User Guide

Table 21 Back-Up battery electrical characteristics

Description Parameter Min Typ Max Unit

Back-Up

Battery Voltage

Vback 0 2.5 2.7 V

RF description

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.

The last stage of the RF Rx chain is an output buffer which feeds the signal and a reference voltage (VREFCM) to

BB ASIC. The AGC stages are used to maintain the voltage swing at the input of the AD converters at an adequate

level.

The gain of the Rx chain is measured in production at one RF frequency and power level, so that RSSI reporting

gets calibrated. If N7501IC is changed this calibration needs to be performed.

GSM receiver

As GSM900, GSM1800 and GSM1900 Rx branches are functionally identical, the following description is applicable

to all of them.

The received signal goes from the GSM antenna to the antenna switch module. The switch module contains PIN

diode switches for a band and Rx/Tx selection and also Rx SAW filters.

RM-1

Nokia Customer Care System Module

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