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Browse Prior Art Database

Echo Canceling for xDSL Applications

IP.com Disclosure Number: IPCOM000022639D
Original Publication Date: 2004-Apr-25
Included in the Prior Art Database: 2004-Apr-25
Document File: 3 page(s) / 135K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

So far, xDSL CO (extended Data Subscriber Line Central Office) chipsets use a bfilter (balancing filter) scheme with a pure resistive hybrid for analog echo canceling (Figure 1). The disadvantage of this method is that two inputs, a receive filter and a bfilter (RX and BF), are required, and a mismatch in the two paths can cause performance degradation. Especially a high gain stage inside the BF can cause high noise and distortion. Therefore, it is proposed to use more sophisticated hybrid impedances plus a simple high pass/low pass filter (hp/lp) to reach a better echo attenuation so that the output of the hybrid can be connected to newer AFE (Analog Front End) pins with lower power consumption, which have a very low max volt peak tolerance. The BF noise source is thereby removed.

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Echo Canceling for xDSL Applications

Idea: Sergio Walter, AT-Villach; Alexander Kahl, AT-Villach

So far, xDSL CO (extended Data Subscriber Line Central Office) chipsets use a bfilter (balancing filter) scheme with a pure resistive hybrid for analog echo canceling (Figure 1). The disadvantage of this method is that two inputs, a receive filter and a bfilter (RX and BF), are required, and a mismatch in the two paths can cause performance degradation. Especially a high gain stage inside the BF can cause high noise and distortion.

Therefore, it is proposed to use more sophisticated hybrid impedances plus a simple high pass/low pass filter (hp/lp) to reach a better echo attenuation so that the output of the hybrid can be connected to newer AFE (Analog Front End) pins with lower power consumption, which have a very low max volt peak tolerance. The BF noise source is thereby removed.

Based on the classic hybrid scheme, an optimized design of the two impedance branches of the hybrid cancels the transmit signal and noises coming from all the DS (Down Stream) blocks, with particular emphasis on the US (Up Stream) frequency range to reach the maximum echo canceling and increase the UP SNR (Signal to Noise Ratio). The lp following the hybrid takes care of the echo signal (DS) suppression together with the hybrid functionality in the DS frequency range. The hp after the lp provides the blocking functionality regarding the voice related signals.

Figure 2 and 3 show two versions of the new hybrid. The second one is a low-budget version, which avoids the use of the cost-intensive capacities Cld_1 and Cld_2 of Figure...