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C1, C2, C5, R1 and R2 compose of a circuit which matches an input impedance.
T I 1 and T21 are transformers which insulate the excitation signal from ground level.
The two excitation signals are consumed by R17 to R20 and R27 to R30 which are the
gate terminating resistors of the RF power MOSFET.
As a RF has the insulated gate, it can be assumed that only the equivalent input
capacitance exists between gate and source.
The gate terminating resistor shunts this input capacitance.
The RF power MOSFET TRI 1 to TRI 6 are connected parallel. They are excited by
the signal voltage at both ends of the gate terminating resistor and they amplify the
output current in a half cycle. On the other hand, TR21 to TR26 amplify the output
current in another half cycle. These output currents of half-cycles are fed to the pri-
mary winding of the output transformer T5 and the current waveform of full-cycle is
composed. These output currents flow to the load circuit via output terminal J4.
As a result, the upper part of the output voltage waveform is amplified by TRI 1 to
TR1 6,and the lower part by TR21 to TR26.
The SEPP circuit, in contrast to the transformer-coupled push-pull circuit, seldom
generates a phase difference when composing output waveforms. Therefore, a wave-
form with less distortion can be obtained.
The transformer T3 provides a gate-bias voltage to the RF power MOSFET for the
operation in class AB.
A DC bias voltage of approx. 2.5 V is provided through T3 to each RF power MOSFET
from CCB-367 PA control circuit. The resistors R61 and R62, connected between the
4
third winding of T3 and the second winding of the input transformer TI, work as a
negative feedback.
(Note): The chips with same charasteristics are packaged to the RF power MOSFET
2SK408 and 2SK409. However, the lead layout differs.
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