Motorola V820, Service Manual

Page: 18 / 47

Theory of Operation
V810
2003 Motorola Confidential Proprietary Page 18
Transmitter
For the 800MHz band, the IC103 (RFT6100) provides the Zero-IF
transmitter
Signal path, from analog baseband to RF driver amplifiers. In analog mode,
also signals are used to generate from MSM6050. In digital mode, the I/Q
signals are fed to I/Q modulator to provide QPSK. IC103 (RFT6100) has
Tx VCO, Tx PLL and Rx PLL.
The final stage of IC103 (RFT6100) is Driver Amp, this provides adequate
Pout and ACPR to PA block. According to Tx lineup calculation, Pout is
0.1dBm and ACPR is 56dBc in this stage. After that main signal pass
cleanup filter, that has 2.4dB insertion loss for 824~849MHz and 38dB for
Rxband rejection. The 800 MHz PA driver, IC104 has gain approximately
29dB. We have HBT PA module, Also High/Low power mode in
conjunction with digital bias control. The transmitter signal is going to the
SAW duplexer TX port, SP3T switch Tx port and finally Ant port will meet
24dBm for digital mode and 27dBm for analog mode.
For the 1900MHz band, RFT6100 output for PCS provides 1.1dBm of Pout
and 58dBc of ACPR to the next stage. After that signal pass through Split
SAW band pass filter, F105, whose typical insertion loss is 2.4 dB and
38dB for Rxband rejection. SPDT switch control to pass Split band, 1850-
1880MHz and 1880-1910MHz, respectively. PA driver, IC107, whose gain
is approximately 28dB. The output of IC107 is fed to PCS FBAR duplexer
and then SP3T switch to Ant, the power level at the feeding point of the
antenna is set to the suitable power output levels for each band of operation.
Synthesizer
The IC103 ( RFT6100) consists of the Rx PLL, Tx PLL and Tx VCO.
The external synthesizer block is composed of the RX dual band VCO
(VCO100) and other supporting circuits including the loop filter and
supports RF RX (Cellular 800Mhz, PCS CDMA and GPS). The TX RF
synthesizer is totally internal to IC103 (RFT6100) except for the loop filter.
All synthesizers are programmable via the data from MSM6050
The reference oscillator, TCXO100 is a temperature compensated crystal
oscillator with frequency stability of 2 ppm over temperature extremes. Its
frequency is 19.2MHz. Output of TCXO100 is supplied to MSM6050
(IC201), PM6000 (IC304), RFR6000 (IC100), and RFT6100 (IC103).
Main VCO covers the frequency range of 1715MHz to 1788MHz for the
800Mhz mode and 1.9Ghz mode. VCO control voltage range is 0.4 volts to
2.3 volts.