Only For Training And Service Purposes - LG -S310 Service Manual

Low Noise Amplifiers
The LNAs have differential inputs which help minimize the effect of unwanted interferers. The inputs are
easily matched to industry standard FEMs or discrete Rx SAW filters. The outputs of the LNAs are directly
coupled to the down-converting mixers. The voltage gain of the LNAs is typically 24 dB. Each LNA can be
switch to a low gain mode when receiving large input signals as part of the AGC system.
Down-Converting Mixers
Two quadrature mixers are used to mix down the signals from the LNAs, one for the high bands (1800 and
1900 MHz) and one for the low bands (850 and 900 MHz). The outputs of the mixers are connected to the
baseband section through an integrated single pole filter with nominal cut-off frequency of 800kHz. This acts
as a "roofing filter" for the largest blocking signals (i.e. those ≥ 3MHz) and prevents the baseband amplifiers
from being overloaded.
Receive Local Oscillator (LO) Generator
The LO generator is used to convert the synthesized VCO signal to the on-frequency quadrature LO required
by the receiver. By operating the VCO at a frequency other than the desired receive frequencies, any leakage
of the VCO (e.g. via package) will fall out of band. The LO generator is implemented as a regenerative
frequency divider, performing a 2/3 multiplication of the synthesized-LO for the high band
(DCS1800/PCS1900) and a 1/3 multiplication for low band (GSM900/GSM850).
Baseband Amplifiers / Low Pass Filters
The baseband amplifiers provide the majority of the analog receiver gain. The filtering is provided by an
integrated 5th order Chebyshev filter giving the necessary adjacent channel and blocking filtering, it is also
acting as an anti-alias filtering for Baseband Converter ICs. The output stage includes an internal resistance so
a final low pass pole can be created with external shut capacitors, if necessary. The on chip filter has an auto
calibration feature ensuring that the filters are tuned for optimum performance in both EDGE and GSM
modes.
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Only for training and service purposes

[Figure 4.2.1-1] GSM Receiver Path
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[Figure 3.2.1-2] Receiver Baseband Section
3. TECHNICAL BRIEF
LGE Internal Use Only