HBT Doherty amplifier using ballast resistor control and arbitrary termination impedance power divider

In this paper, a new HBT Doherty amplifier is designed with arbitrary termination impedance power divider and ballast resistor control method to enhance the dynamic gain flatness. By using the arbitrary termination impedance power divider, circuit size of the proposed HBT Doherty amplifier has been reduced considerably. Also, due to the fact that the gain of a peaking amplifier usually deteriorates the dynamic gain flatness of a Doherty amplifier, we proposed a novel technique of controlling ballast resistors according to the bias condition of a peaking amplifier. By tuning the ballast resistors and bias of peaking amplifier, we improved gain flatness of a Doherty amplifier maintaining permissible power added efficiency (PAE) at the same time. The proposed Doherty amplifier is designed at 1.9GHz with knowledge-on HBT process. Obtained the maximum power and the power gain through the simulation are 29dBm and 14.4dB, respectively. The PAE at the maximum output power was 64% with 3.3V supply voltage and achieved more than 60% over 5dB range.