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RM-25
Nokia Customer Care
RF troubleshooting
Transmitter
Introduction to RM-25 transmitter troubleshooting
A simple block diagram of the TX part of the phone is shown in the following figure. The voice or data signals
to be transmitted come from the UEME IC in the BB (baseband) area, and go to the Helgo IC, where they are up-
converted to RF. The TX signals going from UEME to Helgo are called the IQ-signals, and consist of two balanced
signals {TXIN, TXIP} and {TXQN, TXQP}, i.e. a total of four signal lines. In addition to the IQ signals, there are also
control signals going between BB and RF.
Figure 122 TX RF block diagram
The following picture shows the two shielding cans where the TX circuitry is located (the lids have been
removed). The upper shielding can contains BB-RF interface circuitry, the Helgo RF system IC, a SAW filter for
the GSM/EGSM band, and a balun for the DCS/PCS band. The lower shielding can contains the power amplifier
(PA) and the antenna switch module (ASM).
Page 7–22
Company Confidential
9235618 (Issue 2)
Copyright ©2005 Nokia. All Rights Reserved.
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