User`s guide

106 Agilent X-Series Signal Generators User’s Guide
Optimizing Performance
Using Internal Channel Correction (N5172B/82B Only)
Using Internal Channel Correction (N5172B/82B Only)
NOTE There is an internal calibration routine ( Factory Calibration) that collects correction data
for both the baseband and RF magnitude and phase errors over the entire RF frequency and
power level range on any unit with options 653, 655, 656, and 657. The internal channel
correction cannot be turned on until after the Enhanced Factory Calibration has been
executed once. See “Perform Enhanced Factory Calibration” on page 109.
The internal channel correction feature flattens the system magnitude and phase response across the
maximum bandwidth supported by the instrument (up to 160 MHz BW, depending on the option).
This performance improvement is available at any arbitrary center frequency or amplitude level.
Correction filter generation and application is performed internally. The correction filtering occurs in
real time and is applied to live data.
There are two correction types: factory and user. The Factory Calibration optimizes the performance
at the front panel RF output connector into a precision 50 ohm load. The User Calibration can
extend this performance to a new calibration reference plane and deliver the highest signal quality to
the user’s DUT.
This feature also minimizes unwanted baseband images by flattening (and matching) the magnitude
and phase response of the I and Q channels from the signal DACs to the IQ modulator.
This calibration should be run when the ambient temperature has varied by at least ±5 degrees
Celsius from the ambient temperature at which the previous calibration was run.
When this feature is off, the box will behave as it always has. When this feature is on, the internal
I/Q path is active, the I/Q Correction Optimized Path is RF Output, and the frequency is changed by
more than 1 kHz, the firmware will calculate a channel correction filter. For List/Sweep, the
calculation will be done prior to the first sweep using the specified frequencies when either
waveform sweep is active or the baseband is on and the instrument is optimized for the internal
path. This calculation will cache corrections for up to the maximum number of cache points (256).
For list/sweep, the sweep will pause and recalculate the correction caches before running again.
CAUTION In the case of arbitrary frequency switching, once the correction cache is full (256
unique frequency points), the oldest frequency corrections will be forgotten as new
frequencies are selected.
Whenever I/Q Timing Skew, I/Q Delay, Quadrature Angle Adjustment, or the Int
Equalization Filter is adjusted, all caches are forgotten.
Additional characteristics of the internal channel correction:
• When the internal channel correction is on, arbitrary frequency switching while the baseband is
on will take up to an additional 290 ms (72 ms typical) the first time that frequency is specified.
After the first time that a frequency is selected, switching to that frequency again takes an
additional 1 ms.
• If a frequency sweep is activated, then the calculation and caching will occur up front for the
first 256 unique frequencies, and all additional unique frequencies will have the characteristics of
arbitrary frequency switching.
• If the I/Q Correction Optimized Path softkey is set to Ext I/Q, then only the baseband corrections
will be applied and the frequency switching will be unaffected.