LG -P970 Service Manual page 29

Figure3-3 shows the 2G receiver line-up in a multimode band. Note the gain step given for the external LNA may
vary from the given value. The chain is basically identical to the 3G line-up but many stages in analog and digital
domain are switched into a different operation mode.
switch duplexer
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 PMB5703 through band selection filters and matching networks that transform single-ended
50-Ω sources to differential impedances optimized for gain and noise figure. The PMB5703 input uses a
differential configuration to improve second-order intermodulation and common mode rejection performance.
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.
LGE Internal Use Only
16/-7dB
interstage
LNA1
LNA
filter
[Figure 3-3] 2G Receiver Line Up-GSM Multi Mode Setup
35 dB
17 dB 6 dB
gain range
gain step gain step
(1 dB steps)
analog
mixer buffer
baseband filter
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3. TECHNICAL BRIEF
Only for training and service purposes