Blog post for more info (schematic, etc): http://blog.thelifeofkenneth.com/2012/02/basic-introduction-to-phase-locked.html
I recommend Horowitz "The Art of Electronics" in the beginning: http://www.amazon.com/gp/product/0521370957/ref=as_li_ss_tl?ie=UTF8&tag=theli091-20&linkCode=as2&camp=1789&creative=390957&creativeASIN=0521370957
The control loop theory is weak. I know this already. I'm sorry.