High-Efficient Three-Way Doherty Amplifier with Improved Linearity

– In this paper the operation behavior of three-way Doherty amplifier is analyzed, including the efficiency and linearity. Amplifier is designed in the configuration with two quarter-wave impedance transformers in the output combining circuit with LDMOSFETs in carrier and peaking amplifies. The signals for linearization (the fundamental signals’ second harmonics-IM2 and fourth-order nonlinear signals-IM4 at frequencies that are close to the second harmonics) are extracted at the output of peaking cells biased at various points. The Doherty amplifier is designed with the frequency diplexer at the outputs of the Doherty cells that separates the fundamental signals and signals for linearization. The diplexer includes harmonic control circuit (HCC) which in combination with the output matching of the second harmonics provides optimal impedance for IM2 and IM4 signals enabling their adequate power level, and an open circuit for the third harmonics. The linearization technique results in the suppression of the thirdand fifth order intermodulation products of Doherty amplifier.