1/2/2023 0 Comments Flipclock parameters![]() ![]() Where is short-term jitter a critical factor? In today’s high-speed and wideband systems, jitter is usually in the range of picoseconds or less, or in thousandths of a unit interval (UI), where a UI is a single clock cycle. ![]() There are many types of jitter and units for measuring it, such as time or unit intervals, Table. It can be due to imperfections in the clock source (usually a crystal, but can be a master clock) any associated oscillator, internal noise, external noise, circuit-board crosstalk and EMI and other factors. Jitter is a complicated topic, having many sources and system implications. (Source: Integrated Device Technology, Inc.) (Source: Integrated Device Technology, Inc.) Fig 2: The spectrum of a jitter-free clock in the frequency domain, and a clock with some jitter in that domain. Fig 1: A jitter-free clock as observed in the time domain, and one with a moderate amount of jitter. Again, time and frequency domains are equally valid ways of looking at the same phenomena, and depending on the application and analysis, one perspective may be more revealing than the other. Jitter can be observed and defined in both the time domain ( Figure 1) and the frequency domain ( Figure 2), where it is seen as phase noise. Jitter and phase noise are two of the top-tier parameters. Closely aligned with this is the accuracy of that initial frequency value, given as a percent (such ☐.1%), parts per million (ppm), or an absolute number (5 MHz ± 10 kHz). Also, the numbers are often specified with peak, average, or rms qualifiers, as different applications have different concerns.įor most clock applications, the first number is frequency, of course. Neither is “more correct”, as they are really two equally legitimate perspectives of the same phenomena, but it is a matter of context and ease of associating the parameter value with the observation and its consequences. It is also characterized by change in specifications due to temperature variations, aging, and mechanical considerations such as vibration and shock.īoth time domain and frequency domain numbers are used. The performance of a clock function, which includes the crystal and associated circuitry, is defined by parameters which are measured over both the short term and long term. ![]()
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