An Efficient Broadband Reconfigurable Power Amplifier Using Active Load Modulation

A novel power amplifier (PA) architecture, the Load Modulated Balanced PA (LMBA), is presented. The LMBA is able to modulate the impedance seen by a pair of RF power transistors in a quadrature balanced configuration, by varying the amplitude and phase of an external control signal. This enables power and efficiency to be optimized dynamically at specific power backoff levels and frequencies. Unlike the Doherty PA, the load seen by the active devices can be modulated upwards or downwards, both resistively and reactively, with minimal loss of power combination efficiency. The LMBA is presented as a potentially disruptive technique which enables any specific amplifier characteristic to be controlled dynamically over wide signal amplitude and frequency ranges.