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Table 27 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 N7500.

The receiver is a linear direct conversion receiver containing LNA, band pass filter and demodulator for each

supported system and band. A second band filter is used between the LNA and demodulator in WCDMA.

After the demodulators the signal paths are combined to one common BB path.

WCDMA receiver

In WCDMA mode the received signal is fed from the antenna to the BAW duplex filter. After the duplex filter

the signal goes via balun to the integrated LNA in N7500. After the LNA the signal goes trough band pass

filter.

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.

The Rx channel filter must be calibrated with an automatic routine whenever N7500 IC is changed to a phone.

In 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 analog IQ output pins. Analog

output pins are accompanied by reference voltage output, which sets the DC level for the AD converter in BB

ASIC.

GSM receiver

As GSM850, 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 band and RX/TX. The antenna switch module is followed by integrated LNA stages in

the RF ASIC. The LNAs are followed by demodulators which downconvert the signal to baseband I and Q

signals.

In the BB-chain there are two adjustable gain stages and one mode specific gain. The first one called BB-gain

is just after the demodulator. It has a 12 dB gain range with 6dB steps. After the BB-gain there is the channel

select filter.

Main AGC amplifier proceeds the channel selection filter. It has 30 dB of gain control range with 3 dB steps.

Final amplifier stage is used as an output buffer for IQ signals. This stage is set to 0 dB gain in GSM mode.

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