Radio frequency power amplifier and method using an amplitude control system

Abstract

A radio frequency power amplifier and corresponding method is arranged and configured to drive a resonant load. The radio frequency power amplifier includes a radio frequency switching stage with an output that is coupled to a resonant circuit. The switching stage is configured to provide an output signal with amplitude modulation corresponding to amplitude modulation of an input signal when powered from a fixed voltage power supply. The amplifier further includes a feedback control system coupled to the input signal and the output signal, where the feedback control system includes a sequencer configured to provide a sequencer output that is used to drive the radio frequency switching stage. The amplifier also includes an amplitude control system coupled to the output of the radio frequency switching stage and configured to limit an amplitude of the output signal and in some embodiments a power recovery system.

1 . A radio frequency power amplifier comprising: 
 a feedback control system coupled to a signal corresponding to an input signal and a first feedback signal and configured to provide a sequencer output;    a radio frequency switching stage driven by the sequencer output and configured to provide an output signal to drive a resonant load; and    a clipper system coupled to the output signal and configured to limit an amplitude of the output signal, the first feedback signal corresponding to the output signal as limited.    
   
   
       2 . The radio frequency power amplifier of  claim 1  wherein the clipper system further comprises one or more diodes coupled from the output signal to a reference voltage, the reference voltage corresponding to a maximum amplitude of the output signal.  
   
   
       3 . The radio frequency power amplifier of  claim 2  wherein the clipper system further comprises a voltage source to maintain the reference voltage.  
   
   
       4 . The radio frequency power amplifier of  claim 1  wherein the clipper system further comprises one or more diodes and a power recovery system, the one or more diodes coupled from the output signal to the power recovery system.  
   
   
       5 . The radio frequency power amplifier of  claim 4  wherein the power recovery system further comprises a DC to DC converter coupled to the one or more diodes and configured to provide output power.  
   
   
       6 . The radio frequency power amplifier of  claim 5  wherein the power recovery system further comprises enabling circuitry configured to enable the DC to DC converter when an input voltage compared to a reference voltage satisfies a known condition, the reference voltage corresponding to a maximum amplitude of the output signal.  
   
   
       7 . The radio frequency amplifier of  claim 4  wherein the DC to DC converter is configured to provide an output current when enabled.  
   
   
       8 . The radio frequency power amplifier of  claim 1  wherein the feedback control system further comprises a loop filter with a filter output coupled to an input of a sequencer, the sequencer configured to provide the sequencer output, where the sequencer output has an OFF state with a starting time that corresponds to the filter output and has a minimum duration and an ON state that has a starting time corresponding to a voltage minimum for the output signal.  
   
   
       9 . The radio frequency power amplifier of  claim 1  further comprising a second feedback system responsive to the sequencer output and configured to provide a second feedback signal that is coupled to the feedback control system; where the sequencer output has at least one state with a starting time that is determined by the feedback control system.  
   
   
       10 . The radio frequency power amplifier of  claim 9  wherein the feedback control system comprises a sequencer configured to provide the sequencer output and the second feedback signal is coupled to an input of the sequencer.  
   
   
       11 . The radio frequency power amplifier of  claim 9  wherein the second feedback system comprises one or more delay stages with outputs coupled to a corresponding one or more gain stages with each of the gain stages having an output, where the second feedback signal corresponds to a combination of the signal at the output of each of the one or more gain stages.  
   
   
       12 . The radio frequency power amplifier of  claim 1  wherein the radio frequency switching stage further comprises a radio frequency switching stage configured to switch ON responsive to the sequencer output so that over a multitude of switch ON events an average voltage imposed on the radio frequency switching stage at the switch ON event is less than ½ of a specified breakdown voltage associated with the radio frequency switching stage.  
   
   
       13 . A radio frequency power amplifier arranged and configured to drive a resonant load comprising: 
 a radio frequency switching stage with an output that is coupled to a resonant circuit and configured to provide an output signal with amplitude modulation corresponding to amplitude modulation of an input signal when powered from a fixed voltage power supply;    a feedback control system coupled to the input signal and the output signal, the feedback control system comprising a sequencer configured to provide a sequencer output that is used to drive the radio frequency switching stage; and    an amplitude control system coupled to the output of the radio frequency switching stage and configured to limit an amplitude of the output signal.    
   
   
       14 . The radio frequency power amplifier of  claim 13  wherein the amplitude control system further comprises one or more diodes coupled from the output signal to a load, the load establishing an upper value for the amplitude of the output signal.  
   
   
       15 . The radio frequency power amplifier of  claim 14  wherein the load further comprises a voltage source providing a voltage, where the upper value for the amplitude of the output signal corresponds to the voltage.  
   
   
       16 . The radio frequency power amplifier of  claim 13  wherein the amplitude control system further comprises one or more diodes and a power recovery system, the one or more diodes coupled from the output signal to the power recovery system.  
   
   
       17 . The radio frequency power amplifier of  claim 16  wherein the power recovery system further comprises a DC to DC converter coupled to the one or more diodes and configured to provide a portion of DC power for the radio frequency power amplifier.  
   
   
       18 . The radio frequency power amplifier of  claim 17  wherein the power recovery system further comprises enabling circuitry configured to enable the DC to DC converter when an input voltage compared to a reference voltage satisfies a known condition, the reference voltage corresponding to an upper value for the amplitude of the output signal.  
   
   
       19 . The radio frequency power amplifier of  claim 18  wherein the power recovery system further comprises an electronic switch to isolate the power recovery system from a DC power source when the power recovery system is not providing the portion of the DC power for the radio frequency power amplifier.  
   
   
       20 . The radio frequency power amplifier of  claim 16  wherein the power recovery system comprises a DC to DC converter that is configured to regulate a voltage at an input to the DC to DC converter.  
   
   
       21 . The radio frequency power amplifier of  claim 20  wherein the power recovery system further comprises enabling circuitry configured to enable the DC to DC converter when a comparison of the voltage and a reference voltage satisfies a known condition.  
   
   
       22 . The radio frequency power amplifier of  claim 13  wherein the feedback control system further comprises a loop filter with a filter output coupled to an input of the sequencer, where the sequencer output has an OFF state with a starting time that corresponds to the filter output and has a minimum duration and an ON state that has a starting time corresponding to a voltage minimum for the output signal.  
   
   
       23 . The radio frequency power amplifier of  claim 13  further comprising a second feedback system responsive to the sequencer output and configured to provide a second feedback signal that is coupled to an input of the sequencer; where the sequencer output has at least one state with a starting time that is determined by the feedback control system and the second feedback system.  
   
   
       24 . The radio frequency power amplifier of  claim 13  wherein the radio frequency switching stage as driven by the sequencer output is further configured to provide an output signal that includes an amplified replica of the input signal over an input signal bandwidth, where the input signal includes complex modulation while the radio frequency switching stage is powered from a constant voltage power supply.  
   
   
       25 . The radio frequency power amplifier of  claim 13  wherein the feedback control system further comprises a mixer arrangement configured to: 
 provide a feedback signal, the feedback signal further corresponding to the output signal as down converted by the mixer arrangement; and    provide a sequencer input corresponding to a combination of the input signal and the feedback signal as up converted by the mixer arrangement.    
   
   
       26 . A method of providing a radio frequency signal with complex modulation comprising: 
 filtering a combination of an input signal and a first feedback signal to provide a filtered signal, the input signal including complex modulation;    generating, responsive to the filtered signal, a quantized signal having an OFF state that begins at a variable time;    controlling a radio frequency switching stage with the quantized signal to provide an output signal to a resonant load; and    limiting an amplitude of the output signal, the output signal as limited corresponding to the first feedback signal and further comprising an amplified version of the input signal with the complex modulation.    
   
   
       27 . The method of  claim 26  wherein the limiting an amplitude of the output signal further comprises coupling the output signal to a voltage source through one or more diodes, the voltage source establishing an upper value for the amplitude of the output signal.  
   
   
       28 . The method of  claim 26  further comprising recovering power corresponding to the limiting an amplitude of the output signal.  
   
   
       29 . The method of  claim 28  wherein the recovering power further comprises regulating a voltage using a DC to DC converter having an input coupled to the voltage and an output configured to provide a portion of DC power for the radio frequency switching stage, the voltage corresponding to an upper value for the amplitude of the output signal.  
   
   
       30 . The method of  claim 29  wherein the recovering power further comprises enabling the DC to DC converter when the voltage compared to a reference voltage satisfies a known condition.