AMBE-2000 Digital Voice Systems, Inc., AMBE-2000 Datasheet - Page 41

• Manufacturer Part Number: AMBE-2000
• Description: 2.0 - 9.6 KBPS Single ic For Toll-quality, Low Data Rate, Real Time Speech Compression
• Manufacturer: Digital Voice Systems, Inc.

*Note: AMBE+ is only used for speech rates at 3600 bps and higher. Any rates below 3600 bps use
a modified algorithm similar to the AMBE algorithm.
7.3
The AMBE-2000™ Vocoder Chip provides a 16-millisecond echo canceller that is suitable for canceling the local echo caused
by a 2-to-4 wire hybrid and can achieve echo cancellation of approximately 30dB or more. Only the linear portion of the echo
is cancelled, so circuits should be designed to minimize non-linearities.
The AMBE-2000™ Vocoder Chip employs an adaptive echo cancellation algorithm to cancel echoes of the decoder output
present at the encoder input.
The Echo Return Loss (ERL) of the analog circuit must be 6dB or more (in diagram ERL = Echo Path A – Echo Path B) for
proper echo canceller operation.
The echo canceller can be activated either through the hardware pin 78, ECHOCAN_EN, or through the Control Word
interface described in section 5.2.9. See section 7.1 for an important note about the ECHOCAN_EN pin.
Note: The AMBE-2000™ Echo Canceller will operate with linear codecs only.
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AMBE-2000
Table 7-B Rate Selection Using Rate Info 0-4, AMBE-2000™ only (AMBE+™)*
RATE_SEL4
Echo Cancellation
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Decoder
Encoder
Pin
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Figure 7-A Typical Echo Path
RATE_SEL3
Pin
1
0
0
0
0
1
0
1
0
1
1
0
1
0
1
1
8kHz Speech Data
8kHz Speech Data
RATE_SEL2
Pin
1
0
0
1
0
0
1
0
0
0
0
1
1
1
1
1
A/D-D/A
AMBE-2000™ Vocoder Chip
User’s Manual Version 4.0
RATE_SEL1
Pin
1
0
0
1
1
0
1
0
1
1
1
0
0
0
0
1
Echo Path A
Echo Path B
RATE_SEL0
Pin
1
0
1
0
0
0
1
1
1
0
1
0
0
1
1
0
4 to 2 wire
Converter
Speech Rate
2000*
3600
4000
2400
4800
4000
3600
2400
6400
4000
4400
8000
4000
9600
3600
2400
(bps)
FEC Rate (bps)
1600
1200
2400
2400
2800
4000
6000
7200
800
0
0
0
0
0
0
0
Page 41
Total Rate
2000
3600
4000
4800
6400
7200
8000
9600
(bps)