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LGE Internal Use Only
Copyright © 2009 LG Electronics. Inc. All right reserved.
Only for training and service purposes
3. Technical Brief
GM750
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 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
GM750 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.
