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Technical Description
Transmitter
The transmitter section amplifies the transmitter signal from approximately
0.25 mW to 1.25 W. This section is compound by a driver stage and a power ampli-
fier.
Output power is regulated by a closed feedback loop incorporating a stripline cou-
pler, Schottky rectifier diode, and a power amplifier with high and variable gain and
high efficiency.
F _ T X
TX Blocks
TX Driver Amplifier
The transistor used is a bipolar type in a common emitter configuration, which
offers unconditional stability and good dynamic range.
The output and inputs are matched to 50Ω, and there is an attenuation at the output
to avoid damage in PA.
Power Amplifier Module
The output power of the PA-module is varied by controlling the bias point. The sat-
urated output power of the PA is dependent upon the load presented at its output.
For the required saturated output power and efficiency, a specified load must be
used.
Power Detector
The power sensing is done with a coupled stripline detector. This circuit senses for-
ward power with some directionality. A Schottky diode is used to rectify the RF and
this diode is forward biased to avoid having the diode snap off when detecting low
levels of RF. Direct temperature compensation is achieved by providing the detector
bias voltage via a matched diode
Power Control
The output power from the power amplifier is regulated by an active feedback loop.
The reference value is set via a D/A-converter in BERTINDY and is connected to
the positive input of an op-amp, where the detected output power level is connected
to the negative input of the same op-amp. The op-amp produces an error voltage
that controls the base current of a transistor, which in turn varies the output level of
the PA.
18
TX
Driver
Attenuator
Filter
Figure 8: Transmitter Block Diagram
Power
Duplexer
Amp
Rectifier
Power
Control
P o w e r
Level
A n t e n n a
Coupler
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