Impulse noise effect reduction

• US 5,703,904 A
• Filed: 12/29/1995
• Issued: 12/30/1997
• Est. Priority Date: 12/29/1995
• Status: Expired due to Term

• Current Assignee: Ikanos Communications Incorporated (Qualcomm, Inc.)
• Original Assignee: Globespan Technologies, Inc. (Synaptics Incorporated)
• Inventors: Langberg, Ehud
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): Kim, Kevin
• Application Number:
  US08/586,008
• Time in Patent Office: 732 Days
• Field of Search: 375/229, 375/230, 375/232, 375/348, 375/317, 375/350, 364/724.01, 364/724.19, 364/724.2, 379/406, 379/410, 379/411
• US Class Current: 375/232
• CPC Class Codes: H03H 2021/007 Computation saving measures; Accelerating measures
• CPC Class Codes: H03H 2021/0074 Reduction of the update frequency
• CPC Class Codes: H03H 21/0012 Digital adaptive filters
• CPC Class Codes: H04L 25/03146 with a recursive structure H04L25/03127 takes precedence
• CPC Class Codes: H04L 25/03343 Arrangements at the transmitter end

Abstract

In a receiver system embodying the invention, the amplitude of the input signal is sensed so that when it exceeds a predetermined level, the adaptation of adaptive filters employed in the receiver is inhibited. In one embodiment of the invention the adaptation is inhibited for the extent of time that the sensed signal exceeds the predetermined level. In another embodiment of the invention, the adaptation is inhibited for a fixed period of time whenever the sensed signal exceeds the predetermined level. In still another embodiment of the invention, where the noise impulse has some repetitive pattern, an inhibiting signal is generated in anticipation of a repetitive noise impulse to inhibit adaptation of the adaptive filters during the period of time ("window") the noise impulse occurs.

Claims

1. A receiver comprising:

an input terminal for receiving input signals;

means coupling an adaptive filter means to said input terminal, said adaptive filter means being normally adjustable as a function of the signals received at said input terminal;

detector means for sensing the amplitude of the input signals received at said input terminal and comparing the amplitude to a threshold level for producing a control signal having first value when the amplitude of the input signal is below the threshold level and having a second value when the amplitude of the input signal exceeds the threshold level;

means responsive to said control signal coupled to said adaptive filter means for preventing adjustment of said adaptive filter means when said control signal has said second value; and

means responsive to the expected occurrence of an input signal exceeding the threshold level for producing a control signal coupled to said adaptive filter means for preventing adjustment of said adaptive filter means for a first period of time preceding the expected occurrence of a signal exceeding the threshold level and a second period of time following the expected occurrence of the signal exceeding the threshold level.

2. A receiver as claimed in claim 1, wherein said detector means includes means for producing said control signal having said second value for a predetermined period of time, each time the input signal makes a transition from a value below the threshold level to a value exceeding the threshold level.

3. A receiver as claimed in claim 2, wherein said means for producing said control signal having said second value for a predetermined period of time is a monostable multivibrator.

10. A receiver as claimed in claim 1, further including a timing recovery circuit which provides frequency signals for sampling the input signals, the frequency varying as a function of the amplitude of the received signal;

and

means responsive to said control signal coupled to said timing recovery circuit for inhibiting any change in frequency during the presence of a received signal exceeding said threshold level.

4. A receiver comprising:

an input terminal for receiving input signals;

means coupling an adaptive filter means to said input terminal, said adaptive filter means being normally adjustable as a function of the signals received at said input terminal;

detector means for sensing the amplitude of the input signals received at said input terminal and comparing the amplitude to a threshold level for producing a control signal having first value when the amplitude of the input signal is below the threshold level and having a second value when the amplitude of the input signal exceeds the threshold level;

means responsive to said control signal coupled to said adaptive filter means for preventing adjustment of said adaptive filter means when said control signal has said second value

said means coupling an adaptive filter means to said input terminal includes an analog-to-digital (A/D) converter having an input coupled to said input terminal and having an output; and

a delay means coupled between the output of said A/D converter and said adaptive filter means for delaying the application of the received signals to the adaptive filter means; and

wherein the output of the A/D converter is coupled to the detector for enabling the detector means to sense the presence of any received signal exceeding the threshold level and inhibiting adjustment of the adaptive filter means prior to the propagation of the signal to the adaptive filter means.

5. A receiver as claimed in claim 4, wherein said adaptive filter means includes:

(a) an echo canceler circuit having an input coupled to said output of said A/D converter; and

(b) an adaptive equalizer having an input coupled to said output of said A/D converter.

6. A receiver as claimed in claim 5, wherein each one of said echo canceler and adaptive equalizer includes an adaptive filter having adjustable coefficients, and each adaptive filter includes a means responsive to the signals received by the receiver for producing an error signal which is normally used to adjust the coefficients of its associated filter.

7. A receiver as claimed in claim 5,

wherein the output of the A/D converter is coupled via said delay means to one input of a first adder circuit;

and wherein said echo canceler includes an echo canceler adaptive filter coupled at its output to another input of the first adder for producing at the output of the first adder a first signal in which an estimated echo signal from the echo canceler adaptive filter is subtracted from echo signals present in the signal at the output of the A/D converter;

wherein the signal at the output of the first adder is fed to the echo canceler adaptive filter for adjusting and updating its coefficients; and

wherein any change in the coefficients of the echo canceler adaptive filter is inhibited when the received signal exceeds the predetermined threshold level.

8. A receiver as claimed in claim 7 wherein the output of the first adder is fed to the echo canceler adaptive filter for adjusting its coefficients when the received input signal is below the threshold level and wherein a signal causing no change in the coefficients is fed to the echo canceler adaptive filter when the received input signal exceeds the threshold level.

9. A receiver as claimed in claim 5, wherein the output of the A/D converter is coupled via said delay means to an input of a decision feedback equalizer (DFE) comprising:

an adaptive feed-forward filter;

an adaptive feedback filter;

a slicer circuit; and

a first and a second adder circuit.

11. A method for reducing the effect of a noise impulse on the adaptive filter of a receiver system comprising the steps of:

producing a control signal whenever an input signal to the receiver system exceeds a threshold level;

applying the control signal to the adaptive filter of the receiver system for inhibiting a change in the response of the adaptive filter during the presence of an input signal exceeding the threshold level; and

responsive to the expected occurrence of an input signal exceeding the threshold level, producing a control signal to inhibit a change in the response of said adaptive filter for a predetermined time preceding the expected occurrence of said input signal exceeding the threshold level.

12. A method as claimed in claim 11, wherein the adaptive filter includes coefficients which are normally adapted as a function of the input signal, and wherein the step of applying the control signal to the adaptive filter for inhibiting a change in the response of the adaptive filter includes inhibiting any change in the coefficients of the adaptive filter.

13. A method as claimed in claim 12, wherein the coefficients of the adaptive filter are normally updated as a function of the product of an error signal, a constant multiplier, and a data signal, and wherein the step for inhibiting any change in the coefficients includes the step of setting the product of the error signal, the constant multiplier and the data signal to zero.

14. A method as claimed in claim 12, wherein the coefficients of the adaptive filter are normally updated as a function the product of an error signal, a constant multiplier, and a data signal, and wherein the step for inhibiting any change in the coefficients includes the step of setting the error signal equal to zero to set the product equal to zero.

15. A method as claimed in claim 12, wherein the coefficients of the adaptive filter are normally updated as a function the product of an error signal, a constant multiplier, and a data signal, and wherein the step for inhibiting any change in the coefficients includes the step of setting the constant multiplier equal to zero to set the product equal to zero.

16. A transmitter receiver system comprising:

an input terminal for receiving input signals;

an adaptive filter means having an input for the application thereto of input signals derived from said input terminal and having an output, said adaptive filter means having coefficients which are normally updated as a function of the input signals and an error signal applied to a control terminal of the adaptive filter means;

means coupling the input of said adaptive filter means to said input terminal;

detector means for sensing the amplitude of the input signals received at said input terminal and comparing the amplitude to a threshold level for producing a control signal having a first value when the amplitude of the input signal is below the threshold level and having a second value when the amplitude of the input signal exceeds the threshold level;

means responsive to said control signal coupled to the control terminal of said adaptive filter means for inhibiting adjustment of said adaptive filter means when said control signal has said second value; and

means responsive to the expected occurrence of an input signal exceeding the threshold level for producing a control signal coupled to said control terminal of said adaptive filter means for inhibiting adjustment of said adaptive filter means for a first period of time preceding the expected occurrence of a signal exceeding the threshold level and a second period of time following the expected occurrence of the signal exceeding the threshold level.

17. A receiver as claimed in claim 16, wherein said detector means includes means for producing said control signal having said second value for a predetermined period of time, each time the input signal makes a transition from a value below the threshold level to a value exceeding the threshold level.

18. A transmitter receiver system comprising:

an input terminal for receiving input signals;

an adaptive filter means having an input for the application thereto of input signals derived from said input terminal and having an output, said adaptive filter means having coefficients which are normally updated as a function of the input signals and an error signal applied to a control terminal of the adaptive filter means;

means coupling the input of said adaptive filter means to said input terminal;

detector means for sensing the amplitude of the input signals received at said input terminal and comparing the amplitude to a threshold level for producing a control signal having a first value when the amplitude of the input signal is below the threshold level and having a second value when the amplitude of the input signal exceeds the threshold level;

means responsive to said control signal coupled to the control terminal of said adaptive filter means for inhibiting adjustment of said adaptive filter means when said control signal has said second value;

said means coupling the input of said adaptive filter means to said input terminal includes an analog-to-digital (A/D) converter having an input coupled to said input terminal and having an output; and

a delay means coupled between the output of said A/D converter and the onput of said adaptive filter means for delaying the application of the received signals to the adaptive filter means; and

wherein the output of the A/D converter is coupled to the detector for enabling the detector means to sense the presence of any received signal exceeding the threshold level and inhibiting adjustment of the adaptive filter means prior to the propagation of the signal to the adaptive filter means.

19. A receiver as claimed in claim 18, wherein said adaptive filter means includes:

(a) an echo canceler circuit having an input coupled to said output of said A/D converter; and

(b) an adaptive equalizer having an input coupled to said output of said A/D converter.

20. A receiver as claimed in claim 19, wherein each one of said echo canceler and adaptive equalizer includes an adaptive filter having adjustable coefficients, and each adaptive filter includes a means responsive to the input signals for producing an error signal coupled to said control terminal for normally adjusting the coefficients of its associated filter.

21. A receiver as claimed in claim 19,

wherein the output of the A/D converter is coupled via said delay means to one input of a first adder circuit;

and wherein said echo canceler includes an echo canceler adaptive filter coupled at its output to another input of the first adder for producing at the output of the first adder a first signal in which an estimated echo signal from the echo canceler adaptive filter is subtracted from echo signals present in the signal at the output of the A/D converter;

wherein the signal at the output of the first adder is fed to the control terminal of the echo canceler adaptive filter for adjusting and updating its coefficients; and

wherein any change in the coefficients of the echo canceler adaptive filter is inhibited when the received signal exceeds the predetermined threshold level.

22. A receiver as claimed in claim 21 wherein the output of the first adder is fed to the echo canceler adaptive filter for adjusting its coefficients when the received input signal is below the threshold level and wherein a signal causing no change in the coefficients is fed to the echo canceler adaptive filter when the received input signal exceeds the threshold level.

23. A receiver as claimed in claim 21, wherein the output of the A/D converter is coupled via said delay means to an input of a decision feedback equalizer (DFE) comprising:

an adaptive feed-forward filter;

an adaptive feedback filter;

a slicer circuit; and

a first and a second adder circuit.

24. A receiver comprising:

an input terminal for receiving analog signals;

an analog-to-digital (A/D) converter having an input coupled to said input terminal and having an output;

an echo canceler coupled to the output of said A/D converter, said echo canceler including a first adaptive filter means adjustable as a function of the amplitude of the signal at the output of said A/D converter;

an adaptive equalizer coupled to the output of said A/D converter for processing and propagating the signal produced at the output of said A/D converter, said adaptive equalizer, including a second adaptive filter means adjustable as a function of the amplitude of the signal at the output of said A/D converter;

detector means coupled between the output of said A/D converter and said first and second adaptive filter means for sensing when amplitude of the signal at the output of the A/D converter exceeds a predetermined value for inhibiting the adjustment of the first and second adaptive filter means when the signal exceeds the predetermined value; and

means responsive to the detector means for inhibiting the adjustment of the first and second adaptive filter means for a first time period before the signal exceeds the predetermined value, and continuing the inhibition of the adjustment of the first and second adaptive filter means for a second period of time after the signal drops below the predetermined threshold level.

25. A receiver as claimed in claim 24, wherein said detector means includes a threshold detector having an input coupled to the output of the A/D converter and having another input to which is applied a predetermined threshold level, wherein when the signal at the output of the A/D converter is below the threshold level, the threshold detector produces a control signal having a first value and when the signal at the output of the A/D converter is above the threshold level, the threshold detector produces a control signal having a second value;

and

wherein when the control signal has said second value it inhibits the adjustment of the first and second adaptive filter means.

26. A receiver as claimed in claim 25, wherein the threshold detector produces a control signal having said second value for a preset period of time whenever the output signal of the A/D converter exceeds the threshold level.

27. A receiver as claimed in claim 24, further including a timing recovery circuit which provides frequency signals for sampling the input signals applied to the A/D converter, the frequency signals varying as a function of the amplitude of the received signal;

and

means responsive to said control signal coupled to said timing recovery circuit for inhibiting any change in frequency during the presence of a received signal exceeding said threshold level.