The MAX9450, MAX9451, and MAX9452 are high-precision clock generators with an integrated VCXO, the same PLL core, and three different outputs: LVPECL, HSTL, LVDS. The MAX945x clock generators have four main features: integrated VCXO, wide operating-frequency range, wide PLL frequency divider with very fine granularity, and a function-rich input reference monitor. In this application note, we explain how to select the external crystal and choose the external loop-filter components. The performance measurements for tuning range, jitter, and phase noise with various crystals are discussed.