System and method for DC offset correction in transmit baseband

• US 20060223457A1
• Filed: 04/01/2005
• Published: 10/05/2006
• Est. Priority Date: 04/01/2005
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: Rahman, Mahibur
• Granted Patent: US 7,369,820 B2
• Time in Patent Office: Days
• US Class Current: 455/78
• CPC Class Codes: H04B 1/0475 with means for limiting noise, interference or distortion H04B1/0483 takes precedence

Abstract

A radio frequency (RF) transceiver is provided. The RF transceiver comprises a transmit path comprising an output coupled to an RF antenna, a feedback path comprising an input coupled to the output of the transmit path, and a DC offset calibration module comprising a first input coupled to an output of the feedback path, a second input to receive a first signal and an output connected to an input of the transmit path. The DC offset calibration module is operable to determine a first direct current (DC) offset of a closed-loop path comprising the transmit path and the feedback path and determine a second DC offset based on the feedback path exclusive of the transmit path.

Claims

1. A method comprising:

determining a first direct current (DC) offset of a first closed-loop path of a radio frequency (RF) transceiver, wherein the first closed-loop path comprises a first path and a second path, the first path comprising a portion of a first transmit path of the RF transceiver and the second path comprising a portion of a first feedback path having an input coupled to an output of the first transmit path; and

determining a second DC offset based on the second path exclusive of the first path.

2. The method of claim 1, further comprising:

adjusting a first signal based on a third DC offset representative of a difference between the first and second DC offsets to generate a first adjusted signal; and

providing the first adjusted signal to an input of the first transmit path.

3. The method of claim 2, wherein the third DC offset represents an averaged difference between the first and second DC offsets.

4. The method of claim 1, further comprising:

scaling a third DC offset representative of a difference between the first and second DC offsets based on a gain of a gain stage of the first transmit path;

adjusting a first signal based on the scaled third DC offset to generate a first adjusted signal; and

providing the first adjusted signal to an input of the first transmit path.

5. The method of claim 4, further comprising:

averaging the third DC offset; and

wherein the first signal is adjusted based on the averaged third DC offset.

6. The method of claim 4, wherein the third DC offset is scaled inversely proportional to the gain of the gain stage.

7. The method of claim 1, wherein determining the second DC offset comprises:

providing a calibration signal to an input of the first feedback path; and

wherein the second DC offset is based on a DC offset of a signal output by the first feedback path in response to the provision of the calibration signal.

8. The method of claim 7, wherein the second DC offset is based on a moving average of the DC offset of the signal output by the first feedback path.

9. The method of claim 1, wherein the first feedback path comprises a portion of a receive path of the RF transceiver.

10. The method of claim 1, further comprising:

determining a third DC offset of a second closed-loop path of the RF transceiver, wherein the second closed-loop path comprises a third path and a fourth path, the third path comprising a portion of a second transmit path of the RF transceiver and the fourth path comprising a portion of a second feedback path having an input coupled to an output of the second transmit path; and

determining a fourth DC offset based on the fourth path exclusive of the third path;

wherein the first transmit path is associated with a real component of a received signal and the second transmit path is associated with an imaginary component of the received signal.

11. A method for calibrating a transmit path of a RF transceiver, the method comprising:

when in a first mode;

providing a calibration signal to a feedback path of a closed loop comprising a transmit path and the feedback path;

determining a first DC offset associated with the feedback path based on a first feedback signal output by the feedback path in response to the provision of the first calibration signal;

when in a second mode;

providing a second signal to the closed loop, wherein the feedback path outputs a second feedback signal in response to the provision of the second signal;

determining a second DC offset associated with the second feedback signal;

determining a third DC offset associated with the transmit path based on the first and second DC offsets; and

adjusting the second signal based on the third DC offset.

12. The method of claim 11, wherein determining the first DC offset comprises determining an average DC offset of the first feedback signal and wherein the first DC offset comprises the average DC offset.

13. The method of claim 11, wherein the third DC offset is substantially equal to a difference between the second DC offset and the first DC offset.

14. The method of claim 11, wherein the third DC offset is substantially equal to an averaged difference between the second DC offset and the first DC offset.

15. The method of claim 14, further comprising:

scaling the third DC offset based on a gain of a gain stage of the transmit path; and

wherein the second signal is adjusted based on the scaled third DC offset.

16. The method of claim 11, further comprising:

scaling the third DC offset based on a gain of a gain stage of the transmit path;

averaging the scaled third DC offset; and

wherein the second signal is adjusted based on the averaged scaled third DC offset.

17. The method of claim 11, wherein the feedback path comprises a portion of a receive path of the RF transceiver.

18. A radio frequency (RF) transceiver comprising:

a transmit path comprising an output coupled to an RF antenna;

a feedback path comprising an input coupled to the output of the transmit path; and

a DC offset calibration module comprising a first input coupled to an output of the feedback path, a second input to receive a first signal and an output connected to an input of the transmit path, wherein the DC offset calibration module is operable to;

determine a first direct current (DC) offset of a closed-loop path comprising the transmit path and the feedback path; and

determine a second DC offset based on the feedback path exclusive of the transmit path.

19. The RF transceiver of claim 18, wherein the DC offset calibration module is further operable to:

adjust a first signal based on a third DC offset representative of a difference between the first and second DC offsets to generate a first adjusted signal; and

provide the first adjusted signal to an input of the first transmit path.

20. The RF transceiver of claim 18, wherein the DC offset calibration module is further operable to:

scale a third DC offset representative of a difference between the first and second DC offsets based on a gain of a gain stage of the first transmit path;

adjust a first signal based on the scaled third DC offset to generate a first adjusted signal; and

provide the first adjusted signal to an input of the first transmit path.