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This paper presents a dual-band envelope tracking power amplifier (ET PA) capable of amplif y ing concurrent dual band modulated signals using a t y pical single-band envelope am plifier. The dual-band ET PA succeeded to concurrentl y amplif y widel y spaced dual-band modulated signals with balanced and imbalanced output powers in each band. The dual-band ET PA was linearized using dual-band Volterra based digital pre distortion that accounted for the drain suppl y modulation. When driven with a dual-band signal formed of WCDMA and 5 MHz LTE signals at 780 MHz and 880 MHz respectivel y , the ET PA achieved an average output power and drain efficienc y of better than 39 dBm and 45% with an adjacent channel power ratio of better than -47 dBc for both bands.Index Terms-Concurrent dual-band transmission, envelope tracking, GaN, RF Power amplifiers. I. INTRODUC TIONModern wireless communication networks aim to employ adaptive spectrum management which demands radio fre quency (RF) transmitters and power amplifiers (PAs) capable of operating over multiple bands and supporting multiple standards. Moreover, modern wireless standards result in sig nals with high peak-to-average power ratios (PAPR) in order to maximize spectral efficiency and data throughput. Future transmitters and PAs will be required to be highly power efficient and linear while supporting multiple standards and frequency bands. For example, in the next generation wireless communication systems for long term evolution advanced (LTE-A), carrier aggregation techniques needs to be adopted to meet the demanding high data rate. This means PAs will need to amplify concurrent multi-band signals under different scenarios of output power and frequency spacings.Power efficiency enhancement techniques such as Doherty [1] and envelope tracking (ET) [2], [3] have been successfully applied to enhance the power efficiency of PAs driven with single-band modulated signals. While several recent publi cations have demonstrated operation of Doherty amplifiers under concurrent dual-band signals, concurrent dual-band (or multi-band) operation of ET PAs have not been investigated extensively. The limited speed of the envelope amplifier used to modulate the drain supply of the PA (refer to Fig. 1) has limited the application of ET technique for wideband and multi-band signals. Recently, a few attempts to implement dual-band ET PAs have been published [4]-[6], however, these publications are limited to measurements under single-tone and/or two-tone excitations.In this paper, we present amplification of a concurrent dual band modulated signal using a 45 W gallium nitride (GaN) ET PA. This paper is organized as follows. The concurrent dual band operation of an ET PA is presented in section II. Section III covers envelope shaping for the dual-band ET PA. Finally, the measurement results of the dual-band ET PA are presented in section IV. Q Modified A(I)t � I '--Or iginaIA(I) � _ -Shaped A(I) > ___ ---, 1 Linear and High Efficiency PA Fig. 1. Simplified envelope tracking architect...

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