Linearity error compensator

• US 6,198,416 B1
• Filed: 04/12/2000
• Issued: 03/06/2001
• Est. Priority Date: 04/16/1999
• Status: Expired due to Term

• Current Assignee: Linearity LLC
• Original Assignee: Scott R. Velazquez
• Inventors: Velazquez, Scott R.
• Primary Examiner(s): Tokar, Michael
• Assistant Examiner(s): Lauture, Joseph
• Application Number:
  US09/548,069
• Time in Patent Office: 328 Days
• Field of Search: 341/120, 341/118, 341/143, 341/144, 375/296, 375/27
• US Class Current: 341/118
• CPC Class Codes: H03M 1/0614 of harmonic distortion H03M1/0617 takes precedence
• CPC Class Codes: H03M 1/12 Analogue/digital converters H03M1/001 – H03M1/10 take precedence

Abstract

In one aspect, the present invention is directed to a compensator for compensating linearity errors, such as harmonic distortion and intermodulation distortion, in devices. The compensator includes a means for phase-shifting and a means for exponentiation to generate a compensation signal such that the linearity error distortion signals are canceled in the system output while maintaining the desired fundamental signal. Another aspect of the invention is directed to methods for calibrating the linearity error compensator. Another aspect of the invention is directed to a modeling linearity errors in a device.

Claims

1. A compensator for compensating linearity errors in a device generating a fundamental signal and linearity error distortion signals comprising:

an exponentiator for generating a compensation signal; and

a phase-shifting unit for introducing a phase-shift between the fundamental signal and the compensation signal such that the linearity error distortion signals are canceled and the fundamental signal is maintained.

2. The compensator of claim 1 wherein the exponentiator comprises a power unit for generating an exponentiated compensation signal.

3. The compensator of claim 2 wherein the power unit is constructed and arranged to generate a non-integer-exponentiated signal.

4. The compensator of claim 2 wherein the power unit is operatively coupled to a frequency-dependent gain unit for adjusting the exponentiated compensation signal amplitude.

5. The compensator of claim 2 wherein the phase-shifting unit is operatively coupled to a frequency-dependent gain unit for adjusting the exponentiated compensation signal amplitude.

6. The compensator of claim 2 comprising a plurality of power units and a plurality of phase-shifting units for generating a plurality of exponentiated compensation signals.

7. The compensator of claim 6 further comprising an adder for combining the plurality of exponentiated compensation signals.

8. The compensator of claim 1 further comprising a plurality of adders operatively coupled to a plurality of phase-shifting units for adding a plurality of compensation elements to generate a plurality of factored compensation signals, and wherein the exponentiator comprises a multiplier for combining the plurality of factored compensation signals.

9. The compensator of claim 8 wherein each phase-shifting unit is operatively coupled to a frequency-dependent gain unit for adjusting each factored compensation signal'"'"'s amplitude.

10. The compensator of claim 8 wherein each adder is operatively coupled to a frequency-dependent gain unit for adjusting each factored compensation signal'"'"'s amplitude.

11. The compensator of claim 1 further comprising an adder operatively coupled to the phase-shifting unit for adding a compensation element to generate a factored compensation signal, and wherein the exponentiator comprises a power unit for generating an exponentiated compensation signal and a multiplier for combining the factored compensation signal and the exponentiated compensation signal.

12. The compensator of claim 1 wherein the phase-shifting unit is constructed and arranged to introduce a frequency-dependent phase-shift.

13. The compensator of claim 1 wherein the phase-shifting unit'"'"'s compensation parameters or the exponentiator'"'"'s compensation parameters are adjusted according to the amplitude of the fundamental signal.

14. The compensator of claim 1 wherein the compensator is operatively coupled to the device and the compensator precedes the device.

15. The compensator of claim 14 wherein the device is a digital-to-analog converter.

16. The compensator of claim 1 wherein the compensator is operatively coupled to the device and the compensator follows the device.

17. The compensator of claim 16 wherein the device is an analog-to-digital converter.

18. The compensator of claim 1 wherein the phase-shifting unit'"'"'s compensation parameters and the exponentiator'"'"'s compensation parameters are calibrated according to the measured amplitude and phase of the fundamental signal and linearity error distortion signals.

19. A compensation system for compensating linearity errors comprising:

a device for generating a fundamental signal and linearity error distortion signals;

an exponentiator for generating a compensation signal; and

a phase-shifting unit for introducing a phase-shift between the fundamental signal and the compensation signal such that the linearity error distortion signals are canceled and the fundamental signal is maintained, wherein the phase-shifting unit'"'"'s compensation parameters and the exponentiator'"'"'s compensation parameters are calibrated according to the measured amplitude and phase of the fundamental signal and linearity error distortion signals.

20. A model for modeling linearity errors in a device generating a fundamental signal and linearity error distortion signals comprising:

an exponentiator for generating a modeling signal; and

a phase-shifting unit for introducing a phase-shift between the fundamental signal and the modeling signal, wherein the phase-shifting unit'"'"'s model parameters and the exponentiator'"'"'s model parameters are calculated according to the measured amplitude and phase of the fundamental signal and linearity error distortion signals.

21. A method for calibrating a compensation system that cancels linearity error distortion signals generated by a device and maintains a fundamental signal generated by the device, the method of calibrating comprising steps of:

injecting test signals into the compensation system;

measuring the amplitude and phase of the linearity error distortion signals and the fundamental signal; and

calculating a set of compensator coefficients;

wherein the step of calculating the set of compensator coefficients includes solving for a set of phase-shifting compensation parameters and a set of exponentiator compensation parameters.

22. The method of claim 21 wherein the step of calculating the set of compensator coefficients further includes a step ignoring linearity error distortion signals with amplitudes smaller than a pre-determined threshold.

23. The method of claim 21 wherein the step of calculating the set of compensator coefficients further includes a step of repeating the step of calculating the set of compensator coefficients to generate a plurality of sets of compensator coefficients for a cascaded compensator.

24. The method of claim 23 further comprising a step of mathematically combining the plurality of sets of compensator coefficients into a single combined set of compensator coefficients for a non-cascaded compensator having substantially the same performance as the cascaded compensator.

25. The method of claim 21 wherein the step of calculating a set of compensator coefficients further includes a step of setting the phase-shifting compensation parameters to be substantially equivalent to the measured phase of the linearity error distortion signals and setting the amplitudes of the corresponding exponentiator compensation parameters to be the approximate negative of the measured amplitude of the linearity error distortion signal.

26. The method of claim 21 wherein the step of injecting test signals into the compensation system includes a step of injecting a plurality of sinusoidal test signals, and the step of measuring the amplitude and phase of the linearity error distortion signals and the fundamental signal includes a step of using trigonometric identities to convert powers of sinusoidal functions to sinusoidal functions of harmonics.

27. The method of claim 21 wherein the step of calculating a set of compensator coefficients includes iteratively optimizing the set of phase-shifting compensation parameters and the set of exponentiator compensation parameters.

28. A method of compensating linearity errors in a device generating a fundamental signal and linearity error distortion signals comprising steps of:

exponentiating a compensation signal to generate an exponentiated compensation signal; and

phase-shifting the compensation signal or the exponentiated compensation signal to introduce a phase-shift between the fundamental signal and the exponentiated compensation signal such that the linearity error distortion signals are canceled and the fundamental signal is maintained.

29. The method of claim 28 wherein the step of exponentiating comprises a step of using a power method to generate the exponentiated compensation signal.

30. The method of claim 29 wherein the step of using a power method includes using a non-integer power method to generate a non-integer-exponentiated signal.

31. The method of claim 29 wherein the step of exponentiating further comprises a step of adjusting the amplitude of the exponentiated compensation signal based on the frequency of the fundamental signal.

32. The method of claim 29 wherein the step of phase-shifting includes a plurality of steps of phase-shifting and the step of exponentiating includes a plurality of steps of using a power method to generate a plurality of exponentiated compensation signals.

33. The method of claim 32 further comprising a step of adding the plurality of exponentiated compensation signals.

34. The method of claim 28 wherein the step of phase-shifting includes a plurality of steps of phase-shifting to generate a plurality of phase-shifted compensation signals, the method further comprising a step of adding a plurality of compensation elements to the plurality of phase-shifted compensation signals to generate a plurality of factored compensation signals, and wherein the step of exponentiating comprises multiplying the plurality of factored compensation signals.

35. The method of claim 28 wherein the step of phase-shifting includes generating a phase-shift based on the frequency of the fundamental signal.

36. The method of claim 28 wherein the step of phase-shifting includes adjusting the phase-shift compensation parameters according to the amplitude of the fundamental signal or the step of exponentiating includes adjusting the exponentiation compensation parameters according to the amplitude of the fundamental signal.

37. The method of claim 28 wherein the compensation signal is the output of the device.

38. The method of claim 37 wherein the device is for converting signals from analog to digital.

39. A method of compensating linearity errors comprising steps of:

generating a fundamental signal and linearity error distortion signals;

exponentiating a compensation signal to generate an exponentiated compensation signal; and

phase-shifting the compensation signal or the exponentiated compensation signal to introduce a phase-shift between the fundamental signal and the exponentiated compensation signal such that the linearity error distortion signals are canceled and the fundamental signal is maintained; and

wherein the phase-shifting compensation parameters and the exponentiation compensation parameters are calibrated according to the measured amplitude and phase of the fundamental signal and linearity error distortion signals.

40. A method of modeling linearity errors in a device generating a fundamental signal and linearity error distortion signals comprising steps of:

exponentiating a modeling signal to generate an exponentiated modeling signal; and

phase-shifting the modeling signal or the exponentiated modeling signal to introduce a phase-shift between the fundamental signal and the exponentiated modeling signal; and

wherein the phase-shift model parameters and the exponentiation model parameters are calculated according to the measured amplitude and phase of the fundamental signal and linearity error distortion signals.