AMBE-2000™ Vocoder Chip

User’s Manual Version 3.0

page 35

Confidential Proprietary, Subject to Change

6

A/D-D-A Interface

6.1

A/D-D/A Overview

The interface from the analog world of speech and the AMBE-2000™ is typically an A/D-D/A chip. Selection of the A/D-D/A

chip should be made carefully, with a preference given to 16 bit linear devices. Additionally, consideration should be given for

signal to noise ratios and filtering characteristics typically built into many such devices. Generally speaking, the flatter the

frequency response over the voice spectrum (20-4000Hz) the better the overall system will sound.

The AMBE-2000™ Vocoder Chip operates with a speech data sample rate of 8kHz for both the A/D and D/A interfaces. This

8kHz data is input and output using a serial port on the AMBE-2000.

In order to simplify the process of configuring the interface to the A/D-D/A chip, a number of preset configurations can be

chosen through the CODEC_SEL[1-0] pins shown in Table 6-A. These preset configurations control signal directions for the

interface as well as the sequence of programming words for the programmable devices, specifically the AD7331AR.

6.2

Configuring the A/D-D/A Interface using CODEC_SEL[1-0]

In order to simplify the process of configuring the A/D-D/A interface certain preset configurations are available to the user.

Selection of these preset modes is made through the 3 hardware pins CODEC_SEL[1-0]. In Table 6-A, the 2 digit binary value

for CODEC_SEL[1-0] corresponds to the levels present on the hardware pins, with a 0 corresponding to GND, and a 1

Table 6-A CODEC_SEL[1-0] : A/D-D/A Hardware Configuration Values

A/D-D/A Type

CODEC_SEL[1-0]

pins

85,84

Generic 16 bit Linear

8Khz

00b

Analog Devices 7331

32kHz

01b

10b

Generic Alaw 8kHz

11b