PSB7238 SIEMENS [Siemens Semiconductor Group], PSB7238 Datasheet - Page 20

• Manufacturer Part Number: PSB7238
• Description: Joint Audio Decoder-Encoder - Multimode
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

PSB 7238
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 SAA 7110 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.261/263 and multiplexes/demultiplexes video, audio and data according to
H.221/223. The video processor uses DRAMs and SRAMs to store data and program
code.
When operating in the ISDN mode, the H.221 multiplexed data stream is sent via the two
B-channels of the IOM-2 interface to the ISAC-S-TE (ISDN Subscriber Access Controller
for S-interface) which transmits them to the ISDN according to I.430 S0 interface
recommendation. The ISAC-S-TE also handles, together with the attached
microcontroller (e.g. SAB 83C515), D-channel layer-2 and layer-3 call control signaling.
The reverse functions are performed on the B-channels received from the network.
Instead of an S0, it is conceivable to implement any other layer-1 interface just by
replacing the ISAC-S TE by an appropriate transceiver, e.g. by a transceiver for 2-wire
digital transmission ISAC-P PSB 2196 or ISDN echo canceller for 2B1Q.
When operating in the POTS mode, the H.223 multiplexed data stream is sent via the
PCI interface to a V.34 modem. 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.25ter and V.80. In such cases the physical
interface is implementation specific.
To achieve “lip synchronization”, the audio may be delayed with respect to the video.
This is necessary because of the higher transmission delay suffered by the video signal,
due to the elaborate H.261/263 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.
In videophone applications calling for high quality, 7-kHz wide-band audio, the PSB 7238
can be switched to G.722 mode. In this case the rate of the compressed audio is 48, 56
or 64 Kbit/s.
When decoding MPEG bitstreams, the audio D/A conversion is provided by a stereo
audio DAC.
Demomstration board designs for H.320 PC based videophones containing the chip set
from Siemens AG and 8 8 Inc. are available and can be ordered from Siemens/8 8.
Semiconductor Group
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Data Sheet 1998-07-01