The analysis and design of an RF-input sequential load modulated balanced power amplifier (SLMBA) are presented in this paper. Unlike the existing LMBAs, in this new configuration, an over-driven class-B amplifier is used as the carrier amplifier while the balanced PA pair is biased in class-C mode to serve as the peaking amplifier. It is illustrated that the sequential operation greatly extends the high efficiency power range and enables the proposed SLMBA to achieve high backoff efficiency across a wide bandwidth. An RF-input SLMBA at 3.05-3.55 GHz band using commercial GaN transistors is designed and implemented to validate the proposed architecture. The fabricated SLMBA attains a measured 9.5-10.3 dB gain and 42.3-43.7 dBm saturated power. Drain efficiency of 50.9-64.9/46.8-60.7/43.2-51.4% is achieved at 6/8/10 dB output power back-off within the designed bandwidth. By changing the bias condition of the carrier device, higher than 49.1% drain efficiency can be obtained within 12.8 dB output power range at 3.3 GHz. When driven by a 40 MHz OFDM signal with 8 dB peak to average power ratio (PAPR), the proposed SLMBA achieves adjacent channel leakage ratio (ACLR) better than-25 dBc with an average efficiency of 63.2% without digital predistortion (DPD). When excited by a 10-carrier 200 MHz OFDM signal with 10 dB PAPR, the average efficiency can reach 48.2% and-43.9 dBc ACLR can be obtained after DPD.
This paper presents the theory and design methodology of broadband RF-input continuous mode load modulated balanced power amplifier (CM-LMBA) by introducing the continuous mode output matching networks in the LMBA architecture. It is illustrated that the continuous mode impedance condition can be achieved by properly adjusting the phase difference between the different PA branches in the proposed CM-LMBA during the entire load modulation process. An RF-input CM-LMBA with 1.45-2.45 GHz bandwidth using commercial GaN transistors is designed and implemented to validate the proposed architecture. The fabricated CM-LMBA attains a measured 11.2-13.4 dB gain and around 40 Watts saturated power. Power added efficiency (PAE) of 46.4-56.5% and 43.2-50.3% is achieved at 6 dB and 8 dB output power back-off throughout the designed band. When driven by a 100 MHz OFDM signal with 8 dB peak to average power ratio (PAPR), the proposed CM-LMBA achieves better than -46 dBc adjacent channel leakage ratio (ACLR) and higher than 45% average PAE after digital pre-distortion at 1.8 GHz and 2.1 GHz.
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