Source Leveling Using External Leveling - Agilent Technologies AN 1287-6 Application Note

Source leveling using external leveling

Using power-meter calibration for source leveling
works well, but can slow down the measurements
too much for some applications. A faster method of
source leveling is external leveling. External leveling
makes use of an external amplitude modulation
(AM) input, available on some network analyzers.
Adjusting the voltage at the AM input adjusts the
analyzer's source power. By creating a leveling
circuit that is external to the network analyzer,
and adjusting the voltage to the external AM input,
source power can be leveled on a real-time basis.
The external leveling circuit can be implemented
in several ways. One common implementation is to
create a circuit consisting of a detector diode and
an operational amplifier. Changes in the power
measured by the diode are detected by the opera-
tional amplifier circuit. The circuit connected to
the AM input of the analyzer adjusts the source
power by adjusting the voltage at the AM input
(Figure 4).
16
8753E with Option 011
RF out R A B
Power
splitter
Figure 4. This circuit shows a common way to implement
external leveling.
When using either power-meter calibration or
external leveling, keep the source-leveling process
active, just as it will be during the measurement.
Then perform a response calibration as you would
if source leveling was not used.
Loop gain
–
+
+
Ext AM
REF
–
Attenuator
RF filter
and load
50 Ω
DUT
Detector