User Guide

Issue 1 04/2005 COMPANY CONFIDENTIAL 37

RM-94

7 - System Module Nokia Customer Care

The GSM 900 and the GSM 1800 filters are matched to the corresponding LNA inputs of the

RF ASIC with a differential matching network (LC-type).

For GSM 1900, an external LNA provides a gain of approximately 17 dB. For conversion of the

unbalanced output port to the balances input port of the RF ASIC a balun is applied, followed

by a differential matching network (LC-type).

After amplification in the RF ASIC, the RX signals are down-converted to the baseband I and

Q signals and further amplified by the AGC stages. This signal is passed on to the analog-to-

digital converters in UEM.

The RX paths of the RF ASIC consist of the following sub units:

• Separate LNAs for each of the bands: GSM900, and GSM1800.

• Two PRE-GAIN amplifiers, one for GSM900 and one common for GSM1800 and

GSM1900.

• Two passive I/Q mixers (MIX), one for GSM900 and one common for GSM1800

and GSM1900.

The BB signal paths consist of:

• Integrated BB channel select filter, 3

order tunable active RC-type with equal

paths for I and Q-channel. Each channel consists of 2 stages, 1st stage (DTOS) is a

single ended converter with 1st order RC filter, 2nd stage is an active RC modified

Sallen-Key biquad.

• Automatic gain control (AGC): DTOS has two gain stages producing a 6 dB or 18

dB gain.

• Attenuators in AGC-path.

• DC compensation / AGC amplifiers.

The differential base band amplifiers are internally DC-coupled. Their common mode levels are

set equal to the external reference voltage VrefRF01. The base band outputs RXIP and RXQP

are single-ended and connected directly to the differential ADC inputs (RXI->RXIINP and RXQ-

>RXQINP) of the UEM-ASIC. Its common mode level is set equal to the external reference volt-

age VrefRF02.