R&S SGT100A User Manual page 212

®
R&S SGT100A
and ΔPhase) directly as it is in the look-up table, but you describe the predistortion
function and the R&S SGT derives the correction values out of it.
See
This implementation uses a polynomial with complex coefficients defined as follows:
P
DPD
where:
●
n = "Polynomial Order" ≤ 10
●
x = P
●
a
coordinates.
In Cartesian coordinates system, the coefficients b
The R&S SGT calculates the AM/AM and AM/PM predistortion functions as follows:
●
AM/AM(x) = abs[P
●
AM/PM(x) = tan
A dedicated graphical display visualizes the resulting functions, see
The R&S SGT calculates the correction values (ΔAM/AM and ΔAM/PM functions) as
follows:
●
ΔAM/AM(x) = AM/AM(x) - x = abs[P
●
ΔAM/PM(x) = AM/PM(x) = tan
A dedicated graphical display visualizes the calculated correction functions, see
ure 7-24
File format of the polynomial file
You can store a polynomial function in a file or even define the polynomial coefficients,
store them as a file and load this file into the instrument. The polynomial files are files
with the extension *.dpd_poly.
The file contains an optional header # Rohde & Schwarz - Digital
Predistortion Polynomial Coefficients # a0,b0, a1,b1, a2,b2, ...
and a list of comma-separated coefficient value pairs, stored in Cartesian coordinates.
For values above the selected
a linear ratio of the input to output power.
Example: Polynomial function file content
# Rohde & Schwarz - Digital Predistortion Polynomial Coefficients
# a0,b0, a1,b1, a2,b2, ...
0,0,-0.25,0.2,0.6,-0.3,0.3,0.3,0.5,-0.4
User Manual 1176.8674.02 ─ 07
Chapter 7.6.3.4, "Polynomial Coefficients
(x) = ∑[(a
n
+j*b )*x ],
n n
/P Max
in in
and b are user-defined coefficients, defined as Cartesian (polar) or Cylindrical
n n
(x)]
DPD
-1 {Im[P
DPD
and compare with
Settings",
(x)]/Re[P (x)]}
DPD
(x)] -x
DPD
-1 {Im[P (x)]/Re[P
DPD
Figure 7-23.
Input Range (PEP
in
Signal Generator Settings
Applying Digital Predistortion
on page 193.
are expressed in degrees.
n
Figure
(x)]}
DPD
), the predistortion function assumes
7-23.
Fig-
181