Receiver Troubleshooting; General Description - Nokia 6600 Rf Troubleshooting And Manual Tuning Manual

NHL-10
RF Troubleshooting CCS Technical Documentation

Receiver Troubleshooting

General Description

Figure 4: Receiver Signal Path
The receiver is a direct conversion, triple-band linear receiver. NHL-10 uses Mjølner RFIC with
external VCO.
The received RF signal from the antenna/RF connector goes into the RF antenna switch where
the signal is fed to the E-GSM900, GSM1800 or GSM1900 path. For each band, a RX band-
pass SAW filter with unbalanced input and balanced output follows. All blocks are specified as
50Ω single ended, only the SAW filter output to the Mjølner input is differentially matched to
LNA G . The LNAs are integrated in Mjølner and have two gain levels. The first one is max.
opt
gain nominally 12 dB, the second one is about 30 dB below max. gain. The gain selection con-
trol of the LNAs is done via the serial interface.
The differential RX signals are further amplified in the "pre-gain" stage and then mixed down to
baseband inside Mjølner using two Mixers with a 90° phase shift in the LO signal resulting in
an in- and quadrature phase paths. Local oscillator signal is generated with the external VCO.
The VCO signal is buffered and divided by 2 (DCS/PCS) or by 4 (EGSM). Accurate phasing is
generated in LO dividers.
The Rx BB chain incorporates AGC, channel select filter and DC compensation. The AGC is
adjusted in 6 dB steps in Mjølner. The DCN1 gain can be adjusted to +24/+18/+12/+6/0 dB.
The attenuator gain can step from 0/-6/-12/-18/-24/-30/-36/-42/-48dB. Other BB amplifiers have
rd
a nominal summed gain of 58dB. The total dynamic range of AGC alone is 72dB. The 3 order
active channel filters in Mjølner defines the channel selectivity (flat response up to +/-90kHz
typical). Integrated base band filters are based on active RC filters with on-chip capacitors. The
baseband filters are distributed to following stages: BBAMP1, LPF1, LPF2. DC compensation
is split to DCN1 and DCN2. DCN1 is used to compensate DC offset from RF front-end imper-
ISSUE 2 01/2004 COMPANY CONFIDENTIAL 9
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