Transition Density Dependent

Subtopics

The PLL algorithm can calculate the recovered clock in two different ways:

  • In one mode, the JTF and OJTF responses are static and independent of transition density.
  • In the other mode, the JTF and OJTF change dynamically with varying transition density and are therefore dependent on transition density.

Select or clear the Transition Density Dependent check box to select whether the PLL is dependent on or independent of transition density.

Transition density specifies how often there are transitions in the signal. For example, clock signals and 10101010... data patterns have a transition density of 100%; 11001100... data patterns, pseudo-random binary sequences (PRBS), and 8B/10B have a transition density of 50%.

Transition density can affect a PLL's phase error and loop bandwidth. See How Transition Density Can Affect Jitter Measurements.

Selecting the Transition Density Dependent PLL mode changes how the 3 dB bandwidth, peaking, and damping factor parameters are interpreted.

  • When Transition Density Dependent is unchecked, the JTF and OJTF responses always directly reflect the specified parameters, independent of the input data pattern.
  • When Transition Density Dependent is checked, the JTF and OJTF responses reflect the specified parameters only when the input data pattern has a transition density of 50%.

If you want to specify these parameters at a different transition density, see Adjusting PLL Specifications for Transition Densities Other Than 50%.

This option does not apply to PAM type signals.