Benefon Twin, Service Manual

Page: 28 / 53

08.02.2002
4c2300gb.fm 8
Product:TGP71EU & TGP73EU / OC2300
5.1.1.2 Voice Band Codec
The VBC (ADI chip AD6425) contains complete codecs for the conversion of
voiceband and baseband signals as well as D/A- converters to control the radio
subsystem and auxiliary A/D-converter for signal monitoring purposes.
The voiceband codec is a complete analog front-end, which can interface
directly with a microphone and a speaker.
The baseband codec is a complete low power, two channel, input/output port
with signal conditioning. The transmit path consists of an on-chip burst store, a
GMSK modulator and two high speed DACDs with output reconstruction filters.
The receive path consists of two 15 bit Sigma Delta A/D converters, which
include high performance digital filters for RF-channel selection.
The auxiliary section of the VBC consists of D/A converters for AFC, AGC and
for control of the transmit-burst envelope.
The auxiliary section also includes A/D converters that measures different volt-
ages and temperatures.