Only For Training And Service Purposes - LG GM750 Service Manual

3. Technical Brief
Since GSM-850, GSM-900, GSM-1800, and GSM-1900 signals are time-division duplex (the handset
can only receive or transmit at one time), switches are used to separate RX and TX signals in place of
frequency duplexers – this is accomplished in the switch module. The GSM-850, GSM-900, GSM-1800,
and GSM-1900 receive signals are routed to the RTR6285 through saw filters and matching networks
that transform single-ended 50-
figure. The RTR input uses a differential configuration to improve second-order inter-modulation and
common mode rejection performance. The RTR6285 input stages include MSM-controlled gain
adjustments that maximize receiver dynamic range.
The amplifier outputs drive the RF ports of the quadrature RF-to-baseband downconverters. The
downconverted baseband outputs are multiplexed and routed to lowpass filters (one I and one Q)
having passband and stopband characteristics suitable for GMSK or 8-PSK processing. These filter
circuits include DC offset corrections. The filter outputs are buffered and passed on to the MSM7200A
IC for further processing as shown in Figure 1-3.
LGE Internal Use Only
ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise ga i n and n oise a i n and n oise i n and n oise n and n oise
e e e e e e e e e e e e e e e
Ω
s o u r c e s t o d i f f e r e
- 32 -
and n oise and n oise nd n oise d n oise n oise n oise oise ise se e
n t i a l i m p e d a n c e s o p t i m i z
Copyright © 2009 LG Electronics. Inc. All right reserved.

Only for training and service purposes

GM750
r e nt ia l i m p r e nt ia l i m p r e nt ia l i m p r e nt ia l i m p r e nt ia l i m p r e nt ia l i m p r e nt ia l i m p r e nt ia l i m p r e nt ia l i m p r e nt ia l i m p r e nt ia l i m p r e nt ia l i m p r e nt ia l i m p r e nt ia l i m p r e nt ia l i m p r e nt ia l i m p e nt ia l i m p nt ia l i m p t ia l i m p ia l i m p a l i m p l i m p i m p i m p m p p
e d f o r g a i n a n d n o i s e