Adaptive analog echo/next cancellation

An adaptive analog echo/near-end crosstalk (NEXT) cancellation system 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. A summing module receives the first receive signal and the estimated echo/NEXT signal and generates an echo/NEXT filtered receive signal by subtracting the estimated echo/NEXT signal from the first receive signal.

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 toFIG. 1, first and second exemplary Ethernet network devices10and12, respectively, communicate over a data communications medium with four full-duplex channels14-A,14-B,14-C, and14-D. For example, the first and second Ethernet network devices10and12, respectively, may be Gigabit Ethernet network devices. Each of the channels14at the first and second Ethernet network devices10and12, respectively, are identified as A, B, C, or D and include a transceiver16and a hybrid18. The transceivers16independently process transmitted and received data. The hybrids18facilitate 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. 1illustrates both near echo20and far echo22with respect to the transceiver16-A-1on channel A of the first Ethernet network device10.

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. 1illustrates NEXT interference24-B,24-C, and24-D from channels B, C, and D14-B,14-C, and14-D, respectively, that is received at channel A14-A of the first Ethernet network device10. Therefore, the received signal at channel A14-A of the first Ethernet network device10potentially includes data transmitted from channel A14-A of the second Ethernet network device12, echo20and/or22from channel A14-A of the first Ethernet network device10, and NEXT24-B,24-C, and24-D, respectively, from channels B, C, and D14-B,14-C, and14-D of the first Ethernet network device10.

Referring now toFIG. 2, a physical layer device32of an exemplary Ethernet network device processes data for a full-duplex communications channel of a data communications medium. The physical layer device32includes a receive path34and a transmit path36. An input of a first analog filter38receives an analog receive signal from the communications channel. The first analog filter38filters the analog receive signal and generates a filtered receive signal. An input of an analog-to-digital converter (ADC)40receives the filtered receive signal and generates a digital receive signal. A first input of a digital signal processor (DSP)42receives the digital receive signal and generates a recovered bit pattern. In an exemplary embodiment, the DSP42transmits the recovered bit pattern to a descrambler in a physical coding sublayer (PCS) device in the physical layer device32.

A second input of the DSP42in the receive path34receives a scrambled bit pattern from a scrambler in the PCS device. The DSP42outputs a digital transmission signal based on the scrambled bit pattern. An input of a digital-to-analog converter (DAC)44receives the digital transmission signal and generates an analog transmission signal. An input of a second analog filter45receives the analog transmission signal and outputs a filtered transmission signal. For example, the second analog filter45may transmit the filtered transmission signal to a line driver in the communications channel.

The input of the first analog filter38receives an echo signal. The echo signal is interference from the filtered analog transmission signal. The input of the first analog filter38also 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 filter38. 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.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now toFIG. 3, a physical layer device46includes a receive path47and a transmit path48. The transmit path48may be from the same channel as the receive path47or may be from a different channel of the data communications medium. An input of an analog filter49receives an analog receive signal. The analog filter49filters the analog receive signal and generates a filtered receive signal. An input of an analog-to-digital converter (ADC)50receives the filtered receive signal and generates a digital receive signal. A first input of a digital signal processor (DSP)51receives the digital receive signal and generates a recovered bit pattern. A transmitter52generates a digital transmission signal. An input of a digital-to-analog converter (DAC)53receives the digital transmission signal and generates an analog transmission signal.

The DSP51includes a digital echo/NEXT cancellation system54. Operation of the ADC50is synchronized to an input clock signal. An input of a finite impulse response (FIR) filter56receives the digital receive signal from the ADC50and generates a filtered digital receive signal. An input of a bit detector58receives the filtered digital receive signal and generates the recovered bit pattern. An input of a decision feedback equalizer (DFE)60receives the recovered bit pattern and generates a digital feedback signal. A first summing module62receives the filtered digital receive signal and the digital feedback signal. Therefore, the signal at the input of the bit detector58is equal to a sum of the filtered digital receive signal from the FIR filter56and the digital feedback signal from the DFE60.

Operating parameters of the FIR filter56and the DFE60are periodically adjusted so that the DSP51functions as desired under changing signal conditions. A second summing module64receives the filtered digital receive signal and the recovered bit pattern. The second summing module64generates an error control signal66that is equal to the difference between the recovered bit pattern and the filtered digital receive signal. The FIR filter56and the DFE60receive the error control signal66. Operating parameters of the FIR filter56and the DFE60are adjusted based on value of the error control signal66.

A digital echo canceller (DEC)68receives the digital transmission signal from the transmit path48and generates a digital echo/NEXT cancellation signal. The DEC68also receives the error control signal66from the second summing module64. Operating parameters of the DEC68are adjusted based on a value of the error control signal66. A third summing module70receives the digital receive signal and the digital echo/NEXT cancellation signal. The third summing module70outputs the difference between the digital receive signal and the digital echo/NEXT cancellation signal. Therefore, the DEC68effectively filters the digital receive signal to reduce adverse effects from echo/NEXT interference.

The transmit path48inFIG. 3may be from the same channel as the receive path47or may be a transmit path48from another channel in the data communications medium. When the transmit path48is from the same channel as the receive path47, the DEC68generates an estimated echo signal. When the transmit path48is from another channel in the data communications medium, the DEC68generates an estimated NEXT signal.

The digital echo/NEXT cancellation system54is 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 system54reduces 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 paths47of the data communications channels. This dramatically reduces the resolution of the ADC50in the receive path47.

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 toFIG. 4, a physical layer device78of an exemplary Ethernet network device processes data for a communications channel of a data communications medium. The communications channel includes a receive path80and a transmit path82. The transmit path82may be from the same channel as the receive path80or may be from a different channel of the data communications medium. An analog front end (AFE) device83includes an analog filter84and a first analog-to-digital converter (ADC)86. An input of the analog filter84receives an analog receive signal and generates a filtered receive signal. For example, an analog amplifier may transmit the analog receive signal to the analog filter84. An input of the first ADC86receives the filtered receive signal and a first clock signal and generates a digital receive signal. A DSP88includes an FIR filter90. An input of the FIR filter90receives the digital receive signal and generates a filtered digital receive signal. An input of a bit detector92in the DSP88receives the filtered digital receive signal and generates a recovered bit pattern. For example, the bit detector92may transmit the recovered bit pattern to a descrambler in a PCS device.

A transmitter93in the transmit path82generates a digital transmission signal. An input of a digital-to-analog converter (DAC)94in the transmit path82receives the digital transmission signal and generates an analog transmission signal. For example, the DAC94may transmit the analog transmission signal to a line driver in the in the communications channel. An input of a decision feedback equalizer (DFE)96in the DSP88receives the recovered bit pattern and generates a feedback signal. A first summing module98receives 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 detector92. A second summing module100receives the filtered digital receive signal from the input of the bit detector92and the recovered bit pattern from the output of the bit detector92. The second summing module100outputs an error control signal e2102, which is equal to the difference between the recovered bit pattern and the filtered digital receive signal. The FIR filter90and the DFE96receive the error control signal e2102and a value of the error control signal e2102adjusts the operating parameters of the FIR filter90and the DFE96.

The DSP88includes a digital echo canceller (DEC)104that receives the digital transmission signal and the error control signal e2102. The DEC104generates a digital echo/NEXT cancellation signal based on the digital transmission signal. A third summing module106receives the digital echo/NEXT cancellation signal and outputs the difference between the digital receive signal and the digital echo/NEXT cancellation signal. The DEC104estimates echo and/or NEXT interference signals in the digital receive signal. Operating parameters of the DEC104are adjusted based on a value of the error control signal e2102.

An adaptive analog echo/NEXT cancellation system108according to the present invention includes a bit slicer110that receives the filtered receive signal. The bit slicer110generates an error control signal e1112based on the filtered receive signal. A fourth summing module114in the adaptive analog echo/NEXT cancellation system108receives the digital echo/NEXT cancellation signal and the error control signal e2102. The fourth summing module114generates an error control signal e3116by summing the digital echo/NEXT cancellation signal and the error control signal e2102.

The error control signal e3116includes the error control signal e2102, which is typically used as an adaptation error signal for the DSP88components including the FIR filter90, the DEC104, and the DFE96. Since both the adaptive analog echo/NEXT cancellation system108and the DEC104operate simultaneously in the communications channel, operation of the adaptive analog echo/NEXT cancellation system108and the DEC104is coordinated. Therefore, the digital echo/NEXT cancellation signal and the error control signal e2102are summed to generate the error control signal e3116. A first input of a selector117receives the error control signal e1112and a second input of the selector117receives the error control signal e3116. The selector117outputs the error control signal e1112during a first mode and the error control signal e3116during a second mode.

The adaptive analog echo/NEXT cancellation system108also includes an analog echo/NEXT cancellation module118. The analog echo/NEXT cancellation module118receives the analog transmission signal and one of the error control signal e1112or the error control signal e3116from the selector117. The analog echo/NEXT cancellation module118generates an analog echo/NEXT cancellation signal120based on the analog transmission signal. Operating coefficients of the analog echo/NEXT cancellation module118are adjusted based on a value of one of the error control signal e1112or the error control signal e3116from the selector117. A fifth summing module122in the receive path80receives the analog receive signal and the analog echo/NEXT cancellation signal120. The fifth summing module122subtracts the analog echo/NEXT cancellation signal120from the analog receive signal. Therefore, the value of the analog receive signal at the input of the analog filter84is equal to the value of the analog receive signal less the value of the analog echo/NEXT cancellation signal120.

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 device78when 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 module118operates ideally, the value of the filtered analog signal is equal to zero. Following the start-up mode, if the echo response in the receive path80does not significantly change, the operating coefficients of the analog echo/NEXT cancellation module118may be fixed. In this case, the DEC104in the DSP88employs traditional digital echo/NEXT cancellation techniques to estimate any residual echo/NEXT interference signals in the receive path80that have not been removed by the adaptive analog echo/NEXT cancellation system108.

The echo response in the receive path80may 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 module118to 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 device78. During the second mode, the analog echo/NEXT cancellation module118is preferably not adapted by the value of the error control signal e1112. This is because the presence of a remotely transmitted signal in the receive path80makes the error control signal e1112too noisy. Therefore, during the second mode, the selector117outputs the error control signal e3and the analog echo/NEXT cancellation module118is adapted by the value of the error control signal e3116.

Referring now toFIG. 5, the analog echo/NEXT cancellation module118ofFIG. 4is illustrated in further detail. The analog echo/NEXT cancellation module118includes a delay module130that selectively delays one of the error control signal e1112or the error control signal e3116. The delay module130fixes a relative delay of the error signals so that the delay is matched properly according to the latency between the input of the first ADC86and the output of the bit detector92. The analog echo/NEXT cancellation module118also includes a second ADC132that receives the analog transmission signal and generates a sampled transmission signal. A product module134receives the delayed error control signals and the sampled transmission signal. The product module134generates an adaptation signal136by multiplying the selected error control signal and the sampled transmission signal.

An input of a loop filter138receives the adaptation signal136and generates a filtered adaptation signal140. An adaptive analog filter142receives the analog transmission signal and the filtered adaptation signal140. The adaptive analog filter142generates an estimated echo/NEXT signal that is included in the analog receive signal. A value of the filtered adaptation signal140adjusts the operating coefficients of the adaptive analog filter142. In an exemplary embodiment, the selector117includes a multiplexer144. For example, the selector117may include a 2-to-1 multiplexer144that selectively outputs either the error control signal e1or the error control signal e3based 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 device78is performing an initial start-up procedure.

Referring now toFIG. 6, an exemplary comprehensive analog echo/NEXT cancellation system for channel A of a four channel full-duplex communications medium is shown. The DSP88receives digital transmission signals from all four channels. An analog echo canceller108-A and three analog NEXT cancellers108-B,108-C, and108-D receive analog transmission signals from respective communications channels. For example, the analog echo canceller108-A receives the analog transmission signal from channel A. The analog echo canceller108-A and the analog NEXT cancellers108-B,108-C, and108-D also receive the filtered receive signal from the receive path80.

The analog echo canceller108-A and the analog NEXT cancellers108-B,108-C, and108-D receive respective digital echo/NEXT cancellation signals from the DSP88. For example, the echo canceller108-A receives the digital echo/NEXT cancellation signal from the DSP88with respect to channel A. The analog echo canceller108-A and the analog NEXT cancellers108-B,108-C, and108-D also receive the error control signal e2102from the DSP88. Therefore, each communications channel of the data communications medium includes an analog echo canceller108-A and three analog NEXT cancellers108-B,108-C, and108-D. The analog echo canceller108-A and the analog NEXT cancellers108-B,108-C, and108-D output respective analog echo/NEXT cancellation signals120. The fifth summing module122sums the analog receive signal and the analog echo/NEXT cancellation signals120to filter the analog receive signal. Likewise, each of the DSPs88in the four channels of the communications medium include a DEC104that 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 toFIG. 7, an error control signal selection algorithm begins in step150. In step152, control reads the receive signal and the selector117reads the error control signal e1and the error control signal e3. In step154, control determines whether the receive signal includes a remotely transmitted signal. For example, control may read the mode select signal of the selector117to determine whether the physical layer device78is performing an initial start-up procedure. If true, control proceeds to step156. If false, control proceeds to step158. In step156, the selector117outputs the error control signal e3116and control proceeds to step160. In step158, the selector outputs the error control signal e1112and control proceeds to step160. In step160, the adaptive analog filter142estimates echo/NEXT interference and generates the analog echo/NEXT cancellation signal120and control ends. The adaptive analog filter142estimates the analog echo/NEXT cancellation signal120based on the analog transmission signal and the error control signal that is output by the selector117.

The present invention allows for greater ADC86resolution 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 ADC86to estimate as much echo/NEXT interference as possible. At the same time, the DSP88retains traditional digital echo/NEXT cancellers that estimate additional echo/NEXT interference in the receive path80after the ADC86. Both the bit slicer110and the second ADC132receive a second clock signal that is derived from the first clock signal of the first ADC86. Therefore, clock mismatching problems that are typically associated with multiple echo/NEXT cancellers are avoided.