Teledyne LeCroy Eye Doctor II - Manual (Page 30)

Eye Doctor II Software
Clock Recovery
A recovered clock signal is required for Decision Feedback Equalization. For this reason, a clock recovery
dialog is provided inside the equalizer section of Eye Doctor II.
Clock Recovery dialog for DFE Equalization when working in Eye Dr II or SDAII.
When entering the Clock Recovery dialog, the Data or Bit Rate is set to the nominal bit rate set in either
the Signal Input dialog or Equalizer dialog. DFE requires a more precise bit rate than the Emphasis or FFE
sections. Using the Find Rate button Eye Doctor II calculates the bit rate by analyzing the input wave-
form.
The PLL Setup... section of the Clock Recovery dialog contains the controls for setting the type and band-
width of the digital PLL used to produce the clock (EyeDrClk) for DFE. The PLL has a low pass filter
response; it tracks variations in the data rate that occur below a certain frequency, determined by the
PLL bandwidth setting.
Example: A PLL bandwidth of 5 MHz allows the recovered clock to track frequency variations below
approximately half this frequency, thereby removing their effect from jitter and eye pattern meas-
urements. The software PLL used to produce the clock (EyeDrClk) for DFE allows you to choose among
several types of PLL.
The selected PLL is applied to the data stream under test when the PLL On control is checked. The PLL
recovers a reference clock from the data stream which is used by DFE and available as EyeDrClk.
The Deskew control can be adjusted manually or optimized when the DFE is trained. This time plus 1/2 of
a unit interval is the point at which the decision is made for the decision feedback equalizer. It is the same
control as the Deskew control in the DFE dialog.
The Show check box allows the use view the EyeDrClk waveform on the grid display.
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