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參數(shù)資料
| 型號(hào)： | MT9300BV |
| 廠商： | ZARLINK SEMICONDUCTOR INC |
| 元件分類： | 數(shù)字傳輸電路 |
| 英文描述： | Multi-Channel Voice Echo Canceller |
| 中文描述： | DATACOM, ISDN ECHO CANCELLER, PBGA208 |
| 封裝： | 17 X 17 MM, 1.30 MM HEIGHT, MO-192, LBGA-208 |
| 文件頁數(shù)： | 9/39頁 |
| 文件大小： | 629K |
| 代理商： | MT9300BV |
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MT9300B
Data Sheet
9
Zarlink Semiconductor Inc.
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 128 ms 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.
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.
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 get 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 MT9300B 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 (-5dB), the
hexadecimal value becomes
hex(
0.5625 * 32768
)
= 4800H
Path Change Detector
Integrated into the MT9300B 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 A3/B3 to "1". An optional path
clearing feature can be enabled by setting the PathClr bit in Control Register A3/B3 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) |
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| MT9315 | 制造商:ZARLINK 制造商全稱:Zarlink Semiconductor Inc 功能描述:CMOS Acoustic Echo Canceller |
| MT9315AE | 制造商:ZARLINK 制造商全稱:Zarlink Semiconductor Inc 功能描述:CMOS Acoustic Echo Canceller |
| MT9315AP | 制造商:ZARLINK 制造商全稱:Zarlink Semiconductor Inc 功能描述:CMOS Acoustic Echo Canceller |
| MT933 | 制造商:ZARLINK 制造商全稱:Zarlink Semiconductor Inc 功能描述:3.3V 10/100 Fast Ethernet Transceiver to MII |
| MT933CG | 制造商:ZARLINK 制造商全稱:Zarlink Semiconductor Inc 功能描述:3.3V 10/100 Fast Ethernet Transceiver to MII |
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