22 © 2002 Motorola, Inc.
Theory of Operation
T720
RECEIVER AUDIO
Output from IFR 3000/3300 IC signals
C_RX_Q(DATA0, DATA1,DATA2,DATA3)
and C_RX_I(DATA2,DATA3),
FM_RX_IDATA, FM_RX_QDATA these
signals carries the baseband signal of the
receive digital call to MSM5100.
The received QPSK data is gain controlled
and converted to digital, the Rx data stream
is then decoded by the CSP inside the MSM
to produce a signal containing only the
desired data.
The digital speech is further decoded by the
QCELP vocoder a part of the DSP within
MSM and then converted back into analog
receive audio and routed to the speaker.
TRANSMITTER AUDIO
Audio from the Microphone is routed to the
MSM5100 where it is digitized by the
CODEC inside MSM and the DSP within
processes by QCELP variable rate vocoder
and then coded by the Modem (CSP) which
produces CDMA data stream.
This stream is then converted to analog sig-
nals and send to RFT3100 IC on four lines
TX_I, TX_Q, TX_IN and TX_QN. This
modulates on the TX IF (QPSK Modulation)
228.6Mhz (263.6Mhz for PCS).
Table 6: FREQUENCIES
AMPS VCO
2105.28 to 2155.14
Mhz
CELLULAR
CDMA VCO
2105.28 to 2155.14
Mhz
PCS CDMA
VCO
2113.60 to 2173.60
Mhz
AMPS RX IF
183.6 Mhz
CELLULAR
CDMA RX IF
183.6 Mhz
PCS CDMA
RX IF
183.6 Mhz
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