Bruker BLAH1000 E, Operating & Service Manual

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Operating & Service Manual Version 002 BRUKER BIOSPIN 25 (53)
Theory of Operation
Theory of Operation 5.2
RF Path 5.2.1
The BLAH1000 E Amplifier 700-900MHz (P/N: W1345091) consists of a 3 input
embedded router, a class A / AB driver amplifier, a class AB power amplifier, a
bi-directional high dynamic coupler and a mechanical RF Relay.
A nominal input power level of +4dBm produces a rated linear output power of :
•
100W peak for 25% duty cycle at 100ms pulse width maximum on the High
Resolution channel 100W when selected. In this case, the 100W driver is
directly switched to the front panel via the high dynamic coupler and
mechanical RF relays.
•
1000W peak for 5% duty cycle at 100ms pulse width maximum on the Solid
channel 1000W when selected. In this case, the 100W driver is switched to the
input of the 1000W power stage via a mechanical relay and a 2 ways power
splitter.
The unit is also capable of longer pulses for lower average power, up to 50W CW
power on the 1000W channel for Solid application and 25W CW power on the
100W channel for High Resolution application.
Embedded Input Router
The embedded router consists of a class A RF amplifier IC’s and RF switches,
manufactured on a Gallium Arsenide process.
It is built on a four independent cells architecture with three RF input cells and one
output cell. The RF input cells ensure function of amplification and routing, the
output cell ensures the functions of combining, RF amplitude thermo-stability and
amplification.
The three RF inputs could be routed alone or combined each other to the RF
output by selecting the wished RF path through the BLA controller board. Each
entire RF path has a nominal 15dB of gain and operates at +15VDC.
Also, the router is equipped with an EEPROM for BIS information.
RF Driver
In the first section of the driver, the RF input signal is fed through a 5 poles high
pass filter and the RF detection path. Then, via a thermal PAD attenuator and a
GaAs RF switch, the RF signal is convoyed to a hybrid amplifier.
In this section, the GaAs RF switch requires a control board conditioned gating
signal to control the operation of the switching element.
A commutable H1000/H100 attenuator follows the hybrid amplifier.
This attenuator is built of two GaAs RF switches, commutated by a control board
conditioned signal SEL H1000/H100 and a thermo-compensated attenuator for
compensation of the output power drift with temperature of the amplifier when the
1000W channel for Solid application is selected.
This commutable attenuator is needed to minimize gain of about 6dB when the
amplifier is operating in Solid application and provides full gain in High Resolution
application. It is divided in variable resistive attenuator and Thermal PAD to adjust
output power.