Wide-band amplifiers using clipper circuits for reduced harmonics

Abstract

The present invention breaks up the frequency bands which can be filtered by a simple low-loss band-pass or low pass filter. The second harmonic frequency is reduced by use of a non-linear clipper element which controls the driving waveform symmetry and can reduce the harmonics by as much as 5-15 db which makes the filter much simpler and allows the amplifier to remain wide-band. The output waveform from the amplifier is symmetrical or nearly symmetrical.

1 . (canceled) 
     
     
         2 . A power amplifier circuit comprising:
 a transistor configured as an amplifier stage of a power amplifier; and   a voltage variable clipping element which shapes a peak-to-peak amplitude of a signal applied to the transistor and reduces a second harmonic of the signal, the output of the voltage variable clipping element controlled by a control voltage supplied to the voltage variable clipping element.   
     
     
         3 . The power amplifier circuit of  claim 2  further comprising a voltage generator electrically coupled to the voltage variable clipping element to supply the control voltage. 
     
     
         4 . The power amplifier circuit of  claim 3  wherein the voltage generator is further configure to generate the control voltage based at least in part on an adaptive feedback loop. 
     
     
         5 . The power amplifier circuit of  claim 2  wherein the control voltage is supplied based at least in part on temperature. 
     
     
         6 . The power amplifier circuit of  claim 2  wherein the control voltage is supplied based at least in part on an output power. 
     
     
         7 . The power amplifier circuit of  claim 2  wherein the control voltage is supplied based at least in part on a voltage standing wave ratio under mismatch. 
     
     
         8 . The power amplifier circuit of  claim 2  further comprising a harmonic filter electrically coupled to the power amplifier to reduce harmonic levels of the signal. 
     
     
         9 . The power amplifier circuit of  claim 8  wherein the harmonic filter includes a bandpass filter. 
     
     
         10 . The power amplifier circuit of  claim 8  wherein the harmonic filter includes a low pass filter. 
     
     
         11 . The power amplifier circuit of  claim 2  wherein the voltage variable clipping element includes a negative waveform clipping element. 
     
     
         12 . The power amplifier circuit of  claim 2  further comprising a direct current blocking capacitor in communication with an input of the power amplifier. 
     
     
         13 . The power amplifier circuit of  claim 2  further comprising a direct current blocking capacitor between a harmonic filter and an output of the wideband power amplifier circuit. 
     
     
         14 . The power amplifier circuit of  claim 2  wherein the voltage variable clipping element is created from one or more diodes. 
     
     
         15 . The power amplifier circuit of  claim 14  wherein at least one of the one or more diodes is a Gallium Arsenide diode. 
     
     
         16 . The power amplifier circuit of  claim 14  wherein at least one of the one or more diodes is a Schottky diode. 
     
     
         17 . The power amplifier circuit of  claim 2  wherein the voltage variable clipping element reduces the second harmonic of the signal by at least 5 decibels. 
     
     
         18 . An envelope tracking system comprising:
 a power amplifier including a transistor; and   a voltage variable clipping element which shapes a peak-to-peak amplitude of a signal applied to the transistor and reduces a second harmonic of the signal, the output of the voltage variable clipping element controlled by a control voltage supplied to the voltage variable clipping element.   
     
     
         19 . The envelope tracking system of  claim 18  further comprising a voltage generator to supply the control voltage, the voltage generator responsive to one or more of temperature, output power, or a voltage standing wave ratio under mismatch. 
     
     
         20 . The envelope tracking system of  claim 18  further comprising a harmonic filter in communication with an output of the power amplifier and that reduces harmonic levels of the signal. 
     
     
         21 . The envelope tracking system of  claim 18  further comprising one or more direct current blocking capacitors in communication with the power amplifier.