Clock and data recovery/Structures and types of CDRs/The (slave) CDR based on a second order PLL
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[edit] The (slave) CDR based on a second order PLL - Fundamental equations
A linear, time-invariant model of the circuit is described here.
The case of a second order loop, fit for a slave CDR function, is presented.
This model is in fact the best for applications where the CDR is used in a regeneration application, to recover a clock and to resend the data stream further, as the introductory example has shown. This is also probably the most common scheme of CDR in the technical literature.
The case of R3 = 0 corresponds to a second order system with just two poles and no zero, and is studied in detail in the next pages.
The most important functions that describe the relations amongst the variables shown in the figure, expressed for the sinusoidal jitter condition, are described in the following three subchapters.
The fourth subchapter that follows gives the equations and the diagram for the time function that describes how this circuit reacts to an abrupt change of phase in the received signal.
