Improved efficiency in outphasing power amplifier by mixing outphasing and amplitude modulation

Outphasing amplifier using input signals that are both amplitude and differential phase modulated (mixed mode) has demonstrated higher efficient amplification than pure outphasing or amplitude modulation alone. An algorithm to convert the input signal to the mixed mode modulation was introduced. With LTE signal having 7.5 dB of Peak-to-Average ratio, the mixed mode modulation improved the efficiency of the amplifier as much as 15%. At the best condition, we achieved 77 % of output stage drain efficiency with the ACPR of 27dBc at 40 dBm of average output power before DPD correction. The mixed mode modulation also made it possible to configure a multistage outphasing amplifier with a total gain of 20 dB and 67% of overall efficiency. The paper explains the principle of operation, test bench configuration and actual data obtained.