C1,-C2,
es,
R1
and R2 compose of a circuit which matches an input
imped~nce.-
T11
and
T21
are transformers which insulate the exdtation signal from ground Ievei.
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
inpuf
capacitance exists between gate·and
source~
The gate terminating resistor shunts this input capacitance.
The RF power MOSFET
TR11
to TR16 are connected parallel. They are excited
by
the signal voltage at both ends of the gate terminating resistor and they amplify the
output currentin a half cycle. On the other hand, TR21 to TR26 amplify the output
current in another half cycle. Theseoutput currents
of
half-cycles are fed to the pri-
mary winding
of
the output transformer
TS
and the current waveform of full-cycle is
composed. These output currents flow to the Ioad circuit via output terminal J4. ·
As a result, the upper part of the output voltage waveform is amplified by
TR11
to
TR16,and the lower part by
TR21
to
TR26. -
The SEPP circuit, in contrast to the transformer-coupled push-pull circujt, seldom
generates a phase difference when composing output waveforms. Therefore, a wave-
form with less distortion can be obtained.
The transform er T3 provides
a gate-bias voltage to the RF power MOSFET for the
operation in class AB.
A
DC
bias valtage 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
third winding
of
T3 and the second winding
of
the input transformer T1, work as a
negative feedback.
(Note): The chips with same charasteristics are packaged to the RF power MOSFET
2SK408 and 2SK409. However, the Iead Iayout differs.
2SK408
2SK409
I Dimensions
in
mml
2SKUJ8
2SK409
(JEDEC
T0-220AB)
l.C:.te
I.
Orai"
2.
:ioura
Z.
Source
l.
CaiA!
Fig.1
5
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