http://electronics.wisc-online.com/Category.aspx?ID=4
http://www.allaboutcircuits.com/videos/86.html
http://www.falstad.com/circuit/e-index.html
http://tams-www.informatik.uni-hamburg.de/research/software/applets/cmos/cmosdemo.html
http://www.ied.edu.hk/has/phys/de/
http://www.tpub.com/content/neets/14185/