Adaptive digital predistortion linearization and feed-forward correction of RF power amplifier

• US 5,949,283 A
• Filed: 06/29/1998
• Issued: 09/07/1999
• Est. Priority Date: 09/20/1996
• Status: Expired due to Term

• Current Assignee: Intel Corporation
• Original Assignee: Spectrian Corp. (REMEC, Inc.)
• Inventors: Proctor, James A., Mucenieks, Lance Todd
• Primary Examiner(s): Mottola, Steven J.
• Application Number:
  US09/106,167
• Time in Patent Office: 435 Days
• Field of Search: 330/107, 330/129, 330/136, 330/149, 330/151, 375/296, 375/297
• US Class Current: 330/149
• CPC Class Codes: H03F 1/3223 using feed-forward H03F1/3211 takes precedence
• CPC Class Codes: H03F 1/3229 using a loop for error extraction and another loop for error subtraction
• CPC Class Codes: H03F 1/3247 using feedback acting on predistortion circuits H03F1/3264 takes precedence
• CPC Class Codes: H03F 2201/3233 Adaptive predistortion using lookup table, e.g. memory, RAM, ROM, LUT, to generate the predistortion

Abstract

A digitally implemented, look-up table-based, predistortion and feed-forward correction signal processing mechanism compensates for distortion generated in the RF power amplifier. The input signal to the RF amplifier is stored for comparison with the measured the RF output. In each of predistortion and feed-forward signal processing paths, the magnitude of the complex waveform of the input signal is extracted to derive a read-out address to a dual-port RAM which stores weights to be multiplied by the input signal. In the predistortion signal processing path, the product is coupled to the RF power amplifier. In the feed-forward correction loop, the product is amplified by an auxiliary feed-forward RF amplifier and coupled into the amplified output signal path of the RF power amplifier.

Claims

1. A method for correcting amplitude and phase distortion of an RF power amplifier comprising:

(a) performing RF amplifier distortion measurements upon a digitized baseband input signal that is exclusive of RF amplifier distortion and is representative of the complex waveform of a signal to be up-converted and amplified by said RF power amplifier and upon a digitized baseband output signal representative of the complex waveform of an amplified output signal derived from said RF power amplifier, so as to generate complex weights representative of said amplitude and phase distortion of said RF power amplifier; and

(b) performing at least one of

predistorting said digitized baseband input signal to be converted to analog format, up-converted from baseband, and applied to said RF power amplifier, in accordance with a first complex weight selected in accordance with an input signal to be amplified by said RF power amplifier, and

modifying said digitized baseband input signal in accordance with a second complex weight selected in accordance with said input signal to be amplified by said RF power amplifier, so as to derive a baseband feed-forward correction signal, converting said baseband feed-forward correction signal to analog format, up-converting from baseband the analog feed-forward correction signal and combining the up-converted analog feed-forward correction signal with an amplified output signal from said RF power amplifier.

2. A method according to claim 1, wherein step (a) comprises adaptively adjusting said complex weights in accordance with said successive ones of said RF amplifier distortion measurements on said digitized input and output signals.

3. A method according to claim 1, wherein step (b) includes amplifying said up-converted, analog feed-forward correction signal in an auxiliary RF error amplifier having an operational power range less than that of said RF power amplifier, and coupling the amplified up-converted analog feed-forward correction signal to the amplified output signal from said RF power amplifier.

4. A method according to claim 1, wherein said first and second complex weights are based upon envelope-dependency of distortion-introducing behavior of said RF power amplifier.

5. A method according to claim 1, wherein said first and second complex weights are selected in dependence upon baseband power in said input signal to be amplified by said RF power amplifier.

6. A method according to claim 1, wherein said selected first and second complex weights have the same baseband power as said input signal to be amplified by said RF power amplifier.

7. A method according to claim 1, wherein said first complex weights are derived in accordance with complex division of complex envelopes of said input signal by said output signal, the complex envelope of said RF input signal is multiplied by said one of said first complex weights to derive said predistorted input signal, said second complex weights in are derived accordance with complex division of complex envelopes of said input signal by said output signal, and the complex envelope of said input signal is multiplied by said one of said second complex weights to derive said feed-forward correction signal.

8. A method according to claim 1, wherein step (a) comprises generating a quotient representative of a ratio of said input signal and said output signal, and multiplying said quotient by a complex weight to produce an adaptively adjusted value of said complex weight.

9. A method according to claim 1, wherein step (a) comprises generating a quotient representative of a ratio of said input signal and said output signal, subtracting said quotient from an alignment vector and multiplying said quotient by an output alignment vector which is effective to align the output of said auxiliary error amplifier with the output of said RF power amplifier in amplitude and phase, to produce an adaptively adjusted value of a complex weight.

10. A method according to claim 1, wherein step (a) includes storing said complex weights in digital memory, and step (b) includes accessing a respective complex weight from memory in accordance with an input signal to be amplified by said RF power amplifier.

11. A signal processing arrangement for correcting for amplitude and phase distortion in an RF power amplifier comprising:

a digital distortion measurement unit which is operative to perform RF amplifier distortion measurements upon a digitized baseband input signal that is exclusive of RF amplifier distortion and is representative of the complex waveform of a signal to be up-converted and amplified, by said RF power amplifier and upon a digitized baseband output signal representative of the complex waveform of an amplified output signal derived from said RF power amplifier, and thereby produce first complex weights representative of said amplitude and phase distortion of said RF power amplifier; and

a predistortion unit which is operative to predistort said digitized baseband input signal to be converted to analog format, up-converted from baseband, and applied to said RF power amplifier in accordance with a first complex weight produced by said distortion measurement unit, that is selected in accordance with an input signal to be amplified by said RF power amplifier.

12. A signal processing arrangement according to claim 11, further including a feed-forward correction unit, and wherein said distortion measurement unit is operative to perform RF amplifier distortion measurements on said digitized baseband input and output signals to generate second complex weights representative of said amplitude and phase distortion, and wherein said feed-forward correction unit is operative to modify said digitized baseband input signal by a second complex weight selected in accordance with an input signal to be amplified by said RF power amplifier, so as to produce derive a digitized baseband feed-forward correction signal, and to convert said digitized baseband feed-forward correction signal to analog format and to up-convert the analog feed-forward correction signal from baseband, and to combine the up-converted feed-forward correction signal with an amplified output signal from said RF power amplifier.

13. A signal processing arrangement according to claim 12, wherein said feed-forward correction unit includes an auxiliary RF error signal amplifier having an operational power range less than that of said RF power amplifier, and which is operative to amplify said up-converted feed-forward correction signal, with the amplified up-converted feed-forward correction signal being combined with the amplified output signal from said RF power amplifier.

14. A signal processing arrangement according to claim 12, further including digital memory which stores said first and second complex weights, and wherein each of said predistortion unit and said feed-forward correction unit is operative to read out respective ones of said first and second complex weights from said digital memory.