Service Manual

MM-E 2072-09333-00
2-33
2-5. HI POWER MODULE
The functional block diagram of the HI POWER module is shown in Figure 2-17. The HI POWER
module comprises the power amplifier subsystem, the harmonic filter circuits and their control
circuits, and the Micom-Z power supply subsystem.
2-5.1 Power Amplifier (PA)
2-5.1.1 ALC Attenuator
Refer to Figure A-2.B.
The RF_INPUT_TX signal received via connector P4 from the LORD module is connected to the
ALC attenuator, comprising R77 and the PIN diodes CR8, CR9.
The attenuation is controlled by the V_ALC voltage: a higher voltage increases the attenuation.
2-5.1.2 Power Amplification Chain
Refer to Figure A-2.B.
a. Predriver. The ALC attenuator output signal is amplified by the predriver stages Q5 and Q7.
The supply voltage to Q5 and Q7, VDD_PREAMP, is connected only in the transmit mode, by
a switch comprising Q10, Q12: the switch connects the SW_BATT line only when 9V appear
on the 9T line.
The bias voltage for Q5 and Q7 (3V nominal) is provided by the +3.3V linear regulator, U1, via
voltage dividers connected to their gates.
The bias voltage is present only when the PA_INHIBIT line is at a high level.
b. Driver. The predriver output, PRE_DRIVER, is amplified by a push-pull stage comprising Q3
and Q4. The bias voltages are provided by the +5V linear voltage regulator U6, via the
potentiometers R67, R73.
The bias voltage is present only when the BIAS_EN line is at a high level.
c. Power Amplifier. The driver output signal is amplified by a push-pull stage comprising Q6 and
Q11. The bias voltage is derived from the +3.3V provided by the linear regulator U11, via the
source follower stage, Q8: Q8 source voltage is determined by the collector voltage of Q2,
which can be adjusted by means of potentiometer R22.
The bias voltage is present only when the BIAS_EN line is at a high level, and both the +5V
and +10V voltages are present.
2-5.2 TX/RX Switch
Refer to Figure A-2.C.
The RF output of the power amplifier, PA_OUT, is connected to the TX/RX switch, the relay K1.
a. In the receive mode, K1 is not energized and connects the harmonic filter output to the
RX_TO_LORD line.
b. In the transmit mode, and also in the BIT mode, K1 is energized by the 9T and/or BIT lines, and
connects the PA_OUT line to the harmonic filter bank.
2-5.3 Harmonic Filter Bank
Refer to Figure A-2.C, Figure A-2.D.
The harmonic filter is used to attenuate the unwanted spurious and harmonics of the transmitted and
received signals. The direction of flow through the harmonic filter is determined by the TX/RX
switch, K1, as explained in para. 2-5.2.
The harmonic filter contains seven low pass filters. The filter corresponding to the operating frequency