AMBE-2000™ Vocoder Chip Users Manual
Version 4.92, June, 08
DVSI Confidential Proprietary, Subject to Change
Page 40
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6
A/D-D-A Interface
6.1
A/D-D/A Overview
The interface from the analog world of speech to the AMBE-2020™ 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-2020™ 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-2020™.
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 companding and
sampling rate as well as the sequence of programming words for the programmable devices, specifically the AD73311.
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 2 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
corresponding to V
CC
.
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 73311
32kHz
01b
Generic
µ
law 8kHz
10b
Generic Alaw 8kHz
11b
