Phase-Lock Basics
Chapter One
INTRODUCTION
1.1 WHAT IS A PHASE-LOCKED LOOP (PLL)?
A phase-locked loop is a circuit that synchronizes the signal from an oscillator with a
second input signal, called the reference, so that they operate at the same frequency.
The synchronized oscillator is commonly a voltage-controlled oscillator (VCO), so
we will usually use these terms interchangeably. The loop synchronizes the VCO to
the reference by comparing their phases and controlling the VCO in a manner that
tends to maintain a constant phase relationship between the two. In some types of
phase-locked loops (PLLs) this phase relationship is held constant. In other types it
is allowed to vary somewhat. But the frequency is always synchronized-otherwise
the loop is said to be "out of lock."
1.2 WHY USE A PHASE-LOCKED LOOP?
Phase-locked loops are often used because they provide filtering to the phas ... read full excerpt from Phase-Lock Basics ebook
