Wideband envelope amplifier for envelope-tracking operation of handset power amplifier

This paper presents a wideband envelope amplifier for envelope-tracking operation of handset power amplifiers. The amplifier has a combined structure composed of a linear regulator and a switching converter. A low output impedance class-AB push-pull output stage is employed to expand the bandwidth (BW) of the linear regulator. By reducing the output resistance of the source follower using dual shunt feedbacks, a nondominant pole at the gate of the output buffer is pushed to the higher frequency range. The gain BW product (GBW) of the linear regulator is improved without sacrificing the phase margin (PM) and efficiency. The designed linear regulator achieves the GBW of 129.6-MHz and PM of 73.1°. For a 40-MHz long term evolution signal having a peak-to-average power ratio of 7.4 dB, the envelope amplifier delivers an efficiency of 73.6% at the peak power driving a 7.7Ω resistive load.

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