LG KT520 Service Manual page 74

B. Receiver Part
The W-CDMA receiver architecture is a direct down-conversion Zero Intermediate Frequency (ZIF)
receiver with integrated low-pass channel filter, i.e. the front-end receiver converts the aerial RF signal
from W-CMDA band I down to a ZIF. The first stage consists of one single-ended low noise amplifier
(LNA) with a 16 dB gain step. This LNA is followed through an external filter by an IQ down-mixer
which consists of a mixer in parallel driven by quadrature out-of-phase LO signals. The In phase (I)
and Quadrature phase (Q) ZIF signal are then low pass filtered to provide protection from high
frequency offset interferer fed into the channel filter.
The front-end zero IF I and Q outputs are applied to the integrated low-pass channel filter with a
provision for 4 x 8 dB gain steps in front of the filter. The filter is a self-calibrated 6 pole, 2 zero filter
with a cut-off frequency around 2.15 MHz and a second order group delay compensation (2 poles, 2
zeroes). Once filtered, the zero IF I and Q signals are further amplified with provision of 31 x 1 dB
steps and DC offset compensation.
The zero IF output buffer provides close rail-to-rail outputs signal.
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Figure 3-7-3. WCDMA Transceiver Architecture
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3. TECHNICAL BRIEF
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