Power amplifier saturation detection

Abstract

In a portable radio transceiver, a power amplifier system includes a saturation detector that detects power amplifier saturation in response to duty cycle of the amplifier transistor collector voltage waveform. The saturation detection output signal can be used by a power control circuit to back off or reduce the amplification level of the power amplifier to avoid power amplifier control loop saturation.

1 . (canceled) 
     
     
         2 . A saturation detection system for detecting saturation of a power amplifier, the saturation detection system comprising:
 a first circuit in electrical communication with a first power amplifier, the first circuit configured to block a positive cycle portion of an amplified radio frequency signal output by the first power amplifier and pass a negative cycle portion of the amplified radio frequency signal output by the first power amplifier to a first averaging filter; and   a second circuit including a comparator configured to output a saturation detection signal based at least in part on a comparison of an output of the first averaging filter to a reference signal, the reference signal being based at least in part on a signal from a second power amplifier.   
     
     
         3 . The saturation detection system of  claim 2  wherein an amplification level of the first power amplifier is adjusted based at least in part on the saturation detection signal. 
     
     
         4 . The saturation detection system of  claim 2  wherein the second circuit further includes a power amplifier controller configured to adjust a power level of the first power amplifier based at least in part on the saturation detection signal. 
     
     
         5 . The saturation detection system of  claim 2  wherein the second power amplifier is configured to process a different frequency band than the first power amplifier. 
     
     
         6 . The saturation detection system of  claim 2  wherein the first circuit includes a diode that clips the positive cycle portion of the amplified radio frequency signal output by the first power amplifier and passes the negative cycle portion of the amplified radio frequency signal output by the first power amplifier to the first averaging filter. 
     
     
         7 . The saturation detection system of  claim 2  wherein the first averaging filter is a low-pass filter. 
     
     
         8 . The saturation detection system of  claim 2 , wherein the second circuit further includes a first switch and a second switch, the first switch configured to electrically connect the output of the first averaging filter to a first input of the comparator in response to a band-select signal being received, and the second switch configured to electrically connect an output of a second averaging filter corresponding to the second power amplifier to a second input of the comparator in response to the band-select signal being received. 
     
     
         9 . The saturation detection system of  claim 8  wherein, in response to a second band-select signal being received, the first switch is configured to electrically disconnect the output of the first averaging filter from the first input of the comparator and the second switch is configured to electrically disconnect the output of the second averaging filter from the second input of the comparator. 
     
     
         10 . A transmitter comprising:
 a modulator;   an upconverter; and   a power amplifier system configured to receive a radio frequency signal after it passes through the modulator and the upconverter, the power amplifier system including a first power amplifier configured to amplify the radio frequency signal to produce an amplified radio frequency signal, a first circuit in electrical communication with the first power amplifier, and a second circuit, the first circuit configured to block a positive cycle portion of the amplified radio frequency signal and pass a negative cycle portion of the amplified radio frequency signal to a first averaging filter, and the second circuit including a comparator configured to output a saturation detection signal based at least in part on a comparison of an output of the first averaging filter to a reference signal, the reference signal being based at least in part on a signal from a second power amplifier.   
     
     
         11 . The transmitter of  claim 10  wherein an amplification level of the first power amplifier is adjusted based at least in part on the saturation detection signal. 
     
     
         12 . The transmitter of  claim 10  wherein the power amplifier system further includes a power amplifier controller configured to adjust a power control signal based at least in part on the saturation detection signal and to provide the power control signal to the first power amplifier to cause the first power amplifier to adjust a power level of the radio frequency signal based at least in part on the power control signal. 
     
     
         13 . The transmitter of  claim 10  wherein the second power amplifier is configured to process a different frequency band than the first power amplifier. 
     
     
         14 . The transmitter of  claim 10  wherein the second circuit further includes a first switch and a second switch, the first switch configured to electrically connect the output of the first averaging filter to a first input of the comparator in response to a band-select signal being received, and the second switch configured to electrically connect an output of a second averaging filter corresponding to the second power amplifier to a second input of the comparator in response to the band-select signal being received. 
     
     
         15 . The transmitter of  claim 14  wherein, in response to a second band -select signal being received, the first switch is configured to electrically disconnect the output of the first averaging filter from the first input of the comparator and the second switch is configured to electrically disconnect the output of the second averaging filter from the second input of the comparator. 
     
     
         16 . A wireless device, comprising:
 a user interface;   an antenna;   a baseband subsystem in communication with the user interface; and   a radio frequency subsystem coupled to the baseband subsystem and the antenna, the radio frequency subsystem including a transmitter, the transmitter including a modulator, an upconverter, and a power amplifier system, the power amplifier system configured to receive a radio frequency signal after it passes through the modulator and the upconverter, the power amplifier system including a first power amplifier, a first circuit in electrical communication with the first power amplifier, and a second circuit, the first power amplifier configured to amplify the radio frequency signal to produce an amplified radio frequency signal, the first circuit configured to block a positive cycle portion of the amplified radio frequency signal and pass a negative cycle portion of the amplified radio frequency signal to a first averaging filter, and the second circuit including a comparator configured to output a first saturation detection signal based at least in part on a comparison of an output of the first averaging filter to a reference signal, the reference signal being based at least in part on a signal from a second power amplifier.   
     
     
         17 . The wireless device of  claim 16  wherein the power amplifier system further includes a power amplifier controller configured to adjust a power control signal based at least in part on the first saturation detection signal and to provide the power control signal to the first power amplifier to cause the first power amplifier to adjust a power level of the radio frequency signal based at least in part on the power control signal. 
     
     
         18 . The wireless device of  claim 16  wherein the second power amplifier is configured to process a different frequency band than the first power amplifier. 
     
     
         19 . The wireless device of  claim 16  wherein the first saturation detection signal indicates that the first power amplifier is operating in a saturation state. 
     
     
         20 . The wireless device of  claim 19  wherein the comparator is further configured to output a second saturation detection signal indicating that the second power amplifier is operating in the saturation state, and the second circuit further includes a switching circuit configured to cause the comparator to output one of the first saturation detection signal or the second saturation detection signal based at least in part on a band-selection signal. 
     
     
         21 . The wireless device of  claim 16  wherein the second circuit further includes a first switch and a second switch, the first switch configured to electrically connect the output of the first averaging filter to a first input of the comparator in response to a band-select signal being received, and the second switch configured to electrically connect an output of a second averaging filter corresponding to the second power amplifier to a second input of the comparator in response to the band-select signal being received.