Adaptive envelope tracking based on detected transmit signal bandwidth
Apparatus and methods for power amplifier envelope tracking systems with automatic control of a slew rate and a mode of an error amplifier of the envelope tracking system. The envelope tracker can include a signal bandwidth detection circuit that processes the envelope signal to generate a detected bandwidth signal, and a control circuit that controls the slew rate of the error amplifier based on the detected signal bandwidth.
1 . An envelope tracker for a power amplifier, the envelope tracker comprising:
an input configured to receive an envelope signal corresponding to an envelope of a radio frequency signal;
an error amplifier configured to generate a power amplifier supply voltage, the error amplifier including a biasing stage including a plurality of biasing stages and configured to adjust a slew rate of the error amplifier;
a bandwidth detection circuit configured to generate a bandwidth signal indicating a bandwidth of the envelope signal; and
a control circuit configured to adaptively adjust the biasing stage based on the bandwidth signal to increase the slew rate of the error amplifier for larger envelope bandwidths and decrease the slew rate of the error amplifier for smaller envelope bandwidths by using one or more slew rate switches to selectively activate one or more of the plurality of biasing stages.
2 . The envelope tracker of claim 1 wherein the error amplifier further includes an amplifying stage, and the biasing stage is configured to control a bias of the amplifying stage.
3 . The envelope tracker of claim 1 wherein the control circuit is configured to process the bandwidth signal to determine a number of resource blocks used by the radio frequency signal.
4 . The envelope tracker of claim 1 wherein the envelope tracker further includes a DC-to-DC converter, and the error amplifier and the DC-to-DC converter operate in parallel with one another to generate the power amplifier supply voltage when the bandwidth of the envelope signal satisfies a condition.
5 . A radio frequency front end module comprising:
a power amplifier configured to amplify a radio frequency signal and to receive power from a power amplifier supply voltage;
an envelope tracker including an error amplifier configured to generate the power amplifier supply voltage, the error amplifier including a plurality of biasing stages, one or more of the plurality of biasing stages configured to be selectively controlled to adjust a slew rate of the error amplifier, the envelope tracker further including a bandwidth detection circuit configured to generate a bandwidth signal indicating a bandwidth of an envelope signal, and a control circuit configured to selectively activate the one or more of the plurality of biasing stages based on the bandwidth signal to increase the slew rate of the error amplifier for larger envelope bandwidths and decrease the slew rate of the error amplifier for smaller envelope bandwidths by using one or more slew rate switches.
6 . The front end module of claim 5 wherein the error amplifier further includes an amplifying stage, and the plurality of biasing stages are configured to control a bias of the amplifying stage.
7 . The front end module of claim 5 wherein the control circuit is configured to process the bandwidth signal to determine a number of resource blocks used by the radio frequency signal.
8 . The front end module of claim 5 wherein the envelope tracker further includes a DC-to-DC converter, and the error amplifier and the DC-to-DC converter operate in parallel with one another to generate the power amplifier supply voltage when a bandwidth of the envelope signal satisfies a condition.
9 . A mobile device comprising:
a power amplifier system including a power amplifier configured to amplify a radio frequency signal and to receive power from a power amplifier supply voltage, an error amplifier configured to generate the power amplifier supply voltage, a bandwidth detection circuit, and a control circuit, the error amplifier including a plurality of biasing stages configured to bias an amplifying stage, one or more of the plurality of biasing stages configured to adjust a slew rate of the error amplifier, the bandwidth detection circuit configured to generate a bandwidth signal indicating the bandwidth of an envelope signal, the control circuit configured to control the error amplifier based on the bandwidth signal to increase the slew rate of the error amplifier for larger envelope bandwidths and decrease the slew rate of the error amplifier for smaller envelope bandwidths by using one or more slew rate switches to selectively activate the plurality of biasing stages; and
an antenna configured to transmit the amplified radio frequency signal.
10 . The mobile device of claim 9 wherein the error amplifier further includes an amplifying stage, and the plurality of biasing stages are configured to control a bias of the amplifying stage.
11 . The mobile device of claim 9 wherein the control circuit is configured to process the bandwidth signal to determine a number of resource blocks used by the radio frequency signal.
12 . The mobile device of claim 9 wherein the power amplifier system further includes a DC-to-DC converter, and the error amplifier and the DC-to-DC converter operate in parallel with one another to generate the power amplifier supply voltage when the bandwidth of the envelope signal satisfies a condition.
13 . The mobile device of claim 9 further comprising a packaged radio frequency front end module including the power amplifier system.