A multimode/multiband envelope tracking transmitter with broadband saturated amplifier
A multimode/multiband envelope tracking (ET) transmitter consisting of a hybrid switching amplifier (HSA) and a broadband saturated power amplifier (PA) is developed across 1.3 to 2.7 GHz. For the various standard signals with different bandwidth and peak-to-average power ratio, the HAS efficiently provides a supply signal 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 harmonic component, 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 the 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. The broadband saturated PA is implemented based on load/source-pull methodology. Broadband matching networks for the high efficiency are synthesized by simplified real frequency technique. For the bandwidth from 1.3 to 2.7 GHz (70% fractional bandwidth), 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 ET transmitter is demonstrated at 1.8425-GHz long-term evolution (LTE), 2.14-GHz wideband code division multiple access (WCDMA), and 2.6-GHz mobile worldwide interoperability for microwave access (m-WiMAX) applications. It delivers the PAE of 32.16, 37.24, and 28.75% for LTE, WCDMA, and m-WiMAX applications, which are improved by 3.1, 4.2, and 1.7%, respectively.