Compensation of a DC offset in a receiver

• US 20050250459A1
• Filed: 05/05/2004
• Published: 11/10/2005
• Est. Priority Date: 05/05/2004
• Status: Active Grant

• Current Assignee: RPX Corporation
• Original Assignee: Nokia Corporation
• Inventors: Ruha, Antti, Tervaluoto, Jussi, Jantti, Joni
• Granted Patent: US 7,336,937 B2
• Time in Patent Office: Days
• US Class Current: 455/127.200
• CPC Class Codes: H03D 3/008 Compensating DC offsets
• CPC Class Codes: H04B 1/30 for homodyne or synchrodyne receivers demodulator circuits H03D1/22
• CPC Class Codes: H04L 25/063 Setting decision thresholds using feedback techniques only

Abstract

A method of compensating a direct-current offset coupled into a receiving path of a receiver, the receiving path having at least one gain factor adjustable by a gain control, which method first determines an amount of a direct-current offset present at a selected end point in the receiving path. A compensation quantity is set accordingly. In case of a forthcoming adjustment of the at least one gain factor by the gain control, the compensation quantity is then scaled with a scaling factor to prevent a direct-current step at the selected end point due to this forthcoming adjustment. The final compensation quantity is fed at a selected summing node into the receiving path. The invention is also directed to a corresponding receiver, an electronic device comprising such a receiver, a hardware component for such a receiver and to a corresponding software program product.

Claims

1. A method of compensating a direct-current offset coupled into a receiving path of a receiver, in which receiving path at least one gain factor is adjustable by a gain control, said method comprising:

determining an amount of a direct-current offset present at a selected end point in said receiving path and setting a compensation quantity accordingly;

in case of a forthcoming adjustment of said at least one gain factor by said gain control, scaling said compensation quantity with a scaling factor to prevent a direct-current step at said selected end point due to said forthcoming adjustment of said at least one gain factor; and

feeding said compensation quantity at a selected summing node into said receiving path.

2. The method according to claim 1, further comprising determining said scaling factor by:

estimating a current amount of contributions to said direct-current offset;

determining a relative change in said direct-current offset which would have resulted with said estimated amount of direct-current contributions after a preceding gain adjustment; and

selecting said relative change as scaling factor.

3. The method according to claim 1, further comprising a preceding step of normalizing a signal provided at said selected end point of said receiving path by dividing said signal by a total gain applied by said receiving path between said summing node and said end point of said receiving path, wherein said normalized signal is used for determining said amount of a direct-current offset.

4. The method according to claim 3,

wherein said direct-current offset contributions comprise a first contribution entering said receiving path between said summing node and said end point, which first contribution is multiplied on said receiving path by a first gain factor A3, wherein said direct-current offset contributions comprise a second contribution entering said receiving path at said summing node, which second contribution is multiplied on said receiving path by said first gain factor and in addition by a second gain factor A2, and wherein said direct-current offset contributions comprise a third contribution entering said receiving path before said summing node, which third contribution is multiplied on said receiving path by said first gain factor, by said second gain factor and in addition by a third gain factor A1;

wherein Uoq_A1_last is said compensation quantity before a gain adjustment of gain factor A1 from A1_last to A1_new and wherein Uoq_A1_prev is said compensation quantity before a preceding gain adjustment of gain factor A1 from A1_prev to A1_last;

wherein Uoq_A2_last is said compensation quantity before a gain adjustment of gain factor A2 to from A2_last to A2_new and wherein Uoq_A2_prev is said compensation quantity before a preceding gain adjustment of gain factor A2 from A2_prev to A2_last;

wherein said first contribution is estimated to be Û

o3=(Uoq_A2_prev-Uoq_A2_last)/(1/A2_prev−

/A2_last);

wherein said third contribution is estimated to be Û

o1=(Uoq_A1_prev-Uoq_A1_last)/(A1_prev-A1_last);

wherein said second contribution is estimated to be Û

o2=Uoq_last-A1_new*Û

o1−

1/A2_new*Û

o3; and

wherein said scaling factor is determined to be S=(A1_new*Û

o1+Uo2+1/A2_new*Û

o3)/(A1_last*Û

o1+Û

o2+1/A2_last*Û

o3).

5. The method according to claim 1, wherein determining said amount of a direct-current offset at said end point of said receiving path comprises at least one of integrating a signal available at said end point of said receiving path, windowing a signal available at said end point of said receiving path, detecting positive and negative peaks in a signal available at said end point of said receiving path, and envelope forming of a signal available at said end point of said receiving path.

6. The method according to claim 1, wherein said compensation quantity is determined and scaled in the digital domain, a respective final compensation quantity being converted into the analog domain before it is fed to said summing node.

7. The method according to claim 1, wherein said receiver is a direct conversion radio frequency receiver.

8. A receiver comprising:

a receiving path, in which receiving path at least one gain factor is adjustable by a gain control, wherein a direct-current offset coupled into said receiving path is to be compensated;

a DC estimation portion adapted to estimate an amount of a direct-current offset present at a selected end point in said receiving path, adapted to set a compensation quantity accordingly, adapted to scale said compensation quantity with a provided scaling factor, if any, and adapted to feed said compensation quantity into said receiving path at a selected summing node; and

a DC compensation control portion adapted to determine in case of a forthcoming adjustment of said at least one gain factor a scaling factor preventing a direct-current step at said selected end point due to said forthcoming adjustment of said at least one gain factor, and adapted to provide said scaling factor to said DC estimation portion.

9. The receiver according to claim 8, wherein said DC compensation control portion is adapted to determine said scaling factor by:

estimating a current amount of contributions to said direct-current offset;

determining a relative change in said direct-current offset which would have resulted with said estimated amount of direct-current contributions after a preceding gain adjustment; and

selecting said relative change as scaling factor.

10. The receiver according to claim 8, further comprising a normalization portion adapted to normalize a signal provided at said selected end point of said receiving path by dividing said signal by a total gain applied by said receiving path between said summing node and said end point of said receiving path, which normalization portion is arranged for providing said normalized signal to said DC estimation portion as basis for determining said amount of a direct-current offset.

11. The receiver according to claim 8, wherein said DC estimation portion comprises an integrator for determining said amount of a direct-current offset at said end point of said receiving path by integrating a signal output at said end point.

12. The receiver according to claim 8, wherein said receiving path comprises an analog-to-digital converter, wherein said selected end point corresponds to the output of said analog-to-digital converter, and wherein said DC estimation portion and said DC compensation control portion are adapted to operate in the digital domain, said receiver further comprising a digital-to-analog converter arranged for converting a final digital compensation quantity provided by said DC estimation portion into the analog domain before feeding it to said summing node.

13. The receiver according to claim 8, wherein said receiver is a direct conversion receiver.

14. An electronic device including a receiver, which receiver comprises:

a receiving path, in which receiving path at least one gain factor is adjustable by a gain control, wherein a direct-current offset coupled into said receiving path is to be compensated;

a DC estimation portion adapted to determine an amount of a direct-current offset present at a selected end point in said receiving path, adapted to set a compensation quantity accordingly, adapted to scale said compensation with a provided scaling factor, if any, and adapted to feed said compensation quantity at a selected summing node into said receiving path; and

a DC compensation control portion adapted to determine in case of a forthcoming adjustment of said at least one gain factor a scaling factor preventing a direct-current step at said selected end point due to said forthcoming adjustment of said at least one gain factor, and adapted to provide said scaling factor to said DC estimation portion.

15. The electronic device according to claim 14, wherein said DC compensation control portion is adapted to determine said scaling factor by:

estimating a current amount of contributions to said direct-current offset;

determining a relative change in said direct-current offset which would have resulted with said estimated amount of direct-current contributions after a preceding gain adjustment; and

selecting said relative change as scaling factor.

16. The electronic device according to claim 14, wherein said receiver further comprises a normalization portion adapted to normalize a signal provided at said selected end point of said receiving path by dividing said signal by a total gain applied by said receiving path between said summing node and said end point of said receiving path, which normalization portion is arranged for providing said normalized signal to said DC estimation portion as basis for determining said amount of a direct-current offset.

17. The electronic device according to claim 14, wherein said DC estimation portion comprises an integrator for determining said amount of a direct-current offset at said end point of said receiving path by integrating a signal output at said end point.

18. The electronic device according to claim 14, wherein said receiving path comprises an analog-to-digital converter, wherein said selected end point corresponds to the output of said analog-to-digital converter, and wherein said DC estimation portion and said DC compensation control portion are adapted to operate in the digital domain, said receiver further comprising a digital-to-analog converter arranged for converting a final digital compensation quantity provided by said DC estimation portion into the analog domain before feeding it to said summing node.

19. The electronic device according to claim 14, wherein said receiver is a direct conversion receiver.

20. A hardware component for a receiver comprising a receiving path, in which receiving path at least one gain factor is adjustable by a gain control, wherein a direct-current offset coupled into said receiving path is to be compensated, said hardware component comprising:

a DC estimation portion adapted to estimate an amount of a direct-current offset present at a selected end point in said receiving path, adapted to set a compensation quantity accordingly, adapted to scale said compensation quantity with a provided scaling factor, if any, and adapted to feed said compensation quantity into said receiving path at a selected summing node; and

a DC compensation control portion adapted to determine in case of a forthcoming adjustment of said at least one gain factor a scaling factor preventing a direct-current step at said selected end point due to said forthcoming adjustment of said at least one gain factor, and adapted to provide said scaling factor to said DC estimation portion.

21. A software program product in which a software code for compensating a direct-current offset coupled into a receiving path of a receiver is stored, in which receiving path at least one gain factor is adjustable by a gain control, said software code realizing the following steps when running in said receiver:

determining an amount of a direct-current offset present at a selected end point in said receiving path and setting a compensation quantity accordingly;

in case of a forthcoming adjustment of said at least one gain factor by said gain control, scaling said compensation quantity with a scaling factor to prevent a direct-current step at said selected end point due to said forthcoming adjustment of said at least one gain factor; and

providing said compensation quantity for feeding into said receiving path at a selected summing node.