Didn't mean to sound harsh Gaston. If you'd wanted to create a general discussion just say so in the original post. I'm all for open discussion of just about anything, but a single simple question isn't a discussion =)
That's my biggest problem with a lot of posts in the forums here, it's difficult to tell the difference between someone wanting to discuss a particular type of circuit or design generally and someone that just wants a quick 'do my homework asignment' question asked when the threads are so completly lacking any information or basis for the question that there's no point to base a discussion from.
A discussion starts with a question, a point of view and maybe a little background in the application or reason for asking the question.