The first step to beating the jitter bug is to know your enemy.
What causes jitter?
There are several causes of jitter. Some of them are as follows:
- System phenomena, such as crosstalk from radiated or conducted signals, dispersion effects, and impedance mismatches.
- Data-dependent phenomena, due to the pattern of data in the bitstream data. This can result in inter-symbol interference, duty-cycle distortion, and pseudorandom periodicity in the bitstream.
- Random-noise phenomena, caused by thermal effects, noise associated with electron flow in conductors, shot noise caused by electron and hole noise in semiconductors, or pink noise spectrally related to the inverse of the clock frequency.
Random versus deterministic
Jitter sources are often categorised as ‘bounded’ or ‘unbounded’.
Bounded jitter sources reach maximum and minimum phase deviations within an identifiable time interval. Bounded jitter is due to systematic and data-dependent phenomena. Unbounded jitter sources are random, and can (in theory) have infinite amplitude.
The total jitter on a signal, defined as its phase error, is the sum of the deterministic and random jitter affecting it.
The deterministic jitter component is defined by adding the maximum phase advance and phase delay it produces, while the random jitter is the sum of all the random noise sources affecting the signal.