Tektronix WCA200A, User Manual

Page: 182 / 454

Modulation Analysis (Demod Mode)
3- 56
WCA230A & WCA280A User Manual
Performs digital demodulation processing and displays an AM/AM distortion
graph for measuring non-linearity characteristics of a DUT (device under test)
such as an RF amplifier. Figure 3--47 on page 3--57 shows an example.
The main view displays the XY graph of recovered reference amplitude versus
measured signal amplitude and the table of AM/AM coefficients extracted from
curve fitting.
Meas Setup Menu.
The Meas Setup menu for the AM/AM measurement contains
the following controls. For information about the common controls for the
digital modulation analysis, refer to Meas Setup Menu page 3--45.
Linear Signal Region Unit. Selects the unit to set the Linear Signal Region.
H
dB.
Default. Specifies the Linear Signal Region with a value relative to the
maximum power measured in the analysis range.
H
dBm.
Specifies the Linear Signal Region with an absolute power.
Linear Signal Region. Sets a region that should have an ideal AM/AM
characteristic. Generally, signal distortion increases with amplitude. Linear
Signal Region sets the region where the trend is assumed to be linear (see
Figure 3--46). The analysis is performed with this assumption. The region is
indicated by blue oblique lines in the main view.
Range: --100 to 50 dB (the default is --10 dB)
Measured power
Reference power
Linear Signal Region setting
Linear Signal
Region
Figure 3- 46: Setting Linear Signal Region
Maximum Coefficient. Sets the maximum order of the best-fit curve polyno-
mial. The polynomial is expressed as follows (n: Max 15):
f
(
x
)
=
a
0
x
0
+
a
1
x
1
+
a
2
x
2
+
...
+
a
n
x
n
The values of a
n
are shown in the main view (see Figure 3--47 on page 3--57).
AM/AM Measurement