Book excerpt: Phase Locked Loops (PLLs) are electronic circuits used for frequency control. Anything using radio waves, from simple radios and cell phones to sophisticated military communications gear uses PLLs.The communications industry’s big move into wireless in the past two years has made this mature topic red hot again. The fifth edition of this classic circuit reference comes complete with extremely valuable PLL design software written by Dr. Best. The software alone is worth many times the price of the book. The new edition also includes new chapters on frequency synthesis, CAD for PLLs, mixed-signal PLLs, and a completely new collection of sample communications applications.