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R&S®SGT100A
Signal Generator Settings
Applying Digital Predestortion
File format of the correction table file
The correction table files are files with predefined extension and simple file format, see
table 7-11.
Table 7-11: Shaping table files: format and extensions
Predistortion model
File extension
Header (optional)
AM/AM
*.dpd_magn
# Rohde & Schwarz - Digital AM/AM
Predistortion
Table Pin[dBm],deltaPower[dB]
AM/PM
*.dpd_phase
# Rohde & Schwarz - Digital AM/PM
Predistortion
Table Pin[dBm],deltaPhase[deg]x
The header is optional. The file content is a list of up to 4000 comma separated value
pairs, describing the delta values for amplitude or phase related to the absolute input
power Pin; a new line indicator separates the pairs.
For values above the selected Input Range (PEPin), the predistortion function assumes
a linear ratio of the input to output power.
Example: Shaping table file content (*.dpd_magn file)
# Rohde & Schwarz - Digital AM/AM Predistortion Table
Pin[dBm],deltaPower[dBm]
-30,0.5
3,-0.01
Polynomial function
The polynomial function is an analytical method to describe a predistortion function.
When using the polynomial function, you do not define the correction values (ΔPower
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 chapter 7.6.3.4, "Polynomial Coefficients Setting", on page 168.
This implementation uses a polynomial with complex coefficients defined as follows:
PDPD(x) = ∑[(an+j*bn)*xn],
where:
●
n = "Polynomial Order" ≤ 10
●
x = Pin/PinMax
●
an and bn are user-defined coefficients, defined as Cartesian (polar) or Cylindrical
coordinates.
In Cartesian coordinates system, the coefficients bn are expressed in degrees.
The R&S SGT calculates the AM/AM and AM/PM predistortion functions as follows:
●
AM/AM(x) = abs[PDPD(x)]
●
AM/PM(x) = tan-1{Im[PDPD(x)]/Re[PDPD(x)]}
A dedicated graphical display visualizes the resulting functions, see figure 7-22.
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