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Characterizing phase-locked-loop signal transition behaviors of Microphonic/Phase-hits Application Note Digital communication systems often have unique carrier synchronization and syn- Introduction thesizer requirements such as rapid carrier acquisition/lock, and stable operation in demanding environments. The performance of these requirements is affected by not only oscillator characteristics themselves but also the design of phase-locked loop cir- cuits interacting with unwanted stimulus such as microphonics. This paper discusses how Agilent's Signal Source Analyzer helps you to identify unwanted phase-locked loop transition "phase-hits", and achieve easy, comprehensive and accurate phase-locked loop characterization in both linear and nonlinear regions. 2 Characterizing PLL Linear Starting with test parameters in characterizing phase locked loop linear and non-linear behaviors; there are three different stages of test usage, component evaluation, oscil- and Nonlinear Behaviors lator/phase-locked-loop circuit design, and verification/test at operating conditions. The PLL controls the phase of the output signal to be N times the phase of the refer- ence as shown in figure 1. Similarly, the frequency of the output signal is then N times the reference frequency. Like all linear feedback control systems, PLLs have dynamic behavior characteristics. The linear behavior described by the transfer function method is useful to analyze loop operation in the vicinity of lock. Non-linear effects dominate the behavior of the PLL in unlocked conditions such as when the frequency divider ratio is changed to switch frequencies over a large range. Component Oscillator/PLL Circuit Verification/Test Evaluation Design at Operating Conditions ` Reference Source ` Loop Filter (PLL Response) ` Microphonic ` Phase Noise ` Phase Noise ` RF Transient ` Phase-hits ` VCO ` Phase Noise ` Spurs ` AM Noise ` Harmonics ` Tuning Sensitivity Figure 1. Phase locked loop test parameters and challenges The building blocks common to most phase locked loops are