Adaptive feed-forward method and apparatus for amplifier noise reduction

• US 5,148,117 A
• Filed: 11/25/1991
• Issued: 09/15/1992
• Est. Priority Date: 11/25/1991
• Status: Expired due to Term

• Current Assignee: Exelis Incorporated (L3Harris Technologies, Inc.)
• Original Assignee: American Nucleonics Corp. (Eaton Corporation PLC.)
• Inventors: Talwar, Ashok K.
• Primary Examiner(s): MOTTOLA, STEVEN J
• Application Number:
  US07/797,788
• Time in Patent Office: 295 Days
• Field of Search: 328/162, 328/163, 330/107, 330/149, 330/151
• US Class Current: 330/151
• CPC Class Codes: H03F 1/3229 using a loop for error extraction and another loop for error subtraction
• CPC Class Codes: H03F 2200/372 Noise reduction and elimination in amplifier
• CPC Class Codes: H03F 2201/3212 Using a control circuit to adjust amplitude and phase of a signal in a signal path

Abstract

An adaptive feed-forward cancelling system obtains a reference signal and a sample signal from an amplifier by directional couplers. The sample signal essentially consists of an undistorted input signal component and a noise and distortion component. The reference and sample signals are provided to an adaptive interference canceller which performs an adaptive cancellation process. The interference canceller provides a cancellation signal essentially consisting of the signal component which is common to both the reference signal and the sample signal. The cancellation signal is injected into a transmission line which carries the sample signal so that only an error signal remains which essentially consists of the noise distortion component of the amplifier output signal. The error signal is then amplitude and phase adjusted to have substantially the same amplitude and to be substantially 180° out of phase with the amplifier output signal. The amplitude and phase adjustment error signal is then injected by a directional coupler onto the transmission line which carries the amplifier output signal so that an amplified input signal is provided by the power amplifier without the noise and distortion components added by the amplifier.

Claims

1. An adaptive feed-forward network for connection to an amplifier and for reducing noise and distortion generated by the amplifier, the amplifier having an input on which is provided a substantially distortion free input signal and an output on which is generated by the amplifier an output signal comprising an amplified input signal component and a noise and distortion component, the adaptive feed-forward network comprising:

a first directional coupler, the input signal being provided to the first directional coupler, the first directional coupler having an output and generating thereon a reference signal corresponding to the input signal;

a second directional coupler, the amplifier output signal being provided to the second directional coupler, the second directional coupler having an output and generating thereon a sample signal having an amplified input signal component and a noise and distortion component corresponding to the amplifier output signal;

a third directional coupler, the sample signal being provided to the third directional coupler, the third directional coupler having an input and an output;

a fourth directional coupler, the fourth directional coupler being electrically coupled to the output of the third directional coupler, the fourth directional coupler having an output on which is provided a portion of the sample signal;

an interference canceller, the interference canceller having a reference input and a sample input, the reference input receiving the reference signal from the first directional coupler and the sample input receiving the sample signal from the third directional coupler, the interference canceller further having an output and generating thereon a cancellation signal, the cancellation signal being substantially equal to and opposite in phase to the input signal component of the sample signal, the cancellation signal being provided to the input of the fourth directional coupler, the fourth directional coupler effectively combining the sample signal with the cancellation signal so as to eliminate substantially the input signal component from the sample signal thereby providing an error signal substantially consisting of only the noise and distortion component of the sample signal; and

a fifth directional coupler, the fifth directional coupler being electrically coupled to the output of the fourth directional coupler and to the amplifier output, the error signal and the amplifier output signal being provided to the fifth directional coupler, the fifth directional coupler effectively subtracting the error signal from the amplifier output signal thereby leaving substantially only the amplified input signal component remaining in the amplifier output signal.

2. An adaptive feed-forward network for connection to an amplifier for reducing noise and distortion generated by the amplifier as defined by claim 1 further comprising:

an error amplifier being coupled between the fourth directional coupler and the fifth directional coupler, the error amplifier amplifying the error signal so that the error signal has substantially the same magnitude as the signal noise and distortion components of the amplifier output signal, the error amplifier providing an amplified error signal to the fifth directional coupler.

3. An adaptive feed-forward network for connection to an amplifier for reducing noise and distortion generated by the amplifier as defined by claim 1 further comprising:

phase adjustment means being coupled between the fourth directional coupler and the fifth directional coupler, the phase adjustment means receiving and modifying the phase of the error signal so that the error signal is substantially out of phase with the signal noise and distortion component of the amplifier output signal, the phase adjustment means providing a phase modified error signal to the fifth directional coupler.

4. An adaptive feed-forward network for connection to an amplifier for reducing noise and distortion generated by the amplifier as defined by claim 1 further comprising:

amplitude adjustment means being coupled between the fourth directional coupler and the fifth directional coupler, the amplitude adjustment means receiving and modifying the amplitude of the error signal so that the error signal has substantially the same amplitude as the signal noise and distortion component of the amplifier output signal, the amplitude adjustment means providing an amplitude modified error signal to the fifth directional coupler.

5. An adaptive feed-forward network for connection to an amplifier and for reducing noise and distortion generated by the amplifier, the amplifier having an input on which is provided a substantially distortion free input signal and an output on which is generated by the amplifier an output signal comprising a signal component and a noise and distortion component, the adaptive feed-forward network comprising;

a first directional coupler, the input signal being provided to the first directional coupler, the first directional coupler having an output and generating thereon a reference signal corresponding to the input signal;

a second directional coupler, the amplifier output signal being provided to the second directional coupler, the second directional coupler having an output and generating thereon a sample signal having an amplified input signal component and a noise and distortion component corresponding to the amplifier output signal;

a third directional coupler, the sample signal being provided to the third directional coupler, the third directional coupler having an input and an output;

a fourth directional coupler, the fourth directional coupler being electrically coupled to the output of the third directional coupler, the fourth directional coupler having an output on which is provided a portion of the sample signal;

a first interference canceller, the first interference canceller having a first reference input and a first sample input, the first reference input receiving the reference signal from the first directional coupler and the sample input receiving the sample signal from the third directional coupler, the first interference canceller further having a first output and generating thereon a first cancellation signal, the first cancellation signal being substantially equal to and opposite in phase to the input signal component of the sample signal, the first cancellation signal being provided to the input of the fourth directional coupler, the fourth directional coupler effectively combining the sample signal with the cancellation signal so as to eliminate substantially the input signal component from the sample signal thereby providing a first error signal substantially consisting of only the noise and distortion component of the sample signal;

a fifth directional coupler, the sample signal being provided to the fifth directional coupler, the fifth directional coupler having an input and an output;

a sixth directional coupler, the sixth directional coupler being electrically coupled to the output of the fifth directional coupler, the sixth directional coupler having an output on which is provided a portion of the sample signal; and

a second interference canceller, the second interference canceller having a second reference input and a second sample input, the second reference input receiving the first error signal from the fourth directional coupler as a second reference signal, the second interference canceller further having a second output and generating thereon a second cancellation signal, the second cancellation signal being substantially equal to and opposite in phase to the reference signal component of the sample signal, the second cancellation signal substantially consisting of only the noise and distortion component of the sample signal being provided to the input of the sixth directional coupler, the sixth directional coupler effectively combining the amplifier output signal with the second cancellation signal so as to effectively subtract the second cancellation signal from the amplifier output signal thereby leaving substantially only the amplified input signal component remaining in the amplifier output signal.

6. An adaptive feed-forward network for connection to an amplifier for reducing noise and distortion generated by the amplifier as defined by claim 5 further comprising:

an error amplifier being coupled between the fourth directional coupler and the reference input of the second interference canceller, the error amplifier receiving and amplifying the first altered sample signal so that the first altered sample signal has substantially the same magnitude as the signal noise and distortion component of the amplifier output signal, the error amplifier providing an amplified first altered sample signal to the reference input of the second interference canceller.

7. An adaptive feed-forward network for connection to an amplifier for reducing noise and distortion generated by the amplifier as defined by claim 5 further comprising:

an error amplifier being coupled between the output of the second interference canceller and the sixth directional coupler, the error amplifier receiving and amplifying the second cancellation signal so that the second cancellation signal has substantially the same magnitude as the signal noise and signal distortion component of the amplifier output signal, the error amplifier providing an amplified second cancellation signal to the sixth directional coupler.

8. A method for removing a noise and distortion signal component generated by an amplifier from an amplifier output signal, the amplifier having an input and an output, the method comprising:

sampling an undistorted input signal, which is provided to an input of the amplifier, with a first directional coupler;

providing the undistorted input signal as a reference signal to an interference canceller;

sampling an amplifier output signal which is provided on an output of the amplifier with a second directional coupler to generate a sample amplifier output signal, the amplifier output signal including a substantially undistorted amplified input signal component and a noise and distortion component;

providing the sample amplifier output signal as a sample signal to a third directional coupler which provides the sample signal to the interference canceller;

comparing the reference signal and the sample signal and generating a cancellation signal which is substantially equal to and opposite in phase to the amplified input signal component of the sample signal;

providing the cancellation signal to a fourth directional coupler for injecting the cancellation signal onto a transmission line which carries the sample signal so as to provide an error signal which is substantially equal to the noise and distortion component of the amplifier output signal; and

providing the error signal to a fifth directional coupler for injecting the error signal onto a transmission line which carries the amplifier output signal so as to effectively subtract the error signal from the amplifier output signal thereby leaving substantially only the amplified input signal component remaining in the amplifier output signal.