A 50 W unsymmetrical GaN Doherty amplifier for LTE applications

In this contribution the design of a high efficiency unsymmetrical Doherty power amplifier (PAs) will be reported. The Doherty PA was designed to achieve high average efficiency for digitally modulated signals with high peak to average power ratio (PAR) used in third (3G) and fourth (4G) generation systems. To achieve constant efficiency up to 6 dB output power back-off (OPBO), a combined design technique of an uneven power divider and the use of unsymmetrical devices were employed. For demonstration, a 50 W Doherty PA was realized to operate at 2.5 GHz. A drain efficiency of 54 % (48 % power added efficiency (PAE)) was measured at the maximum output power of 47 dBm. The efficiency remains constant up to 6 dB output power back-off (OPBO). Moreover, the Doherty PA was linearized using digital predistortion (DPD) in order to achieve an Adjacent Channel Leakage Ratio (ACLR) of −46 dBc (−35 dBc before linearization) for a 10 MHz Universal Mobile Telecommunication System-Long Term Evolution (UMTS-LTE) signal with a PAR of 8.5 dB at an average output power of 39 dBm and 43 % PAE.

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