The weight of the on resistance in Doherty PAs

This contribution highlights how the active device on resistance (R_ON) can play a significant role in the achievable performances from a Doherty Power Amplifier (DPA). Benefits as well as limitations are stressed comparing two DPAs (DPA₁ and DPA₂) for X-band applications. Both of them have been realized in the same monolithic technology based on GaAs PHEMT 0.4um power process provided by Selex-SI. Moreover, the DPA₁ has been obtained following the classical design approach, i.e. assuming a constant and fixed swing for the main device output voltage. Conversely, the DPA₂ has been optimized accounting for the linear behavior of the device knee voltage, due to the effect of R_ON. From measures an output power at 1dB compression point of about 29dBm, with an associate power gain of 6.5dB, is registered. Finally, DPA₁ has shown an efficiency greater than 38% in 6dB of output power back-off, while an efficiency larger than 42% has been achieved with DPA₂ in the same output back-off range.