Pre-Distortion Architecture for Compensating Non-Linear Effects

• US 20120286865A1
• Filed: 02/16/2012
• Published: 11/15/2012
• Est. Priority Date: 05/12/2011
• Status: Active Grant

• Current Assignee: Procomm International Pte. Ltd. (Transpacific IP Group Limited)
• Original Assignee: Andrew LLC (CommScope Holding Company, Inc.)
• Inventors: Chandrasekaran, Rajiv
• Granted Patent: US 8,711,976 B2
• Time in Patent Office: Days
• US Class Current: 330/149
• CPC Class Codes: H03F 1/3247 using feedback acting on predistortion circuits H03F1/3264 takes precedence
• CPC Class Codes: H03F 1/3294 Acting on the real and imaginary components of the input signal
• CPC Class Codes: H03F 2200/336 A I/Q, i.e. phase quadrature, modulator or demodulator being used in an amplifying circuit
• CPC Class Codes: H03F 2200/451 the amplifier being a radio frequency amplifier
• CPC Class Codes: H03F 2201/3212 Using a control circuit to adjust amplitude and phase of a signal in a signal path
• 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 3/195 in integrated circuits
• CPC Class Codes: H03F 3/24 of transmitter output stages
• CPC Class Codes: H04L 27/368 adaptive predistortion

Abstract

An input signal is pre-distorted to reduce distortion resulting from subsequent signal amplification. Frequency-dependent pre-distortion is preferably implemented in combination with frequency-independent pre-distortion, where the frequency-dependent pre-distortion is generated by expanding the derivative of a product of a pre-distortion function and the input signal and then relaxing constraints on the pre-distortion function and/or on frequency-dependent filtering associated with the frequency-dependent pre-distortion. In one implementation, four different frequency-dependent pre-distortion signals are generated for the expansion using up to four different pre-distortion functions and up to four different frequency-dependent filters.

Claims

1. A method for reducing distortion in an output signal by applying pre-distortion to an input signal to generate a pre-distorted signal, such that, when the pre-distorted signal is applied to a non-linear system to generate the output signal, the pre-distortion reduces the distortion in the output signal, wherein the pre-distorted signal is generated by:

(a) generating a first frequency-dependent pre-distortion signal corresponding to a product of (i) a derivative of a first pre-distortion function (e.g., f₁₁) and (ii) the input signal;

(b) generating a second frequency-dependent pre-distortion signal corresponding to a product of (i) a derivative of a second pre-distortion function (e.g., f₂₁) and (ii) the input signal;

(c) generating a third frequency-dependent pre-distortion signal corresponding to a product of (i) a third pre-distortion function (e.g., f₁₂) and (ii) a derivative of the input signal;

(d) generating a fourth frequency-dependent pre-distortion signal corresponding to a product of (i) a fourth pre-distortion function (e.g., f₂₂) and (ii) a derivative of the input signal; and

(e) generating the pre-distorted signal based on the first, second, third, and fourth frequency-dependent pre-distortion signals.

2. The invention of claim 1, further comprising:

(f) applying the pre-distorted signal to the non-linear system to generate the output signal.

3. The invention of claim 2, wherein the non-linear system comprises an amplifier that generates the output signal.

4. The invention of claim 1, wherein at least one of the first and second pre-distortion functions is different from both of the third and fourth pre-distortion functions.

5. The invention of claim 4, wherein each of the first and second pre-distortion functions is different from both of the third and fourth pre-distortion functions.

6. The invention of claim 1, wherein:

step (a) comprises applying a first filter function (e.g., h_B1) to generate the first frequency-dependent pre-distortion signal;

step (b) comprises applying a second filter function (e.g., h_B2) to generate the second frequency-dependent pre-distortion signal;

step (c) comprises applying a third filter function (e.g., h_B3) to generate the third frequency-dependent pre-distortion signal; and

step (d) comprises applying a fourth filter function (e.g., h_B4) to generate the fourth frequency-dependent pre-distortion signal.

7. The invention of claim 6, wherein the first, second, third, and fourth filter functions are frequency-dependent functions.

8. The invention of claim 6, wherein at least one of the first and second filter functions is different from both of the third and fourth filter functions.

9. The invention of claim 8, wherein each of the first and second filter functions is different from both of the third and fourth filter functions.

10. The invention of claim 1, further comprising:

(f) generating a frequency-independent pre-distortion signal corresponding to a product of (i) a fifth pre-distortion function (e.g., f₀) and (ii) the input signal, wherein step (e) comprises generating the pre-distorted signal based on the first, second, third, and fourth frequency-dependent pre-distortion signals and the frequency-independent pre-distortion signal.

11. The invention of claim 1, wherein the pre-distorted signal is generated according to:

12. The invention of claim 11, wherein at least one of:

f₁₁ is different from both f₂₁ and f₂₂;

f₁₂ is different from both f₂₁ and f₂₂;

h_B1 is different from both h_B3 and h_B4; and

h_B2 is different from both h_B3 and h_B4.

13. The invention of claim 11, wherein:

f₁₁ is different from both f₂₁ and f₂₂;

f₁₂ is different from both f₂₁ and f₂₂;

h_B1 is different from both h_B3 and h_B4; and

h_B2 is different from both h_B3 and h_B4.

14. Apparatus for reducing distortion in an output signal by applying pre-distortion to an input signal to generate a pre-distorted signal, such that, when the pre-distorted signal is applied to a non-linear system to generate the output signal, the pre-distortion reduces the distortion in the output signal, wherein apparatus comprises:

a first signal path (e.g., 314-322) configured to generate a first frequency-dependent pre-distortion signal corresponding to a product of (i) a derivative of a first pre-distortion function (e.g., f₁₁) and (ii) the input signal;

a second signal path (e.g., 324-332) configured to generate a second frequency-dependent pre-distortion signal corresponding to a product of (i) a derivative of a second pre-distortion function (e.g., f₂₁) and (ii) the input signal;

a third signal path (e.g., 334-342) configured to generate a third frequency-dependent pre-distortion signal corresponding to a product of (i) a third pre-distortion function (e.g., f₁₂) and (ii) a derivative of the input signal;

a fourth signal path (e.g., 344-352) configured to generate a fourth frequency-dependent pre-distortion signal corresponding to a product of (i) a fourth pre-distortion function (e.g., f₂₂) and (ii) a derivative of the input signal; and

a summer configured (e.g., 312) to generate the pre-distorted signal based on the first, second, third, and fourth frequency-dependent pre-distortion signals.

15. The invention of claim 14, further comprising the non-linear system.

16. The invention of claim 15, wherein the non-linear system comprises an amplifier configured to generate the output signal.

17. The invention of claim 14, wherein:

the first, second, third, and fourth pre-distortion functions are implemented using lookup tables (e.g., 316, 326, 338, 348); and

each derivative is generated by applying a differentiating filter (e.g., 318, 328, 334, 344).

18. The invention of claim 14, wherein at least one of the first and second pre-distortion functions is different from both of the third and fourth pre-distortion functions.

19. The invention of claim 14, wherein:

the first signal path comprises a first filter (e.g., 322) configured to apply a first filter function (e.g., h_B1) to generate the first frequency-dependent pre-distortion signal;

the second signal path comprises a second filter (e.g., 332) configured to apply a second filter function (e.g., h_B2) to generate the second frequency-dependent pre-distortion signal;

the third signal path comprises a third filter (e.g., 342) configured to apply a third filter function (e.g., h_B3) to generate the third frequency-dependent pre-distortion signal; and

the fourth signal path comprises a fourth filter (e.g., 322) configured to apply a fourth filter function (e.g., h_B4) to generate the fourth frequency-dependent pre-distortion signal.

20. The invention of claim 19, wherein the first, second, third, and fourth filter functions are frequency-dependent functions.

21. The invention of claim 19, wherein at least one of the first and second filter functions is different from both of the third and fourth filter functions.

22. The invention of claim 14, further comprising:

a frequency-independent signal path (e.g., 306-310) configured to generate a frequency-independent pre-distortion signal corresponding to a product of (i) a frequency-independent pre-distortion function (e.g., f₀) and (ii) the input signal, wherein the summer is configured to generate the pre-distorted signal based on the first, second, third, and fourth frequency-dependent pre-distortion signals and the frequency-independent pre-distortion signal.

23. The invention of claim 14, wherein the pre-distorted signal is generated according to:

24. The invention of claim 23, wherein at least one of:

f₁₁ is different from both f₂₁ and f₂₂;

f₁₂ is different from both f₂₁ and f₂₂;

h_B1 is different from both h_B3 and h_B4; and

h_B2 is different from both h_B3 and h_B4.