AMBE-1000 Digital Voice Systems, Inc., AMBE-1000 Datasheet - Page 15

• Manufacturer Part Number: AMBE-1000
• Manufacturer: Digital Voice Systems, Inc.

2.2.1
2.2.2
The AMBE-1000 is not recommended for new designs.
Please refer to the AMBE-2000/2020 product line.
A/D – D/A Overview
Channel Interface Overview
The choice of the A/D-D/A chip is critical to designing a system with superior voice
quality. Given that Alaw and law companding chips are already incorporating some
compression to reduce the number of bits per sample, it is recommended that, when
possible, a 16-bit linear device be used for maximum voice quality. When choosing a
device, pay particular attention to Signal to Noise ratios and Frequency Responses of
any filters that may be present on the analog front end of these chips. The Alaw and
existing conditions or is under other cost type restraints.
The specifics of the hardware interface to the A/D-D/A data are flexible. Clocking and
strobe signals can be internal or external to the AMBE-1000™.
interface to send ‘control’ words to a programmable A/D-D/A is provided. For a full
description of the A/D-D/A interface see Section 5.
The channel interface is meant to be flexible to allow for easy integration with the
system under design. The basic hardware unit of the interface is either a parallel port
or a serial port. Both parallel and serial modes can run in passive or active modes.
Simply stated, the control signals for parallel and serial modes can be derived by the
AMBE-1000™ chip or they can be derived externally.
Under normal operation, every 20msec the encoder outputs a frame of coded bits, and
the decoder needs to be delivered a frame of coded bits. There is some formatting of
the data for both the encoder and the decoder. The primary purpose of the formatting
is to provide alignment information for the encoded bit stream.
formats, Framed and Unframed (in previous versions of this manual these modes
corresponded to packetized and unformatted modes respectively). Parallel mode runs
exclusively in Framed mode.
mode.
The Framed and Unframed modes are explained in full detail in Section 4, but
essentially the two formats are trying to achieve the same function, to provide
positional information regarding the outgoing and incoming coded data streams.
Framed mode each 20msecs of output data from the encoder is preceded by a known
structure. This structure also embeds some status type flags, meant for local control
purposes, within it. The only data from the Framed format that is typically sent across
the transmission channel under design are the actual encoded bits at the desired rate.
In Framed mode, it is the responsibility of the designed system to pass enough
information along with the encoded bits such that the Framed format needed by the
decoder can be reconstructed on the other side. This extra information, or overhead, is
going to be very specific to the system under design, but at a minimum needs to pass
enough information to reliably reconstruct the 20msec frame structure at the other end
for the decoder.
In Unframed mode the data coming out of the encoder can be thought of as a
continuous stream of voice data with the framing information embedded within the
encoded bits. One advantage of this type of set-up is that the system does not have to
add any bandwidth for overhead to the channel. The disadvantage is that the decoder
needs 10-12 incoming frames in order to gain synchronization with the data stream
before it can properly synthesize the speech waveform.
only commits a single bit per frame to maintaining data alignment. In higher error rate
channels the performance will be improved by adding more bits per frame to the
alignment information (which is more easily performed when using Framed mode)
law interfaces are also provided for the design engineer who is trying to fit to pre-
The AMBE-1000 is not recommended for new designs.
Please refer to the AMBE-2000/2020 product line.
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Serial mode can run in either Framed or Unframed
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Also, the Unframed mode
The data has two
Additionally, an
In