Gsm Part - LG GD910 Service Manual
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4.2 GSM Part
4.2.1 GSM Receiver
The constant gain direct conversion receiver contains all active circuits for a complete receiver chain for
GSM/GPRS/EDGE (see [Figure 4.2.1-1] ). The GSM900/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
GSM900 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 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.
Copyright © 2009 LG Electronics. Inc. All right reserved.
Only for training and service purposes
[Figure 4.2.1-1] GSM Receiver Part Block Diagram
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4. RF Circuit Technical Brief
GD910 service manual
LGE Internal Use Only
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