Receiver Part - LG GX500 Service Manual

3. TECHNICAL BRIEF
GX500 Operational Description

3.17 Receiver part

Figure 3-32 Receiver part block diagram
The constant gain direct conversion receiver contains all active circuits for a complete receiver chain for
GSM/GPRS/EDGE (see Figure 39). 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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