Agilent Technologies N4906B Serial BERT User Manual page 57

Input and Output Ports
Agilent N4906B Serial BERT, User's Guide, October 2005
Terms:
• ECL
Emitter Coupled Logic
• SCFL
Source Coupled FET Logic
• LVPECL
Low Voltage Positive Emitter Coupled Logic (PECL Lite)
• LVDS
Low Voltage Differential Signaling
• CML
Current Mode Logic
Why Incorrect Terminations Could Damage Your Device
Choosing wrong terminations may cause your device to output voltage
levels that are not as expected. It may also cause excessive current or
current flow in the wrong direction, which can damage your device.
Note that an internal protection algorithm becomes active if both the
termination voltage is wrongly adjusted and the termination voltage is
below +1.5 V. The protection algorithm sets the output voltages to safe
levels:
• V = termination voltage +1 V
high
• V = termination voltage +0.9 V
low
• termination voltage remains unchanged
AC Coupling and Bias Tees
The pattern generator's outputs are normally DC-coupled; even when
AC termination is selected. For this reason, extreme caution must be
taken when connecting your instrument to a device or test setup.
The diagram below shows a device that is AC coupled. Notice that the
capacitor is part of the test setup.
Setting up the Pattern Generator
57