When starting a clock tree design, the design team needs to carefully assess the system requirements and layout. The system’s clocking requirements will determine what type of components to use, their performance levels within the system and its overall network, and will also likely indicate whether or not clock generators can provide signals or if crystals and XOs are needed. Of course, the system may require a mixture of the various timing components. The decisions to be addressed are: selecting a clock generator versus a crystal, XO or VCXO, determining if the system is free-running or synchronous, determining the system’s clock jitter requirements, selecting timing components that meet the system requirements, and finally, estimating the overall clock tree jitter with the selected components and making adjustments if needed.