1. Department of Electronics and Information, Milan Polytechinics, Piazza Leonardo da Vinci 32, 20133 Milan, Italy. E-mail: bittanti@elet.polimi.it, sgaratti@elet.polimi.it
2. Institute of Electronics, Information and Telecommunication Engineering, National Research Council, Milan, Italy. E-mail: liberati@elet.polimi.it
3. Department of Bioengineering, Milan Polytechnics, Piazza Leonardo da Vinci 32, 20133 Milan, Italy