Integrated adaptive cable equalizer using a continuous-time filter

• US 5,940,441 A
• Filed: 10/29/1996
• Issued: 08/17/1999
• Est. Priority Date: 10/29/1996
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Cranford, Hayden Clay Jr., Huss, Scott David
• Primary Examiner(s): Chan, Jason
• Assistant Examiner(s): Corrielus, Jean B
• Application Number:
  US08/739,391
• Time in Patent Office: 1,022 Days
• Field of Search: 375/229, 375/232, 375/233, 375/285, 375/257, 375/344, 375/345, 375/346, 375/350, 375/377, 364/724.2, 364/724.011, 364/724.19, 333/18, 333/28 R
• US Class Current: 375/232
• CPC Class Codes: H03H 11/0433 Two integrator loop filters H03H11/0455 takes precedence

Abstract

A method and apparatus for equalizing a communications signal transmitted through a transmission medium includes an integrated continuous-time filter and circuitry for developing a feedback signal to compensate for distortion in the signal caused by the transmission medium. The control signal adjusts the transfer characteristics of the integrated continuous-time filter thereby compensating for loss and distortion of the signal caused by the transmission medium and further tunes the integrated continuous-time filter thereby compensating for semiconductor process variations in the integrated continuous-time filter.

Claims

1. An adaptive equalizer comprising:

an integrated continuous-time filter fabricated on a substrate for receiving and filtering an input signal from a cable and generating an output signal, the output signal being an equalized version of the input signal; and

circuitry for processing the output signal and generating a control signal for feedback to the integrated continuous-time filter, the control signal controlling transfer characteristics of the integrated continuous-time filter such that distortion in the input signal from the cable is compensated wherein the control signal comprises;

a bandwidth control signal for controlling the bandwidth of the integrated continuous-time filter; and

a gain control signal for controlling the gain of the integrated continuous-time filter.

2. The equalizer in accordance with claim 1 wherein the circuitry for processing is fabricated on the substrate.

3. The equalizer in accordance with claim 1 wherein semiconductor process variations in the integrated continuous-time filter are compensated.

4. The equalizer in accordance with claim 3 wherein the circuitry for processing is fabricated on the substrate.

5. The equalizer in accordance with claim 3 wherein the equalizer is a higher order equalizer whereby the transfer characteristics of the continuous-time filter includes at least two poles and two zeros.

6. An adaptive equalizer comprising:

an integrated continuous-time filter fabricated on a substrate for receiving and filtering an input signal from a cable and generating an output signal, the output signal being an equalized version of the input signal; and

circuitry for processing the output signal and generating a control signal for feedback to the integrated continuous-time filter, the control signal controlling transfer characteristics of the integrated continuous-time filter such that distortion in the input signal from the cable is compensated wherein the circuitry for processing comprises analog signal processing circuitry for generating the control signal in response to a comparison between amplitude characteristics of the output signal of the integrated continuous-time filter and ideal amplitude characteristics of the input signal.

7. The equalizer in accordance with claim 6 wherein the analog signal processing circuitry comprises a peak detector.

8. An adaptive equalizer comprising:

an integrated continuous-time filter fabricated on a substrate for receiving and filtering an input signal from a cable and generating an output signal, the output signal being an equalized version of the input signal; and

circuitry for processing the output signal and generating a control signal for feedback to the integrated continuous-time filter, the control signal controlling transfer characteristics of the integrated continuous-time filter such that distortion in the input signal from the cable is compensated wherein the circuitry for processing comprises digital signal processing circuitry for generating the control signal in response to a comparison between frequency and amplitude characteristics of the output signal of the integrated continuous-time filter and ideal frequency and amplitude characteristics of the input signal.

9. The equalizer in accordance with claim 8 wherein the control signal comprises:

a bandwidth control signal for controlling the bandwidth of the integrated continuous-time filter; and

a gain control signal for controlling the gain of the integrated continuous-time filter.

10. The equalizer in accordance with claim 9 wherein the digital signal processing circuitry comprises:

an analog-to-digital converter for converting the output signal into a digital output signal;

circuitry means for processing the digital output signal using an autocorrelation algorithm and generating a digital bandwidth control signal and a digital gain control signal;

a first digital-to-analog converter for converting the digital bandwidth control signal into the bandwidth control signal for input to the integrated continuous-time filter; and

a second digital-to-analog converter for converting the digital gain control signal into the gain control for input to the integrated continuous-time filter.

11. An adaptive equalizer comprising:

an integrated continuous-time filter fabricated on a substrate for receiving and filtering an input signal from a cable and generating an output signal, the output signal being an equalized version of the input signal; and

circuitry for processing the output signal and generating a control signal for feedback to the integrated continuous-time filter, the control signal controlling transfer characteristics of the integrated continuous-time filter, such that distortion in the input signal from the cable is compensated wherein semiconductor process variations in the integrated continuous-time filter are compensated wherein the circuitry for processing comprises analog signal processing circuitry for generating the control signal in response to a comparison between amplitude characteristics of the output signal of the integrated continuous-time filter and ideal amplitude characteristics of the input signal.

12. The equalizer in accordance with claim 11 wherein the analog signal processing circuitry comprises a peak detector.

13. An adaptive equalizer comprising:

an integrated continuous-time filter fabricated on a substrate for receiving and filtering an input signal from a cable and generating an output signal, the output signal being an equalized version of the input signal; and

circuitry for processing the output signal and generating a control signal for feedback to the integrated continuous-time filter, the control signal controlling transfer characteristics of the integrated continuous-time filter such that distortion in the input signal from the cable is compensated wherein semiconductor process variations in the integrated continuous-time filter are compensated wherein the circuitry for processing comprises digital signal processing circuitry for generating the control signal in response to a comparison between frequency and amplitude characteristics of the output signal of the integrated continuous-time filter and ideal frequency and amplitude characteristics of the input signal.

14. The equalizer in accordance with claim 13 wherein the control signal comprises:

a bandwidth control signal for controlling the bandwidth of the integrated continuous-time filter; and

a gain control signal for controlling the gain of the integrated continuous-time filter.

15. The equalizer in accordance with claim 14 wherein the digital signal processing circuitry comprises:

an analog-to-digital converter for converting the output signal into a digital output signal;

circuitry means for processing the digital output signal using an autocorrelation algorithm and generating a digital bandwidth control signal and a digital gain control signal;

a first digital-to-analog converter for converting the digital bandwidth control signal into the bandwidth control signal for input to the integrated continuous-time filter; and

a second digital-to-analog converter for converting the digital gain control signal into the gain control for input to the integrated continuous-time filter.

16. An adaptive cable equalizer comprising:

an integrated continuous-time filter fabricated on a substrate receiving and filtering an input signal from a cable and generating an output signal, the output signal being an equalized version of the input signal; and

circuitry, coupled to the integrated continuous-time filter in a feedback loop, for processing the output signal and generating a gain control signal and a bandwidth control signal for feedback to the integrated continuous-time filter, the gain control signal and the bandwidth control signal adjusting the transfer characteristics of the integrated continuous-time filter thereby compensating for loss and distortion of the input signal caused by the cable and tuning the integrated continuous-time filter to compensate for semiconductor process variations in the integrated continuous-time filter.

17. The adaptive cable equalizer in accordance with claim 16 wherein the continuous-time filter comprises a plurality of transconductors implemented in a transconductance-capacitor configuration.

18. The adaptive cable equalizer in accordance with claim 17 wherein the transconductance of the plurality of transconductors adjusted in response to the gain control signal and the bandwidth control signal.

19. The adaptive cable equalizer in accordance with claim 16 wherein the continuous-time filter comprises:

a first transconductor coupled to the gain control signal, the gain control signal controlling the gain of the integrated continuous-time filter; and

a second transconductor coupled to the bandwidth control signal, the bandwidth control signal controlling the bandwidth of the integrated continuous-time filter.

20. The adaptive cable equalizer in accordance with claim 19 wherein the circuitry for processing comprises digital signal processing circuitry for generating the gain control signal and the bandwidth control signal in response to minimizing an autocorrelation of the input signal.

21. The adaptive cable equalizer in accordance with claim 20 wherein the digital signal processing circuitry comprises:

an analog-to-digital converter for converting the output signal into a digital output signal;

circuitry means for processing the digital output signal using an autocorrelation algorithm and generating a digital bandwidth control signal and a digital gain control signal;

a first digital-to-analog converter for converting the digital bandwidth control signal into the bandwidth control signal for input to the integrated continuous-time filter; and

a second digital-to-analog converter for converting the digital gain control signal into the gain control for input to the integrated continuous-time filter.

22. The adaptive cable equalizer in accordance with claim 19 wherein the circuitry for processing comprises analog signal processing circuitry for generating the gain control signal and the bandwidth control signal in response to a comparison between amplitude characteristics of the output signal of the integrated continuous-time filter and ideal amplitude characteristics of the input signal.

23. The adaptive cable equalizer in accordance with claim 22 wherein the analog signal processing circuitry comprises a peak detector.

24. The adaptive cable equalizer in accordance with claim 16 wherein the circuitry for processing is fabricated on the substrate and the integrated continuous-time filter and the circuitry for processing are fabricated using CMOS technology.

25. The adaptive cable equalizer in accordance with claim 16 wherein the continuous-time filter includes at least one pole location and at least one zero location and the control signal shifts the at least one pole location and the at least one zero location thereby controlling the transfer characteristics of the continuous-time filter.

26. A method for compensating for distortion of a signal caused by the transmission of the signal through a transmission medium, comprising the steps of:

receiving the signal;

performing an adaptive algorithm on the received signal using one or more known parameters of the received signal;

generating a control signal in response to the performance of the adaptive algorithm;

feeding back the control signal to an integrated continuous-time filter; and

filtering the received signal with the integrated continuous-time filter to generate an equalized signal, wherein the control signal comprises a gain control signal for adjusting gain of the integrated continuous-time filter and a bandwidth control signal for adjusting bandwidth of the integrated continuous-time filter.

27. The method in accordance with claim 26 wherein the performance of the adaptive algorithm minimizes an autocorrelation of the received signal.

28. The method in accordance with claim 26 further including the step of compensating for semiconductor process variations.