METHOD AND APPARATUS FOR COMPENSATING DC OFFSETS IN COMMUNICATION SYSTEMS

• US 20080089391A1
• Filed: 12/12/2007
• Published: 04/17/2008
• Est. Priority Date: 06/20/2002
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: O'Shea, Helena
• Granted Patent: US 8,559,559 B2
• Time in Patent Office: Days
• US Class Current: 375/136
• CPC Class Codes: H04L 25/063 Setting decision thresholds using feedback techniques only

Abstract

A communications system receiver incorporates a time-averaged DC component subtracter to subtract a time-averaged DC offset component from a received, processed signal. The time-averaged DC offset is selectably calculated from a moving average or a running average. The selection of the time-averaged DC offset can be done depending on whether the receiver operates in a frequency hop mode or not.

Claims

1. An apparatus for use in a communications system, the apparatus comprising:

a DC estimator to receive an input signal and generate estimate values of the input signal'"'"'s DC level;

a DC averager to receive the estimate values and generate a DC average, the DC average selectable from a moving average of the estimate values or a running average of the estimate values; and

a subtracter unit to subtract the DC average from the input signal.

2. The apparatus of claim 1, the DC averager configured to select from a moving average or a running average based on an operating mode of the receiver.

3. The apparatus of claim 2, the DC averager configured to select a moving average if the receiver is in a frequency hop mode, the DC averager further configured to select a running average if the receiver is not in a frequency hop mode.

4. The apparatus of claim 3, the input signal comprising an in-phase (I) component and a quadrature (Q) component, the DC estimator configured to generate estimate values for each of the I and Q components, the DC averager configured to generate DC averages for the estimate values generated for each of the I and Q components, and the subtracter unit configured to subtract a DC average from each of the I and Q components.

5. The apparatus of claim 3, further comprising:

an automatic gain correction unit to receive an uncorrected modulated composite signal, provide gain correction, and output a corresponding gain corrected modulated composite signal to the demodulator; and

a symbol decoder to receive the demodulated component output from the subtracter unit and output a corresponding plurality of symbol bits.

6. The apparatus of claim 5, wherein the apparatus is a handset in a wireless communication system, further comprising:

an antenna to communicate a wireless signal to the automatic gain correction unit;

a converter unit to convert the plurality of symbol bits output from the symbol decoder into a corresponding analog signal; and

a transducer for converting the analog signal from the converter unit into an acoustic signal.

7. The apparatus of claim 5, wherein the apparatus is an integrated circuit adapted for use in a handset, the handset comprising:

an antenna to communicate a wireless signal to the automatic gain correction unit;

a converter unit to convert the plurality of symbol bits output from the symbol decoder into a corresponding analog signal; and

a transducer for converting the analog signal from the converter unit into an acoustic signal.

8. The apparatus of claim 7, wherein the communication system further comprises a transmitter to transmit the wireless signal to the antenna.

9. The apparatus of claim 3, wherein the apparatus is a programmable microprocessor running executable code in a handset configured to operate within the communications system.

10. The apparatus of claim 3, wherein the uncorrected modulated composite signal is a quadrature phase shift keying signal.

11. A method for use in a communication system, the method comprising:

receiving an input signal and generating estimate values of the input signal'"'"'s DC level using a DC estimator;

receiving the estimate values using a DC averager to generate a DC average, the DC average selectable from a moving average of the estimate values or a running average of the estimate values; and

subtracting the DC average from the input signal.

12. The method of claim 11, further comprising selecting from a moving average or a running average based on an operating mode of the receiver.

13. The method of claim 12, further comprising selecting a moving average if the receiver is in a frequency hop mode, and selecting a running average if the receiver is not in a frequency hop mode.

14. The method of claim 13, the input signal comprising an in-phase (I) component and a quadrature (Q) component, the DC estimator configured to generate estimate values for each of the I and Q components, the DC averager configured to generate DC averages for the estimate values generated for each of the I and Q components, and the subtracting comprising subtracting a DC average from each of the I and Q components.

15. The method of claim 13, further comprising:

receiving an uncorrected modulated composite signal, providing gain correction, and outputting a corresponding gain corrected modulated composite signal as the input signal; and

symbol demodulating the output of said subtracting.

16. The method of claim 15, further comprising:

decoding the demodulated symbols;

converting the decoded symbols into a corresponding analog signal; and

converting the analog signal from the converter unit into an acoustic signal.

17. An apparatus for use in a communications system, the apparatus comprising:

DC estimator means for receiving an input signal and generating estimate values of the input signal'"'"'s DC level;

DC averager means for receiving the estimate values to generate a DC average, the DC average selectable from a moving average of the estimate values or a running average of the estimate values; and

subtracter means for subtracting the DC average from the input signal.

18. The apparatus of claim 17, further comprising means for selecting from a moving average or a running average based on an operating mode of the receiver.

19. The apparatus of claim 18, further comprising means for selecting a moving average if the receiver is in a frequency hop mode, and selecting a running average if the receiver is not in a frequency hop mode.

20. The apparatus of claim 19, the input signal comprising an in-phase (I) component and a quadrature (Q) component, the DC estimator means configured to generate estimate values for each of the I and Q components, the DC averager means configured to generate DC averages for the estimate values generated for each of the I and Q components, and the subtracter means comprising subtracting a DC average from each of the I and Q components.

21. The apparatus of claim 19, further comprising:

means for receiving an uncorrected modulated composite signal, providing gain correction, and outputting a corresponding gain corrected modulated composite signal as the input signal; and

means for symbol demodulating the output of said subtracting.

22. The apparatus of claim 21, further comprising:

means for decoding the demodulated symbols;

means for converting the decoded symbols into a corresponding analog signal; and

means for converting the analog signal from the converter unit into an acoustic signal.

23. The apparatus of claim 19, wherein the communication system further comprises a transmitter to transmit the wireless signal to the antenna.

24. The apparatus of claim 19, wherein the apparatus is a programmable microprocessor running executable code in a handset configured to operate within the communications system.

25. The apparatus of claim 19, wherein the uncorrected modulated composite signal is a quadrature phase shift keying signal.