LG KG70c Service Manual page 15

KG70C
6.1.3.1 Description on the Internal Circuit of MSM6100 (U200) and RFT6122 (U106)
For the transmit data path(Tx), the MSM6100 modulates, interpolates, and converts the digital signal
into an analog baseband before sending it to the RFT6122. The RFT6122 upconverts the Tx analog
baseband into RF. The MSM6100 communicates with the external RF and analog baseband to control
signal gain in the RF Rx and Tx signal paths, educe base band offset errors, and tune the system
frequency reference.
The RFT6122 baseband-to-RF Transmit Processor performs all Tx signal-processing functions
required between digital baseband and the Power Amplifier Module (PAM). The baseband quadrature
signals are upconverted to the Cellular frequency bands and amplified to provide signal drive
capability to the PAM. The RFT6122 includes an mixer for up-converting analog baseband to RF, a
programmable PLL for generating Tx and Rx LO frequency, cellular driver amplifier and Tx power
control through an 85 dB VGA. As added benefit, the single sideband upconversion eliminates the
need for a band-pass filter normally required between the upconverter and driver amplifier.
I, I/, Q and Q/ signals proceed from the MSM6100 to RFT6122 are analog signal. In CDMA mode,
These signals are modulated by Offset Quadrature Phase Shift King (OQPSK). I and Q are 90 deg.
out of phase, and I and I/ are 180 deg. The mixer in RFT6122 converts baseband signals into RF
signals. After passing through the upconverters, RF signal is inputted into the Power Amplifier Module.
The RFT6122 Cellular CDMA RF specifications are described below:
Parame
Rated Output Power
Min Output Power
Rx band noise power
ACPR
6.1.3.2 Power Amplifier (U104)
The power amplifier that can be used in the CDMA mode has linear amplification capability.
For higher efficiency, it is made up of one module (Monolithic Microwave Integrated Circuit) for which
RF input terminal and internal interface circuit are integrated onto one IC after going through the GaAs
HBT (heterojunction bipolar transistor) process.
The module of power amplifier is made up of an output end interface circuit including this module.
The maximum power that can be inputted through the input terminal is -+7dBm and conversion gain is
about 28.5dB. RF transmit signals that have been amplified through the power amplifier are sent to
the duplexer.
Condition
Average CDMA Cellular
Average CDMA Cellular
CDMA Cellular
Cellular: Fc±885kHz
Fc±1.98MHz
14
Min. Typ. Max.
6
-75
-132
-52
-63
Unit
dBm
dBm
dBm/Hz
dBc
dBc