Feed-forward amplifier of a type preventing unwanted waves from being outputted in the initial operation

A feed-forward amplifier of a type preventing unwanted waves from being outputted in an initial operation having a main amplifier having a front stage and a rear stage and amplifying a main signal in a main signal path, a distortion extracting loop circuit supplying a pilot signal fed from a pilot signal generator to said main signal path and generating a main signal cancelling signal to cancel said main signal outputted from said main amplifier, and a distortion eliminating loop circuit obtaining a signal in which components of said main signal in an output of said main amplifier have been cancelled on the basis of an output of said main amplifier and said main signal cancelling signal fed from said distortion extracting loop circuit in the rear stage of said main amplifier and outputting the components of said main signal obtained from a signal in said main signal path in the rear stage of said main amplifier using said signal in which the components of said main signal have been cancelled, said feed-forward amplifier comprising:

• a pilot signal variably attenuating unit attenuating said pilot signal supplied to said main signal path in the front stage of said main amplifier;
• a main signal variably attenuating unit attenuating said main signal in said main signal path in said front stage of said main amplifier;
• a power source start-up detecting means detecting a start-up of a power source of said main amplifier;
• a first main signal detecting means having a main signal cancelling signal detecting means detecting a main signal cancelling signal fed from said distortion extracting loop circuit and a judging means judging an input of the main signal when the main signal cancelling signal detected by said main signal cancelling signal detecting means exceeds a reference value which is set to a level smaller than a signal cancelling marginal level at the time of a minimum input;
• a second main signal detecting means having an output signal detecting means detecting an output signal from the rear stage of said main amplifier and a judging means judging an input of the main signal when the output signal detected by said output signal detecting means exceeds a reference value which is set to a level smaller than a level of the output signal level at the time of a minimum input;
• an initial operation control unit controlling said pilot signal variably attenuating unit so as to gradually decrease an attenuation quantity of the pilot signal using results of detection by said power source start-up detecting means and said first main signal detecting means as timing information after a start-up of said power source of said main amplifier, and controlling said main signal variable attenuating unit so as to gradually decrease an attenuation quantity of the main signal after said pilot signal variably attenuating unit has decreased the attenuation quantity of the pilot signal;
• and
• a main control unit controlling said distortion extracting loop circuit and said distortion eliminating circuit on the basis of a result of detection by said second main signal detecting means after a control by said initial operation control unit while watching a failure condition of said main amplifier.

A feed-forward amplifier of a type preventing unwanted waves from being outputted in an initial operation having a main amplifier having a front stage and a rear stage and amplifying a main signal in a main signal path, a distortion extracting loop circuit supplying a pilot signal fed from a pilot signal generator to said main signal path and generating a main signal cancelling signal to cancel said main signal outputted from said main amplifier, and a distortion eliminating loop circuit obtaining a signal in which components of said main signal in an output of said main amplifier have been cancelled on the basis of an output of said main amplifier and said main signal cancelling signal fed from said distortion extracting loop circuit in said rear stage of said main amplifier and outputting the components of said main signal obtained from a signal in said main signal path in said rear stage of said main amplifier using said signal in which the components of said main signal have been cancelled, said feed-forward amplifier comprising:

• a pilot signal variably attenuating unit attenuating said pilot signal supplied to said main signal path in said front stage of said main amplifier;
• a main signal variably attenuating unit attenuating said main signal in said main signal path in said front stage of said main amplifier;
• a power source start-up detecting means detecting a start-up of a power source of said main amplifier;
• a first main signal detecting means having a main signal cancelling signal detecting means detecting a main signal cancelling signal fed from said distortion extracting loop circuit and a judging means judging an input of the main signal when the main signal cancelling signal detected by said main signal cancelling signal detecting means exceeds a reference value which is set to a level smaller than an initial operation level set larger than a signal cancelling marginal level at the time of a minimum input;
• a second main signal detecting means having an output signal detecting means detecting an output signal from the rear stage of said main amplifier and a judging means judging an input of the main signal when the output signal detected by said output signal detecting means exceeds a reference value which is set to a level smaller than a level of the output signal level at the time of the minimum input;
• an initial operation control unit altering a control setting mode in said distortion extracting loop circuit so that said initial operation level is a signal cancelling marginal level after said first main signal detecting means has detected an input of the main signal with use of results of detection by said power source start-up detecting means and said first main signal detecting means, under such condition, said initial operation control unit controlling said pilot signal variably attenuating unit so as to gradually decrease an attenuation quantity of the pilot signal, and controlling said main signal variably attenuating unit so as to gradually decrease an attenuation quantity of the main signal after said pilot signal variably attenuating unit has decreased the attenuation quantity of the pilot signal;
• and
• a main control unit controlling said distortion extracting loop circuit and said distortion eliminating loop circuit on the basis of a result of detection by said second main signal detecting means after a control by said initial operation control unit, while watching a failure condition of said main amplifier.