Linearization of power amplifier

• US 6,546,233 B1
• Filed: 06/06/2000
• Issued: 04/08/2003
• Est. Priority Date: 06/06/2000
• Status: Expired due to Term

• Current Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Aleiner, Boris, Lieu, Winston Hong
• Primary Examiner(s): Le, Thanh Cong
• Assistant Examiner(s): Nguyen, Thuan T.
• Application Number:
  US09/587,893
• Time in Patent Office: 1,036 Days
• Field of Search: 455/115, 455/126, 455/67.1, 455/69, 455/85, 455/91, 455/11.1, 375/285
• US Class Current: 455/126
• CPC Class Codes: H03F 1/3241 using predistortion circuits H03F1/3211, H03F1/3217 take precedence

Abstract

A apparatus linearizing and technique for linearizing a non-linear power amplifier used in a transmitter of, e.g., a TDMA mobile wireless telephone. Linearization of the non-linear amplifier by changing the shape of the input signal is performed when the input signal level is high, thus increasing efficiency or reducing power consumption at that time, albeit at the cost of increased inter-symbol interference (ISI). However, since the input signals at that time are at a high level, the increased ISI can be tolerated and adjacent symbols can still be distinguished from one another. The invention allows use of a non-linear power amplifier which typically enjoys a lower current consumption than that of a linear power amplifier, thus increasing the time between battery recharges and/or reducing the overall size of the wireless telephone device. The power amplifier is operated in a linear mode when transmitted power is low, thus allowing differentiation between adjacent symbols (i.e., improvement of ISI). At high input power, the power amplifier is used in its non-linear mode to reduce current consumption. The signal shape is changed by changing the parameters of the root raised cosine filters. When the input level is low, the existing, otherwise conventional filter'"'"'s parameters are used. However, when the input power level is high, modified parameters are used. Switching between the two sets of filter parameters is preferably performed at baseband. Thus, a relationship between RRCF filter parameters and the amount of spectrum utilized by the transmitted signal is utilized, and RRCF filter parameters are adjusted based on a desired limitation to an output spectrum.

Claims

1. A transmitter of a wireless device, comprising:

a power amplifier;

a root raised cosine filter;

a first set of parameters for said root raised cosine filter to adapt said root raised cosine filter to provide a first level of linearization to a modulated signal amplified by said power amplifier; and

a second set of parameters for said root raised cosine filter to adapt said root raised cosine filter to provide a second level of linearization to said modulated signal amplified by said power amplifier.

2. The transmitter of a wireless device according to claim 1, wherein:

said first set of parameters are a traditional set of parameters for said root raised cosine filter.

3. The transmitter of a wireless device according to claim 1, wherein:

said power amplifier is a non-linear power amplifier.

4. The transmitter of a wireless device according to claim 1, wherein:

said wireless device is a time division multiple access (TDMA) device.

5. The transmitter of a wireless device according to claim 4, wherein:

said TDMA device is a wireless telephone.

6. The transmitter of a wireless device according to claim 1, wherein:

said wireless device is a CDMA device.

7. The transmitter of a wireless device according to claim 1, wherein:

said wireless device is a frequency division multiple access (FDMA) device.

8. The transmitter of a wireless device according to claim 1, wherein:

said modulated signal passes through said power amplifier before passing through said root raised cosine filter.

9. The transmitter of a wireless device according to claim 1, wherein:

said modulated signal passes through said root raised cosine filter before passing through said power amplifier.

10. A method of improving efficiency of a power amplifier in a transmitter, comprising:

adaptively configuring a first set of parameters in a root raised cosine filter when a transmit power of said power amplifier is below a predetermined level; and

adaptively configuring a second set of parameters in said root raised cosine filter when a transmit power of said power amplifier is above said predetermined level.

11. The method of improving efficiency of a power amplifier in a transmitter according to claim 10, wherein:

said first set of parameters reduce inter-symbol interference in a time division multiple access system.

12. The method of improving efficiency of a non-linear power amplifier according to claim 10, wherein:

said predetermined level is approximately a maximum operable transmit level.

13. The method of improving efficiency of a non-linear power amplifier according to claim 10, wherein:

said power amplifier is a non-linear amplifier.

14. Apparatus for improving efficiency of a power amplifier in a transmitter, comprising:

means for adaptively configuring a first set of parameters in a root raised cosine filter when a transmit power of said power amplifier is below a predetermined level; and

means for adaptively configuring a second set of parameters in said root raised cosine filter when a transmit power of said power amplifier is above said predetermined level.

15. The apparatus for improving efficiency of a power amplifier in a transmitter according to claim 14, wherein:

said first set of parameters reduce inter-symbol interference in a time division multiple access system.

16. The apparatus for improving efficiency of a non-linear power amplifier according to claim 14, wherein:

said predetermined level is approximately a maximum operable transmit level.

17. The apparatus for improving efficiency of a non-linear power amplifier according to claim 14, wherein:

said power amplifier is a non-linear amplifier.