1. Department of Electronics and Computer Science University of Santiago de Compostela, Santiago de Compostela, Spain Email: p.lopez@usc.es
2. Fraunhofer Institute for Integrated Circuits Am Wolfsmantel 33, 91058 Erlangen, Germany Email: johann.hauer@iis.fraunhofer.de
3. Department of Electronics and Computer Science University of Santiago de Compostela, Santiago de Compostela, Spain