User Guide

RH-37

System Module Nokia Customer Care

Page 54 Nokia Corporation Issue 1 07/04

input to output ports:

• GSM 900: 1.3 dB

• GSM 1800: 1.6 dB

• GSM 1900: 1.6 dB

The SAW filters provide the wanted out-of-band blocking immunity. The SAW filters have

approximately 2.5 to 3 dB insertion loss.

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). The filters are used to con-

vert the single-ended to a balanced signal, required as input for the RF ASIC.

For GSM 1900 an external LNA improves the noise figure of the receiver. The 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 differen-

tial 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. The AGC provides a programma-

ble gain in order to obtain an output signal within a certain level range. 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, 1

stage (DTOS) is a

single-ended converter with 1

order RC filter, 2

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.