JRC JRL-2000F Service Manual page 6

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
Downloaded by
RadioManuai.EU