LG E900 Service Manual page 22

A generic, high-level functional block diagram of C900k is shown in Figure 1-1. One antenna collects base
station forward link signals and radiates handset reverse link signals.
The antenna connects with receive and transmit paths through a SKY77544 (FEM, Front End Module + GSM
PAM). The UMTS receive paths each include an LNA, an RF band-pass filter, and a downconverter that
translate the signal directly from RF-to-baseband using radioOne
ZIF techniques. The RFIC's RX analog baseband outputs, for the receive chains, connect to the MSM IC. The
UMTS and GSM RX baseband outputs share the same inputs to the MSM IC.
For the transmit chains, the RTR6285 IC directly translates the TX baseband signals (from the MSM device) to
an RF signal using an internal LO generated by integrated on-chip PLL and VCO. The RTR6285 IC outputs
deliver fairly high-level RF signals that are first filtered by
1 QUALCOMM's branded chipset that implements a Zero-IF radio architecture.
TX SAWs and then amplified by their respective UMTS PAs.
In the GSM receive path, the received RF signals are applied through their band-pass filters and down-
converted directly to baseband in the RTR6285 transceiver IC. These baseband outputs are shared with the
UMTS receiver and routed to the MSM IC for further signal processing.
The GSM/EDGE transmit path employs one stage of up-conversion and, in order to improve efficiency, is
divided into phase and amplitude components to produce an open-loop Polar topology:
1. The on-chip quadrature up-converter translates the GMSK-modulated signal or 8-PSK modulated signal, to
a constant envelope phase signal at RF;
2. The amplitude-modulated (AM) component is applied to the ramping control pin of Polar power amplifier
from a DAC within the MSM
C900k power supply voltages are managed and regulated by the PM7540 Power Management IC. This
versatile device integrates all wireless handset power management, general housekeeping, and user
interface support functions into a single mixed signal IC. It monitors and controls the external power source
and coordinates battery recharging while maintaining the handset supply voltages using low dropout,
programmable regulators.
The device's general housekeeping functions include an ADC and analog multiplexer circuit for monitoring
on-chip voltage sources, charging status, and current flow, as well as user-defined off-chip variables such as
temperature, RF output power, and battery ID. Various oscillator, clock, and counter circuits support IC and
higher-level handset functions. Key parameters such as under-voltage lockout and crystal oscillator signal
presence are monitored to protect against detrimental conditions.
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3. TECHNICAL BRIEF
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