Motorola Cleartone CM5000 Basic Service Manual page 33

OVERVIEW
Transmit Mixer and Peripheral Circuit
The 1st local signal is amplified by the buffer amplifier (IC507 and TR1005) and fed to the transmit
mixer (CD1002).
The transmit mixer (CD1002) mixes the 1st local signal and 2nd local signal to generate the transmit
signal. High linearity double balanced mixer is used.
Mixed signal is fed to the 2 stages of the band pass filter and buffer amplifier.
The output of the mixer is filtered by the 1st band pass filter. Center frequency of the filter is control-
led by the tuning voltage from the control circuit. The control voltage is generated by the DAC
(IC701) and fed to the filter via buffer amplifier (IC1002).
The output of the band pass filter is amplified by the buffer amplifier (IC2001) and fed to the 2nd
band pass filter. The 2nd band pass filter is also tunable filter same as 1st filter.
The output signal of the 2nd band pass filter is divided into 2, and fed to the quadrature modulator
and quadrature demodulator in the Cartesian Loop through the buffer amplifier (IC510 and IC511).
PLL
CNT
REF1
PLL1
Rx 1st. Local ① = 306.10 - 356.10MHz
Tx 1st. Local ① = 306.55 - 356.55MHz
PLL
CNT
REF2
PLL2
Rx 1st. Local ② = 306.10 - 356.10MHz
Tx 1st. Local ② = 306.55 - 356.55MHz
PLL
CNT
13.0
MHz
PLL3
Rx 2nd. Local = 73.45MHz
Tx 2nd. Local = 73.45MHz
Transmitter I/Q modulator and buffer circuit
The base band signal of the digital signal processing circuit is fed to the quadrature modulator
(IC306) via OP amplifier (IC301), comparator (IC302) and buffer amplifier (IC305). The carrier signal
from PLL synthesizer is fed to the quadrature modulator.
The comparator in the modulation circuit operates as linearizer. Error correct signal of I and Q sig-
nals are generated at the linearizer circuit and fed to the comparator.
Carrier signal is modulated as pi/4 shift DQPSK signal by I and Q signal. Modulated signal is ampli-
fied by the buffer amplifier (TR301) to the appropriate level to drive the power amplifier.
Output of the buffer amplifier is fed to variable attenuator (CD301). Variable attenuator is controlled
by the digital signal processing circuit to output suitable level.
The output of the attenuator is fed to the Power amplifier module (HC201).
CM5000 Mobile Repeater/Gateway - Basic Service Manual
Figure 6. PLL (Phase lock loop) frequency synthesizer
To RX 2nd
Mix.
19
To RX 1st Mix.
To Q- Mod.
To Q- Dem.