RF transmitter with variably biased RF power amplifier and method therefor

• US 20070281635A1
• Filed: 06/02/2006
• Published: 12/06/2007
• Est. Priority Date: 06/02/2006
• Status: Active Grant

• Current Assignee: Crestcom Incorporated
• Original Assignee: Crestcom Incorporated
• Inventors: Brombaugh, Eric M., McCallister, Ronald Duane
• Granted Patent: US 7,570,931 B2
• Time in Patent Office: Days
• US Class Current: 455/126
• CPC Class Codes: H03C 5/00 Amplitude modulation and angle modulation produced simultaneously or at will by the same modulating signal H03C7/00 takes precedence
• 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 1/0205 in transistor amplifiers
• CPC Class Codes: H03F 1/0227 using supply converters
• CPC Class Codes: H03F 1/0261 with control of the polarisation voltage or current, e.g. gliding Class A
• CPC Class Codes: H03F 1/3241 using predistortion circuits H03F1/3211, H03F1/3217 take precedence
• CPC Class Codes: H03F 2200/105 A non-specified detector of the power of a signal being used in an amplifying circuit
• 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 2200/435 A peak detection being used in a signal measuring circuit in a controlling circuit of an amplifier
• CPC Class Codes: H03F 2200/451 the amplifier being a radio frequency amplifier
• CPC Class Codes: H03F 3/189 High-frequency amplifiers, e.g. radio frequency amplifiers
• CPC Class Codes: H03F 3/24 of transmitter output stages
• CPC Class Codes: H04B 1/0475 with means for limiting noise, interference or distortion H04B1/0483 takes precedence
• CPC Class Codes: H04B 2001/045 with means for improving efficiency

Abstract

An RF transmitter (30) includes an RF power amplifier (32) for which the power input bias voltage (40) and signal input bias voltage (80) are controlled within feedback loops. A peak detector (44) generates a lowered-spectrum, peak-tracking signal (34) that follows the largest amplitude peaks of a wide bandwidth communication signal (16) but exhibits a lower bandwidth. This signal (34) is scaled in response to the operation of a drain bias tracking loop (146) then used to control a switching power supply (36) that generates the power input bias voltage. The tracking loop (146) is responsive to out-of-band power detected in a portion of the amplified RF communication signal (16″). A ratio of out-of-band power (128) to in-band power (126) is manipulated in the tracking loop (146) so that the power input bias voltage is modulated in a way that holds the out-of-band power at a desired predetermined level.

Claims

1. An RF transmitter configured to transmit an RF signal within a predetermined frequency band using a variably biased RF power amplifier, said RF transmitter comprising:

a power source;

an RF power amplifier having a power input, a signal input, and a signal output;

a switching element coupled between said power source and said power input of said RF power amplifier, said switching element supplying a bias voltage to said RF power amplifier;

a communication-signal source configured to supply a communication signal, said communication-signal source being coupled to said signal input of said RF power amplifier;

a peak detector having an input coupled to said communication-signal source and an output;

an out-of-band power estimator having an input coupled to said output of said RF power amplifier and having an output, said out-of-band power estimator being configured to estimate power occurring outside of said predetermined frequency band; and

a control section having a first input coupled to said output of said peak detector, a second input coupled to said output of said out-of-band power estimator, and an output coupled to said switching element, said control section being configured to adjust said bias voltage supplied to said RF power amplifier so that said out-of-band power estimated by said out-of-band power estimator is less than or equal to a predetermined power level.

2. An RF transmitter as claimed in claim 1 wherein:

said control section includes a transmitter-efficiency-measurement generator configured to generate a signal responsive to transmitter efficiency; and

said control section is configured to adjust said bias voltage in response to said transmitter-efficiency-measurement generator.

3. An RF transmitter as claimed in claim 1 wherein said out-of-band power estimator is configured to generate a signal describing RF power amplifier linearity.

4. An RF transmitter as claimed in claim 1 wherein said control section is configured to estimate a derivative of RF power amplifier linearity with respect to transmitter efficiency.

5. An RF transmitter as claimed in claim 1 wherein:

said control section is configured to generate a plurality of coefficients that influence RF power amplifier linearity and that influence transmitter efficiency; and

said control section is further configured so that when RF power amplifier linearity exceeds a predetermined level, said control section selects one of said plurality of coefficients to alter, said selected one of said coefficients being the one that exerts the least influence over RF power amplifier linearity per unit of transmitter efficiency.

6. An RF transmitter as claimed in claim 5 wherein said control section is configured to alter said selected one of said coefficients by an amount calculated to cause said RF power amplifier linearity to be less than said predetermined level.

7. An RF transmitter as claimed in claim 1 wherein:

said control section is configured to generate a plurality of coefficients that influence RF power amplifier linearity and that influence transmitter efficiency; and

said control section is further configured so that when RF power amplifier linearity is less than a predetermined level, said control section selects one of said plurality of coefficients to alter, said selected one of said coefficients being the one that exerts the greatest influence over RF power amplifier linearity per unit of transmitter efficiency.

8. An RF transmitter as claimed in claim 7 wherein said control section is configured to alter said selected one of said coefficients by an amount calculated to cause said RF power amplifier linearity to exceed said predetermined level.

9. An RF transmitter as claimed in claim 1 wherein:

said control section is configured to generate a plurality of coefficients each of which influences RF power amplifier linearity and transmitter efficiency;

said control section is further configured to cause each of said coefficients to dither over time in accordance with a perturbation function substantially orthogonal to other ones of said perturbation functions; and

said control section is further configured, for each of said coefficients, to correlate a signal describing RF power amplifier linearity with said perturbation function for said coefficient and to correlate a signal describing transmitter efficiency with said perturbation function for said coefficient.

10. An RF transmitter as claimed in claim 1 wherein said communication-signal source is configured to provide a communication signal exhibiting a bandwidth of greater than 10 MHz.

12. An RF transmitter as claimed in claim 1 wherein said power source, said RF power amplifier, said switching element, and said control section are mutually configured so that an amplified communication signal output by said RF power amplifier exhibits greater than 5 Watts.

13. An RF transmitter as claimed in claim 1 wherein:

said communication signal exhibits a bandwidth; and

said switching element switches at a frequency less than one-fifth said bandwidth.

14. An RF transmitter as claimed in claim 1 wherein:

said predetermined power level is a first predetermined power level; and

said control section is configured to maintain said out-of-band power estimated by said out-of-band power estimator to be greater than or equal to a second predetermined power level.

15. An RF transmitter as claimed in claim 1 wherein:

said out-of-band power estimator provides an out-of-band power signal at its output;

said out-of-band power estimator includes a first power detector that estimates out-of-band power and a second power detector that estimates in-band power; and

said out-of-band power estimator includes a ratio section that generates said out-of-band power signal to be proportional to one of said out-of-band and in-band powers and inversely proportional to the other of said out-of-band and in-band powers.

16. An RF transmitter as claimed in claim 1 wherein:

said out-of-band power estimator provides an out-of-band power signal at its output;

said out-of-band power estimator includes a first power detector that estimates out-of-band power and a second power detector that estimates total power; and

said out-of-band power estimator includes a ratio section that generates said out-of-band power signal to be proportional to one of said out-of-band and total powers and inversely proportional to the other of said out-of-band and total powers.

17. An RF transmitter as claimed in claim 1 wherein:

said communication signal exhibits a bandwidth and a varying magnitude; and

said peak detector generates a lowered-spectrum, peak-tracking signal that is responsive to said varying magnitude of said communication signal and that exhibits a fundamental frequency less than said communication signal bandwidth.

18. An RF transmitter as claimed in claim 1 wherein:

said output of said control section is a first output and said bias voltage supplied by said switching element is a first bias voltage; and

said control section has a second output coupled to said signal input of said RF power amplifier to provide a second bias voltage to said signal input of said RF power amplifier; and

said control section is configured to adjust said second bias voltage supplied to said signal input of said RF power amplifier in response to said out-of-band power detected by said out-of-band power estimator so that said out-of-band power is less than or equal to said predetermined power level.

19. An RF transmitter as claimed in claim 18 wherein:

said peak detector is a first peak detector and is configured to generate a first lowered-spectrum, peak-tracking signal that exhibits a first fundamental frequency;

said control section is configured so that said first bias voltage is responsive to said first lowered-spectrum, peak-tracking signal;

said RF transmitter additionally comprises a second peak detector having an input coupled to said communication-signal source and an output coupled to said control section, said second peak detector being configured to generate a second lowered-spectrum, peak-tracking signal that exhibits a second fundamental frequency which is greater than said first fundamental frequency; and

said control section is configured so that said second bias voltage is responsive to said second lowered-spectrum, peak-tracking signal.

20. A method of managing bias voltage for an RF power amplifier in an RF transmitter, said method comprising:

a) maintaining a plurality of coefficients, wherein each of said coefficients influences transmitter efficiency and RF power amplifier linearity;

b) generating an efficiency signal which is responsive to transmitter efficiency;

c) generating a linearity signal which is responsive to RF power amplifier linearity;

d) when said linearity signal indicates RF power amplifier linearity greater than a predetermined level, altering the one of said plurality of coefficients that achieves the least change in RF power amplifier linearity per unit change in transmitter efficiency; and

e) when said linearity signal indicates RF power amplifier linearity less than said predetermined level, altering the one of said plurality of coefficients that achieves the greatest change in linearity per unit change in transmitter efficiency.

21. A method as claimed in claim 20 additionally comprising controlling a bias voltage for said RF power amplifier in response to said plurality of coefficients.

22. A method as claimed in claim 20 wherein:

said RF transmitter is configured to transmit an RF signal within a predetermined frequency band;

said linearity-signal generating activity comprises distinguishing, from said RF signal, a portion of power outside of said predetermined frequency band from a portion of power inside of said predetermined frequency band; and

forming said linearity signal to be responsive to said portion of power outside of said predetermined frequency band.

23. A method as claimed in claim 20 additionally comprising estimating a derivative of RF power amplifier linearity with respect to transmitter efficiency in responsive to said linearity signal and said efficiency signal.

24. A method as claimed in claim 20 wherein said activity d) is configured to alter said selected one of said coefficients by an amount calculated to cause said RF power amplifier linearity to be less than said predetermined level.

25. A method as claimed in claim 20 wherein said activity e) is configured to alter said selected one of said coefficients by an amount calculated to cause said RF power amplifier linearity to be greater than said predetermined level.

26. An method as claimed in claim 20 additionally comprising:

causing each of said coefficients to dither over time in accordance with a perturbation function substantially orthogonal to other ones of said perturbation functions;

for each of said coefficients, correlating said linearity signal with said perturbation function for said coefficient; and

for each of said coefficients, correlating said efficiency signal with said perturbation function for said coefficient.

27. A method as claimed in claim 20 additionally comprising:

processing a communication signal to generate a peak-identifying signal;

scaling said peak-identifying signal in response to one of said plurality of coefficients to generate a scaled peak-identifying signal; and

controlling a bias voltage for said RF power amplifier in response to said scaled peak-identifying signal.

28. A method as claimed in claim 27 wherein:

said communication signal exhibits a bandwidth and a varying magnitude; and

said processing activity is configured so that said peak-identifying signal is responsive to said varying magnitude of said communication signal and exhibits a fundamental frequency less than said communication signal bandwidth.

40. An RF transmitter as claimed in claim 28 wherein:

said feedback tracking loop is a first feedback tracking loop;

said bias voltage is a first bias voltage;

said RF transmitter additionally comprises a second feedback tracking loop that generates a second bias voltage which is supplied to a signal input of said RF power amplifier; and

said second feedback tracking loop is configured to change said second bias voltage to maintain an average of said out-of-band power greater than or equal to said predetermined power level.

29. A method of managing bias voltage for an RF power amplifier in an RF transmitter, said method comprising:

providing a switching power supply to generate said bias voltage for said RF power amplifier;

estimating out-of-band power from an amplified signal generated by said RF power amplifier, said out-of-band power representing a portion of the power realized in said amplified signal outside a predetermined frequency band; and

operating a feedback loop in which said bias voltage changes to maintain an average of said out-of-band power greater than a predetermined power level.

30. A method as claimed in claim 29 wherein:

said predetermined power level is a first predetermined power level; and

said feedback-loop operating activity additionally changes said bias voltage to maintain an average of said out-of-band power less than or equal to a second predetermined power level.

31. A method as claimed in claim 29 wherein said estimating activity comprises:

determining an out-of-band power level, which represents power realized in said amplified signal outside of said predetermined frequency band;

determining an in-band power level, which represents power realized in said amplified signal within said predetermined frequency band; and

expressing said out-of-band power as being proportional to one of said out-of-band and in-band power levels and inversely proportional to the other of said out-of-band and in-band power levels.

32. A method as claimed in claim 29 wherein said estimating activity comprises:

determining an out-of-band power level, which represents power realized in said amplified signal outside of said predetermined frequency band;

determining a total power level, which represents substantially all power realized in said amplified signal; and

expressing said out-of-band power as being proportional to one of said out-of-band and total power levels and inversely proportional to the other of said out-of-band and total power levels.

33. A method as claimed in claim 29 wherein said method additionally comprises:

processing a communication signal to generate a peak-identifying signal and a delayed communication signal;

driving said RF power amplifier with said delayed communication signal; and

operating said feedback loop so that said bias voltage is responsive to said peak-identifying signal.

34. A method as claimed in claim 33 wherein:

said communication signal exhibits a bandwidth and a varying magnitude; and

said processing activity is configured so that said peak-identifying signal is responsive to said varying magnitude of said communication signal and exhibits a fundamental frequency less than said communication signal bandwidth.

35. A method as claimed in claim 34 wherein said processing activity is performed digitally.

36. A method as claimed in claim 33 wherein:

said communication signal exhibits a bandwidth of greater than 10 MHz; and

said processing activity is configured to process said bandwidth.

37. A method as claimed in claim 29 wherein said amplified signal exhibits a total power level greater than 5 W.

38. An RF transmitter configured to transmit an RF signal within a predetermined frequency band using a variably biased RF power amplifier, said RF transmitter comprising:

an RF power amplifier;

a switching power supply configured to generate a bias voltage for said RF power amplifier;

an out-of-band power estimator configured to estimate out-of-band power from an amplified signal generated by said RF power amplifier, said out-of-band power representing a portion of the power realized in said amplified signal outside a predetermined frequency band;

and a feedback tracking loop coupled between said out-of-band power estimator and said switching power supply, said feedback tracking loop being configured to change said bias voltage to maintain an average of said out-of-band power greater than or equal to a predetermined power level.

39. An RF transmitter as claimed in claim 38 wherein:

said predetermined power level is a first predetermined power level; and

said feedback tracking loop is further configured to change said bias voltage to maintain an average of said out-of-band power less than or equal to a second predetermined power level.