LG CU920 Manual page 18

3. TECHNICAL BRIEF
receive and transmit paths through a FEM(Front End Module) (plus two duplexers for UMTS highband
and low-band operations).
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 highband UMTS
receiver path and low-band path are accommodated int the RFR6275IC. 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(at ADC1).
For the transmit chains, the RTR6275 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 RTR6275 IC outputs deliver fairly high-level RF signals that are first filtered by Tx SAWs and then
amplified by their respective UMTS PAs. The high- and low-band UMTS RF transmit signals emerge
from the RTR6275 transceiver.
In the GSM receive path, the received RF signals are applied through their band-pass filters and
down-converted directly to baseband in the RTR6275 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
CU920/CU915 power supply voltages are managed and regulated by the PM6650 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 offchip
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 undervoltage lockout
and crystal oscillator signal presence are monitored to protect against detrimental conditions.
LGE Internal Use Only Copyright © 2008 LG Electronics. Inc. All right reserved.
- 20 -
Only for training and service purposes