Dynamic error vector magnitude compensation

Abstract

Aspects of this disclosure relate to compensating for dynamic error vector magnitude. A compensation circuit can generate a compensation signal based at least partly on an amount of time that an amplifier, such as a power amplifier, is turned off between successive transmission bursts of the amplifier. For example, the compensation circuit can charge a capacitor based at least partly on an amount of time that the amplifier is turned off between successive transmission bursts and generate the compensation signal based at least partly on an amount of charge stored on the capacitor. A bias circuit can receive the compensation signal, generate a bias signal based at least partly on the compensation signal, and provide the bias signal to the amplifier to bias the amplifier.

1 . (canceled) 
     
     
         2 . An amplifier system comprising:
 a radio frequency amplifier including an amplifying transistor, the radio frequency amplifier configured to receive a bias signal and to amplify a radio frequency signal;   a compensation circuit configured to generate a compensation signal based at least partly on an amount of time between successive bursts of the radio frequency amplifier; and   a bias circuit including a reference transistor, the bias circuit configured to generate the bias signal based at least partly on the compensation signal so as to compensate for a change in an effective ratio between the reference transistor and the amplifying transistor due to a change in temperature difference between the reference transistor and the amplifying transistor.   
     
     
         3 . The amplifier system of  claim 2  wherein the bias signal increases gain of the amplifying transistor at a beginning of a burst. 
     
     
         4 . The amplifier system of  claim 2  wherein the compensation circuit is configured to generate the compensation signal such that the compensation signal has a first magnitude associated with a first duty cycle of the radio frequency amplifier and a second magnitude associated with a second duty cycle of the radio frequency amplifier, the first magnitude being greater than the second magnitude, and the first duty cycle being less than the second duty cycle. 
     
     
         5 . The amplifier system of  claim 2  wherein the compensation circuit includes a capacitor, and the compensation circuit is configured to charge the capacitor based at least partly on the amount of time between the successive bursts of the radio frequency amplifier. 
     
     
         6 . The amplifier system of  claim 5  wherein the compensation circuit is configured to charge the capacitor to less than a full amount of charge between the successive bursts of the radio frequency amplifier. 
     
     
         7 . The amplifier system of  claim 5  wherein the compensation circuit includes a scaling circuit configured to scale a signal from the capacitor to generate the compensation signal. 
     
     
         8 . The amplifier system of  claim 2  wherein the amplifying transistor and the reference transistor are NPN transistors. 
     
     
         9 . The amplifier system of  claim 2  wherein the amplifying transistor and the reference transistor form a current mirror. 
     
     
         10 . The amplifier system of  claim 9  further comprising a radio frequency trap circuit coupled between the reference transistor and the amplifying transistor. 
     
     
         11 . The amplifier system of  claim 2  wherein the amplifying transistor has a base electrically connected to a base of the reference transistor, and the bias circuit further includes a base current helper transistor electrically connected to the reference transistor. 
     
     
         12 . A mobile device comprising:
 a radio frequency power amplifier including an amplifying transistor, the radio frequency power amplifier configured to receive a bias signal and output an amplified radio frequency signal;   an antenna configured to transmit the amplified radio frequency signal;   a compensation circuit configured to generate a compensation signal based at least partly on an amount of time between successive transmission bursts of the radio frequency power amplifier; and   a bias circuit including a reference transistor, the bias circuit configured to generate the bias signal based at least partly on the compensation signal so as to compensate for a change in an effective ratio between the reference transistor and the amplifying transistor due to a change in temperature difference between the reference transistor and the amplifying transistor.   
     
     
         13 . The mobile device of  claim 12  wherein the amplified radio frequency signal is a wireless local area network signal. 
     
     
         14 . The mobile device of  claim 12  wherein the amplified radio frequency signal is a Wi-Fi signal. 
     
     
         15 . The mobile device of  claim 12  wherein further comprising a switch module configured to selectively couple the radio frequency power amplifier to the antenna. 
     
     
         16 . A method of biasing a radio frequency amplifier, the method comprising:
 generating, using a compensation circuit, a compensation signal based at least partly on an amount of time between successive bursts of a radio frequency amplifier; and   biasing the radio frequency amplifier based at least partly on the compensation signal so as to compensate for a change in an effective ratio between a reference transistor of a bias circuit and an amplifying transistor of the radio frequency amplifier due to a change in temperature difference between the reference transistor of the bias circuit and the amplifying transistor of the radio frequency amplifier.   
     
     
         17 . The method of  claim 16  wherein the generating is performed such that the compensation signal decreases in magnitude as a duty cycle of the radio frequency amplifier increases. 
     
     
         18 . The method of  claim 16  wherein the generating includes charging a capacitor while the radio frequency amplifier is deactivated and discharging the capacitor while the radio frequency amplifier is activated. 
     
     
         19 . The method of  claim 16  wherein the method is performed in a mobile device that includes an antenna configured to transmit a wireless local area network signal from the radio frequency amplifier. 
     
     
         20 . The method of  claim 16  further comprising transmitting, via an antenna, a wireless local area network signal generated by the radio frequency amplifier. 
     
     
         21 . The method of  claim 16  further comprising wirelessly transmitting, via an antenna, a Wi-Fi signal generated by the radio frequency amplifier.