A power amplifier receives an input signal and generates an amplified
output signal. A switching converter generates a regulated voltage and
performs power control for the power amplifier. A linear amplifier
performs modulation envelope control for the power amplifier. The
switching converter may be coupled in series with the linear amplifier,
and this circuit may operate in one of multiple modes. For example, the
linear amplifier may output a tracked voltage to the power amplifier in
GSM/polar EDGE mode, and the switching converter may output the regulated
voltage to the power amplifier in WCDMA/UMTS mode. The linear amplifier
could also output the tracked voltage in both modes, and a selector could
select the appropriate feedback voltage for the switcher. The switching
converter could also provide the regulated voltage directly to the power
amplifier, and the linear converter could adjust a bias of the power
amplifier to provide envelope tracking.