Reducing power amplifier gain drift during a data burst

Abstract

A bias circuit provides additional bias current for power amplifiers during data bursts to compensate for the gain droop caused by a rise in the power amplifier temperature during the data burst. A bias circuit includes a difference amplifier and switches coupled to the difference amplifier. The switches operate the bias circuit in a first mode when a transmit data burst is detected and operate the bias circuit in a second mode after the bias circuit has operated in the first mode for a predetermined period of time. In the first mode, the bias circuit charges a storage capacitor and sets an output current to zero. In the second mode, the bias circuit outputs the output current that increases above the initial value of zero as the PA warms up, where the excursion of this increase of current is determined by a register. The switches disable the bias circuit when the transmit data burst ends.

1 . (canceled) 
     
     
         2 . A power amplifier system, comprising:
 a power amplifier configured to amplify a radio frequency signal; and   a sampling circuit configured to charge a storage capacitor for a time period when a data burst is detected and to provide an indication of a change in temperature of the power amplifier when the time period has elapsed.   
     
     
         3 . The power amplifier system of  claim 2  further comprising a temperature sensor configured to provide an indication of temperature of the power amplifier to the sampling circuit. 
     
     
         4 . The power amplifier system of  claim 2  further comprising a bias circuit configured to generate a bias compensation signal based at least in part on the indication of the change in temperature of the power amplifier. 
     
     
         5 . The power amplifier system of  claim 4  wherein an output current of the bias circuit increases as the temperature of the power amplifier increases during the data burst. 
     
     
         6 . The power amplifier system of  claim 4  wherein the bias compensation signal compensates for a change in gain of the power amplifier during the data burst. 
     
     
         7 . The power amplifier system of  claim 2  wherein the data burst is less than 1 millisecond. 
     
     
         8 . The power amplifier system of  claim 2  wherein the data burst is between and including 1 millisecond and 5 milliseconds. 
     
     
         9 . The power amplifier system of  claim 2  wherein the data burst is greater than 5 milliseconds. 
     
     
         10 . The power amplifier system of  claim 2  wherein the power amplifier is implemented on a first semiconductor die and the sampling circuit is implemented on a second semiconductor die. 
     
     
         11 . The power amplifier system of  claim 10  wherein the first semiconductor die includes a gallium arsenide die and the second semiconductor die includes a complementary metal-oxide die. 
     
     
         12 . The power amplifier system of  claim 3  wherein the power amplifier and the temperature sensor are implemented on a first semiconductor die and the sampling circuit is implemented on a second semiconductor die. 
     
     
         13 . The power amplifier system of  claim 10  further comprising a bias circuit implemented on the second semiconductor die and configured to generate a bias compensation signal based on the indication of change in temperature of the power amplifier and a temperature coefficient. 
     
     
         14 . A method of adjusting a gain of a power amplifier, comprising:
 measuring a temperature of the power amplifier during a data burst;   sampling an indication of the temperature of the power amplifier for a first time interval after the data burst is detected; and   adjusting a gain of the power amplifier based at least in part on an indication of a change in temperature of the power amplifier during the data burst.   
     
     
         15 . The method of  claim 14  further comprising providing the indication of the change in temperature of the power amplifier during a second time interval of the data burst that begins after the first time interval has ended. 
     
     
         16 . The method of  claim 14  further comprising multiplying the indication of the change in temperature of the power amplifier by a temperature coefficient. 
     
     
         17 . The method of  claim 14  further comprising disabling sampling circuitry when the data burst has ended. 
     
     
         18 . A wireless communication device comprising:
 a power amplifier configured to amplify a radio frequency signal;   a sampling circuit configured to sample an indication of temperature of the power amplifier for a first time interval after a data burst is detected and to provide an indication of a change in temperature of the power amplifier during a second time interval that begins after the first time interval has ended; and   an antenna configured to transmit the amplified radio frequency signal.   
     
     
         19 . The wireless communication device of  claim 18  wherein the sampling circuit includes a storage capacitor that is configured to charge during the first time interval. 
     
     
         20 . The wireless communication device of  claim 18  further comprising a bias circuit configured to generate a bias signal based on the change in temperature of the power amplifier. 
     
     
         21 . The wireless communication device of  claim 18  further comprising a temperature sensor configured to provide the indication of temperature of the power amplifier.