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Copyright © 2009 LG Electronics. Inc. All right reserved.
Only for training and service purposes
LGE Internal Use Only
4. RF Circuit Technical Brief
GM310f service manual
4.2 GSM Part
4.2.1 GSM Receiver
[Figure 4.2.1-1] GSM 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 4.2.1-1] ). 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 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.
Содержание GM310
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