AMBE2000 Datasheet, PDF (8/47 Pages) List of Unclassifed Manufacturers – VOCODER CHIP

AMBE-2000™ Vocoder Chip
User’s Manual Version 3.0
2 AMBE™-2000 Application Design Overview
2.1 Basic Operation
In its simplest model, the AMBE-2000™ can be viewed as two separate components, the Encoder and the Decoder. The
Encoder receives an 8kHz. sampled stream of speech data (16-bit linear, 8-bit Alaw, or 8-bit ulaw) and outputs a stream of
channel data at the desired rate. Conversely the Decoder receives a stream of channel data and synthesizes a stream of speech
data. The timing for the interfaces for the AMBE-2000™ Encoder and Decoder are fully asynchronous.
Figure 2-A Basic Operation
AMBE-2000
AMBE-2000
8kHz Speech Data
Encoder
Compressed Data @ 2400-9600bps
Decoder
8kHz Speech Data
8kHz Speech Data
Decoder
Compressed Data @ 2400-9600bps
Encoder
8kHz Speech Data
Typically the speech interface is an external A/D-D/A chip. The format of the incoming and outgoing speech data streams are
coupled, that is to say they must be the same format (16-bit linear, 8-bit Alaw, or 8-bit µlaw). The channel interface is
commonly (but not limited to) an 8 or 16 bit microprocessor or other suitable ‘glue logic’ hardware capable of performing the
rudimentary formatting functions between the AMBE-2000™ channel format and the format of the system channel under
design.
Optional functions of the chip, such as echo cancellation, voice activation/detection, power mode control, data/FEC rate
selection, etc. are controlled either through hardware control pins (see Section 0) and/or through the decoder command
interface (see Section 4) Data sent into the decoder for function control purposes is distinguished from the data to be decoded
into speech through a channel format which is described in Section 4.
2.2 Initial Design Considerations
Some of the initial design considerations the application engineer will face are the following:
• Choice of A/D-D/A chip.
• Choice of Channel Interface.
• Speech and FEC Rates.
2.2.1
A/D – D/A Overview
The choice of the A/D-D/A chip is critical to designing a system with superior voice quality. Given that Alaw and µlaw
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 µlaw interfaces are also provided for the design engineer who is trying to fit to pre-existing conditions or
is under other cost type restraints.
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