**Acknowledgements**

This work has been supported by the European FEDER fund and the Spanish Ministry of Science and Innovation under Grant no. AP2006‐03170 and TEC2008‐04501 and TEC2011‐ 25017 projects. It has also received funding to support competitive research groups from the Balearic Government (2011–2013), financed jointly by FEDER fund.

In addition, I want to sincerely thank all the members of the Electronics Systems Group (GSE‐ UIB) of the University of the Balearic Islands who have contributed to this research.
