Non-Linear Pre-Distorter Functions - Promax MO-180 Manual De Usuario

USER'S MANUAL MO-180
Level changes are applied immediately to the RF output, to allow smooth and
easy adjustment of RF output conditions. Pressing the encoder or MENU key exits this
function.
Fine Adjust
Select this function to program the RF output reference level. For a correct
reference, adjust the output attenuation to 0 dB, before the fine adjustment.
Changes are also applied in real time. Turning the knob clockwise increases the
output level. Turn it counter-clockwise decreases the level.
The displayed characters are integers. The range goes from a maximum
attenuation of —31 to a minimum attenuation of +31 (i.e. 0 to 63 attenuation steps).
To exit this function, press the MENU or encoder keys.

4.9.1 Non-Linear Pre-Distorter functions

NLPD Mode
The Non-Linear Pre-Distortion (NLPD) block is enabled when this entry is set to
ON.
The NLPD block uses a set of 2 to 16 points to linearly approximate the
complex gain curve that is used to counter the AM/AM and AM/PM characteristics of an
RF power amplifier. The AM/AM curve defines the amplitude distortion that the
amplifier introduces as a function of its input power. The AM/PM curve defines the
phase distortion that the amplifier causes as a function of the input power.
The complex correction gain for the n-th point can be expressed as:
with n = 0...15. The amplitude of g
Figure 3 shows an example of how to obtain these complex linearising gains.
On the x-axis we have the power at the input to the RF power amplifier expressed in
dB relative to the RMS power of the COFDM signal (or, alternatively, the RMS test tone
which has exactly the same average power but is easier to measure). On the y-axis we
have the power measured at the output of the amplifier also referred to the RMS power
assuming a normalised gain (0 dB).
04/2008
= ℜ + ℑ = θ
g g j g g j
( ) ( ) exp(
n n n n n
| and its phase in radians is θ
is |g
n n
)
.
n
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