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Patent Issued for Transceiver with Single Coefficient Based Equalizer Taps

June 25, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- A patent by the inventor He, Runsheng (Sunnyvale, CA), filed on November 20, 2012, was published online on June 10, 2014, according to news reporting originating from Alexandria, Virginia, by VerticalNews correspondents.

Patent number 8750367 is assigned to Marvell International Ltd. (Hamilton, BM).

The following quote was obtained by the news editors from the background information supplied by the inventors: "A feedforward equalizer is an extremely useful component of a digital signal processor used to shape and otherwise to filter an input signal so as to obtain an output signal with desired characteristics. Feedforward equalizers may be used in such diverse fields as Ethernet transceivers, read circuits for disk drives, ghost cancellation in broadcast and cable TV transmission, channel equalization for communication in magnetic recording, echo cancellation, estimation/prediction for speech processing, adaptive noise cancellation, etc.

"A feedforward equalizer is particularly suited for filtering inter-symbol interference (ISI). To varying degrees, ISI is always present in a data communications system. ISI is the result of the transmission characteristics of the communications channel, i.e., the 'channel response,' and, generally speaking, causes neighboring data symbols, in a transmission sequence, to spread out and interfere with one another. If the channel response is bad, or severe, ISI becomes a major impediment to having low error rate communications between two data endpoints. In fact, at higher data rates, i.e., frequencies, the effect of ISI is more severe since there is more high frequency attenuation in the transmission channel. Consequently, current efforts to push transmission speeds higher and higher in the local loop environment must effectively contend with ISI effects on a transmitted data signal to be successful.

"Generally speaking, the ISI can be divided into two components, namely precursor and post cursor ISI. Conventionally a feedforward equalizer (FFE) attempts to remove precursor ISI, and decision feedback equalization (DFE) attempts to remove postcursor ISI. FIG. 1 is illustrative of a conventional feedforward equalizer used in conjunction with decision feedback equalizer in a data communications channel. As shown in FIG. 1, an analog input signal from a communication channel is converted to a digital signal by analog-to-digital converter 102. The digital signal is processed by FFE 104 and DFE 105 in a conventional manner. DFE 105 includes decision circuit 108 and feedback filter 110. Examples of conventional arrangements are discussed in U.S. Pat. Nos. 5,513,216 and 5,604,769, the contents of each of which are incorporated by reference herein.

"However, in conventional arrangements, the length of the postcursor ISI is rather large, as shown in FIG. 2. To process a signal with a long tail, the feedback filter needs to have a proportionately large number of taps. This results in higher complexity and severe error propagation."

In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventor's summary information for this patent: "A transceiver is provided and includes an equalizer configured to receive an input signal. A control circuit is configured to (i) select a predetermined coefficient, (ii) maintain the predetermined coefficient at a fixed value, and (iii) based on the predetermined coefficient, select first coefficients and second coefficients. The control circuit is configured to, while maintaining the predetermined coefficient at the fixed value and while the equalizer is receiving the input signal, adjust a coefficient of one of (i) the first coefficients, or (ii) the second coefficients. The equalizer includes: first taps configured to, based on the first coefficients, filter the input signal to generate a first filtered signal; a unity tap configured to, based on the predetermined coefficient, filter the first filtered signal to generate a second filtered signal; and second taps configured to, based on the second coefficients, filter the second filtered signal to generate a third filtered signal. An output is configured to transmit the third filtered signal.

"A method is provided and includes: receiving an input signal; selecting a predetermined coefficient; maintaining the predetermined coefficient at a fixed value; and based on the predetermined coefficient, selecting first coefficients and second coefficients. While maintaining the predetermined coefficient at the fixed value and while receiving the input signal, adjusting a coefficient of one of (i) the first coefficients, or (ii) the second coefficients. Based on the first coefficients, filter the input signal via first taps to generate a first filtered signal. Based on the predetermined coefficient, filter the first filtered signal via a unity tap to generate a second filtered signal. Based on the second coefficients, filter the second filtered signal via second taps to generate a third filtered signal. The third filtered signal is transmitted.

"According to another aspect of the present disclosure, a signal processing apparatus includes an input circuit to receive an input signal. A feedforward equalizer includes a high-pass filter and is responsive to the input circuit. A decision feedback equalizer includes a decision circuit responsive to the feed forward equalizer and a feedback filter responsive to the decision circuit. The decision circuit is responsive to the feedback filter.

"According to another aspect of the present disclosure, the high-pass filter has a low cutoff frequency.

"According to another aspect of the present disclosure, the high-pass filter has a flat response.

"According to another aspect of the present disclosure, the high-pass filter has high attenuation at low frequency.

"According to another aspect of the present disclosure, the high-pass filter has high attenuation at low frequencies.

"According to another aspect of the present disclosure, the high attenuation is at least 20 db.

"According to another aspect of the present disclosure, the high-pass filter includes a first finite impulse response (FIR) filter.

"According to another aspect of the present disclosure, the first FIR filter includes M taps to filter precursor intersymbol interference (ISI), one main tap and N taps to filter postcursor ISI.

"According to another aspect of the present disclosure, each tap of the first FIR filter has a corresponding coefficient W as follows:

"##EQU00001## <.times..times..times..times..times.

"According to another aspect of the present disclosure, the input circuit includes an analog-to-digital converter.

"According to another aspect of the present disclosure, the decision circuit includes a threshold circuit.

"According to another aspect of the present disclosure, the decision circuit includes a Viterbi detector.

"According to another aspect of the present disclosure, a first adaptive control circuit is provided to adapt the M taps for filtering precursor ISI and N taps for filtering.

"According to another aspect of the present disclosure, each of the N taps includes a limiter to limit the range of adaptation of the N taps.

"According to another aspect of the present disclosure, the first adaptive control circuit is operable only during signal acquisition.

"According to another aspect of the present disclosure, the feedback filter includes a second finite impulse response (FIR) filter.

"According to another aspect of the present disclosure, a second adaptive control circuit to adapt taps of the second FIR.

"According to another aspect of the present disclosure, a signal processing apparatus includes an input means for receiving an input signal. A feedforward equalizer means is provided for feedforward equalizing by high-pass filtering the input signal received by the input means. A decision feedback equalizer means includes a decision means for recovering data from an output of the feedforward equalizer means and a feedback filter means for filtering an output of the decision means. The decision means is responsive to the feedback filter means.

"According to another aspect of the present disclosure, the feedforward equalizer means has a low cutoff frequency.

"According to another aspect of the present disclosure, the feedforward equalizer means has a flat response.

"According to another aspect of the present disclosure, the feedforward equalizer means has high attenuation at low frequency.

"According to another aspect of the present disclosure, the feedforward equalizer means has high attenuation at low frequencies.

"According to another aspect of the present disclosure, the feedforward equalizer means shortens a length of postcursor inter-symbol interference.

"According to another aspect of the present disclosure, the feedforward equalizer means attenuates any DC noise.

"According to another aspect of the present disclosure, the feedforward equalizer means attenuates baseline wander.

"According to another aspect of the present disclosure, the high attenuation is at least 20 dB.

"According to another aspect of the present disclosure, the feedforward equalizer means includes a first finite impulse response (FIR) filter means for filtering the input signal.

"According to another aspect of the present disclosure, the first FIR filter means includes M taps for filtering precursor ISI, one main tap and N taps for filtering postcursor ISI.

"According to another aspect of the present disclosure, each tap of the first FIR filter means has a corresponding coefficient W as follows:

"##EQU00002## <.times..times..times..times..times.

"According to another aspect of the present disclosure, the input means includes an analog-to-digital converter means for converting an analog input signal to a digital signal.

"According to another aspect of the present disclosure, the decision means includes a threshold circuit.

"According to another aspect of the present disclosure, the decision means includes a Viterbi detector.

"According to another aspect of the present disclosure, a first adaptive control means is provided for adapting the M taps for filtering precursor ISI and N taps for filtering.

"According to another aspect of the present disclosure, each of the N taps includes a limiting means for limiting the range of adaptation of the N taps.

"According to another aspect of the present disclosure, the first adaptive control means is operable only during signal acquisition.

"According to another aspect of the present disclosure, the feedback filter means includes a second finite impulse response (FIR) filter means for filtering the output of the decision means.

"According to another aspect of the present disclosure, a second adaptive control means is provided for adapting taps of the second FIR means."

URL and more information on this patent, see: He, Runsheng. Transceiver with Single Coefficient Based Equalizer Taps. U.S. Patent Number 8750367, filed November 20, 2012, and published online on June 10, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8750367.PN.&OS=PN/8750367RS=PN/8750367

Keywords for this news article include: Electronics, Signal Processing, Marvell International Ltd..

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Source: Electronics Newsweekly


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