Advanced Architecture of Doherty Amplifier

When the Doherty amplifier is designed based on the identical two amplifiers, the first peak-efficiency point is located at the fixed 6 dB back-off power. However, to get a higher efficiency for amplification of the highly modulated signal, the point should be located at a larger back-off point, or the efficiency can be even higher by increasing the number of the maximum efficiency points. These behaviors can be achieved from the N -way Doherty amplifier and the N -stage Doherty amplifier. The design methods and the problems for implementation of these amplifiers are discussed. It is also shown that the N -way Doherty amplifier can be used as a highly linear amplifier by tuning the multiple cells for accurate harmonic cancellation.