3. TECHNICAL BRIEF
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3.22. Receiver part
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.
Figure 37 Receiver part block diagram
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