LG KE800 Service Manual page 15

3. TECHNICAL BRIEF
(1) Receiver
Figure. 3-2 Receiver path Overview
The constant gain direct conversion receiver contains all active circuits for a complete receiver chain for
GSM/GPRS/EDGE (see Figure3-2). The GSM850/900/DCS1800/ PCS1900 LNAs with balanced inputs are
fully integrated. No interstage 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 DCoffset compensation. The 3rd
order lowpass 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.
(2) Transmitter
Figure. 3-3 Transmitter architecture Overview
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