Nokia 6680 RM-36, Руководство по обслуживанию

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Back-up battery interface connections and electrical characteristics
Table 35 Back-up battery connections
Pin name I/O Connection Notes
L2207, VBack -> Retu, VBack Back-up battery G2200 is connected to RETU via
coil
Table 36 Back-up battery electrical characteristics
Description Parameter Min Typ Max Unit
Back-Up
Battery Voltage
Vback 0 2.5 2.7 V
RF description
Receiver
Introduction to receiver functionality
Receiver functions are implemented in RF ASIC N7501.
The receiver is a linear direct conversion receiver consisting of separate front ends (LNA and demodulator) for
each supported system.
After the demodulators, the signal paths are combined to one common BB path.
WCDMA receiver
In the WCDMA mode, the received signal is fed from the antenna to the duplex filter. After the duplex filter the
signal goes via balun to the integrated LNA residing in N7501. After the LNA, the signal goes trough an off chip
band pass SAW filter. The main task of the filter is to attenuate the Tx signal which is leaking trough the duplex
filter and amplified by LNA.
After filtering, the signal goes to the down conversion mixer, which converts the signal into baseband I and Q
signals (90 degrees phase shift). After the demodulator output there is a RC low pass filter with f0 of ca. 1.5
MHz. It is effectively part of the BB selectivity filtering.
At BB frequency the signal is amplified and fed to a low pass filter giving the selectivity of the receiver. The
filters need RC constants, which suffer of process variations. Therefore the integrated resistors are adjustable
by digital control word.
Rx channel filter must be calibrated with automatic routine whenever N7501 IC is changed to a phone.
In the WCDMA mode, the corner frequency of the filter is set to ca. 2.1MHz. The filter is followed by an AGC
amplifier with adjustable gain. Signal is further amplified before it is fed to balanced analogue IQ output pins.
Analogue output pins are accompanied by reference voltage output, which sets the DC level for the AD converter
in BB ASIC RAP3G.
The gain of the Rx chain can be adjusted in multiple phases. The first adjustable gain is in LNA which has low,
mid and high gain settings and isolation mode. After the mixer, there are adjustable gains (AGC) inside the
N7501 IC.
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