Abstract
A multimode/multiband envelope tracking (ET) transmitter consisting of a hybrid switching amplifier (HSA) and a broadband saturated power amplifier (PA) is developed for operation across 1.3 to 2.7 GHz. For the various standard signals with different bandwidth (BW) and peak-to-average power ratio, the HSA efficiently provides supply signals to the PA by changing the reference value of the hysteresis comparator. The saturated amplifier employs the nonlinear output capacitor to shape the voltage waveform, resulting in the half-sinusoidal or rectangular waveform. Since the nonlinear capacitor generates large out-of-phased second harmonic component with small higher order harmonics, the voltage shaping is mainly carried out by the capacitor and slightly supported by the harmonic loading circuit. Thus, with the harmonic load higher than that of output capacitor, the saturated amplifier can operate with high efficiency. This characteristic enables the saturated PA to operate with broadband characteristic and high efficiency because the design is mainly focused on the fundamental matching problem while the harmonics can be easily kept out of a low efficiency region through the subsequent optimization of the matching circuit. The broadband saturated PA is implemented based on load/source-pull methodology. The broadband matching networks for the high efficiency are synthesized using the simplified real frequency technique. For the BW from 1.3 to 2.7 GHz (70% fractional BW), the measured output power, drain efficiency, and power-added efficiency (PAE) performances are between 39.8-42.0 dBm, 55.8-69.7%, and 51.2-65.3%, respectively. The multimode/multiband ET transmitter with the designed broadband saturated PA is demonstrated at 1.8425-GHz long-term evolution (LTE), 2.14-GHz wideband code division multiple access (WCDMA), and 2.6-GHz mobile world wide interoperability for microwave access (m-WiMAX) applications. This transmitter delivers a PAE of 32.16, 37.24, and 28.75% for LTE, WCDMA, and m-WiMAX applications.
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