Logic/Audio Module - Benefon VEGA TGP-60-EU Service Manual

5.3 Logic/audio module

OA1800
Main functions of the GSM phone are composed with Siemens HiGold chipset. It
operates on 3 V power source.
Baseband board is hereafter often referred as OA board.
RX: The amplified differential baseband signal is fed to the receive path input of
Gaim. Both components I and Q are converted independently from each other from
analog to digital forming two 13 Mbit/s bit streams. After signal reconstruction and
digital filtering, equalization, channel and speech decoding and voiceband (interpo-
lation) filtering on Gold-SP a resulting 1Mbit/s bit stream is digital-to-analog con-
verted and ampilified by a programmable gain stage in the voiceband processing
part of GAIM. The output signal is directly connected to the earpiece.
TX: GAIM amplifies the input signal from the microphone. After analog-to-digital con-
version a 1 Mbit/s bit stream is generated and fowarded to Gold-SP where voice-
band (decimation) filtering, speech and channel encoding and GMSK modulation is
performed. The digital 10 bit I and Q baseband components (GMSK modulated and
8 times oversampled) are delivered to GAIM in double-multiplexed form. They are
converted in parallell from digital to analog and fed into RF.
4a1800gb
Product: TGP-60-EU (Vega) /
15.1.1999
OA1800
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