LG LG-S310, Руководство по обслуживанию

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Only for training and service purposes LGE Internal Use Only
3. TECHNICAL BRIEF
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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.
[Figure 3.2.1-2] Receiver Baseband Section
The baseband amplifiers have programmable gain for system AGC. A total of 57 dB of gain control is provided
in 3dB steps programmable over the serial interface. This together with the LNA gain control gives a total of
77dB of gain control range. The receive baseband outputs are routed to the common Rx/Tx I/Q ports for
connection with the baseband converters.
Baseband Output D.C. Offset Correction
In order to minimize DC offsets inherent in the receiver and maximize dynamic range a DC offset correction
circuit is integrated. The one-off calibration is triggered over the serial bus upon initialization and then a fully
automatic offset tracking loop is enabled to minimize residual offsets during operation.
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3.2 GSM Part
3.2.1 GSM Receiver
The LG-S310 receiver section fully integrates all the RF and baseband signal processing. Each block is
described in the following sections.
[Figure 4.2.1-1] GSM Receiver Path
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.