Receiver Part - LG KE970 Service Manual

3. TECHNICAL BRIEF

3.20. Receiver part

Figure 35 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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