Timing is an important element in any hardware system design. A clock signal provides the timing reference to synchronize different components in a system to ensure data is accurately transmitted. A clock tree is a simplified way to represent distribution of all the clocks needed in a system. Systems often have several ICs with different clock performance requirements and frequencies needed to drive them; a “clock tree” refers to the multiple clocks required to meet the system’s needs. The complexity of the clock tree and the number of clocking components used depends on the hardware design. A single reference clock is sometimes cascaded and synthesized into many different output clocks. The diagram shown here on the right is an example of a clock tree. The system needs clocks to drive the PCIe sockets, CPU or SoC, Graphics controller and PHYs. To generate all the clocks (or frequencies) needed for the system, the engineer used a Skyworks Solutions clock generator, Si5335, to generate the different frequencies needed – 100 MHz, 50 MHz, 156.25 MHz and 25 MHz. Since multiple copies of each frequency are needed, buffers are used to distribute multiple copies of the same frequencies. The result is a diagram which looks a bit like a sideways tree.