Nokia NHM-8NX Series Troubleshooting Instructions page 19

PAMS Technical Documentation
SAW
RX/TX
Z602
INPL
Z700
RX900
INML
RX
GSM
SAW
TX
Z601
INPM
RX RX1800
INMM
PCN
TX
INPH
RX1900
INMH
2
2
VANTL / VANTM
From the RX/TX switch the GSM900 signal is routed to the SAW filter (Z602). The pur-
pose of the SAW filter is to provide out-of band blocking immunity and to provide the
LNA in Mjoelner (N600) with a balanced signal. The front end of Mjoelner is divided into
a LNA and Pre-Gain amplifier before the mixers.
The output from the mixer is feed to Baseband part of Mjoelner where the signals ampli-
fied in the BBAMP and low pass filtered in LPF1 before the DC compensation circuits in
DCN1. The DCN1 output is followed by a controlled attenuator and a second lowpass fil-
ter LPF2. The output from LPF2 is DC centered in DCN2 before being feed to the BB for
demodulation.
The GSM1800 signal chain is similar to GSM900, the SAW filter numbered Z601.
Transmitter signal path
The I/Q signal from the BB is routed two the modulators for both 900 and 1800 MHz. The
output of the modulators is either terminated in a SAW filter ( Z603 ) for GSM 900 or a
balun for GSM1800. Both signals are amplified in buffers whereby a limiting effect takes
place to suppress some of the AM contents of the signal. The amplitude limited signal is
then amplified in the PA (N700) where the gain control takes place. In order to control
the TX level a sample of the signal is taken in a directional coupler ( L709 for GSM900
and L704 for GSM1800) and used in the power loop amplifier in Mjoelner to establish
the right output power. The TX signal from the couplers is feed to the RX/TX switch, used
to select which signal to route to the antenna.
Issue 1 05/02
Figure 1: Receiver signal path
RX
Supply
filter
LNA
Bias
Pre-
LNA
gain
Pre-
LNA
gain
2
LNA
VDDDIG
1/2
RF
Controls
ãNokia Corporation
Troubleshooting Instructions
BBAMP LPF1
BBAMP LPF1
2 2 2
1/4
NHM-8NX
VRX
BIQUAD
AGC
DCN2
DCN1
LPF2
BIQUAD
AGC
DCN2
DCN1
LPF2
Mjoelner
N600
Page 19
VR6
RXIP
RXIM
RXQP
RXQM