Optimized peaking amplifier of Doherty amplifier using an inductive input second harmonic load

An optimized peaking amplifier for proper operation of a Doherty amplifier is investigated. The peaking amplifier operates at a class-C bias and has a lower maximum output power than that of the carrier amplifier. Because of the low output power of the peaking amplifier, the load modulation of the Doherty network cannot be properly carried out. To solve the problem, an inductive second harmonic load is employed at the input. The conduction angle of the input voltage waveform is enlarged due to the out-of-phased second harmonic, restoring the decreased conduction angle and output power. In addition, the peaking amplifier turns on at a higher input power and the first peak efficiency of the Doherty amplifier is enhanced. Based on the concept of the inductive input harmonic load of the peaking amplifier, a Doherty amplifier is implemented with the GaN pHEMT MMIC process at 2.14 GHz and demonstrated the expected good performance.