參數(shù)資料
型號(hào)： ZL50212
廠商： Zarlink Semiconductor Inc.
英文描述： 288 Channel Voice Echo Canceller
中文描述： 288頻道語(yǔ)音回聲消除器
文件頁(yè)數(shù)： 10/43頁(yè)
文件大?。?/td> 2166K
代理商： ZL50212
ZL50212
Data Sheet
10
Zarlink Semiconductor Inc.
1.1
Adaptive Filter
The adaptive filter adapts to the echo path and generates an estimate of the echo signal. This echo estimate is then
subtracted from Sin. For each group of echo cancellers, the adaptive filter is a 1024 tap FIR adaptive filter which is
divided into two sections. Each section contains 512 taps providing 64ms of echo estimation. In
Normal
configuration
, the first section is dedicated to channel A and the second section to channel B. In
Extended Delay
configuration
, both sections are cascaded to provide 128ms of echo estimation in channel A. In
Back-to-Back
configuration
, the first section is used in the receive direction and the second section is used in the transmit
direction for the same channel.
2.0
Double-Talk Detector
Double-Talk is defined as those periods of time when signal energy is present in both directions simultaneously.
When this happens, it is necessary to disable the filter adaptation to prevent divergence of the Adaptive Filter
coefficients. Note that when double-talk is detected, the adaptation process is halted but the echo canceller
continues to cancel echo using the previous converged echo profile. A double-talk condition exists whenever the
relative signal levels of Rin (Lrin) and Sin (Lsin) meet the following condition:
Lsin > Lrin + 20log
10
(DTDT)
where DTDT is the Double-Talk Detection Threshold. Lsin and Lrin are signal levels expressed in dBm0.
A different method is used when it is uncertain whether Sin consists of a low level double-talk signal or an echo
return. During these periods, the adaptation process is slowed down but it is not halted. The slow convergence speed
is set using the Slow sub-register in Control Register 4. During slow convergence, the adaptation speed is reduced
by a factor of 2
Slow
relative to normal convergence for non-zero values of Slow. If Slow equals zero, adaptation is
halted completely.
In the G.168 standard, the echo return loss is expected to be at least 6 dB. This implies that the Double-Talk Detector
Threshold (DTDT) should be set to 0.5 (-6 dB). However, in order to achieve additional guardband, the DTDT is set
internally to 0.5625 (-5 dB).
In some applications the return loss can be higher or lower than 6 dB. The EVP allows the user to change the
detection threshold to suit each application’s need. This threshold can be set by writing the desired threshold value
into the DTDT register.
The DTDT register is 16 bits wide. The register value in hexadecimal can be calculated with the following equation:
DTDT
(hex)
= hex(DTDT
(dec)
* 32768)
where 0 < DTDT
(dec)
< 1
Example:
For DTDT = 0.5625 (-5 dB), the hexadecimal value becomes
hex(
0.5625 * 32768
)
= 4800
hex
2.1
Path Change Detector
Integrated into the EVP is a Path Change Detector. This permits fast reconvergence when a major change occurs
in the echo channel. Subtle changes in the echo channel are also tracked automatically once convergence is
achieved, but at a much slower speed.
The Path Change Detector is activated by setting the PathDet bit in Control Register 3 to “1”. An optional path
clearing feature can be enabled by setting the PathClr bit in Control Register 3 to “1”. With path clearing turned on,
the existing echo channel estimate will also be cleared (i.e. the adaptive filter will be filled with zeroes) upon detection
of a major path change.
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
ZL50212/GBC 制造商:Microsemi Corporation 功能描述:ECHO CANCELLER CHIP 288CH G.164/G.165/G.168/G.711 W/ TONE DE - Trays
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ZL50232 制造商:ZARLINK 制造商全稱:Zarlink Semiconductor Inc 功能描述:32 Channel Voice Echo Canceller
ZL50232/GDC 制造商:Microsemi Corporation 功能描述:ECHO CANCELLER CHIP 32CH G.164/G.165/G.168/G.711 W/ TONE DET - Trays
ZL50232/QCC 制造商:Microsemi Corporation 功能描述:ECHO CANCELLER CHIP 32CH G.164/G.165/G.168/G.711 W/ TONE DET - Trays
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