PSB7230 데이터 시트보기 (PDF) - Siemens AG
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PSB7230 Datasheet PDF : 179 Pages
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PSB 7230
Introduction
The ARCOFI-SP (Audio Ringing Codec Filter) is a hands-free codec for 3.1 kHz voice
which performs detection and elaborate balancing of the received and transmitted audio
to suppress undesirable effects due to acoustical feedback of the signal from the remote
subscriber. The quality obtained is very close to that of echo-free full duplex
conferencing.
The video is captured by a PAL/NTSC camera and digitized and demodulated e.g. by a
standard SAA7110 which is directly connected to the video processor. Alternatively, a
digital camera may be used, which can be connected directly to the video processor.
The video processor compresses and decompresses video according to the ITU-T
standards H.263 and multiplexes/demultiplexes video, audio and data according to
H.223. The video processor uses DRAMs and SRAMs to store data and program code.
The H.223 multiplexed data stream is either sent via the PCI interface to an external
V.34+ modem or via host or IOM-interface to an on-board modem (e.g. Siemens
ISAR-34 (PSB7115) and ALIS (PSB 4595/4596)). The modem must be able to work in
synchronous mode, i.e. the H.223 multiplexed data shall be applied directly to the V.34+
synchronous data pump. When an external, non-integrated V.34+ modem is utilized,
control between the modem and the terminal shall be via ITU-T V.80.
For the on-board modem the ISAR 34 constitutes the data pump transferring the data
with 33.6 Kbit/s in both directions.
The ALIS chipset substitutes the conventional codec and DAA circuit. Since the ALIS it
is a programmable solution, it can be configured by software to fit the approval
requirements of all different countries, thus one hardware solution can be produced for
all markets over the world. The decoupling between line and modem is done by
capacitors instead of transmformers, thus offering very small size and low cost
implementations.
To achieve “lip synchronization”, the audio may be delayed with respect to the video.
This is necessary because of the higher transmission delay caused by the video signal,
due to the elaborate H.263 video compression. A delay of approximately 0.5 seconds is
enough in most practical cases. To make maximum use of the existing memory in the
system, the delay is performed by the video processor with its external RAMs.
When decoding MPEG bitstreams, the audio D/A conversion is provided by a stereo
audio DAC.
Semiconductor Group
18
Data Sheet 1998-07-01
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