BNC 645 - Manual (Page 24)

24
Figure 3-7
• The default output unit is Vpp, but one may also choose from Vrms
and dBm. But the output unit cannot be set to dBm if the output
termination is set to “high impedance”. In such a case, the unit is
automatically reset to Vpp.
The unit setting is stored in volatile memory. The default unit (Vpp)
will be restored after a power-on cycle or a remote interface reset.
• Offset Voltage limitations: The value of output amplitude is
constrained by the equation below:
Vpp ≤ 2× ( Vmax - |Voffset| )
where Vmax is the maximum peak voltage allowed for the
selected output termination (5 volts for a 50 Ω load or 10 volts for
a high-impedance load).
• Limits with Unit Selection: The output amplitude limits may be
affected by the output units selected. You may encounter this
when the units are Vrms or dBm due to the differences in crest
factor for the various output functions. For instance, if you output
a 5 Vrms square wave (into 50 ohms) and then change it to the
sine wave function, the waveform generator automatically adjust
the output amplitude to 3.536 Vrms, which is the maximum for
sine waves in Vrms.
• Output Termination Limits: When the Output Termination Setting
is changed, the Output Amplitude is automatically adjusted. For
instance, when you change the output termination from 50 ohms
to “high impedance”, your offset voltage doubles, thus it affects
your output amplitude, and when Output Termination has been
changed from “high impedance” to 50 ohms, the offset voltage
decreases by half.
• Arbitrary Waveform Limitations: For arbitrary waveforms, if the
data points do not span the full range of the output DAC
(Digital-to-Analog converter), the maximum amplitude will be