Swept performance monitor for measuring and correcting RF power amplifier distortion

• US 6,384,681 B1
• Filed: 08/10/2001
• Issued: 05/07/2002
• Est. Priority Date: 01/07/2000
• Status: Expired due to Term

• Current Assignee: Intel Corporation
• Original Assignee: Spectrian Corp. (REMEC, Inc.)
• Inventors: Bonds, David Kent
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): Choe, Henry
• Application Number:
  US09/927,814
• Publication Number:
  US 20020027474A1
• Time in Patent Office: 270 Days
• Field of Search: 330/149, 330/136, 375/97
• US Class Current: 330/149
• CPC Class Codes: H03F 1/3229 using a loop for error extraction and another loop for error subtraction
• CPC Class Codes: H03F 1/3247 using feedback acting on predistortion circuits H03F1/3264 takes precedence

Abstract

RF power amplifier distortion is measured in the presence of multi-frequency input signals, by sweeping a local oscillator to tune RF input and output receivers. When the power detected by the input receiver exceeds a carrier energy threshold, the operation of a predistortion processor is blanked. This creates an adaptive notch filter, which allows for the direct measurement of low level distortion power in the presence of high power carriers. The unnecessary complexity of using controllably interrupted high isolation switches in the signal flow path of the output receiver in certain applications may be effectively obviated by buffer amplifier—passband filter stages. These buffer-filter stages provide additional gain to offset the fact that the signal level extracted from the output amplifier is very low, and prevent producing IMDs in the swept receiver'"'"'s mixer. They are preferably implemented of the same bandpass filter in the swept input receiver.

Claims

1. An RF power amplifier arrangement comprising:

an RF input port to which an RF input signal is applied;

an RF output port from which an amplified RF output signal is derived; and

an RF signal processing path coupled between said input and output ports, and containing an RF power amplifier and an RF distortion correction unit, that is controllably operative to adjust one or more parameters of said RF signal processing path, so as to compensate for distortion introduced by said RF power amplifier, said RF distortion correction unit being coupled to derive information representative of said distortion introduced by said RF power amplifier over a prescribed bandwidth, but excluding the effect of an RF carrier frequency of said RF input signal, and including a frequency swept output receiver coupled to monitor energy contained in said amplified RF output signal, and being coupled over a non-interrupted output signal path that supplies information representative of said distortion introduced by said RF power amplifier over said prescribed bandwidth.

2. An RF power amplifier arrangement according to claim 1, including an adjustable threshold detector that is operative to controllably interrupt operation of said RF distortion correction unit, in response to said RF output signal containing RF carrier energy in excess of a controllably selectable threshold.

3. An RF power amplifier arrangement according to claim 2, wherein said RF distortion correction unit includes an RF predistortion correction unit that controllably imparts distortion onto said RF input signal upstream of said RF amplifier, so as to cancel the distortion contributed by said RF amplifier.

4. An RF power amplifier arrangement according to claim 3, wherein said RF distortion correction unit further includes a frequency swept input receiver coupled to monitor energy contained in said RF input signal, and wherein said controllably selectable threshold of said adjustable threshold detector is determined in accordance with energy contained in said RF input signal.

5. An RF power amplifier arrangement according to claim 1, wherein said RF signal processing path includes a swept input receiver coupled to measure carrier power at said input port, a swept output receiver, having an operational bandwidth less than that of said swept input receiver, and being coupled to measure distortion energy at said output port, and a swept local oscillator that is operative to sweep the frequency of operation of each of said input and output receivers in common.

6. An RF power amplifier arrangement according to claim 5, including an adjustable threshold detector that is operative to controllably interrupt operation of said RF distortion correction unit, in response to said RF output signal containing RF carrier energy in excess of a controllably selectable threshold.

7. An RF power amplifier arrangement according to claim 6, wherein said controllably selectable threshold of said adjustable threshold detector is determined in accordance with energy contained in said RF input signal.

8. An RF power amplifier arrangement according to claim 7, wherein said RF distortion correction unit includes a predistortion correction unit coupled in an input path of said amplifier, and being operative to controllably impart distortion onto an input signal upstream of said amplifier, so as to cancel distortion contributed by said amplifier, in accordance with said distortion energy measured by said swept output receiver.

9. An RF power amplifier arrangement according to claim 5, wherein said swept output receiver is coupled through a first buffer amplifier and narrowband filter circuit arrangement to an RF predistortion correction processor, operation of which is controllably interrupted by said adjustable threshold detector, in response to said RF output signal containing RF carrier energy in excess of said controllably selectable threshold.

10. An RF power amplifier arrangement according to claim 9, wherein a signal path from said input port through said swept input receiver to said RF predistortion correction processor is coupled through a second buffer amplifier and narrowband filter circuit arrangement.

11. An RF power amplifier arrangement according to claim 10, wherein said first and second buffer amplifier and narrowband filter circuit arrangements employ the same narrowband filter circuit components.

12. A method of measuring and compensating for distortion in an RF power amplifier to an input port of which an RF input signal is coupled and from an output port of which an amplified RF output signal is derived, said method comprising the steps of:

(a) deriving information representative of said distortion introduced by said RF power amplifier over a prescribed bandwidth, by varying the frequency of operation of an output receiver that is coupled in an uninterrupted output signal path through which energy contained in said amplified RF output signal may be monitored, and extracting therefrom said information representative of said distortion introduced by said RF power amplifier over said prescribed bandwidth; and

(b) controllably adjusting one or more parameters of said RF signal processing path so as to compensate for distortion introduced by said RF power amplifier, in accordance with said information derived in step (a) and excluding said RF carrier frequency.

13. A method according to claim 12, wherein step (a) further includes controllably interrupting the derivation of information representative of said distortion introduced by said RF power amplifier, in response to said RF output signal containing RF carrier energy in excess of a controllably selectable threshold.

14. A method according to claim 13, wherein step (b) includes controlling the operation of an RF predistortion correction unit installed in said RF input signal upstream of said RF amplifier, so as to cancel the distortion contributed by said RF amplifier.

15. A method according to claim 13, wherein step (a) includes monitoring energy contained in said RF input signal through a frequency swept input receiver, and establishing said controllably selectable threshold in accordance with energy contained in said RF input signal.

16. A method according to claim 13, wherein step (a) comprises deriving said information through a swept input receiver that is coupled to measure carrier power at said input port, a swept output receiver, having an operational bandwidth less than that of said swept input receiver, that is coupled to measure distortion energy at said output port, and controlling the operation of a local oscillator so as to sweep the frequency of operation of each of said input and output receivers in common.

17. A method according to claim 16, wherein said swept output receiver is coupled through a first buffer amplifier and narrowband filter circuit arrangement to an RF predistortion correction processor, operation of which in performing step (b) is controllably interrupted by said adjustable threshold detector, in response to said RF output signal containing RF carrier energy in excess of said controllably selectable threshold.

18. A method according to claim 17, wherein a signal path from said input port through said swept input receiver to said RF predistortion correction processor is coupled through a second buffer amplifier and narrowband filter circuit arrangement.

19. A method according to claim 18, wherein said first and second buffer amplifier and narrowband filter circuit arrangements employ the same narrowband filter circuit components.