Teledyne LeCroy SDA III-CompleteLinQ - Manual (Page 24)

SDAIII-CompleteLinQ Software
The DVI selection displays the DVI PLL dialog at the far right of the screen and follows the requirements
of the DVI (Digital Video Interactive) and HDMI (High Definition Multimedia Interface) specifications.
These specifications call out a clock recovery function having a single-pole PLL loop response with a cutoff
of 4 MHz.
FB-DIMM
The FB-DIMM selection applies a filter that replicates Fully-buffered DIMM.
USB
The USB selection applies a filter that meets the USB 3.0 SS requirements.
C USTOM
The Custom selection shows the Custom PLL dialog on the far right of the screen and allows you to select
either a first or second order loop response. The first order response allows you to select a pole
frequency that sets the PLL cutoff, and a zero frequency that must be higher than the pole frequency
that limits the stop-band attenuation.
The second order PLL allows you to select the natural frequency and damping factor. The damping factor
determines the transient behavior of the phase locked loop and is variable from 2 to 0.5.
l
A damping factor above 0.707 results in an under-damped response and the PLL is over-corrected
to a sudden change in frequency; however, reacts quicker to the change.
l
A damping factor below 0.707 provides an under-damped response that reacts more slowly to sud-
den changes in frequency; however, does not over-correct.
The default value of 0.707 represents a critically damped response that provides the fastest reaction time
without over-correcting.
The second order PLL with a damping factor of 0.707 is specified in the serial ATA generation II document.
This type of PLL is also very useful for measuring signals with spread-spectrum clocking because it can
accurately track and remove the low-frequency clock spreading while allowing the signal jitter to be meas-
ured. The natural frequency is somewhat lower than the actual 3 dB cutoff frequency given by the equa-
tion:
The quantity is the damping factor, and is the natural frequency. For a damping factor of 0.707,
22 921143 Rev A