System and method for adaptive DC offset compensation in wireless transmissions

• US 20060217100A1
• Filed: 03/22/2005
• Published: 09/28/2006
• Est. Priority Date: 03/22/2005
• Status: Active Grant

• Current Assignee: VIXS Systems Incorporated (Pixelworks Incorporated)
• Original Assignee: VIXS Systems Incorporated (Pixelworks Incorporated)
• Inventors: Astrachan, Paul M.
• Granted Patent: US 7,400,869 B2
• Time in Patent Office: Days
• US Class Current: 455/296
• CPC Class Codes: H04B 1/30 for homodyne or synchrodyne receivers demodulator circuits H03D1/22

Abstract

A first direct current (DC) component of a first amplified representation of a received signal at an output of an amplifier set to a first gain setting is determined during a first expected idle period of a received signal. A second DC component of a second amplified representation of the received signal at the output of the amplifier set to the first gain setting is determined during a second expected idle period of the received signal. A first average DC component is determined based at least in part on the first and second DC components and a DC offset used by the amplifier when set to the first gain setting is adjusted based on a comparison of the first average DC component to one or more threshold values.

Claims

1. A method comprising:

determining, during a first expected idle period of a received signal, a first direct current (DC) component of a first amplified representation of the received signal at an output of an amplifier, wherein the amplifier is set to a first gain setting;

determining, during a second expected idle period of the received signal, a second DC component of a second amplified representation of the received signal at the output of the amplifier, wherein the amplifier is set to the first gain setting;

determining a first average DC component based at least in part on the first and second DC components; and

adjusting a DC offset used by the amplifier when set to the first gain setting based on a comparison of the first average DC component to one or more threshold values.

2. The method of claim 1, wherein determining the first average DC component includes determining a moving average using at least the first and second DC components.

3. The method of claim 1, wherein:

adjusting the DC offset includes reducing the DC offset when the first average DC component is greater than a first threshold; and

adjusting the DC offset includes increasing the DC offset when the average DC component is less than a second threshold.

4. The method of claim 1, wherein adjusting the DC offset includes adjusting a value input to a digital-to-analog converter that outputs the DC offset used by the amplifier.

5. The method of claim 1, further comprising:

determining, during a third expected idle period of the received signal, a third DC component of a third amplified representation of the received signal at the output of the amplifier, wherein the amplifier is set to the first gain setting;

determining a second average DC component based at least in part on the third DC component and at least one of the first and second DC components; and

adjusting the DC offset used by the amplifier when set to the first gain setting based on a comparison of the second average DC component to one or more threshold values.

6. The method of claim 1, further comprising:

determining whether a transmission burst preceding the second idle period is a valid transmission burst;

when the transmission burst is determined as invalid;

identifying the second DC component as an invalid DC component;

determining a third average DC component based at least in part on the first DC component but not the second DC component; and

adjusting the DC offset used by the amplifier when set to the first gain setting based on a comparison of the third average DC component to one or more threshold values.

7. A system comprising:

a variable gain amplifier having a first input to receive a first signal, a second input to receive a DC offset and an output to provide a second signal, the second signal including an amplified representation of the first signal having an adjustment based on the DC offset;

a first table having an entry for each of a set of gain settings of the amplifier, each entry to store a value representative of a DC offset provided to the second input of the amplifier when the amplifier is set to the corresponding gain setting; and

an offset adjustment module operably coupled to the second input and the output of the amplifier and to the first table, wherein the offset adjustment module is operable to, for each of one or more gain settings;

determine an average DC component of the second signal for the gain setting based on one or more DC components measured from the second signal for one or more periods of the second signal when the amplifier is set to the gain setting; and

adjust the value representative of a DC offset stored in the entry of the first table corresponding to the gain setting based on a comparison of the average DC component to one or more thresholds.

8. The system of claim 7, wherein the offset adjustment module is operable to determine the average DC component based on a moving average.

9. The system of claim 7, wherein:

the offset adjustment module adjusts the value representative of a DC offset to represent a decreased DC offset when the average DC component is greater than a first threshold; and

the offset adjustment module adjusts the value representative of a DC offset to represent an increased DC offset when the DC component is less than a second threshold.

10. The system of claim 7, further comprising a digital-to-analog converter having an input to receive a value representative of a DC offset from the first table and an output to provide a DC voltage substantially equivalent to the DC offset to the second input of the amplifier.

11. The system of claim 7, wherein the offset adjustment module is operable to determines the average DC component for a first gain setting by:

determining, during a first period of the second signal, a first DC component, wherein the amplifier is set to the first gain setting;

determining, during a second period of the received signal, a second DC component, wherein the amplifier is set to the first gain setting; and

determining a first average DC component based at least in part on the first and second DC components.

12. The system of claim 11, wherein the first period includes a first expected idle period following a first transmission burst and the second period includes a second expected idle period following a second transmission burst.

13. The system of claim 12, wherein the offset module is further operable to:

determine whether the second transmission burst is a valid transmission burst;

when the second transmission burst is determined as invalid;

identify the second DC component as an invalid DC component;

determine a second average DC component exclusive of the second DC component; and

adjust the value representative of a DC offset stored in the entry of the first table corresponding to the first gain setting based on a comparison of the second average DC component to one or more thresholds.

14. The system of claim 11, further comprising an integrator having an input operably coupled to the output of the amplifier and an output operably coupled to the offset adjustment module, wherein the integrator is adapted to output a value representative of the first DC component over the first period and a value representative of the second DC component over the second period.

15. The system of claim 11, wherein the first and second periods comprise at least one of:

first and second transmission bursts or first and second expected idle periods.

16. A method comprising:

determining a first average direct current (DC) component for an amplified representation of a first signal, the first average DC component based on a measured DC component for the amplified representation of the first signal obtained during one or more periods of the first signal;

adjusting a DC offset supplied to an amplifier used to provide the amplified representation of the first signal based on a comparison of the first average DC component to one or more thresholds.

17. The method of claim 16, wherein the one or more periods comprise at least one of a transmission burst or an expected idle period.

18. The method of claim 16, wherein determining the first average DC component includes determining a moving average.

19. The method of claim 16, further comprising:

determining whether a first measured DC component is valid based on a validity of a transmission burst preceding a period during which the first measured DC component is determined; and

determining a second average DC component exclusive of the first measured DC component when the first measured DC component is determined to be invalid.

20. The method of claim 19, further comprising:

adjusting a DC offset supplied to the amplifier used to provide the amplified representation of the first signal based on a comparison of the second average DC component to one or more thresholds.