Receiver Part - LG GM360i Service Manual

3.17 Receiver part

The constant gain direct conversion receiver contains all active circuits for a complete receiver chain for
GSM/GPRS/EDGE (see Figure 25). The GSM850/900/DCS1800/ PCS1900 LNAs with balanced inputs are fully
integrated. No inter-stage filtering is needed. The orthogonal LO signals are generated by a divider-by-four for
GSM850/900 band and a divider-by-two for the DCS1800/PCS1900 band. Down conversion to baseband domain
is performed by low/high band quadrature direct down conversion mixers. The baseband chain contains a LNB
(low noise buffer), channel filter, output buffer and DC-offset compensation. The 3rd order low pass filter is fully
integrated and provides sufficient suppression of blocking signals as well as adjacent channel interferers and
avoids anti-aliasing through the baseband ADC. The receive path is fully differential to suppress on-chip
interferences. Several gain steps are implemented to cope with the dynamic range of the input signals.
Depending on the baseband ADC dynamic range, single- or multiple gain step switching schemes are applicable.
Furthermore an automatic DC-offset compensation can be used (depending on the gain setting) to reduce the
DC-offset at baseband-output. A programmable gain correction can be applied to correct for front end- and
receiver gain tolerances.
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Figure 25 Receiver part block diagram
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3. TECHNICAL BRIEF
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