Method and apparatus for DC offset correction

• US 6,327,313 B1
• Filed: 12/29/1999
• Issued: 12/04/2001
• Est. Priority Date: 12/29/1999
• Status: Expired due to Term

• Current Assignee: Apple Inc.
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Traylor, Kevin B., Fang, Jing
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): JIANG, LENNY R
• Application Number:
  US09/473,673
• Time in Patent Office: 706 Days
• Field of Search: 375/316, 375/340, 375/346, 375/354, 375/371, 375/318, 375/317, 329/306, 329/300, 341/110, 341/155, 341/144
• US Class Current: 375/316
• CPC Class Codes: H04L 25/063 Setting decision thresholds using feedback techniques only

Abstract

A DC offset correction loop (200, 300) utilizes a peak estimator (218, 322) to determine peaks associated with a digital signal (238, 338). The peak estimator (218, 322) averages the peaks in order to estimate the DC offset. A summer (216, 326) sums the DC offset (242, 350) with the digital signal to produce a corrected output.

Claims

1. A method of correcting for DC offsets in a digital signal, comprising the steps of:

receiving a digital signal (an I/Q signal);

estimating the peaks of the digital signal using envelope estimation;

averaging the peaks of the digital signal to estimate the DC offset; and

correcting for the DC offset by summing the DC offset with the digital signal.

2. The method of claim 1, wherein the envelope estimation is determined by performing the steps of:

determining peak values in the digital signal;

updating the peak values when the digital signal exceeds current peak values;

adjusting the peak value resulting in an instantaneous positive peak or an instantaneous negative peak; and

estimating the DC offset by averaging the instantaneous positive and negative peaks.

3. The method of claim 2, wherein the step of adjusting comprises the step of increasing or decreasing the peak value by a predetermined step thereby providing a fixed envelope estimation scheme.

4. The method of claim 2, wherein the step of adjusting comprises the step of increasing or decreasing the peak value by an adaptive step thereby providing an adaptive envelope estimation scheme.

5. A method of correcting for DC offsets in a digital signal, comprising the steps of:

receiving a digital signal (an I/Q signal);

estimating the peaks of the digital signal using fixed block processing peak estimations;

averaging the peaks of the digital signal to estimate the DC offset; and

correcting for the DC offset by summing the DC offset with the digital signal.

6. The method of claim 5, wherein the fixed block processing is performed by:

performing order statistics filtering on the fixed window size to produce decimated signals;

extracting local positive and negative peaks from the decimated signals; and

estimating DC offsets by averaging the local positive and negative peaks.

7. The method of claim 5, wherein the fixed block processing is performed by:

performing order statistics filtering on the fixed window size to produce decimated signals;

extracting local positive and negative peaks from the decimated signals;

determining global positive and negative peaks using the local positive and negative peaks;

estimating DC offsets by averaging the global positive and negative peaks.

8. The method of claim 7, wherein the step of determining global positive and negative peaks is based on an amplitude relationship between I and Q signals.

9. The method of claim 7, wherein the step of determining global positive and negative peaks is based on an amplitude relationship of the decimated signals.

10. The method of claim 7, wherein the step of determining global positive and negative peaks is based on derivative of I and Q signals.

11. The method of claim 7, wherein the step of determining global positive and negative peaks is based on an amplitude relationship between I and Q signals and derivatives of the I and Q signals.

12. A method of correcting for DC offsets in a digital signal, comprising the steps of:

receiving a digital signal (an I/Q signal);

estimating the peaks of the digital signal using adaptive block processing peak estimations;

averaging the peaks of the digital signal to estimate the DC offset; and

correcting for the DC offset by summing the DC offset with the digital signal.

13. The method of claim 12, wherein the adaptive block processing of peak estimations is performed by:

estimating the frequency of the I and Q signals in order to determine a window size;

performing order statistics filtering on the determined window size to produce decimated signals;

extracting local positive and negative peaks from the decimated signals; and

estimating DC offsets by averaging the local positive and negative peaks.

14. The method of claim 12, wherein the adaptive block processing of peak estimations is performed by:

estimating the frequency of the I and Q signals in order to determine a window size;

performing order statistics filtering on the determined window size to produce decimated signals;

extracting local positive and negative peaks from the decimated signals;

determining global positive and negative peaks using the local positive and negative peaks; and

estimating DC offsets by averaging the global positive and negative peaks.

15. The method of claim 14, wherein the step of determining global positive and negative peaks is based on an amplitude relationship between I and Q signals.

16. The method of claim 14, wherein the step of determining global positive and negative peaks is based on an amplitude relationship of the decimated signals.

17. The method of claim 14, wherein the step of determining global positive and negative peaks is based derivative of I and Q signals.

18. The method of claim 14, wherein the step of determining global positive and negative peaks is based on an amplitude relationship between I and Q signals and derivatives of the I and Q signals.

19. A DC offset correction loop, comprising:

a first summer having first and second inputs and an output, the first input for receiving a zero intermediate frequency (ZIF) signal;

a baseband filter coupled to the output of the first summer, the baseband filter for filtering the ZIF signal into a filtered signal;

an analog-to-digital converter (A/D) for converting the filtered signal into a digital signal;

an attenuator for receiving the digital signal and generating an attenuated digital signal;

a second summer for summing the attenuated signal and an I/Q offset output signal and generating a ZIF equivalent digital signal;

a peak estimator for digitally estimating the peaks of the ZIF equivalent digital signal and calculating DC offsets;

a smoothing device for interpolating the estimated DC offsets and producing the I/Q offset output signal, the I/Q offset output signal being fed back to the second summer;

an amplifier for amplifying the I/Q offset output signal;

a digital-to-analog (D/A) converter for converting the I/Q offset output signal to an analog offset signal, the analog offset signal being fed back to the second input of the first summer; and

the digital signal generated from the A/D converter providing an output of the DC offset correction loop.

20. The DC offset correction loop of claim 19, wherein the smoothing device comprises a lowpass filter.

21. The DC offset correction loop of claim 19, wherein the smoothing device comprises a weighted accumulator.

22. The DC offset correction loop of claim 19, further comprising a predictor between the peak estimator and the smoothing device for predicting future peaks.

23. A DC offset correction loop, comprising:

a first summer having first and second inputs and an output, the first input for receiving a zero intermediate (ZIF) signal;

a baseband filter coupled to the output of the summer, the baseband filter for filtering the ZIF signal into a filtered signal;

an analog-to-digital (A/D) converter for converting the filtered signal into a digital I/Q signal;

an attenuator for receiving the digital I/Q signal and generating an attenuated digital signal;

a weighted accumulator for receiving the attenuated digital signal and producing a first I/Q offset output signal;

an amplifier for amplifying the first I/Q offset output signal and producing an amplified I/Q offset signal;

a digital-to-analog (D/A) converter for converting the amplified I/Q offset signal into an analog offset signal, the analog offset signal being fed back to the second input of the first summer;

a peak estimator for digitally estimating the peaks of the digital I/Q signal and calculating DC offset residue;

a smoothing device for interpolating the estimated DC offset residue and producing a second I/Q offset output signal;

a second summer for summing the digital I/Q signal and the second I/Q offset output signal to generate an output for the DC offset correction loop.

24. The DC offset correction loop of claim 23, further comprising a predictor between the peak estimator and the smoothing device for predicting further peaks.

25. The DC offset correction loop of claim 23, further comprising a delay device at the input to the second summer for delaying the I/Q signal.

26. The DC offset correction loop of claim 23, wherein the smoothing device comprises a lowpass filter.

27. A method of minimizing DC offsets, comprising the steps of:

receiving a baseband signal;

converting the baseband signal to a digital signal;

summing the digital signal with previously estimated DC offsets to produce a ZIF equivalent offset signal;

digitally estimating the DC offsets in the ZIF equivalent signal;

amplifying the estimated digital DC offsets;

converting the amplified estimated digital DC offsets into an analog signal; and

summing the analog signal with the received baseband signal to provide a corrected baseband signal;

repeating the steps of receiving through summing the analog signal using the corrected baseband signal.

28. The method of claim 27, wherein the step of estimating is performed using first or second peak detection criteria selected from the group of fixed envelope estimations or adaptive envelope estimations.

29. The method of claim 27, wherein the step of estimating is performed using first or second peak detection criteria selected from the group of fixed block processing peak estimations or adaptive block processing peak estimations.

30. The method of claim 27, wherein the digital signal is provided as an output.

31. The method of claim 27, further including the step of attenuating the digital signal prior to the step of summing the digital signal with the previously estimated DC offsets.

32. A digital DC offset estimation circuit, comprising:

a baseband filter for receiving a baseband signal and generating a filtered baseband signal;

an attenuator for compensating signal amplitude of the filtered baseband signal and generating a gained signal;

a peak estimator for estimating peaks of the gained signal and estimating DC offsets associated with the gained signal;

a smoothing device for smoothing and interpolating the estimated DC offsets and generating a smoothed DC offset;

an amplifier for scaling the smoothed DC offset signal and generating an amplified signal; and

a summer for summing the amplified signal with the baseband signal to generate a ZIF equivalent signal.

33. A digital DC offset estimation circuit as described in claim 32, further comprising a predictor device coupled between the peak estimator and the smoothing device for estimating future peaks.

34. A digital DC offset estimation circuit, comprising:

a baseband filter for filtering the baseband signal;

a weighted accumulator for estimating DC offset in the filtered baseband signal;

an amplifier for scaling the estimated DC offset and producing a scaled signal;

a first summer for summing the scaled signal and the baseband signal;

a peak estimator for estimating peaks of the filtered baseband signal and calculating DC residue;

a lowpass filter for interpolating and smoothing the DC residue; and

a second summer for canceling the DC residue of the filtered baseband signal.

35. A DC offset correction loop, including:

a negative regenerative feedback loop, including within the loop;

an attenuator for receiving an I/Q signal and generating a gain compensated waveform;

a summer having first and second inputs, the first input receiving the gain compensated waveform;

a peak estimator for estimating peaks of the gain compensated waveform and calculating DC offset; and

a smoothing device for smoothing and interpolating the DC offset estimation, a smoothed DC offset being fed back to the second input of the summer; and

an amplifier for scaling the smoothed DC offset and feeding it back the first summer.

36. A DC offset correction loop, including:

a negative regenerative feedback loop, including;

an attenuator for receiving an I/Q signal and generating an attenuated signal;

a weighted accumulator for estimating DC offset in the attenuated signal;

an amplifier for scaling the estimated DC offset;

an output signal path coupled to the input of the attenuator, the output signal path including;

a peak estimator for estimating peaks of the I/Q signal and calculating DC residue of the I/Q signal;

a lowpass filter for interpolating and smoothing the DC residue; and

a summer for summing the DC residue of the I/Q signal with the I/Q signal to produce an I/Q output signal as the output of the DC correction loop.