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V.120c
TRANSMITTER CIRCUITRY
The four signals TXIP, TXIM, TXQP, TXQM from
WALLY modulates the Tx offset VCO signal which is
external but controlled by ZIF/SYN – U932. The Tx IF
modulated signal 189.8Mhz is input to the ME3 IC –
U600 where it get mixed with the 2039-2100 Mhz local
oscillator signal. The Tx signal then passes through the
filter FL601 into the Power Amplifier (PA) – U900
where it is amplified and the output passes through TX
band pass mono block duplex filter FL10 and through
diplexer FL11 to the antenna or RF test port.
FREQUENCY SYNTHESIZER CIRCUITRY
The phone contains three PLL frequency synthesizers
controlled by U932.
1. The main VCO : there is only one VCO modules-
which controls the tunable 979 – 1004Mhz main local
oscillator – and is ON during Cellular or 800Mhz mode.
and also controls the tunable 2039-2100Mhz main local
oscillator, which is ON during PCS or 1900Mhz mode.
2. The Tx offset VCO: there are two modes and two
frequency at which this oscillator which is internal to
U932 works, but the tank circuit is external. There are
two tank circuits one for Cellular mode (800 Mhz)
which will set 309.6Mhz frequency for the oscillator to
oscillate on. Another tank circuit for PCS mode
(1900Mhz) which will set 379.6Mhz frequency for the
oscillator to oscillate on. The Tx offset frequency is
divided by 2 before being fed into the mixer for
modulation.
3. The second LO: the second local oscillator also
operates in two modes with two different frequencies:
For AMPS mode the frequency is 219.3Mhz and for
CDMA mode at cellular or 800Mhz band and PCS or
1900Mhz band the frequency is 219.8Mhz. The tank
circuit is external to the U932. The frequency is divided
by 2 before being fed into the mixer.
All the synthesizers obtain their reference
frequency from the 16.8Mhz reference
oscillator.
TRANSMIT POWER CONTROL
CIRCUITRY
The transmit signal power (the output RF power)
is controlled by the three control signals
ZIF_VCA and ME_VCA from WALLY IC and
PA_VCC from CCAP IC. The output power is
controlled at three places, ZIFSYN – U932 which
has a gain control of max 40dB and ME3 IC-
U600 which has a total gain of max 36dB and PA
has a gain of max 27-32dB.
In Amps mode the power range is +8dBM to
+28dBM. In CDMA mode the RF power range is
from –50dBM to +23dBM.
In CDMA mode the power control operates in
two mode: Open loop and Close loop. In open
loop mode (at the beginning of registering –
access probe) the power level is proportional to
the received signal level, in close loop mode the
power level is controlled by the CDMA cell based
on the received signal strength at the cell site.
© 2001 Motorola, Inc.
Theory of Operation
10
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