Frequency Synthesizer Circuitry; Transmit Power Control Cir- Cuitry - Motorola V60i Service Manual

60i

FREQUENCY SYNTHESIZER CIRCUITRY

The phone contains three PLL frequency synthe-
sizers controlled by U700.
1. The main VCO: there are two main VCO
modules- a) one synthesizer controls the
tunable 979 – 1004Mhz main local oscillator –
U626, which is ON during Cellular or 800Mhz
mode. b) another synthesizer controls the
tunable 2039-2100Mhz main local oscillator –
U636, 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 U700 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 oscil-
late on. Another tank circuit for PCS mode
(1900Mhz) which
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 U700. The frequency is divided
by 2 before being fed into the mixer.
All the synthesizers obtain their reference fre-
quency from the 16.8Mhz reference oscillator.
22
All manuals and user guides at all-guides.com
will set 379.6Mhz
Circuit Description &
Theory of Operation
TRANSMIT POWER CONTROL CIR-
CUITRY
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_BIAS from CCAP IC. The output power is
controlled at three places, ZIFSYN – U700
which has a gain control of max 40dB and ME3
IC- U400 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.
4/2/02