Apparatus and method for compensating for an offset of a power amplifier in a mobile communication system

• US 20050255814A1
• Filed: 05/11/2005
• Published: 11/17/2005
• Est. Priority Date: 05/11/2004
• Status: Abandoned Application

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Lee, Seung-Hwan, Maeng, Seung-Joo, Lee, Jae-Hyok, Jeon, Jae-Ho, Hwang, Ki-Hwan, Song, Yoo-Seung
• Application Number:
  US11/126,251
• Publication Number:
  US 20050255814A1
• Time in Patent Office: Days
• US Class Current: 455/114.300
• CPC Class Codes: H03F 1/30 Modifications of amplifiers to reduce influence of variations of temperature or supply voltage or other physical parameters in differential amplifiers H03F3/45479
• CPC Class Codes: H03F 1/3241 using predistortion circuits H03F1/3211, H03F1/3217 take precedence

Abstract

An apparatus and method for compensating for an error of a power amplifier in a digital mobile communication system having a predistorter are provided. The apparatus and method comprise a gain compensator for pre-correcting a gain error occurring in a path of each phase signal while an in-phase signal and a quadrature-phase signal, output from the predistorter, undergo digital-to-analog (D/A) conversion; a digital-to-analog converter (DAC) for converting a digital signal output from the gain compensator into an analog signal; and a transmission signal converter for converting an output of the DAC into a radio frequency (RF) signal, and outputting the RF signal to the power amplifier.

Claims

1. An apparatus for compensating for an error of a power amplifier in a digital mobile communication system having a predistorter, the apparatus comprising:

a gain compensator for pre-correcting a gain error occurring in a path of each phase signal while an in-phase signal and a quadrature-phase signal, output from the predistorter, undergo during digital-to-analog (D/A) conversion;

a digital-to-analog converter (DAC) for converting a digital signal output from the gain compensator into an analog signal; and

a transmission signal converter for converting an output of the DAC into a radio frequency (RF) signal, and outputting the RF signal to the power amplifier.

2. The apparatus of claim 1, further comprising:

a feedback converter for feeding back a part of output signals of the power amplifier, down-converting the feedback signal, converting the down-converted signal into a digital signal, and outputting an in-phase signal and a quadrature-phase signal; and

a gain measurer for calculating a gain error in a path of each signal output from the feedback converter, calculating a correction value using an output value of the predistorter, and outputting the calculated correction value to the gain compensator.

3. The apparatus of claim 2, further comprising:

an offset measurement and compensation block for measuring an offset in a path of each signal output from the feedback converter and compensating for the offset; and

a digital quadrature digital modulator (DQDM) for receiving an output of the offset measurement and compensation block, shifting a center of the received signal to a direct current (DC) band, and outputting the center-shifted signal to the gain measurer.

4. The apparatus of claim 2, wherein the gain measurer calculates the correction value using the following equation,

$\alpha$

= ( ∑

n = 1 N ⁢

I n 2 ∑

n = 1 N ⁢

Q n 2 ∑

n = 1 N ⁢

I n ′

2 ∑

n = 1 N ⁢

Q n ′

2 )

where α

denotes a correction value of a path, In denotes an in-phase signal component output from the DQDM, Qn denotes a quadrature-phase signal component output from the DQDM, I'"'"'n denotes an in-phase signal component output from the predistorter, Q'"'"'n denotes a quadrature-phase signal component output from the predistorter, and N denotes the number of samples.

5. The apparatus of claim 4, wherein the gain compensator performs gain compensation by multiplying a particular signal component by a reciprocal of an output value of the gain measurer.

6. The apparatus of claim 3, wherein the offset measurement and compensation block calculates an average of a predetermined number of samples for each of signal components output from the feedback converter, and determines the calculated average as a DC offset during analog-to-digital (A/D) conversion.

7. The apparatus of claim 6, wherein the offset measurement and compensation block performs offset compensation by subtracting the determined DC offset from an output signal of the feedback converter.

8. The apparatus of claim 3, wherein the offset measurement and compensation block comprises:

a sample averager for calculating an average for a predetermined number of signals from among the input signals; and

an adder for calculating a difference by subtracting an output of the sample averager from the input signals.

9. The apparatus of claim 1, wherein the gain compensator comprises:

a first multiplier for gain-compensating the in-phase signal; and

a second multiplier for gain-compensating the quadrature-phase signal.

10. The apparatus of claim 9, wherein the gain compensator applies a gain value of ‘

1’

to both the first multiplier and the second multiplier when there is no error in the signal converter during signal conversion.

11. The apparatus of claim 9, wherein when there is an error in the transmission converter during signal conversion, the gain compensator gain-compensates a predistorted signal by applying a gain compensation value to a multiplier for a corresponding phase component.

12. A method of compensating for an error of a power amplifier in a digital mobile communication system having a predistorter, comprising:

pre-correcting a gain error occurring in a path of each phase signal while an in-phase signal and a quadrature-phase signal, output from the predistorter, undergo during digital-to-analog (D/A) conversion;

converting a digital signal output from the gain compensator into an analog signal; and

converting an output of a digital analog converter (DAC) into a radio frequency (RF) signal, and outputting the RF signal to the power amplifier.

13. The method of claim 12, further comprising:

feeding back a part of output signals of the power amplifier, down-converting the feedback signal, converting the down-converted signal into a digital signal, and outputting an in-phase signal and a quadrature-phase signal; and

calculating a gain error in a path of each signal output from a feedback converter, calculating a correction value using an output value of the predistorter, and outputting the calculated correction value to a gain compensator.

14. The method of claim 13, further comprising:

measuring an offset in a path of each signal output from the feedback converter and compensating for the offset via; and

receiving an output, shifting a center of the received signal to a direct current (DC) band, and outputting the center-shifted signal to the gain measurer.

15. The method of claim 13, wherein the gain measurer calculates the correction value measures a gain using the following equation,

$\alpha$

= ( ∑

n = 1 N ⁢

I n 2 ∑

n = 1 N ⁢

Q n 2 ∑

n = 1 N ⁢

I n ′

2 ∑

n = 1 N ⁢

Q n ′

2 )

where α

a denotes a correction value of a path, In denotes an in-phase signal component output from a digital quadrature digital modulator (DQDM), Qn denotes a quadrature-phase signal component output from the DQDM, I'"'"'n denotes an in-phase signal component output from the predistorter, Q'"'"'n denotes a quadrature-phase signal component output from the predistorter, and N denotes the number of samples.

16. The method of claim 15, wherein the gain compensator performs gain compensation by multiplying a particular signal component by a reciprocal of an output value of the gain measurer.

17. The method of claim 14, wherein the step of measuring further compnses:

calculating an average of a predetermined number of samples for each of signal components output from the feedback converter, and

determining the calculated average as a DC offset during the analog-to-digital (A/D) conversion.

18. The method of claim 17, wherein the step of calculating further comprises:

performing offset compensation by subtracting the determined DC offset from an output signal of the feedback converter.

19. The method of claim 14, wherein the step of measuring further comprises:

calculating an average for a predetermined number of signals from among the input signals; and

calculating a difference by subtracting an output of the sample averager from the input signals.

20. The method of claim 13, wherein the step of pre-correcting further comprises:

gain-compensating the in-phase signal; and

gain-compensating the quadrature-phase signal.