Jitter Fundamentals: Sources, Types, and Characteristics

As this application note explains, understanding the type of jitter, its component characteristics, and measurement vantage points can help engineers identify its causes and diminish its effects on circuits and products.

Introduction

Jitter refers to how early or late a signal transition is compared with the time it should transition. This applies whether the time reference comes from the sampled data or an outside source. Transmission errors can occur when jitter causes a signal to be on the “wrong side” of the transition threshold at the sampling point. Therefore, causing the receiving circuit to interpret that bit differently than the transmitter intended (see Figure 1).

Table of Content

• Sources of Jitter
  • System  phenomena
  • Data-dependent phenomena
  • Random noise phenomena
  • Bounded and unbounded jitter
• Jitter Eye Diagram
• Other ways to View Jitter
  • The histogram
  • The bathtub plot
  • Frequency-domain jitter vantage points
• Appendix
• Conclusion
• Related Information

Sources of Jitter

Jitter on a signal will exhibit different characteristics depending on its causes. Thus, categorizing the sources of jitter is important. The primary phenomena that cause jitter are as follows:

System phenomena

These are effects on a signal that result from it being a digital system in an analog environment. Examples of these system-related sources include the following:

• cross talk from radiated or conducted signals
• dispersion effects
• impedance mismatch

Data-dependent phenomena

These are patterns or other characteristics of the transferred data that affect the net jitter arriving in the receiver. Data-dependent jitter sources include the following:

• intersymbol interference
• duty-cycle distortion
• pseudorandom, bit-sequence periodicity

Random noise phenomena

Some jitter phenomena randomly introduce noise in a system. These sources include the following:

• thermal noise, or kTB noise, which is associated with electron flow in conductors and increases with bandwidth, temperature, and noise resistance
• shot noise, which is electron and hole noise in semiconductors in which bias current and measurement bandwidth govern the magnitude
• “pink” noise, which is the noise that is spectrally related to 1/f

These phenomena occur in all semiconductors and components. You will encounter them in phase-locked-loop designs, oscillator topologies and designs, and crystal performance.