Bruker BLAH1000 E, Operating & Service Manual

Page: 26 / 54

26 (53) BRUKER BIOSPIN Operating & Service Manual Version 002
Technical Description
The second section of the driver includes a class AB LDMOSFET transistor
followed by two cascaded class AB LDMOSFET transistors.
The polarization of these transistors require a control board conditioned gating
signal to control the bias voltage on the gate of the FETs and depends of the
selection H1000/H100 to prevent the increasing of anti-droop behaviour. If the
1000W channel is selected, the gating signal is unblanked else if the 100W
channel is selected, it is blanked.
Note : The polarization of the Class AB LDMOSFET transistor used as driver is
always blanked.
The circuitry around the transistors consists of complementary input and output
transformers and baluns and operates the device in Push-Pull.
The RF driver has a nominal 32 to 34dB gain and operates at +32VDC.
With the embedded router gain, the entire path has a nominal 48dB gain in 100W
mode for High Resolution operation and 42dB gain to drive the 1000W power
amplifier stage for Solid operation.
RF Relays H1000/H100 Selection
The selection or not of the 1000W power amplifier is made by a pair of RF
mechanical relays, one placed before the power amplifier and the other after.
In case of 100W operation, the pair of relays straps the power amplifier to deliver
the 100W RF power directly to the bi-directional high dynamic coupler when the
SEL H1000/H100 signal is controlled at TTL level high or not connected.
In case of 1000W operation, the pair of relays passes the RF power from the
driver to the power amplifier when the SEL H1000/H100 signal is controlled at
TTL level low, and feeds the power to the same bi-directional high dynamic
coupler.
RF Splitter
The RF Splitter acts as a 2 ways in-phase splitter between the output of the RF
driver and the inputs of the two power amplifiers.
RF Power Amplifier
Each power amplifier includes four class AB LDMOSFET transistors mounted on
a single flange. They are coupled with -6dB four ways splitter/combiner to built a
nominal 16dB gain and operates at +32VDC. The power amplifier requires a
control board conditioned gating signal to control the bias voltage on the gate of
the FETs.
The PA is followed by an isolator and an in-phase combiner.
RF Combiner
The RF Combiner acts as a 2 ways in-phase combiner between the outputs of the
power amplifier and the mechanical relay and feeds the power to the input of the
bi-directional high dynamic coupler.