Analysis of Phase Offset Impact on Millimeter-wave Broadband Doherty Amplifier MMIC

This paper investigates phase offset impact on millimeter-wave broadband Doherty amplifier MMIC based on reduced-alpha DPA topology. The analysis results clarify the limited amplitude and phase variation to realize the desired performances of the Doherty amplifier. On the E-band 0.1 mu m GaAs pHEMT Doherty amplifier, the amplitude and the phase variations at the amplifier outputs must be kept below 1 dB and 15 degrees to achieve more than 16% power conversion efficiency, respectively. The results also indicate that the phase variation on the main amplifier side has a larger impact on the overall performances than on the peak amplifier side. The same condition mentioned above applies to the amplitude and the phase variations on the combining and dividing circuits. Finally, the paper indicates the design points of the millimeter-wave Doherty power amplifier.