a wideband impedance matching, a p-MOSFET Gilbert’s quad as multiplier stage, and active loads. The circuit has been designed and fabricated in 90nm CMOS. Given the few works on similar analog circuits having inferior performance with respect to those requested, an innovative circuit solution has been identified. Moreover, a novel time-domain metric has been introduced in order to put in evidence the real behaviour of the system that differs from a traditional mixer commonly analyzed using frequency-domain metrics. This new metric, namely Input-Output Energy Ratio (IOER), aims at the optimization of the multiplier circuit design so that the output voltage corresponding to maximum correlation between two input pulses is maximized.
The experimental characterization and the comparison with the state of the art have shown that the multiplier exhibits one of the best set of performance available in literature.
The novel multiplier has been co-integrated with the other building blocks of the radar. The preliminary experimental characterization of the test-chips carried out by the research group, has demonstrated that the proposed UWB radar sensor works properly. It can detect a reflective target consisting of a half-centimetre-thick board surface (26×26 cm2) covered by aluminium foil, up to a distance of 70 cm. Moreover, it can detect the respiratory rate of a person placed at a distance of 25 cm. This work presents the first implementation, including experimental evidences, of a SoC UWB pulse radar front-end based on a correlation receiver, in 90nm CMOS technology.