Signal Generator Settings
R&S
®
SGT100A
184
User Manual 1176.8674.02 ─ 07
●
Define the absolute maximum input power Pin
max
, the number of subsequent
points, and the normalized values Vin/Vmax,
Δ
V/V,
Δ
Phase [deg] as binary data.
[:SOURce<hw>]:IQ:DPD:SHAPing:NORMalized:DATA
7.6.2.3
Finding Out the Correction Values
If you know the properties of the used power amplifier, you can calculate suitable cor-
rection values.
To explain the principle, we assume that the characteristics of a power amplifier have
been measured and that the left graphic in the following table shows the AM/AM curve
of this amplifier.
Defining correction coefficients for an AM/AM predistortion
(Example)
Resulting AM/AM predistortion function (Example)
a = ideal characteristic; if the amplifier did not distort the signal,
the normalized magnitude would a line
b = measured AM/AM curve; the normalized magnitude varies
as a function of input power
a = ideal characteristic
b = measured AM/AM curve
c = resulting AM/AM predistortion function, i.e. correction values
curve
d = ideal predistorted signal
The required correction coefficient
Δ
Power is the difference between the ideal and the
real normalized amplitude for one particular input power. To compensate for the non-
linearity and the deviation from the ideal line, select a negative correction value (-
Δ
) for
any input power where the real normalized amplitude is greater than the ideal one (1).
Logically, a positive correction value (+
Δ
) compensates for (i.e. boost) an amplitude
that is smaller than the ideal one (2).
Ideally, a signal predistorted with a suitable function (c) and then amplified by the par-
ticular PA would have a linear characteristic (a).
7.6.3 Digital Predistortions AM/AM and AM/PM Settings
You can add digital predistortion to the generated baseband signal and thus compen-
sate an amplitude as well as a phase distortion of the DUT, for example of the tested
power amplifier (PA).
Applying Digital Predistortion
