Motorola Tarpon V. 120C, Service Manual

Page: 9 / 81

V.120c
© 2001 Motorola, Inc. 9
Theory of Operation
from WALLY modulates the Tx offset VCO signal
which is external but controlled by ZIF/SYN –
U932. The T x IF modulated signal 154.8Mhz is
input to the ME3 IC – U600 where it get mixed
with the 979 – 1004 Mhz local oscillator signal.
The T x signal then passes through the band pass
filter FL605 into the Power Amplifier (PA) – U430
where it is amplified and the output passes through
TX band pass mono block duplex filter FL12 and
through diplexer FL11 to the antenna or RF test
port.
III. CDMA PCS (1900Mhz) MODE OF
OPERATION
RECEIVER
RECEIVER CIRCUITRY
The phone receives the RF signal from the Antenna
or the RF test port, the received RF signal is routed
through the Diplexer - FL11 to mono block duplex
ceramic filter – FL10. The RF signal is then routed
to the Front End IC(FE IC) – U100 , which contains
LNA which provides three stage gain to the
received RF signal based on its strength, and U100
provides inter stage filtering and it contains Mixer
which down converts the frequency of the signal to
IF which is 109.8Mhz.
The FE IC is controlled by WALLY through the
following signals: FEIC_G1, FEIC_G2, and
MODE.
The local oscillator signal RX_LO_PCS is 2039-
2100 Mhz. The VCO module U680 is controlled by
the ZIF/SYN IC – U932.
The mixer output IF signal 109.8Mhz is routed
through IF filter- FL200 into the ZIF/SYN IC U932
for mixing with the second LO ,filtering and
demodulation.
RECEIVER AUDIO
Four outputs from U932 – RXIP, RXIM,
RXQP, RXQM carries the base band signal
of the receive digital call to the WALLY, the
received QPSK data is gain controlled and
converted to digital, the 1.2288 Mb/sec Rx
data stream is then decoded by the CSP
inside the WALLY to produce a signal
containing only the desired data. The digital
speech data is further decoded by the CELP
vocoder a part of DSP within WALLY and
then converted back into analog receive
audio and routed to CCAP IC – U2000 on
signals AUDIO_P and AUDIO_M.
The CCAP - U2000 amplifies and route the
audio signal (receive audio) to the speaker
(phone speaker, boom speaker or external
speaker). The alert tone originates in
WALLY IC and follows the same path as
receive audio except from CCAP it is routed
to the alert.
TRANSMITTER
TRANSMITTER AUDIO
Audio from the Microphone (internal, boom
or external) is routed through and amplified
by CCAP – U2000 and then travel to the
WALLY IC – U1100 on MIC1 and MICREF
lines which is digitized by the CODEC
inside the WALLY and the DSP present in
WALLY processes by CELP variable rate
vocoder and then processed by the modem
(CSP) within the WALLY which produces
the 1.2288Mb/sec CDMA data stream. This
stream is then converted to analog signals
and send to ZIFSYN IC on four lines TXIP,
TXIM, TXQP, TXQM. This modulates on
the TX IF (QPSK modulation) 189.8Mhz
TX offset VCO.
TRANSMITTER CIRCUITRY
The four signals TXIP, TXIM, TXQP,
TXQM