Teledyne LeCroy SDA II - Manual (Page 13)

Operator's Manual
Clock Recovery
Set Up Clock Recovery
An accurate reference clock is central to any jitter measurement, including all the measurements per-
formed by SDAIII-CompleteLinQ. The recovered clock is defined by the times at which the specified signal
(either data or reference clock) crosses the specified threshold. Starting with zero, the clock edges are
computed at specific time intervals relative to each other. A 2.5 GHz clock, for example, will have edges
separated in time by 400 ps.
On the Serial Data Analysis II dialog, touch the Setup Clock Recovery button to access the Clock Recov-
ery dialog.
Data or Bit Rate section - Lets you define a custom expected bit rate, or you can click the Find Rate Now
button to automatically find the bit rate from the signal. If you do neither, this field remains set to the
standard's nominal bit rate. For more information, see
Bit Rate .
Reference Clock section - Enables positioning of the clock edges relative to the data signal. It shifts the
clock signal relative to the data signal. For convenience, it duplicates controls found elsewhere: the Use
Explicit Clock Ref checkbox (serving the same function as the multiplexer switch on the SDAII dialog) and
Multiplier field (also found on the Ref. Clock dialog). For more information, see
Reference Clock .
PLL Setup... section - Sets the type and bandwidth of the digital PLL used in SDAII measurements. The
PLL bandwidth limits the response of the recovered clock to high rate variations in the data rate. For
example,depending on the type of PLL, a PLL bandwidth of 5 MHz will allow the recovered clock to track
frequency variations below approximately half this rate, thereby removing their effect from jitter and eye
pattern measurements. Configure this section to match the behavior of the receiver's PLL.
Bit Rate
The Data or Bit Rate section of the Clock Recovery dialog lets you define a custom expected bit rate or
find the bit rate from the signal.
Reference Clock
The Reference Clocksection on the Clock Recovery dialog allows you to shift the clock edges relative to
the data signal.
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