Nokia 6610i Service Manual

CCS Technical Documentation

7-System Module and User Interface

                                 

Company confidential 

RM-37

Issue 1  04/2004

  ©Nokia Corporation.

Page 43

Backup battery is used in case when main battery is either removed or discharged. 
Backup battery is used for keeping real-time clock running for minimum of 30 minutes. 

Rechargeable backup battery is connected between UEM VBACK and GND. In UEM 
backup battery charging high limit is set to 3.2V. The cut–off limit voltage (V BUCoff–) 
for backup battery is 2.0V. Backup battery charging is controlled by MCU by writing into 
UEM register. 

Li-Ion SMD battery type is used. The nominal capacity of the battery is 0.01 mAh.

The RF module performs the necessary high frequency operations of the EGSM900/
DCS1800/PCS1900 tripleband engine. Both the transmitter and receiver have been 
implemented by using direct conversion architecture which means that the modulator 
and demodulator operate at the channel frequency. 

The core of the RF is an application-specific integrated circuit, Helga. Another core com-
ponent is a power amplifier module which includes two amplifier chains, one for 
EGSM900 and the other for DCS1800/PCS1900. 

Other key components include

• 26 MHz VCTCXO for frequency reference

• 3420-3980 MHz SHF VCO (super high frequency voltage controlled oscillator)

• front end module comprising a RX/TX switch and two RF bandpass SAW filters 

• three additional SAW filters 

The control information for the RF is coming from the baseband section of the engine 
through a serial bus, referred later on as RFBus. This serial bus is used to pass the infor-

Back-up battery voltage

VBACK

2.43

3.3

V

Back-up battery cut-off limit

V_BU

COFF+

V_BU

COFF-

2.04
1.94

2.10

2.0

2.16
2.06

V
V

Charging voltage (VBAT

 ? 3.4V)

VBU

3.1

3.2

3.3

V

Charging current

I

LIMVBU

150

500

mA