Abstract:
A physical layer (PHY) device including i) an input configured to receive a first transmit signal transmitted from a remote device, and ii) an output configured to transmit a second transmit signal from the PHY device to the remote device. The second transmit signal causes interference in a receive signal at the input of the PHY device. The PHY device further including a selection module configured to select a first control signal to cancel the interference in the receive signal when the receive signal does not include the first transmit signal and a second control signal to cancel the interference in the receive signal when the receive signal includes the first transmit signal. The interference includes (i) an echo due to the second transmit signal or (ii) crosstalk due to a third transmit signal output by a local PHY device proximate to the PHY device.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 10/942,761, filed Sep. 16, 2004. The disclosure of the above application is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to echo/near-end crosstalk (NEXT) cancellation systems for network devices, and more particularly to echo/NEXT cancellation systems for Ethernet network devices. 
     BACKGROUND OF THE INVENTION 
     Ethernet network devices commonly utilize data communications media that include multiple full-duplex communications channels. For example, an Ethernet communications medium may include two or four pairs of twisted wire. An Ethernet network device that is compliant with IEEE 802.3ab (1000BASE-T) Gigabit Ethernet standards utilizes a data communications medium that includes 4 pairs of twisted wire. The Gigabit Ethernet network device also employs a full-duplex transmission scheme. Therefore, each of the 4 pairs of twisted wire simultaneously transmit and receive data. However, the transmit and receive signals overlap and may interfere with each other. 
     Referring now to  FIG. 1 , first and second exemplary Ethernet network devices  10  and  12 , respectively, communicate over a data communications medium with four full-duplex channels  14 -A,  14 -B,  14 -C, and  14 -D. For example, the first and second Ethernet network devices  10  and  12 , respectively, may be Gigabit Ethernet network devices. Each of the channels  14  at the first and second Ethernet network devices  10  and  12 , respectively, are identified as A, B, C, or D and include a transceiver  16  and a hybrid  18 . The transceivers  16  independently process transmitted and received data. The hybrids  18  facilitate full-duplex communications over the data communications medium. 
     Echo is interference between transmitted and received data on an individual channel. Echo may be generated when a near-end transmitted signal is reflected from a transmit path onto a receive path. Echo may also be generated when at least a portion of a transmitted signal on an individual pair of twisted wire is reflected back from the target device.  FIG. 1  illustrates both near echo  20  and far echo  22  with respect to the transceiver  16 -A- 1  on channel A of the first Ethernet network device  10 . 
     Near-end crosstalk (NEXT) is interference between received data on one channel and transmitted data on one or more of the remaining channels of a data communications medium.  FIG. 1  illustrates NEXT interference  24 -B,  24 -C, and  24 -D from channels B, C, and D  14 -B,  14 -C, and  14 -D, respectively, that is received at channel A  14 -A of the first Ethernet network device  10 . Therefore, the received signal at channel A  14 -A of the first Ethernet network device  10  potentially includes data transmitted from channel A  14 -A of the second Ethernet network device  12 , echo  20  and/or  22  from channel A  14 -A of the first Ethernet network device  10 , and NEXT  24 -B,  24 -C, and  24 -D, respectively, from channels B, C, and D  14 -B,  14 -C, and  14 -D of the first Ethernet network device  10 . 
     Referring now to  FIG. 2 , a physical layer device  32  of an exemplary Ethernet network device processes data for a full-duplex communications channel of a data communications medium. The physical layer device  32  includes a receive path  34  and a transmit path  36 . An input of a first analog filter  38  receives an analog receive signal from the communications channel. The first analog filter  38  filters the analog receive signal and generates a filtered receive signal. An input of an analog-to-digital converter (ADC)  40  receives the filtered receive signal and generates a digital receive signal. A first input of a digital signal processor (DSP)  42  receives the digital receive signal and generates a recovered bit pattern. In an exemplary embodiment, the DSP  42  transmits the recovered bit pattern to a descrambler in a physical coding sublayer (PCS) device in the physical layer device  32 . 
     A second input of the DSP  42  in the receive path  34  receives a scrambled bit pattern from a scrambler in the PCS device. The DSP  42  outputs a digital transmission signal based on the scrambled bit pattern. An input of a digital-to-analog converter (DAC)  44  receives the digital transmission signal and generates an analog transmission signal. An input of a second analog filter  45  receives the analog transmission signal and outputs a filtered transmission signal. For example, the second analog filter  45  may transmit the filtered transmission signal to a line driver in the communications channel. 
     The input of the first analog filter  38  receives an echo signal. The echo signal is interference from the filtered analog transmission signal. The input of the first analog filter  38  also receives NEXT interference from the other communications channels of the data communications medium. The contribution of echo/NEXT interference may be significant compared to a remotely transmitted signal. 
     An echo/NEXT cancellation system may be employed to reduce adverse effects caused by echo/NEXT interference at the input of the first analog filter  38 . In one approach, multiple analog and/or digital echo/NEXT cancellers are employed to reduce adverse effects from echo/NEXT interference signals in the channel. However, adjusting the operating parameters of multiple echo/NEXT cancellers is very complicated. Also, additional echo/NEXT cancellers require additional clock signals in the channel, which makes clock signal synchronization difficult. 
     SUMMARY OF THE INVENTION 
     An adaptive analog echo/near-end crosstalk (NEXT) cancellation system according to the present invention includes a selector that outputs a first error control signal when a first receive signal does not include a remotely transmitted signal and a second error control signal when the first receive signal includes a remotely transmitted signal. An echo/NEXT cancellation module communicates with the selector and generates an estimated echo/NEXT signal based on the first error control signal and a first transmit signal when the first receive signal does not include a remotely transmitted signal and based on the second error control signal and the first transmit signal when the first receive signal includes a remotely transmitted signal. 
     In other features, the first receive signal and the first transmit signal are from a first communications channel. In this case, the echo/NEXT cancellation module generates an estimated echo signal that is included in the first receive signal. Alternatively, the first receive signal is from a first communications channel and the first transmit signal is from a second communications channel. In this case, the echo/NEXT cancellation module generates an estimated NEXT signal that is included in the first receive signal. 
     In still other features of the invention, a system comprises the adaptive analog echo/NEXT cancellation system and further comprises a summing module that receives the first receive signal and the estimated echo/NEXT signal and that generates an echo/NEXT filtered receive signal by subtracting the estimated echo/NEXT signal from the first receive signal. A system comprises the adaptive analog echo/NEXT cancellation system and further comprises an analog filter that receives the first receive signal and that generates a filtered receive signal. The adaptive analog echo/NEXT cancellation system includes a bit slicer that receives the filtered receive signal and that generates the first error control signal. 
     In yet other features, a system comprises the adaptive analog echo/NEXT cancellation system and further comprises a first analog-to-digital converter (ADC) that receives the first receive signal and that generates a digital receive signal. A digital signal processor (DSP) receives the digital receive signal and generates a recovered bit pattern based on the digital receive signal. The DSP generates third and fourth error control signals. The adaptive analog echo/NEXT cancellation system includes a summing module that receives the third and fourth error control signals and that generates the second error control signal by summing the third and fourth error control signals. 
     In still other features of the invention, a digital-to-analog converter (DAC) receives a digital transmit signal and generates the first transmit signal. The DSP includes a digital echo canceller (DEC) module that generates the third error control signal based on the digital transmit signal and the fourth error control signal. The DSP includes a finite impulse response (FIR) filter that receives the digital receive signal and that generates a filtered digital signal. A bit detector receives the filtered digital signal and generates the recovered bit pattern. A summing module receives the filtered digital signal and the recovered bit pattern and generates the fourth error control signal by subtracting the filtered digital signal from the recovered bit pattern. 
     In yet other features, the selector includes a multiplexer that selectively outputs one of the first error control signal or the second error control signal. The echo/NEXT cancellation module includes a first ADC converter that receives the first transmit signal and that generates a sampled transmit signal. A product module receives the first error control signal when the first receive signal does not include a remotely transmitted signal and the second error control signal when the first receive signal includes a remotely transmitted signal and receives the sampled transmit signal. The product module generates an adaptation signal by multiplying one of the first or second error control signals and the sampled transmit signal. An adaptive analog filter generates the estimated echo/NEXT signal based on the first transmit signal and the adaptation signal. 
     In still other features of the invention, the echo/NEXT cancellation module further includes a delay module that selectively delays the one of the first or second error control signals. The echo/NEXT cancellation module further includes a loop filter that receives the adaptation signal and that generates a filtered adaptation signal. The adaptive analog filter generates the estimated echo/NEXT signal based on the first transmit signal and the filtered adaptation signal. A physical layer device comprises the adaptive analog echo/NEXT cancellation system. An Ethernet network device comprises the physical layer device. The physical layer device is compliant with at least one of IEEE 802.3ab (1000BASE-T) and/or IEEE 802.3an (10GBASE-T) standards. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a functional block diagram of a data communications medium that includes four full-duplex communications channels according to the prior art; 
         FIG. 2  is a functional block diagram of a physical layer device that processes incoming/outgoing data for a communications channel of a data communications medium according to the prior art; 
         FIG. 3  is a functional block diagram of a physical layer device with a digital signal processor (DSP) that includes a digital echo/NEXT cancellation system; 
         FIG. 4  is a functional block diagram of an adaptive analog echo/NEXT cancellation system according to the present invention; 
         FIG. 5  is a functional block diagram of the adaptive analog echo/NEXT cancellation system of  FIG. 4  illustrated in further detail; 
         FIG. 6  is a functional block diagram of an exemplary comprehensive analog echo/NEXT cancellation system for a communications channel of a data communications medium; and 
         FIG. 7  is a flowchart illustrating steps performed by the adaptive analog echo/NEXT cancellation system to select the error control signal that is output by the selector. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the term module and/or device refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. 
     Referring now to  FIG. 3 , a physical layer device  46  includes a receive path  47  and a transmit path  48 . The transmit path  48  may be from the same channel as the receive path  47  or may be from a different channel of the data communications medium. An input of an analog filter  49  receives an analog receive signal. The analog filter  49  filters the analog receive signal and generates a filtered receive signal. An input of an analog-to-digital converter (ADC)  50  receives the filtered receive signal and generates a digital receive signal. A first input of a digital signal processor (DSP)  51  receives the digital receive signal and generates a recovered bit pattern. A transmitter  52  generates a digital transmission signal. An input of a digital-to-analog converter (DAC)  53  receives the digital transmission signal and generates an analog transmission signal. 
     The DSP  51  includes a digital echo/NEXT cancellation system  54 . Operation of the ADC  50  is synchronized to an input clock signal. An input of a finite impulse response (FIR) filter  56  receives the digital receive signal from the ADC  50  and generates a filtered digital receive signal. An input of a bit detector  58  receives the filtered digital receive signal and generates the recovered bit pattern. An input of a decision feedback equalizer (DFE)  60  receives the recovered bit pattern and generates a digital feedback signal. A first summing module  62  receives the filtered digital receive signal and the digital feedback signal. Therefore, the signal at the input of the bit detector  58  is equal to a sum of the filtered digital receive signal from the FIR filter  56  and the digital feedback signal from the DFE  60 . 
     Operating parameters of the FIR filter  56  and the DFE  60  are periodically adjusted so that the DSP  51  functions as desired under changing signal conditions. A second summing module  64  receives the filtered digital receive signal and the recovered bit pattern. The second summing module  64  generates an error control signal  66  that is equal to the difference between the recovered bit pattern and the filtered digital receive signal. The FIR filter  56  and the DFE  60  receive the error control signal  66 . Operating parameters of the FIR filter  56  and the DFE  60  are adjusted based on value of the error control signal  66 . 
     A digital echo canceller (DEC)  68  receives the digital transmission signal from the transmit path  48  and generates a digital echo/NEXT cancellation signal. The DEC  68  also receives the error control signal  66  from the second summing module  64 . Operating parameters of the DEC  68  are adjusted based on a value of the error control signal  66 . A third summing module  70  receives the digital receive signal and the digital echo/NEXT cancellation signal. The third summing module  70  outputs the difference between the digital receive signal and the digital echo/NEXT cancellation signal. Therefore, the DEC  68  effectively filters the digital receive signal to reduce adverse effects from echo/NEXT interference. 
     The transmit path  48  in  FIG. 3  may be from the same channel as the receive path  47  or may be a transmit path  48  from another channel in the data communications medium. When the transmit path  48  is from the same channel as the receive path  47 , the DEC  68  generates an estimated echo signal. When the transmit path  48  is from another channel in the data communications medium, the DEC  68  generates an estimated NEXT signal. 
     The digital echo/NEXT cancellation system  54  is effective at filtering the digital receive signal when the level of echo/NEXT interference in the digital receive signal is below a maximum threshold. However, the effectiveness of the digital echo/NEXT cancellation system  54  reduces as the contribution of echo/NEXT interference signals in the analog receive signal increases. For example, Ethernet network devices that are compliant with IEEE 802.3an (10GBASE-T) are being developed. The increased data transmission rate requirements of 10GBASE-T lead to increased levels of echo/NEXT interference in receive paths  47  of the data communications channels. This dramatically reduces the resolution of the ADC  50  in the receive path  47 . 
     The present invention is an adaptive analog echo/near-end crosstalk (NEXT) cancellation system. The adaptive analog echo/NEXT cancellation system includes an adaptive analog filter that generates estimated echo/NEXT signals to reduce echo/NEXT interference in the receive paths of communications channels. Operation of the adaptive analog filter is analogous to operation of a finite impulse response (FIR) filter in a digital signal processor (DSP) and the adaptive analog filter includes adjustable coefficients. The adaptive analog filter operates in two modes based on the presence of remotely transmitted signals in the receive path as will be further described below. 
     Referring now to  FIG. 4 , a physical layer device  78  of an exemplary Ethernet network device processes data for a communications channel of a data communications medium. The communications channel includes a receive path  80  and a transmit path  82 . The transmit path  82  may be from the same channel as the receive path  80  or may be from a different channel of the data communications medium. An analog front end (AFE) device  83  includes an analog filter  84  and a first analog-to-digital converter (ADC)  86 . An input of the analog filter  84  receives an analog receive signal and generates a filtered receive signal. For example, an analog amplifier may transmit the analog receive signal to the analog filter  84 . An input of the first ADC  86  receives the filtered receive signal and a first clock signal and generates a digital receive signal. A DSP  88  includes an FIR filter  90 . An input of the FIR filter  90  receives the digital receive signal and generates a filtered digital receive signal. An input of a bit detector  92  in the DSP  88  receives the filtered digital receive signal and generates a recovered bit pattern. For example, the bit detector  92  may transmit the recovered bit pattern to a descrambler in a PCS device. 
     A transmitter  93  in the transmit path  82  generates a digital transmission signal. An input of a digital-to-analog converter (DAC)  94  in the transmit path  82  receives the digital transmission signal and generates an analog transmission signal. For example, the DAC  94  may transmit the analog transmission signal to a line driver in the in the communications channel. An input of a decision feedback equalizer (DFE)  96  in the DSP  88  receives the recovered bit pattern and generates a feedback signal. A first summing module  98  receives the feedback signal and the filtered digital receive signal is equal to the sum of the filtered digital receive signal and the feedback signal at the input of the bit detector  92 . A second summing module  100  receives the filtered digital receive signal from the input of the bit detector  92  and the recovered bit pattern from the output of the bit detector  92 . The second summing module  100  outputs an error control signal e 2    102 , which is equal to the difference between the recovered bit pattern and the filtered digital receive signal. The FIR filter  90  and the DFE  96  receive the error control signal e 2    102  and a value of the error control signal e 2    102  adjusts the operating parameters of the FIR filter  90  and the DFE  96 . 
     The DSP  88  includes a digital echo canceller (DEC)  104  that receives the digital transmission signal and the error control signal e 2    102 . The DEC  104  generates a digital echo/NEXT cancellation signal based on the digital transmission signal. A third summing module  106  receives the digital echo/NEXT cancellation signal and outputs the difference between the digital receive signal and the digital echo/NEXT cancellation signal. The DEC  104  estimates echo and/or NEXT interference signals in the digital receive signal. Operating parameters of the DEC  104  are adjusted based on a value of the error control signal e 2    102 . 
     An adaptive analog echo/NEXT cancellation system  108  according to the present invention includes a bit slicer  110  that receives the filtered receive signal. The bit slicer  110  generates an error control signal e 1    112  based on the filtered receive signal. A fourth summing module  114  in the adaptive analog echo/NEXT cancellation system  108  receives the digital echo/NEXT cancellation signal and the error control signal e 2    102 . The fourth summing module  114  generates an error control signal e 3    116  by summing the digital echo/NEXT cancellation signal and the error control signal e 2    102 . 
     The error control signal e 3    116  includes the error control signal e 2    102 , which is typically used as an adaptation error signal for the DSP  88  components including the FIR filter  90 , the DEC  104 , and the DFE  96 . Since both the adaptive analog echo/NEXT cancellation system  108  and the DEC  104  operate simultaneously in the communications channel, operation of the adaptive analog echo/NEXT cancellation system  108  and the DEC  104  is coordinated. Therefore, the digital echo/NEXT cancellation signal and the error control signal e 2    102  are summed to generate the error control signal e 3    116 . A first input of a selector  117  receives the error control signal e 1    112  and a second input of the selector  117  receives the error control signal e 3    116 . The selector  117  outputs the error control signal e 1    112  during a first mode and the error control signal e 3    116  during a second mode. 
     The adaptive analog echo/NEXT cancellation system  108  also includes an analog echo/NEXT cancellation module  118 . The analog echo/NEXT cancellation module  118  receives the analog transmission signal and one of the error control signal e 1    112  or the error control signal e 3    116  from the selector  117 . The analog echo/NEXT cancellation module  118  generates an analog echo/NEXT cancellation signal  120  based on the analog transmission signal. Operating coefficients of the analog echo/NEXT cancellation module  118  are adjusted based on a value of one of the error control signal e 1    112  or the error control signal e 3    116  from the selector  117 . A fifth summing module  122  in the receive path  80  receives the analog receive signal and the analog echo/NEXT cancellation signal  120 . The fifth summing module  122  subtracts the analog echo/NEXT cancellation signal  120  from the analog receive signal. Therefore, the value of the analog receive signal at the input of the analog filter  84  is equal to the value of the analog receive signal less the value of the analog echo/NEXT cancellation signal  120 . 
     The first mode is a start-up mode and occurs when the analog receive signal does not include a remotely transmitted signal. For example, the first mode may be initiated as part of a start-up procedure of the physical layer device  78  when the analog receive signal does not typically include a remotely transmitted signal. In other words, the analog receive signal only includes echo, NEXT, and/or other interference signal impairments. For example, during the first mode when the analog echo/NEXT cancellation module  118  operates ideally, the value of the filtered analog signal is equal to zero. Following the start-up mode, if the echo response in the receive path  80  does not significantly change, the operating coefficients of the analog echo/NEXT cancellation module  118  may be fixed. In this case, the DEC  104  in the DSP  88  employs traditional digital echo/NEXT cancellation techniques to estimate any residual echo/NEXT interference signals in the receive path  80  that have not been removed by the adaptive analog echo/NEXT cancellation system  108 . 
     The echo response in the receive path  80  may change dramatically during normal operations. For example, the echo response may change due to a change in temperature or another adverse condition. Therefore, it is desirable for the analog echo/NEXT cancellation module  118  to remain adaptive during normal operations. The second mode occurs when the analog receive signal includes a remotely transmitted signal (or during normal operations). For example, the analog receive signal typically includes a remotely transmitted signal following an initial start-up procedure of the physical layer device  78 . During the second mode, the analog echo/NEXT cancellation module  118  is preferably not adapted by the value of the error control signal e 1    112 . This is because the presence of a remotely transmitted signal in the receive path  80  makes the error control signal e 1    112  too noisy. Therefore, during the second mode, the selector  117  outputs the error control signal e 3  and the analog echo/NEXT cancellation module  118  is adapted by the value of the error control signal e 3   116 . 
     Referring now to  FIG. 5 , the analog echo/NEXT cancellation module  118  of  FIG. 4  is illustrated in further detail. The analog echo/NEXT cancellation module  118  includes a delay module  130  that selectively delays one of the error control signal e 1    112  or the error control signal e 3    116 . The delay module  130  fixes a relative delay of the error signals so that the delay is matched properly according to the latency between the input of the first ADC  86  and the output of the bit detector  92 . The analog echo/NEXT cancellation module  118  also includes a second ADC  132  that receives the analog transmission signal and generates a sampled transmission signal. A product module  134  receives the delayed error control signals and the sampled transmission signal. The product module  134  generates an adaptation signal  136  by multiplying the selected error control signal and the sampled transmission signal. 
     An input of a loop filter  138  receives the adaptation signal  136  and generates a filtered adaptation signal  140 . An adaptive analog filter  142  receives the analog transmission signal and the filtered adaptation signal  140 . The adaptive analog filter  142  generates an estimated echo/NEXT signal that is included in the analog receive signal. A value of the filtered adaptation signal  140  adjusts the operating coefficients of the adaptive analog filter  142 . In an exemplary embodiment, the selector  117  includes a multiplexer  144 . For example, the selector  117  may include a 2-to-1 multiplexer  144  that selectively outputs either the error control signal e 1  or the error control signal e 3  based on a value of a mode select signal. For example, in an exemplary embodiment, the value of the mode select signal changes depending on whether the physical layer device  78  is performing an initial start-up procedure. 
     Referring now to  FIG. 6 , an exemplary comprehensive analog echo/NEXT cancellation system for channel A of a four channel full-duplex communications medium is shown. The DSP  88  receives digital transmission signals from all four channels. An analog echo canceller  108 -A and three analog NEXT cancellers  108 -B,  108 -C, and  108 -D receive analog transmission signals from respective communications channels. For example, the analog echo canceller  108 -A receives the analog transmission signal from channel A. The analog echo canceller  108 -A and the analog NEXT cancellers  108 -B,  108 -C, and  108 -D also receive the filtered receive signal from the receive path  80 . 
     The analog echo canceller  108 -A and the analog NEXT cancellers  108 -B,  108 -C, and  108 -D receive respective digital echo/NEXT cancellation signals from the DSP  88 . For example, the echo canceller  108 -A receives the digital echo/NEXT cancellation signal from the DSP  88  with respect to channel A. The analog echo canceller  108 -A and the analog NEXT cancellers  108 -B,  108 -C, and  108 -D also receive the error control signal e 2    102  from the DSP  88 . Therefore, each communications channel of the data communications medium includes an analog echo canceller  108 -A and three analog NEXT cancellers  108 -B,  108 -C, and  108 -D. The analog echo canceller  108 -A and the analog NEXT cancellers  108 -B,  108 -C, and  108 -D output respective analog echo/NEXT cancellation signals  120 . The fifth summing module  122  sums the analog receive signal and the analog echo/NEXT cancellation signals  120  to filter the analog receive signal. Likewise, each of the DSPs  88  in the four channels of the communications medium include a DEC  104  that operates as an echo canceller and three digital filters that operate as NEXT cancellers. Those skilled in the art can appreciate that multiple echo and/or NEXT cancellers may be integrated into a single device. 
     Referring now to  FIG. 7 , an error control signal selection algorithm begins in step  150 . In step  152 , control reads the receive signal and the selector  117  reads the error control signal e 1  and the error control signal e 3 . In step  154 , control determines whether the receive signal includes a remotely transmitted signal. For example, control may read the mode select signal of the selector  117  to determine whether the physical layer device  78  is performing an initial start-up procedure. If true, control proceeds to step  156 . If false, control proceeds to step  158 . In step  156 , the selector  117  outputs the error control signal e 3    116  and control proceeds to step  160 . In step  158 , the selector outputs the error control signal e 1    112  and control proceeds to step  160 . In step  160 , the adaptive analog filter  142  estimates echo/NEXT interference and generates the analog echo/NEXT cancellation signal  120  and control ends. The adaptive analog filter  142  estimates the analog echo/NEXT cancellation signal  120  based on the analog transmission signal and the error control signal that is output by the selector  117 . 
     The present invention allows for greater ADC  86  resolution in communications channels that operate in high-speed full-duplex communications systems. This allows for reliable and increased data communications rates in communications systems such as IEEE 10GBASE-T systems. Analog echo/NEXT cancellers are utilized before the ADC  86  to estimate as much echo/NEXT interference as possible. At the same time, the DSP  88  retains traditional digital echo/NEXT cancellers that estimate additional echo/NEXT interference in the receive path  80  after the ADC  86 . Both the bit slicer  110  and the second ADC  132  receive a second clock signal that is derived from the first clock signal of the first ADC  86 . Therefore, clock mismatching problems that are typically associated with multiple echo/NEXT cancellers are avoided. 
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, specification, and the following claims.