Now that we have gone over the various functions of clocking devices, we will look at the common parameters of a clock to help determine which solution will best meet the needs of your system. It is important to note that a specific system will require a unique combination of the above parameters. The first characteristic to determine the appropriate clocking solution will be the signaling level that the system requires. A signaling level is either single-ended or differential. The common types of single-ended signals are LVCMOS, TTL, and LVTTL and they support up to roughly 250 MHz. The common types of differential signals are LVDS, LVPECL, CML PCI Express, SSTL, HSTL and they can support up to 10+ GHz. The signaling level will be defined by the type of system and application needing the clock. For example, if you are choosing a clocking device to support a communications basestation you would be using a differential signal that supports higher frequencies such as LVDS or LVPECL. The second characteristic used to determine the appropriate solution is the required system performance. Common performance metrics are Jitter, Propagation Delay, and Output Skew. We will go into more detail on each of these in the following slides. Other factors to consider in selecting a clocking solution will be number of outputs needed, number of frequencies, the input voltage and frequency, and the required output frequencies.