Adaptive predistortion for a transmit system with gain, phase and delay adjustments

• US 7,423,484 B2
• Filed: 01/13/2006
• Issued: 09/09/2008
• Est. Priority Date: 07/03/2003
• Status: Expired due to Term

• Current Assignee: Zarbana Digital Fund LLC (Intellectual Ventures LLC)
• Original Assignee: Zarbana Digital Fund LLC (Intellectual Ventures LLC)
• Inventors: Saed, Aryan
• Primary Examiner(s): NGUYEN, PATRICIA T
• Application Number:
  US11/332,505
• Publication Number:
  US 20060125560A1
• Time in Patent Office: 970 Days
• Field of Search: 330/149, 330/107, 330/136, 330/260, 330/124.R
• US Class Current: 330/149
• CPC Class Codes: H03F 1/0294 using vector summing of two or more constant amplitude phase-modulated signals
• CPC Class Codes: H03F 1/32 Modifications of amplifiers to reduce non-linear distortion by negative feedback H03F1/34
• CPC Class Codes: H03F 1/3247 using feedback acting on predistortion circuits H03F1/3264 takes precedence
• CPC Class Codes: H03F 1/3282 Acting on the phase and the amplitude of the input signal
• CPC Class Codes: H03F 2200/331 Sigma delta modulation being used in an amplifying circuit
• CPC Class Codes: H03F 2201/3233 Adaptive predistortion using lookup table, e.g. memory, RAM, ROM, LUT, to generate the predistortion
• CPC Class Codes: H03F 3/24 of transmitter output stages

Abstract

Systems and methods relating to the provision of gain, phase and delay adjustments to signals to be used by a predistortion subsystem. A portion of an input signal is delayed by delay elements prior to being received by the predistortion subsystem. The delayed input signal portion is also received by a feedback signal processing subsystem that adjusts the gain and phase of the feedback signal based on the delayed input signal portion. The adjusted feedback signal is used, along with the delayed portion of the input signal, to determine an appropriate predistortion modification to be applied to the input signal.

Claims

1. A method of processing an input signal to produce a system output signal, the method comprising:

a) receiving said input signal;

b) applying a deliberate predistortion to said input signal to result in a predistorted signal;

c) decomposing said predistorted signal into at least two component signals;

d) combining said at least two component signals to produce said system output signal;

e) adjusting said deliberate predistortion based on said system output signal

f) concurrent with steps b)-e), executing the following steps;

f1) delaying a replica of said input signal;

f2) diverting a diverted replica of said system output signal to a feedback path;

f3) processing said diverted replica to produce a corrected version of said diverted replica; and

f4) determining said deliberate predistortion using said corrected version and said replica of said input signal.

2. A method according to claim 1 wherein said system output signal is an RF modulated version of said input signal.

6. A method according to claim 1 wherein step a) further includes the step of accessing an entry in a lookup table, said deliberate predistortion being based on said entry.

7. A method according to claim 6 wherein said deliberate predistortion is based on an interpolation of entries in said table.

8. A method according to claim 1 further including the step of taking a difference between said replica of said input signal and said diverted replica of said system output signal to determine said characteristics of said system output signal.

9. A method according to claim 6 further including the step of updating at least one entry in said table.

14. A method according to claim 1 wherein said proccssing in step f3) comprises adjusting a phase of said diverted replica based on said input signal.

15. A method according to claim 1 wherein said processing in step f3) comprises adjusting a magnitude of said diverted replica based on said input signal.

17. A method according to claim 15 wherein said magnitude is adjusted by multiplying said diverted replica by A_xx(k) where

A_xx(k+1)=A_xx(k)+μ

_A·

(|x_δ

(k)|−

A_xx(k)·

|z(k)|)

For k_A≦

k ≦

k≦

k_A+W_A−

1

where

k_A=commencement time for magnitude adjustments

W_A=number of samples for which adjustments are performed

μ

_A=update step size and 0≦

μ

_A≦

1

z(k) is said feedback signal.

18. A method according to claim 14 wherein said phase is adjusted by applying a phase correction to said diverted replica, said phase correction being initialized by a method for initializing a phase correction to be applied to a feedback signal, said feedback signal to be used in determining a deliberate predistortion for a signal processing system, the method comprising:

a) initiating a coarse delay search

b) selecting a time window of W samples of said feedback signal and an input signal with a predetennined sample delay increments of δ

between samples

c) calculating an inner product P_δ

by performing a complex multiply and accumulate process for the W samples in the time window

d) storing a maximum Pδ

found

e) repeating steps c) and d) for subsequent time windows and incrementing δ

by a predetermined amount for each time window

f) repreating steps b)-e) for a fine delay search using fractional sample increments to cover a predetermined delay range, said delay range being centered on a maximum delay increment δ

_max found during said coarse delay search.

19. A method according to claim 1 wherein said deliberate predistortion is at least partially based on said system output signal.

20. A method according to claim 19 wherein said deliberate predistortion is determined in an iterative manner during transmission of said system output signal.

21. A method according to claim 1 wherein for step e), said deliberate predistortion is adjusted based on said system output signal and said input signal.

3. A method according to claimy 1 further including a processing step of separately processing each of said at least two component signals prior to step d).

4. A method according to claim 3 wherein said processing step includes amplifying at least one of said at least two component signals.

5. A method according to claim 3 wherein said processing step includcs phase modulating at least one of said at least two component signals.

10. An adaptive predistortion subsystem for use with a signal processing system which produces a system output signal, the predistortion subsystem comprising:

determining means for determining a deliberate predistortion to be applied to an input signal;

adjustment means for applying said deliberate predistortion to said input signal; and

update means for periodically updating said determining means based on characteristics of said system output signal;

wherein said adaptive predistortion subsystem uses

an output of a delay subsystem for delaying said input signal and

an output of a feedback processing subsystem for processing a feedback signal derived from said system output signal to determine said deliberate predistortion; and

wherein said deliberate predistortion is dependent on differences between said input signal and a replica of said system output signal.

11. An adaptive predistortion subsystem according to claim 10 wherein said adjustment means receives parameters of said deliberate predistortion from, said determining means.

12. An adaptive predistortion subsystem according to claim 10 wherein said determining means comprises a lookup table having entries, said entries being used to determine said deliberate predistortion.

13. An adaptive predistortion subsystem according to claim 12 wherein said determining means further comprises interpolating means for determining values not found in said lookup table.

16. An adaptive predistortion subsystem according to claim 10 wherein said delay subsystem comprises:

a plurality of delay elements;

means for sampling said input signal;

means for storing samples of said input signal;

means for selecting selected samples of said input signal; and

means for combining said selected samples of said input signal.