LG U830 KU830 Service Manual page 17

3. TECHNICAL BRIEF
A generic, high-level functional block diagram of U830 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 switch module (plus a duplexer for UMTS dual band operation).
The UMTS receive signal is amplified by the RFR6250 LNA then passes through a bandpass filter
before being applied to the RFR6250 Receiver IC. On-chip circuits downconvert the received signal
directly from RF to baseband using radioOne Zero-IF techniques. Generation of the UMTS
downconverter LO is distributed between the RTR6250 (phase-locked loop), the RFR6250 (buffer
amplifiers and LO distribution circuits) and external UHF VCO and loop filter circuits. The RFR6250 IC
outputs analog baseband signals for further processing by the MSM device. This baseband interface is
shared with the RTR6250 GSM900 /DCS/PCS receiver outputs.
GSM900, DCS and PCS receive signals pass through their bandpass filters then are applied to the
RTR6250 IC. Similar to the UMTS path, RTR6250 circuits downconvert the received signals directly
from RF to baseband. The GSM900/DCS/PCS downconverter LO is generated mostly within the
RTR6250 (PLL and distribution functions); the UMTS Rx CH VCO and loop filter are off-chip.
The RTR analog baseband outputs are routed to the MSM6275 IC for further processing (an interface
shared with the RFR).
The UMTS transmit path begins with analog baseband signals from the MSM device that drive the
RTR6250 IC. Integrated PLL and VCO circuits generate the Tx LO used in the quadrature upconverter
that translates baseband signals directly to RF. The RTR6250 output driver stages deliver fairly high-
level signals that are filtered and applied to the power amplifiers module(PAM). The PAM output is
routed to the antenna through a duplexer and switch module.
The shared GSM-900, DCS-1800, and PCS-1900 transmit path begins with the same baseband
interface from the MSM6275 IC that is used for the UMTS band. A single GSM900/DCS/PCS
quadrature upconverter translates the GMSK-modulated signal to a convenient intermediate frequency
(IF) that forms one input to an offset phase-locked loop (OPLL). OPLL functions are split between the
RTR6250 IC and off-chip loop filter and dual Tx VCO circuits, and translate the GMSK-modulated
signal to the desired GSM-900, DCS-1800 or PCS-1900 channel frequency. This signal is applied to a
dual power amplifier (only one is active at a time). The enabled path continues with the PAM, an
automated power control (APC) circuit that samples the transmit power and adjusts its level, the switch
module (which includes a band-appropriate lowpass filter), and the antenna.
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