Distortion compensating apparatus

• US 6,757,525 B1
• Filed: 10/25/2002
• Issued: 06/29/2004
• Est. Priority Date: 03/29/2002
• Status: Active Grant

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Sasaki, Tohru, Hamano, Mitsuharu, Kanno, Yuki, Hanada, Koichi, Hamada, Hajime, Nagatani, Kazuo, Ishikawa, Hiroyoshi, Fudaba, Nobukazu, Oishi, Yasuyuki, Kubo, Tokuro
• Primary Examiner(s): APPIAH, CHARLES NANA
• Application Number:
  US10/280,705
• Time in Patent Office: 613 Days
• Field of Search: 455/126, 455/127, 455/501, 455/63.1, 455/114.3, 375/296, 375/346, 375/345, 375/295, 375/297, 330/149, 330/150, 330/151, 332/159, 332/160, 332/161, 332/162
• US Class Current: 455/114.3
• CPC Class Codes: H03F 1/3241 using predistortion circuits H03F1/3211, H03F1/3217 take precedence
• CPC Class Codes: H03F 1/3247 using feedback acting on predistortion circuits H03F1/3264 takes precedence
• CPC Class Codes: H03F 1/3288 to compensate phase shift as a function of the amplitude
• CPC Class Codes: H03F 2200/372 Noise reduction and elimination in amplifier
• CPC Class Codes: H04B 2001/0425 with linearisation using predistortion

Abstract

In an adaptive predistorter type distortion compensating apparatus for calculating a distortion compensating coefficient by using an adaptive algorithm so as to reduce an error between a reference signal and a feedback signal of a circuit which generates a distortion on the basis of the reference signal, and for compensating the distortion by providing the distortion compensating coefficient to the reference signal, a phase adjustment circuit is provided for determining a phase shift value which reduces a phase difference between a reference signal and a feedback signal, for correcting the phase of the reference signal or the feedback signal by the phase shift value, and for calculating the distortion compensating apparatus after the correction.

Claims

1. A distortion compensating apparatus comprising:

an adaptive predistorter type distortion compensating circuit for calculating a distortion compensating coefficient by using an adaptive algorithm so as to reduce an error between a reference signal and a feedback signal of a circuit which generates a distortion on a basis of the reference signal, and for compensating the distortion by providing the distortion compensating coefficient to the reference signal, and

a phase adjustment circuit for determining a phase shift value which reduces a phase difference between the reference signal and the feedback signal, and for correcting the phase of one of the reference signal and the feedback signal received by the distortion compensating circuit by the phase shift value.

2. The distortion compensating apparatus as claimed in claim 1 wherein the phase adjustment circuit determines the phase shift value from the distortion compensating coefficient.

3. The distortion compensating apparatus as claimed in claim 2 wherein except when a real part of the distortion compensating coefficient is positive and an absolute value of an imaginary part is equal to or less than a predetermined threshold value, the phase adjustment circuit determines the phase shift value based on a sign of the imaginary part.

4. The distortion compensating apparatus as claimed in claim 1 wherein the phase adjustment circuit determines the phase shift value from a correlation between the reference signal and the feedback signal.

5. The distortion compensating apparatus as claimed in claim 3 wherein the phase adjustment circuit includes an up/down counter for adding the sign of the imaginary part, a phase update determination circuit for deciding whether or not a counter value of the up/down counter has reached a fixed value, and a phase counter for updating the phase shift value when the phase update determination circuit decides that the counter value has reached the fixed value.

6. The distortion compensating apparatus as claimed in claim 5 wherein the phase update determination circuit changes the fixed value according to a phase adjustment stage.

7. The distortion compensating apparatus as claimed in claim 1 wherein the phase adjustment circuit determines the phase shift value from the error between the reference signal and the feedback signal.

8. The distortion compensating apparatus as claimed in claim 2 wherein the phase adjustment circuit decides a presence/absence of an update of the distortion compensating coefficient, and determines the phase shift value in presence of the update.

9. The distortion compensating apparatus as claimed in claim 4 wherein the phase adjustment circuit decides a presence/absence of an update of the distortion compensating coefficient, and determines the phase shift value in absence of the update.

10. The distortion compensating apparatus as claimed in claim 1 wherein the phase adjustment circuit determines the phase difference between the reference signal and the feedback signal by a quadrant determination of a complex plane.

11. The distortion compensating apparatus as claimed in claim 10 wherein the phase adjustment circuit determines the phase difference between the reference signal and the feedback signal by the quadrant determination of the complex plane and a large/small comparison of a real part and an imaginary part.

12. The distortion compensating apparatus as claimed in claim 4 wherein the phase adjustment circuit includes an up/down counter for adding the sign of the imaginary part, a phase update determination circuit for deciding whether or not a counter value of the up/down counter has reached a fixed value, and a phase counter for updating the phase shift value when the phase update determination circuit decides that the counter value has reached the fixed value.

13. The distortion compensating apparatus as claimed in claim 3 wherein the phase adjustment circuit decides a presence/absence of an update of the distortion compensating coefficient, and determines the phase shift value in presence of the update.

14. The distortion compensating apparatus as claimed in claim 5 wherein the phase adjustment circuit decides a presence/absence of an update of the distortion compensating coefficient, and determines the phase shift value in absence of the update.