Transmitter Linearized In Response To Signal Magnitude Derivative Parameter and Method Therefor

• US 20120106676A1
• Filed: 02/01/2011
• Published: 05/03/2012
• Est. Priority Date: 11/02/2010
• Status: Active Grant

• Current Assignee: Crestcom Incorporated
• Original Assignee: Crestcom Incorporated
• Inventors: McCallister, Ronald Duane, Brombaugh, Eric M.
• Granted Patent: US 8,615,208 B2
• Time in Patent Office: Days
• US Class Current: 375/297
• CPC Class Codes: H03F 1/02 Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation
• CPC Class Codes: H03F 1/0266 by using a signal derived from the input signal
• CPC Class Codes: H03F 1/3241 using predistortion circuits H03F1/3211, H03F1/3217 take precedence
• CPC Class Codes: H03F 1/3247 using feedback acting on predistortion circuits H03F1/3264 takes precedence
• CPC Class Codes: H03F 1/34 Negative-feedback-circuit arrangements with or without positive feedback H03F1/02 - H03F1/30, H03F1/38 - H03F1/50, H03F3/50 take precedence ; for rejection of common mode signals H03F3/45479
• 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 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: H03F 3/245 with semiconductor devices only
• CPC Class Codes: H04B 1/0475 with means for limiting noise, interference or distortion H04B1/0483 takes precedence
• CPC Class Codes: H04B 2001/0425 with linearisation using predistortion
• CPC Class Codes: H04B 2001/0433 with linearisation using feedback
• CPC Class Codes: H04B 2001/045 with means for improving efficiency

Abstract

A transmitter (50) includes a low power nonlinear predistorter (58) that inserts predistortion configured to compensate for a memoryless nonlinearity (146) corresponding to gain droop and another memoryless nonlinearity (148) corresponding to a video signal. When efforts are taken to reduce memory effects, such as configuring a network of components (138) that couple to an HPA (114) to avoid resonance frequencies within a video bandwidth (140), high performance linearization at low power results without extending linearization beyond that provided by the memoryless nonlinear predistorter (58). A look-up table (282) has address inputs responsive to a magnitude parameter (152) of a communication signal (54), a magnitude derivative parameter (204) of the communication signal (54), and possibly one or more variable bias parameters (85). The look-up table (282) produces a gain-correcting signal (284) that adjusts the gain applied to the communication signal (54) prior to amplification. The look-up table (282) is updated in response to an LMS control loop.

Claims

1. A method of linearizing a transmitter having an amplifier which applies a nonlinear amplifier transform to a signal input at said amplifier said method comprising:

providing a communication signal;

producing a gain-correcting signal responsive to a magnitude parameter of said communication signal and a magnitude derivative parameter of said communication signal;

adjusting gain of said communication signal in response to said gain-correcting signal to form a predistorted communication signal; and

forming said signal input at said amplifier from said predistorted communication signal.

2. A method as claimed in claim 1 wherein:

a network of components is coupled to said amplifier; and

said method additionally comprises configuring said network of components to exhibit an impedance to said amplifier that either remains constant with increasing frequency or increases with increasing frequency throughout a video signal bandwidth.

3. A method as claimed in claim 1 wherein said magnitude derivative parameter is formed by taking a derivative with respect to time of said magnitude parameter.

4. A method as claimed in claim 1 wherein said gain-correcting signal is produced by a look-up table having first address bits responsive to said magnitude parameter and having at least one second address bit responsive to said magnitude derivative parameter.

5. A method as claimed in claim 4 wherein said look-up table has at least one third address bit responsive to a variable bias parameter for said amplifier.

6. A method as claimed in claim 4 wherein:

a variable bias supply is coupled to said amplifier and configured to generate a variable bias signal for said amplifier, said variable bias signal being characterized by a variable bias parameter;

said method additionally comprises combining said magnitude derivative parameter and said variable bias parameter to form a combined video parameter; and

said at least one second address bit is responsive to said combined video parameter.

7. A method as claimed in claim 1 wherein:

a variable bias supply is coupled to said amplifier and configured to generate a variable bias signal for said amplifier, said variable bias signal being characterized by a variable bias parameter; and

said gain-correcting signal is produced in response to said variable bias parameter.

8. A method as claimed in claim 1 wherein said gain-correcting signal is produced by applying a polynomial to said magnitude and magnitude derivative parameters, and said method additionally comprises:

updating said polynomial at a rate defined by a first loop bandwidth;

normalizing an amplitude parameter of said predistorted communication signal; and

operating a control loop to control gain applied to normalizing said amplitude parameter, said control loop being updated at a rate defined by a second loop bandwidth, said second loop bandwidth being greater than said first loop bandwidth.

9. A method as claimed in claim 8 wherein:

said amplifier exhibits a nonlinearity characterized as a thermal memory effect; and

said second loop bandwidth is sufficiently wide to substantially track said thermal memory effect.

10. A method as claimed in claim 8 wherein:

said amplifier exhibits one or more nonlinearities characterized as memory effects; and

said first loop bandwidth is sufficiently narrow to substantially avoid tracking said memory effects.

11. A method as claimed in claim 1 wherein said gain-correcting signal is a first gain-correcting signal, and said method additionally comprises:

generating a second gain-correcting signal responsive to said magnitude parameter of said communication signal; and

joining said first and second gain-correcting signals so that said gain of said communication signal is adjusted in response to said first and second gain-correcting signals to form said predistorted communication signal.

12. A method as claimed in claim 11 wherein said second gain-correcting signal is substantially unresponsive to said magnitude derivative parameter.

13. A method as claimed in claim 11 wherein:

said first gain-correcting signal is produced by a look-up table having a first address input responsive to said magnitude parameter and having a second address input responsive to said magnitude derivative parameter; and

said second gain-correcting signal is generated by a look-up table having a third address input responsive to said magnitude parameter.

14. A linearized transmitter having an amplifier which applies a nonlinear amplifier transform to a signal input at said amplifier, said transmitter comprising:

a communication signal source configured to produce a communication signal; and

a polynomial generator having an input coupled to said communication signal source, said polynomial generator being responsive to a magnitude parameter of said communication signal and a magnitude derivative parameter of said communication signal, and said polynomial generator having an output producing a gain-correcting signal; and

a gain-adjusting section configured to generate a predistorted communication signal in which gain is applied to said communication signal in response to said gain-correcting signal;

wherein said signal input at said amplifier is formed from said predistorted communication signal.

15. A linearized transmitter as claimed in claim 14 additionally comprising a network of components coupled to said amplifier, said network of components being configured to exhibit an impedance to said amplifier that either remains constant with increasing frequency or increases with increasing frequency throughout a video signal bandwidth.

16. A linearized transmitter as claimed in claim 14 additionally comprising a differentiator having an input responsive to said magnitude parameter and having an output which provides said magnitude derivative parameter, said differentiator being configured to form a derivative of said magnitude parameter with respect to time.

17. A linearized transmitter as claimed in claim 14 wherein said polynomial generator comprises a look-up table having first address bits responsive to said magnitude parameter and having at least one second address bit responsive to said magnitude derivative parameter.

18. A linearized transmitter as claimed in claim 17 wherein said look-up table has at least one third address bit responsive to a variable bias parameter for said amplifier.

19. A linearized transmitter as claimed in claim 14 additionally comprising:

a network of components coupled to said amplifier; and

a variable bias supply coupled to said network of components and configured to generate a variable bias signal characterized by a variable bias parameter, wherein said polynomial generator is responsive to said variable bias parameter.

20. A linearized transmitter as claimed in claim 14 additionally comprising:

a network of components coupled to said amplifier; and

a variable bias supply coupled to said network of components and configured to generate a variable bias signal characterized by a variable bias parameter, wherein said polynomial generator is responsive to a sum of said magnitude derivative parameter and said variable bias parameter.

21. A linearized transmitter as claimed in claim 14 additionally comprising;

a first adaptive control section having an input coupled to an output of said amplifier and an output coupled to said polynomial generator, said first adaptive control section being configured to update a polynomial said polynomial generator applies to said magnitude parameter and said magnitude derivative parameter to produce said gain-correcting signal, said first adaptive control section being further configured to update said polynomial at a rate defined by a first loop bandwidth; and

an automatic gain controller configured to normalize an amplitude parameter of said predistorted communication signal, wherein said automatic gain controller operates a control loop configured to adjust said amplitude parameter of said predistorted communication signal at an update rate defined by a second loop bandwidth, wherein said second loop bandwidth is greater than said first loop bandwidth.

22. A linearized transmitter as claimed in claim 21 wherein:

said amplifier exhibits a nonlinearity characterized as a thermal memory effect; and

said second loop bandwidth is sufficiently wide to substantially track said thermal memory effect.

23. A linearized transmitter as claimed in claim 21 wherein:

said amplifier exhibits one or more nonlinearities characterized as memory effects; and

said first loop bandwidth is sufficiently narrow to substantially avoid tracking said memory effects.

24. A linearized transmitter as claimed in claim 14 wherein said gain-correcting signal is a first gain-correcting signal and said predistorter comprises:

a first processing section responsive to said magnitude parameter of said communication signal and said magnitude derivative parameter of said communication signal, and said first processing section having an output producing said first gain-correcting signal;

a second processing section responsive to said magnitude parameter of said communication signal and configured to generate a second gain-correcting signal; and

a joining section having first and second inputs responsive to said first and second gain-correcting signals, respectively, and having an output coupled to said gain-adjusting section.

25. A linearized transmitter as claimed in claim 24 wherein:

said first processing section comprises a first look-up table having first address inputs responsive to said magnitude parameter and a second address input response to said magnitude derivative parameter; and

said second processing section comprises a second look-up table having third address inputs responsive to said magnitude parameter.

26. A method of linearizing a transmitter having an amplifier which applies a nonlinear amplifier transform to a signal input at said amplifier said method comprising:

configuring a network of components coupled to said amplifier to exhibit an impedance to said amplifier that either remains constant with increasing frequency or increases with increasing frequency throughout a video signal bandwidth;

providing a communication signal;

determining a magnitude parameter of said communication signal;

taking a derivative with respect to time of said magnitude parameter to form a magnitude derivative parameter;

producing a gain-correcting signal using a look-up table having a first address input responsive to said magnitude parameter and having a second address input responsive to said magnitude derivative parameter;

adjusting gain of said communication signal in response to said gain-correcting signal to form a predistorted communication signal; and

forming said signal input at said amplifier from said predistorted communication signal.