Preserving Linearity of a RF Power Amplifier

Abstract

A method and circuit for preserving linearity of a RF power amplifier, the power amplifier including a RF power output unit having a characteristic drive level and fed by a supply voltage, comprising measuring the output voltage of the RF power output unit; comparing the measured output voltage to at least one threshold voltage to produce a control signal; and adapting the drive level or the supply voltage of the RF power output unit by means of the control signal to operate the output unit below its saturation level. A method and circuit for stabilizing an antenna circuit comprising a RF power amplifier and a matching circuit by preserving linearity of a RF power amplifier, where the above power amplifier is used.

1 . A method for preserving linearity of a RF power amplifier, the power amplifier including a RF power output unit having a characteristic drive level and fed by a supply voltage, comprising:
 measuring the output voltage of the RF power output unit;   comparing the measured output voltage to at least one threshold voltage to produce a control signal; and   selecting between reducing the drive level of the RF power output unit responsive to the control signal and increasing the supply voltage of the RF power output unit responsive to the control signal to thereby operate the output unit below its saturation level.   
   
   
       2 . The method of  claim 1 , wherein the power amplifier includes a variable gain preamplifier supplying the drive voltage to the RF power output unit and wherein the control signal is used to adapt the gain of the preamplifier. 
   
   
       3 . The method of  claim 2 , wherein the control signal is combined with the gain control signal of the preamplifier. 
   
   
       4 . The method of  claim 1 , wherein the output voltage of the RF power output unit is rectified before being compared to the threshold voltage. 
   
   
       5 . The method of  claim 1 , wherein the output voltage of the RF power output unit is compared to the threshold voltage by means of an operational amplifier. 
   
   
       6 . The method of  claim 5 , wherein the output voltage of the RF power output unit is compared in at least two parallel operational amplifiers to threshold voltages to produce at least two control signals, and wherein the at least two control signals are fed to a base-band controller. 
   
   
       7 . The method of  claim 6 , wherein the at least two threshold voltages have different voltage levels. 
   
   
       8 . The method of  claim 1 , wherein the supply voltage is adapted by a programmable DC-DC converter controlled by a base-band controller which is fed by the control signal. 
   
   
       9 . A method for controlling an antenna circuit comprising a RF power amplifier and a matching circuit by preserving linearity of a RF power amplifier, the power amplifier comprising a RF power output unit having a characteristic drive level and fed by a supply voltage source, comprising:
 measuring the output voltage of the RF power output unit;   comparing the measured output voltage to at least one threshold voltage to produce a control signal; and   adapting the output matching circuit by selecting between reducing the drive level of the RF power output unit responsive to the control signal and increasing the supply voltage of the RF power output unit responsive to the control signal, thereby operating the output unit below its saturation level.   
   
   
       10 . The method of  claim 9 , wherein adapting of the output matching circuit includes changing a magnitude or a phase of an impedance transform function. 
   
   
       11 . The method of  claim 9 , wherein adapting the output matching circuit includes optimizing a power amplifier efficiency responsive to multiple threshold detection by an analog-to-digital converter. 
   
   
       12 . A circuit for preserving linearity of a RF power amplifier wherein the power amplifier includes a RF power output unit having a characteristic drive level, comprising:
 a measuring unit measuring the output voltage of the RF power output unit;   a comparing unit comparing the measured output voltage of the RF power output unit to a threshold voltage to produce a control signal;   an adaptation unit configured to operate the output unit below its saturation level for preserving linearity of the RF power amplifier, the adaptation unit including a drive level adaptation unit for reducing the drive level of the RF power output unit and a supply voltage adaptation unit for increasing a supply voltage of the RF power output unit.   
   
   
       13 . The circuit of  claim 12 , wherein the power amplifier includes a variable gain preamplifier supplying the drive voltage to the RF power output unit, and wherein the control signal is fed from the comparing unit to the preamplifier to adapt the gain of the preamplifier. 
   
   
       14 . The circuit of  claim 13 , comprising a combining circuit between the comparing unit and the preamplifier to combine the control signal with the gain control signal of the preamplifier. 
   
   
       15 . A circuit for stabilizing an antenna circuit comprising a RF power amplifier and a matching circuit, wherein the RF power amplifier comprises a RF power output unit having a characteristic drive level, comprising:
 a measuring unit measuring the output voltage of the RF power output unit;   a comparing unit comparing the measured output voltage of the RF power output unit to a threshold voltage to produce a control signal; and   an adaptation unit configured to adapt the output matching circuit responsive to the control signal to thereby operate the RF output unit below its saturation level for preserving linearity of the RF power amplifier, the adaptation unit including a drive level adaptation unit and a supply voltage adaptation unit.   
   
   
       16 . The circuit of  claim 15 , wherein the output matching circuit is configured to be adaptable with respect to either a magnitude or a phase of its impedance transform function. 
   
   
       17 . The circuit of  claim 12 , comprising a rectifier between the RF power output unit and the comparing unit. 
   
   
       18 . The circuit of  claim 12 , wherein the comparing unit comprises an operational amplifier. 
   
   
       19 . The circuit of  claim 18 , comprising at least two parallel operational amplifiers to produce at least two control sub-signals, and wherein the at least two control sub-signals are fed to a base-band controller to adapt the gain of the RF power output unit to adapt the gain thereof.