Apparatus and methods of calibrating a power amplifier system to compensate for envelope amplitude misalignment

Abstract

Apparatus and methods of calibrating a power amplifier system to compensate for envelope amplitude misalignment are provided. In certain configurations, a method of calibrating a power amplifier system includes generating a supply voltage of a power amplifier using an envelope tracker based on shaping a scaled envelope signal using shaping data generated at a target gain compression, controlling a variable gain of a variable gain amplifier based on a gain control level signal, changing the variable gain by adjusting the gain control level signal using a calibration module, monitoring an output of the power amplifier to determine an amount of variable gain at which a detected gain compression of the power amplifier corresponds to the target gain compression of the shaping data, and calibrating the power amplifier system to compensate for envelope amplitude misalignment based on the determined amount of variable gain.

What is claimed is: 
     
         1 . A method of calibrating for envelope amplitude misalignment, the method comprising:
 amplifying a radio frequency signal from a transceiver using a variable gain amplifier and a power amplifier of a power amplifier system;   generating a supply voltage of the power amplifier using an envelope tracker of the power amplifier system, including generating a scaled envelope signal based on a power control level signal and an envelope signal from the transceiver, and shaping the scaled envelope signal using shaping data generated at a target gain compression;   controlling a variable gain of the variable gain amplifier based on a gain control level signal from the transceiver, and changing the variable gain by adjusting the gain control level signal using a calibration module;   monitoring an output of the power amplifier to determine an amount of variable gain at which a detected gain compression of the power amplifier corresponds to the target gain compression of the shaping data; and   calibrating the power amplifier system to compensate for envelope amplitude misalignment based on the determined amount of variable gain.   
     
     
         2 . The method of  claim 1  wherein changing the variable gain includes controlling the variable gain to a first gain level associated with substantially no gain compression of the power amplifier. 
     
     
         3 . The method of  claim 2  wherein changing the variable gain further includes increasing the variable gain to a second gain level at which the detected gain compression of the power amplifier is about equal to the target gain compression of the shaping data. 
     
     
         4 . The method of  claim 1  wherein calibrating the power amplifier system includes compensating for a variation in insertion loss of a duplexer that is connected to the output of the power amplifier. 
     
     
         5 . The method of  claim 1  wherein changing the variable gain including multiplying the gain control level signal and an output signal of the calibration module. 
     
     
         6 . The method of  claim 1  wherein generating the supply voltage includes controlling the voltage level of the supply voltage based on the shaping data, the shaping data relating a plurality of scaled envelope signal amplitudes to a plurality of supply voltage levels. 
     
     
         7 . The method of  claim 6  wherein generating the supply voltage further includes using a modulator to generate the supply voltage from a battery voltage based on the shaping data. 
     
     
         8 . The method of  claim 7  wherein generating the supply voltage further includes generating an analog input signal of the modulator based on the shaping data using a digital-to-analog converter. 
     
     
         9 . The method of  claim 1  wherein monitoring the output of the power amplifier includes sensing a radio frequency output signal from the output of the power amplifier using a directional coupler, and generating a power measurement from the sensed radio frequency output signal using a power detector. 
     
     
         10 . The method of  claim 9  further comprising sensing the radio frequency output signal along a signal path between the output of the power amplifier and an input to a duplexer. 
     
     
         11 . A power amplifier system with calibration for envelope amplitude misalignment, the power amplifier system comprising:
 a variable gain amplifier and a power amplifier configured to amplify a radio frequency signal;   an envelope tracker configured to generate a supply voltage of the power amplifier, the envelope tracker configured to generate a scaled envelope signal based on a power control level signal and an envelope signal, and to shape the scaled envelope signal based on shaping data generated at a target gain compression;   a transceiver configured to generate the radio frequency signal, the power control level signal, the envelope signal, and a gain control level signal that controls a variable gain of the variable gain amplifier, the transceiver configured to monitor an output of the power amplifier to determine an amount of variable gain of the gain control level signal at which a detected gain compression of the power amplifier corresponds to the target gain compression; and   a calibration module configured to change the variable gain by adjusting the gain control level signal, and to compensate for envelope amplitude misalignment based on the determined amount of variable gain at which the detected gain compression corresponds to the target gain compression.   
     
     
         12 . The power amplifier system of  claim 11  wherein the calibration module is further configured to control the variable gain to a first gain level associated with substantially no gain compression of the power amplifier. 
     
     
         13 . The power amplifier system of  claim 12  wherein the calibration module is further configured to increase the variable gain to a second gain level at which the detected gain compression is about equal to the target gain compression. 
     
     
         14 . The power amplifier system of  claim 11  further including a multiplier configured to multiply the gain control level signal and an output signal of the calibration module. 
     
     
         15 . The power amplifier system of  claim 11  wherein the shaping data relates a plurality of scaled envelope signal amplitudes to a plurality of supply voltage levels. 
     
     
         16 . The power amplifier system of  claim 11  wherein the envelope tracker further includes a modulator configured to generate the supply voltage from a battery voltage based on the shaping data. 
     
     
         17 . The power amplifier system of  claim 16  wherein the envelope tracker further includes a digital-to-analog converter configured to generating an analog input signal of the modulator based on the shaping data. 
     
     
         18 . The power amplifier system of  claim 11  further comprising a directional coupler configured to generate a sensed signal based on sensing the output of the power amplifier. 
     
     
         19 . The power amplifier system of  claim 18  wherein the transceiver includes a power detector configured to detect an output power of the power amplifier based on the sensed signal. 
     
     
         20 . The power amplifier system of  claim 18  further comprising a duplexer including an input electrically connected to the output of the power amplifier, the directional coupler configured to sense a radio frequency output signal provided from the output of the power amplifier to the input of the duplexer.