Model 500A250D
26
Rev A
3.2.2
A2 100W 250MHz Driver Module Assembly (Schematic
10039874)
The 100W 250MHz Module Assembly consists of RF matching circuits, an RF transistor (Q1), a bias control
circuit, and a fault detection circuit.
The RF input is fed to a 4:1 balun transformer composed of T1 and T2. The output signal of the 4:1
transformer is connected to the gates of Q1. The drains of Q1 are connected to a 4:1 balun transformer
composed of T3 and T4. Q1 has approximately 35 VDC applied to both drains at a total current of 8.5A. The
RF stage has approximately 21 dB of gain and an output compression point of 75W or greater.
The current through Q1 is monitored by U1. The output of U1 is fed to an op amp (U3) which has a reference
voltage on the non-inverting input. U3 compares the output of U1 to the reference voltage and generates an
error signal. This error signal varies the gate voltages of Q1 which in turn controls Q1’s current draw.
U5 is a comparator that monitors the output of U1 and generates a fault signal if the drain current varies
outside normal operating conditions. It also monitors the module temperature via a thermistor (R31) and
generates a fault signal if the module heatsink exceeds approximately 80
o
C.
3.2.3
A3 Two-Way Splitter
The Two-Way Splitter is a broadband splitter. The input signal is split into two equal-amplitude equal-phase
signals. The amplitude of each signal is 3-3.5 dB below the input signal when all outputs are terminated into
50
Ω
loads.
3.2.4
A4, A5 Three-Way Splitter
The Three-Way Splitter is a broadband splitter. The input signal is split into four equal-amplitude, equal-
phase signals. The amplitude of each signal is 4.8-5.5dB below the input signal when all outputs are
terminated into 50
Ω
loads.
3.2.5
A6, A8, A9, A10, A12, A13 100W 250MHz Module Assembly
(Schematic 10039874)
The 100W 250MHz Module Assembly consists of RF matching circuits, an RF transistor (Q1), a bias control
circuit, and a fault detection circuit.
The RF input is fed to a 4:1 balun transformer composed of T1 and T2. The output signal of the 4:1
transformer is connected to the gates of Q1. The drains of Q1 are connected to a 4:1 balun transformer
composed of T3 and T4. Q1 has approximately 40 VDC applied to both drains at a total current of 8.5A. The
RF stage has approximately 21 dB of gain and an output compression point of 75W or greater.
The current through Q1 is monitored by U1. The output of U1 is fed to an op amp (U3) which has a reference
voltage on the non-inverting input. U3 compares the output of U1 to the reference voltage and generates an
error signal. This error signal varies the gate voltages of Q1 which in turn controls Q1’s current draw.
Summary of Contents for 500A250D
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