Digital baseband receiver in a multi-carrier power amplifier

• US 6,829,471 B2
• Filed: 03/06/2002
• Issued: 12/07/2004
• Est. Priority Date: 03/07/2001
• Status: Expired due to Fees

• Current Assignee: CommScope Technologies, LLC (CommScope Holding Company, Inc.)
• Original Assignee: Andrew Corporation (CommScope Holding Company, Inc.)
• Inventors: Snyder, Robert, Bachman, Thomas A. II, Kooker, Robert W., Everline, Paul, Sarver, Leonard, White, Paul E.
• Primary Examiner(s): NGUYEN, THUAN T
• Application Number:
  US10/091,756
• Publication Number:
  US 20020127986A1
• Time in Patent Office: 1,007 Days
• Field of Search: 455/194.2, 455/195.1, 455/199.1, 455/200.1, 455/202, 455/205, 455/219, 455/63.1, 455/67.11, 455/67.13, 455/63.3, 455/570, 455/114.2, 455/114.3, 455/118, 455/125, 455/126, 330/149, 330/139, 330/136, 330/270, 330/279, 375/297
• US Class Current: 455/194.2
• CPC Class Codes: H03F 1/3235 using a pilot signal
• CPC Class Codes: H04B 1/123 using adaptive balancing or compensation means adaptive filter circuits and algorithms H03H

Abstract

A power amplifier system and method for locating carrier frequencies across a frequency band, identifying the modulation format of each carrier, and locating and suppressing undesired intermodulation distortion (IMD) products generated by the power amplifier. The system includes an amplifier for amplifying RF carrier signals in a main signal path, a variable phase shifter and variable attenuator on a feed forward path, and a tunable receiver that digitizes a portion of the frequency band to baseband. The tunable receiver includes a tunable voltage controlled oscillator which provides an oscillating frequency to a mixer and is phase-locked to a highly stable reference oscillator. The mixer downconverts a desired RF based on the oscillating frequency to IF. A filter passes only a selected portion of the IF signals, and the filter has a passband sufficient to discern both narrowband and wideband carriers and their associated IMD products. Based on the locations of the carrier frequencies, a processing unit determines the IMD locations of the carrier frequencies, determines the IMD locations, and adjusts the variable phase shifter and variable attenuator on the feed forward path until the IMD products in the main signal path are suppressed below a desired threshold.

Claims

1. An apparatus, comprising:

(a) a signal path having an input and an output and configured to communicate an RF communications signal disposed in a frequency band;

(b) a tunable receiver coupled to the signal path and configured to downconvert at least a portion of the frequency band to an Intermediate Frequency (IF) signal;

(c) at least one intermodulation distortion (IMD) reduction component coupled to the signal path; and

(d) a circuit arrangement configured to convert a time domain representation of the IF signal output by the tunable receiver to a frequency domain representation, identify an IMD product from the frequency domain representation of the IF signal, and control the IMD reduction component to suppress the IMD product at the output of the signal path.

2. The apparatus of claim 1, further comprising an amplifier disposed within the signal path.

3. The apparatus of claim 1, further comprising a feed forward path, wherein the IMD reduction component comprises a variable attenuator and a variable phase shifter disposed within the feed forward path.

4. The apparatus of claim 1, wherein the RF communications signal comprises a multi-carrier RF communications signal.

5. The apparatus of claim 1, wherein the tunable receiver comprises:

(a) a downconverter configured to downconvert the RF communications signal to an intermediate frequency; and

(b) a bandpass filter coupled to the downconverter and configured to pass a predetermined band of frequencies and generate therefrom the IF signal.

6. The apparatus of claim 5, wherein the bandpass filter has a pass band with a sufficient range so as to discern both wideband and narrowband RF carriers and their associated IMD products.

7. The apparatus of claim 5, wherein the downconverter comprises:

(a) a local oscillator configured to output a local oscillator signal under the control of the circuit arrangement; and

(b) a mixer configured to mix the local oscillator signal with the RF communications signal to downconvert the RF communications signal to the intermediate frequency.

8. The apparatus of claim 7, wherein the circuit arrangement comprises a processing unit, and wherein the local oscillator comprises a processing unit-controlled frequency synthesizer.

9. The apparatus of claim 5, wherein the bandpass filter outputs an analog IF signal, and wherein the tunable receiver further comprises an analog to digital converter configured to digitize the analog IF signal to a digital time domain representation of the IF signal.

10. The apparatus of claim 1, wherein the circuit arrangement comprises a processing unit configured to receive the IF signal from the tunable receiver, and to output a control signal to the tunable receiver to tune the tunable receiver to a predetermined frequency.

11. The apparatus of claim 10, wherein the circuit arrangement further comprises a digital signal processor (DSP).

12. The apparatus of claim 11, wherein the DSP is configured to convert the time domain representation of the IF signal to the frequency domain representation using a Fast Fourier Transform (FFT).

13. The apparatus of claim 10, wherein the processing unit is configured to sequentially tune the tunable receiver to a plurality of predetermined frequencies, and to store a frequency spectrum comprising the frequency domain representation of the IF signal when the tunable receiver is tuned to each of the plurality of predetermined frequencies.

14. The apparatus of claim 13, wherein the processing unit is configured to first tune the tunable receiver to a first plurality of predetermined frequencies to identify at least one wideband signal, and to second tune the tunable receiver to a second plurality of predetermined frequencies to identify at least one narrowband signal.

15. The apparatus of claim 10, wherein the processing unit is further configured to identify a carrier signal from the frequency domain representation of the IF signal by detecting a power peak in the frequency domain representation of the IF signal.

16. The apparatus of claim 15, wherein the processing unit is further configured to determine a modulation format for the carrier signal from the frequency domain representation of the IF signal.

17. The apparatus of claim 15, wherein the processing unit is configured to identify the IMD product by detecting a signal in the frequency domain representation of the IF signal that has a power level below a threshold used to identify a carrier signal.

18. The apparatus of claim 15, wherein the processing unit is configured to identify the IMD product based upon the location of the carrier signal.

19. The apparatus of claim 10, wherein the processing unit is further configured to tune the tunable receiver to a frequency proximate that for the IMD product and monitor a power level for the IMD product while controlling the IMD reduction component.

20. The apparatus of claim 1, wherein the frequency band is selected from the group consisting of AMPS, DCS, PCS, UMTS, MMDS, and combinations thereof.

21. The apparatus of claim 1, wherein the RF communication signal includes at least one signal modulated using a modulation format selected from the group consisting of WCDMA, CDMA, GSM, TDMA, QAM, OFDM, and combinations thereof.

22. The apparatus of claim 1, wherein the circuit arrangement is configured to identify a plurality of carrier signals from the frequency domain representation of the IF signal, and to determine from the plurality of carrier signals whether a channel configuration is valid.

23. A multi-carrier power amplifier, comprising:

(a) a main signal path having an input and an output and configured to communicate a multi-carrier RF communications signal disposed in a frequency band;

(b) an amplifier disposed within the main signal path;

(c) a feed forward path coupled to the main signal path;

(d) a tunable receiver coupled to the main signal path and configured to downconvert at least a portion of the frequency band to an Intermediate Frequency (IF) signal;

(e) at least one intermodulation distortion (IMD) reduction component disposed in the feed forward path; and

(f) a circuit arrangement configured to convert a time domain representation of the IF signal output by the tunable receiver to a frequency domain representation, identify a plurality of carrier signals and an IMD product from the frequency domain representation of the IF signal, and control the IMD reduction component to suppress the IMD product at the output of the main signal path.

24. A method of suppressing an intermodulation distortion (IMD) product from an RF communications signal disposed in a frequency band, the method comprising:

(a) downconverting at least a portion of the frequency band for the RF communications signal to an Intermediate Frequency (IF) signal;

(b) converting a time domain representation of the IF signal to a frequency domain representation;

(c) identifying an IMD product from the frequency domain representation of the IF signal; and

(d) controlling an IMD reduction component to suppress the IMD product from the RF communications signal.

25. The method of claim 24, further comprising amplifying the RF communications signal with an amplifier.

26. The method of claim 24, wherein the RF communications signal is disposed within a main signal path, and wherein controlling the IMD reduction component comprises controlling a variable attenuator and a variable phase shifter disposed within a feed forward path coupled to the main signal path.

27. The method of claim 24, wherein the RF communications signal comprises a multi-carrier RF communications signal.

28. The method of claim 24, further comprising digitizing the IF signal, wherein converting the time domain representation of the IF signal comprises converting the digitized IF signal to the frequency domain representation.

29. The method of claim 24, wherein converting the time domain representation of the IF signal to the frequency domain representation is performed in a digital signal processing (DSP) using a Fast Fourier Transform (FFT).

30. The method of claim 24, wherein downconverting the portion of the frequency band to the IF signal is performed by a tunable receiver, the method further comprising:

(a) sequentially tuning the tunable receiver to a plurality of predetermined frequencies; and

(b) storing a frequency spectrum comprising the frequency domain representation of the IF signal when the tunable receiver is tuned to each of the plurality of predetermined frequencies.

31. The method of claim 30, further comprising:

(a) tuning the tunable receiver to a first plurality of predetermined frequencies to identify at least one wideband signal; and

(b) thereafter tuning the tunable receiver to a second plurality of predetermined frequencies to identify at least one narrowband signal.

32. The method of claim 30, further comprising identifying a carrier signal from the frequency domain representation of the IF signal by detecting a power peak in the frequency domain representation of the IF signal.

33. The method of claim 32, further comprising determining a modulation format for the carrier signal from the frequency domain representation of the IF signal.

34. The method of claim 32, further comprising identifying the IMD product by detecting a signal in the frequency domain representation of the IF signal that has a power level below a threshold used to identify a carrier signal.

35. The method of claim 32, further comprising identifying the IMD product based upon the location of the identified carrier signal.

36. The method of claim 30, further comprising:

(a) tuning the tunable receiver to a frequency proximate that for the IMD product; and

(b) monitoring a power level for the IMD product while controlling the IMD reduction component.

37. The method of claim 24, further comprising:

(a) identifying a plurality of carrier signals from the frequency domain representation of the IF signal; and

(b) determining from the plurality of carrier signals whether a channel configuration is valid.