Apparatus and methods for power amplifier biasing

Abstract

Apparatus and methods for power amplifier biasing are disclosed herein. In certain implementations, a power amplifier system includes a power amplifier bias circuit and a power amplifier. The power amplifier bias circuit includes a reference current source that generates a reference current, a bipolar reference transistor, and a transimpedance amplifier that amplifies a difference between a collector current of the bipolar reference transistor and the reference current, and that provides a base bias voltage to a base of the bipolar reference transistor. The power amplifier generates a radio frequency output signal at an output based on amplifying a radio frequency input signal received at an input. The power amplifier includes a bipolar power amplifier transistor including a base biased by the base bias voltage such that the power amplifier has a substantially flat gain response versus time.

1 . (canceled) 
     
     
         2 . A power amplifier system comprising:
 an array of transistor elements;   a power amplifier including a bipolar power amplifier transistor implemented by a plurality of transistor elements of the array, the bipolar power amplifier transistor including a base configured to receive a radio frequency input signal and a collector configured to output an amplified radio frequency signal; and   a bias circuit including a bipolar reference transistor implemented by one or more transistor elements of the array, the bipolar reference transistor having a base electrically connected to the base of the bipolar power amplifier transistor, the bias circuit further including a current source electrically connected to a collector of the bipolar reference transistor and configured to generate a reference current.   
     
     
         3 . The power amplifier system of  claim 2  wherein the bias circuit further includes a selection circuit configured to select the one or more transistor elements from the array. 
     
     
         4 . The power amplifier system of  claim 2  wherein the bias circuit further includes an amplifier including an input electrically connected to the collector of the reference bipolar transistor and an output configured to control a base voltage of the reference bipolar transistor. 
     
     
         5 . The power amplifier system of  claim 4  wherein the bias circuit further includes an isolation circuit electrically connected between the output of the amplifier and the base of the bipolar power amplifier transistor. 
     
     
         6 . The power amplifier system of  claim 4  wherein the amplifier is a transimpedance amplifier. 
     
     
         7 . The power amplifier system of  claim 4  wherein the amplifier is configured to control the base voltage such that a collector current of the bipolar reference transistor is substantially equal to the reference current. 
     
     
         8 . The power amplifier system of  claim 2  wherein the bias circuit further includes a control circuit configured to control the reference current to compensate for temperature variation. 
     
     
         9 . The power amplifier system of  claim 2  wherein each transistor element of the array has a substantially identical geometry and is implemented in a common layout. 
     
     
         10 . A packaged module comprising:
 a package substrate; and   a semiconductor die attached to the package substrate and including an array of transistor elements in a common layout, the semiconductor die further including a bipolar power amplifier transistor implemented by a plurality of transistor elements of the array and configured to amplify a radio frequency input signal, a bipolar reference transistor implemented by one or more transistor elements of the array and having a base electrically connected to a base of the bipolar power amplifier transistor, and a current source electrically connected to a collector of the bipolar reference transistor and configured to generate a reference current.   
     
     
         11 . The packaged module of  claim 10  wherein the semiconductor die further includes an amplifier including an input electrically connected to the collector of the reference bipolar transistor and an output configured to control a base voltage of the reference bipolar transistor. 
     
     
         12 . The packaged module of  claim 11  wherein the semiconductor die further includes an isolation circuit electrically connected between the output of the amplifier and the base of the bipolar power amplifier transistor. 
     
     
         13 . The packaged module of  claim 11  wherein the amplifier is a transimpedance amplifier. 
     
     
         14 . The packaged module of  claim 11  wherein the amplifier is configured to control the base voltage such that a collector current of the bipolar reference transistor is substantially equal to the reference current. 
     
     
         15 . The packaged module of  claim 10  wherein the semiconductor die further includes a control circuit configured to control the reference current to compensate for temperature variation. 
     
     
         16 . A mobile device comprising:
 a transceiver configured to generate a radio frequency signal;   a power amplifier system configured to amplify the radio frequency signal to generate an amplified radio frequency signal, the power amplifier system including an array of transistor elements, a bipolar power amplifier transistor implemented by a plurality of transistor elements of the array and having a collector configured to output the amplified radio frequency signal, a bipolar reference transistor implemented by one or more transistor elements of the array and having a base electrically connected to a base of the bipolar power amplifier transistor, and a current source electrically connected to a collector of the bipolar reference transistor and configured to generate a reference current; and   an antenna configured to receive the amplified radio frequency signal from the power amplifier system.   
     
     
         17 . The mobile device of  claim 16  wherein the power amplifier system further includes an amplifier including an input electrically connected to the collector of the reference bipolar transistor and an output configured to control a base voltage of the reference bipolar transistor. 
     
     
         18 . The mobile device of  claim 17  wherein the power amplifier system further includes an isolation circuit electrically connected between the output of the amplifier and the base of the bipolar power amplifier transistor. 
     
     
         19 . The mobile device of  claim 17  wherein the amplifier is a transimpedance amplifier. 
     
     
         20 . The mobile device of  claim 17  wherein the amplifier is configured to control the base voltage such that a collector current of the bipolar reference transistor is substantially equal to the reference current. 
     
     
         21 . The mobile device of  claim 16  wherein the power amplifier system further includes a control circuit configured to control the reference current to compensate for temperature variation.