AMBE-2000™ Vocoder Chip

User’s Manual Version 3.0

page 19

Confidential Proprietary, Subject to Change

4 Channel Interface

4.1

Overview

The Channel Interface is the general term used for the interface for the compressed bits coming from the encoder and the

compressed bits going to the decoder. This same interface is also used to output status information from the encoder and

decoder such as whether a DTMF tone has just been detected in the speech input, or whether the decoder has detected and

synthesized a frame of silence. Additionally, this interface is used to perform more complex control operations on both the

encoder and decoder (usually at start-up). These control functions include speech data and FEC rate control as well as enabling

features such as echo cancellation.

It is important to realize that not all data being output from the AMBE-2000 is intended for transmission over the channel.

Status type of data is typically only useful at the ‘local’ end. In most voice transmission systems, the actual encoded bits are

extracted from the channel formatting, combined into the systems transmission stream, sent over the transmission path,

extracted from the transmission path at the receiving end, and reassembled into the AMBE-2000’s channel format for synthesis

by the decoder.

Figure 4-A Channel Interface Overview

Overhead Data

(Header, Status)

Voice Data (48 to 192 bits)

System extracts

relevant Voice Data bits

and formats them for

transmission over

Channel

System Overhead

Voice Data (48 to 192 bits)

Typical Voice Frame Output From Encoder

Overhead Data

(Header, Control)

Voice Data (48 to 192 bits)

Typical Voice Frame Input to the Decoder

System extracts

relevant Voice Data bits

and formats them for

Input into the Decoder

adding Header and

Control Information

Transmission Channel

4.2

Serial Configuration Selection

The hardware interface to the Channel Interface is configured as a serial interface based exclusively on the hardware settings of

CHANN_SEL[1-0]. See Table 4-A.