Nokia 6020b 服务手册

Issue 1 03/2005

COMPANY CONFIDENTIAL

RM-31
7 - System Module

Nokia Customer Care

The SAW filters provide the wanted out-of-band blocking immunity. The SAW filters have ap-
proximately 2.5 to 3 dB insertion loss.

The GSM850 and the GSM1800 filters are matched to the corresponding LNA inputs of the RF
ASIC with a differential matching network (LC-type).

For GSM1900, 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 differential matching net-
work (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: GSM850, and GSM1800.

• Two PRE-GAIN amplifiers, one for GSM850 and one common for GSM1800 and
GSM1900.

• Two passive I/Q mixers (MIX), one for GSM850 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.