Envelope Voltage Adaptation Modes - R&S SGT100A User Manual

®
R&S SGT100A
The R&S SGT generates the envelope signal directly from the baseband signal. The
envelope signal is a voltage signal, with voltage level V
the RF signal (
function, the envelope signal follows the variation of the envelope of the RF signal line-
arly dependent.
The envelope signal is output at the I OUT and I BAR OUT rear panel connectors. This
envelope signal is then further fed to an external DC modulator.
The PA receives the RF input signal and the dynamically adapted supply voltage v
Ideally, the PA gain should stay constant.
Suitable baseband signal to observe the effect of the envelope tracking settings
To simplify the explanation in the following sections, we use a simple ramp function as
a baseband signal modulated on the RF carrier.
Other suitable baseband signals are signals with relative constant envelope. You find a
choice of predefined signals in the "Baseband > Custom Dig Mod" dialog. For instance,
with the default settings in this dialog ("Custom Dig Mod > Set acc. to the standard >
GSM"), you can observe the generated envelope signal and the effects of enabled
shaping.
7.5.2.1

Envelope Voltage Adaptation Modes

In the R&S SGT, you define the voltage of the generated envelope signal using one of
the following modes:
●
Auto Power/Normilized Envelope Voltage Adaptation:
In this mode, you define the desired input characteristics of the power amplifier.
Based on these values and depending on the crest factor of the currently gener-
ated signal, the R&S SGT calculates:
–
–
The auto voltage adaptation mode is a suitable choice, if you have knowledge on
the power amplifier components and characteristics, like for example the supply
voltage V
as the gain characteristics of the external DC modulator.
You find the required values in the documentation of your power amplifier, for
example in its data sheet.
●
Manual Envelope Voltage Adaptation:
In this mode, you can additionally define the operating range of the power amplifier
based on a pre-gain and a post-gain range. Based on these values, the instrument
calculates the supply voltage V
All modes support envelope shaping.
User Manual 1176.8674.02 ─ 07
√ [I(t)
2 +Q(t) 2 ]) of the corresponding path. If you do not apply a shaping
The voltage on the I OUT/I BAR OUT connectors
(Bias),
The RMS level of the RF signal
, the input power PEP
cc
Generation of Envelope Tracking Signals
out
required for working in the linear range, as well
in
.
cc
Signal Generator Settings
proportional to the power of
(V Min/Max) and a bias
out
.
cc
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