Agilent Technologies N4906B Serial BERT User Manual page 55

Input and Output Ports
Changing the Amplitude
Changing the Output Levels
Voltage Level Restrictions
Agilent N4906B Serial BERT, User's Guide, October 2005
• V is the amplitude of the signal.
ampt
When adjusting the output levels, it is important to understand the
concept of how the Serial BERT handles voltages.
Typically, during tests, when you adjust the amplitude, you want to
keep the offset constant. This keeps the ideal sampling point within
the eye. The Serial BERT handles this by keeping V
V is changed.
ampt
On the other hand, you may want to adjust the output voltage level
without changing the amplitude. The Serial BERT handles this by
keeping V
The Serial BERT cannot generate a signal that has voltage levels out of
range. If you try to enter a value for one parameter that would put
another parameter out of limits, the Serial BERT rejects the change.
This could happen, for example, if V
you try to lower either of V
Understanding Delay and Crossover
The Serial BERT provides the possibility of modifying the output data
signal by varying the signal's delay to the clock signal, and the signal's
crossover.
Delay The exact time delay through a test setup can vary. The delay function
allows you to compensate for this by adjusting the frequency reference
for the data outputs. This varies the phase relationship of the data and
clock outputs (causes the data pulse to have a certain time delay after
the clock pulse). The higher the delay, the greater the time difference
between the clock signal and the data signal.
Data Out
Clock Out
Crossover Crossover is the voltage level where the overlapped rising and falling
edges of the logic levels intersect. This adjustment varies the widths of
the logic highs and lows.
constant when either V
ampt
or V
hi
Delay
Setting up the Pattern Generator
constant when
of
, V , or V is changed.
of hi lo
is already at the minimum, and
lo
, or increase V .
of ampt
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