Motorola Tarpon V. 120C, Service Manual

Page: 7 / 81

V.120c
© 2001 Motorola, Inc. 7
Theory of Operation
I. AMPS
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 SAW filter –
FL12. The RF signal is then routed to the Front End
IC(FE IC) – U100 , which contains LNA which provides
a 10-12 dB gain to the received RF signal, and U100
provides inter stage filtering and it contains Mixer which
down converts the frequency of the signal to IF which is
109.65Mhz.
The local oscillator signal which is input to the FEIC is
978 – 1004 Mhz. The VCO module U680 is controlled by
the ZIF/SYN IC – U932.
The mixer output IF signal 109.65Mhz is routed through
IF filter- FL201 into the ZIF/SYN IC U932 for mixing
with the second LO ,filtering and demodulation.
RECEIVER AUDIO
DISC - signal an AMPS discriminator audio which is the
output of FM demodulator in U932 is produced by mixing
the IF signal with the second LO (which is controlled by
U932) and then filtered. The audio on DISC line goes to
WALLY IC-U1100 to be digitized. All receive audio
filtering and gain control is performed in the digital
domain within the WALLY which contains DSP, the
processed RX audio is converted back to analog 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 performs the compression, pre-emphasis,
limiting and band pass filtering function in the digital
domain. All Amps signaling (SAT, ST, DTMF) is
also generated in the digital domain by the DSP inside
the WALLY. The digitized amps TX audio signal is
converted back to analog inside the WALLY and
Theory of Operation