Transmitter linearized in response to derivative signal and method therefor

• US 8,976,896 B2
• Filed: 10/21/2011
• Issued: 03/10/2015
• Est. Priority Date: 11/02/2010
• Status: Active Grant

• Current Assignee: Crestcom Incorporated
• Original Assignee: Crestcom Incorporated
• Inventors: McCallister, Ronald Duane, Brombaugh, Eric M.
• Primary Examiner(s): Garcia, Santiago
• Application Number:
  US13/881,219
• Publication Number:
  US 20130259159A1
• Time in Patent Office: 1,236 Days
• Field of Search: 375/297
• 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 substantially throughout 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 pre-distorted communication signal (60) is responsive to the output of the look-up table, a derivative signal (204), and possibly one or more variable bias parameters (85). 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 complex communication signal;

extracting a magnitude parameter from said complex communication signal;

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

distorting said complex communication signal in response to said derivative signal to produce a predistorted communication signal; and

forming said signal input at said amplifier in response to said predistorted communication signal.

2. A method as claimed in claim 1 wherein said magnitude parameter is a first magnitude parameter and said distorting step comprises:

producing a gain-correcting signal responsive to one of said first magnitude parameter and a second magnitude parameter of said communication signal and said gain-correcting signal being separately responsive to said derivative signal; and

adjusting gain of said communication signal in response to said gain-correcting signal to form said predistorted communication signal.

3. A method as claimed in claim 2 wherein said gain-correcting signal is responsive to a look-up table having first address bits responsive to one of said first magnitude parameter and said second magnitude parameter and having at least one second address bit responsive to said derivative signal.

4. 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 substantially throughout a video bandwidth.

5. 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 predistorted communication signal is produced in response to said variable bias parameter.

15. A method as claimed in claim 1 wherein said taking a derivative step is configured so that said derivative signal is a substantially accurate approximation of a derivative with respect to time over half of a video bandwidth.

16. A method as claimed in claim 3 wherein said look-up table has at least one third address bit responsive to a variable bias parameter for said amplifier.

17. A method as claimed in claim 4 wherein said network of components is configured to exhibit an impedance to said amplifier that has no more than one impedance minima in an upper 99% portion of a video bandwidth.

6. 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 complex communication signal;

a magnitude-extracting section coupled to said communication-signal source and configured to extract a magnitude parameter from said complex communication signal;

a differentiator coupled to said magnitude-extracting section and configured to take a derivative with respect to time of said magnitude parameter and to produce a derivative signal; and

a gain-adjusting section coupled to said differentiator and configured to generate a predistorted communication signal in response to said derivative signal;

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

7. A linearized transmitter as claimed in claim 6 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 substantially throughout a video bandwidth.

8. A linearized transmitter as claimed in claim 6 additionally comprising a polynomial generator coupled to said magnitude-extracting section and to said differentiator, said polynomial generator being responsive to said magnitude parameter.

10. A linearized transmitter as claimed in claim 6 wherein:

said linearized transmitter additionally 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 derivative signal, said look-up table having an output coupled to said gain-adjusting section.

11. A linearized transmitter as claimed in claim 10 wherein said look-up table has at least one third address bit responsive to a variable bias parameter for said amplifier.

12. A linearized transmitter as claimed in claim 6 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 gain-adjusting section is responsive to said variable bias parameter.

13. A linearized transmitter as claimed in claim 6 additionally comprising a network of components coupled to said amplifier, said network of components being configured to exhibit an impedance to said amplifier that has no more than one impedance minima in an upper 99% portion of a video bandwidth.

14. A linearized transmitter as claimed in claim 13 wherein said network of components includes a resonant circuit coupled in series between said amplifier and a bias signal source, wherein said resonant circuit includes an inductor coupled in parallel with a capacitor and is configured to exhibit a resonant frequency in a fundamental RF band for said linearized transmitter.

18. A linearized transmitter as claimed in claim 6 wherein said differentiator is configured so that said derivative signal is a substantially accurate approximation of a derivative with respect to time over half of a video bandwidth.

9. A linearized transmitter as claimed 8 wherein said polynomial generator has an input coupled to an output of said differentiator.

19. 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 complex communication signal;

a magnitude-extracting section coupled to said communication-signal source and configured to extract a first magnitude parameter from said complex communication signal;

a differentiator coupled to said magnitude-extracting section and configured to take a derivative with respect to time of a signal responsive to said first magnitude parameter and to produce a derivative signal;

a look-up table having first address bits responsive to one of said first magnitude parameter and a second magnitude parameter of said complex communication signal and having at least one second address bit responsive to said derivative signal, said look-up table being configured to provide a gain-correcting signal;

a gain-adjusting section adapted to receive said complex communication signal and said gain-correcting signal and configured to generate a predistorted communication signal; and

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 substantially throughout a video bandwidth;

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