Page 166 - Phase-Locked Loops Design, Simulation, and Applications

PLL PERFORMANCE IN THE PRESENCE OF NOISE Ronald E. Best 102

Figure 4.6 Average time T between two succeeding unlocking events plotted as a function of th
av
(SNR) at the output of the PLL. T is normalized to the natural frequency ω of the PLL
L
av
n
1
Note that this result is valid only for linear second-order PLLs. (Adapted from Gardner wit
permission.)
Summary of noise theory. Although the noise theory of the PLL is difficult, for practical
design purposes it’s important to remember some rules of thumb:

■ Stable operation of the PLL is possible if (SNR) is approximately 4.
L
■ (SNR) is calculated from
L

where P = signal power at the reference input
s