Transmitter Signal Path - Nokia NPM-10 Series Troubleshooting Instructions

CCS Technical Documentation
From the Antenna switch, the GSM850 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
an LNA and Pre-Gain amplifier before the mixers.
The output from the mixer is fed to the Baseband part of Mjoelner where the signal is
amplified in the BBAMP and low pass filtered in LPF1 before the DC compensation cir-
cuits in DCN1. The DCN1 output is followed by a controlled attenuator and a second
lowpass filter LPF2. The output from LPF2 is DC centered in DCN2 before being fed to the
BB for demodulation.
The GSM1900 signal chain is similar to GSM850, the SAW filter numbered Z601.

Transmitter Signal Path

The I/Q signal from the BB is routed to the modulators for both 850 MHz and 1900 MHz.
The output of the modulators is either terminated in a SAW filter (Z603) for GSM850 or
a balun (T602) for GSM1900. Both signals are amplified in buffers, which are operated in
a soft compression region to suppress some of the AM contents of the signal and to
maintain a certain signal level at the PA inputs. The amplitude limited signal is then
amplified in the PA (N700). The detector diode (V700), some discrete components, and
the Mjoelner IC (N600) make up the transmitter gain control circuitry. In order to estab-
lish the right TX output power level, a sample of the signal is taken in a directional cou-
pler (L709 for GSM850 and L704 for GSM1900) and used in the gain control loop. The TX
signal from the couplers is fed to the Antenna switch, which is used to select which sig-
nal to route to the antenna.
Issue 1 03/2003
Nokia Corporation
Troubleshooting Instructions RF
Confidential
NPM-10
Page 7