Acquisition

Abstract

The treatment given so far has assumed that the loop is either in lock or close to its stable locked state where the phase error is within the usual phase detector operating range — thus allowing accurate analysis by linear methods. However, there are many occasions when the fed-back VCO frequency is very different to the input frequency and so the loop is far from its stable locked condition; for example, when the loop is initially switched on or as a result of a power supply transient. The process of attaining lock is called acquisition, which is a complex subject requiring non-linear analysis and/or simulation, and is of great importance in many PLL circuits.