PLL
PLL means phased locked loop. nowadays vast majority of PLLs available in the market today . The charge pump PLL offers many advantages
over the classical voltage phase detector PLL including an infinite pull-in range and zero steady
state phase error. Furthermore, there is already a considerable amount of literature that discusses
features that are specific only to the voltage phase detector in great depth. By not focusing on
the classical voltage phase detector, there is more time to focus on other features of the PLL.
The charge pump PLL allows the use of a passive filter while still retaining the benefits of an
active filter with the voltage phase detector. Passive filters are generally recommended, because
they have the advantages of lower cost and no active devices to add noise. The exception to this
case is when the VCO tuning voltage needs to be higher than the charge pump can supply – in
this case, an active filter is necessary.