Predistorter

• US 6,587,513 B1
• Filed: 08/20/1999
• Issued: 07/01/2003
• Est. Priority Date: 08/24/1998
• Status: Expired due to Term

• Current Assignee: Lenovo Innovations Ltd Hong Kong (Lenovo Group Ltd.)
• Original Assignee: NEC Corporation
• Inventors: Ichihara, Masaki
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): AHN, SAM K
• Application Number:
  US09/377,797
• Time in Patent Office: 1,411 Days
• Field of Search: 375/296, 375/297, 375/295, 330/149, 330/151
• US Class Current: 375/296
• CPC Class Codes: H03C 3/406 using a feedback loop containing mixers or demodulators
• CPC Class Codes: H03D 7/168 using a feedback loop containing mixers or demodulators
• CPC Class Codes: H03F 1/3241 using predistortion circuits H03F1/3211, H03F1/3217 take precedence

Abstract

Disclosed is a predistorter for preliminarily compensating a distortion caused in a circuit comprising a modulator, a variable gain amplifier, and a non-linear amplifier, the predistorter comprising: an amplitude detector for detecting an amplitude of an input signal; a gain detector for detecting a gain of the variable gain amplifier; a first multiplier for multiplying the amplitude of the input signal with the gain of the variable gain to output a product therebetween; a generator for generating a predistortion function corresponding to the product; and a second multiplier for multiplying the input signal with the predistortion function to output a product therebetween to the modulator.

Claims

1. A predistorter for preliminarily a compensating a distortion caused in a circuit comprising a modulator, a variable gain amplifier, and a non-linear amplifier, said predistorter comprising:

an amplitude calculation circuit for detecting an amplitude of an input signal;

a gain calculation circuit for detecting a gain of said variable gain amplifier;

a first multiplier for multiplying the amplitude of the input signal with the gain of said variable gain to output a product therebetween;

a generator for generating a predistortion function corresponding to the product;

and a second multiplier for multiplying the input signal with the predistortion function to output a product therebetween to said modulator.

2. The predistorter according to claim 1, wherein said gain calculation circuit detects the gain of said variable gain amplifier on the basis of a gain control signal for said variable gain amplifier.

3. The predistorter according to claim 1, wherein said gain calculation circuit detects the gain of said variable gain amplifier on the basis of an output of said non-linear amplifier.

6. The predistorter according to claim 1,

wherein said input signal is represented in a complex number;

said amplitude calculation circuit detects the amplitude of the input signal by using a real part and imaginary part of the input signal;

said generator generates the predistortion function represented in a complex number;

said second multiplier is a complex multiplier; and

said modulator is a quadrature modulator.

7. The predistorter according to claim 6, further comprising:

two digital-to-analog converters inserted between said second multiplier and said modulator;

wherein the input signal is represented in a digital number; and

said amplitude calculation circuit, said gain calculation circuit, said first and second multiplier, and said generator operate in digital.

8. The predistorter according to claim 1, further comprising:

a digital-to-analog said converter inserted between second multiplier and said modulator;

wherein the input signal is represented in a digital number; and

said amplitude calculation circuit, said gain calculation circuit, said first and second multiplier, and said generator operate in digital.

9. The predistorter according to claim 1, wherein said generator comprises a look-up table.

10. The predistorter according to claim 9, wherein said look-up table comprises a read only memory.

18. A transmitter comprising:

the predistorter claimed in any one of claims 1 through 10,

a modulator for modulating an output of said predistorter;

a variable gain amplifier for amplifying an output of said modulator;

a non-linear amplifier for amplifying an output of said variable gain amplifier; and

an antenna for transmitting an output of said non-linear amplifier as a radio wave.

19. A radio communication apparatus comprising the transmitter claimed in claim 18.

4. The predistorter according to claim further 3, comprising:

a coupler for generating a shunt signal from an output of said non-linear amplifier;

a wave detector for detecting the shunt signal to output a detected signal; and

a low pass filter for filtering the detected signal to output a filtered signal;

wherein said gain calculation circuit detects the gain of said variable gain amplifier on the basis of the filtered signal.

5. The predistorter according to claim 4, further comprising:

an analog-to-digital converter inserted between said low pass filter and said gain calculation circuit and for converting the filtered signal to a digital signal;

wherein said gain calculation circuit detects the gain of said variable gain amplifier on the basis of the digital signal.

11. A method for preliminarily compensating a distortion caused in a circuit comprising a modulator, a variable gain amplifier, and a non-linear amplifier, said method comprising steps of:

calculating an amplitude of an input signal;

calculating a gain of said variable gain amplifier;

multiplying the amplitude of the input signal with the gain of said variable gain to output a product therebetween;

generating a predistortion function corresponding to the product; and

input multiplying the signal with predistortion the function to output a product therebetween to said modulator.

12. The method according to claim 11, wherein the gain of said variable gain amplifier is calculated on the basis of a gain control signal for said variable gain amplifier.

13. The method according to claim 11, wherein the gain of said variable gain amplifier is calculated on the basis of an output of said non-linear amplifier.

14. The method according to claim 13, further comprising steps of:

generating a shunt signal from an output of said nonlinear amplifier;

detecting the shunt signal to output a detected signal; and

filtering the detected signal to output a filtered signal;

wherein the gain of said variable gain amplifier is detected on the basis of the filtered signal.

15. The method according to claim 14, further comprising a step of:

converting the filtered signal to a digital signal;

wherein the gain of said variable gain amplifier is detected on the basis of the digital signal.

16. The method according to claim 11,

wherein said input signal is represented in a complex number;

the amplitude of the input signal is calculated by using a real part and imaginary part of the input signal;

the predistortion function is represented in a complex number;

said step of multiplying the input signal with the predistortion function is a complex multiplication; and

said modulator is a quadrature modulator.

17. The method according to claim 11, further comprising a step of:

converting the result of multiplying the input signal with the predistortion function to an analog signal;

wherein the input signal is represented in a digital number; and

said step of detecting the amplitude of the input signal, said step of detecting the gain of said variable gain amplifier, said step of multiplying the amplitude of the input signal with the gain of said variable gain, said step of generating the predistortion function corresponding to the product; and

said step of multiplying the input signal with the predistortion function, are performed digitally.