Active Load-Modulated Devices: A General PA Network Solution Identifying Highly Efficient Linearizer Systems

We present a general analytical solution for the active input impedances of a given
$N$
-port impedance network as a function of the loading of its ports by either active or passive devices. To demonstrate the simplicity and ease of use of our approach, we derive the input impedance equations of a conventional balanced power amplifier (BPA) and the load-modulated balanced amplifier (LMBA) and the effects of mismatching the output load. We next focus on the properties of the hybrid coupler and present a general heuristic of categorization, as well as the identification of a missing topology. This missing topology is what we refer to as the load-modulated linearizer (LML), which utilizes active load-modulation to absorb individual out-of-band (OOB) amplitude to amplitude (AM/AM) intermodulation distortion (IMD) components at the output of a power amplifier (PA). When properly designed, the LML requires only slightly more additional power than the IMD power it absorbs, making it very efficient. It retains the power conservation properties of the LMBA and achieves better linearization than an equivalent digital predistortion (DPD) system, at a very low power and complexity penalty. As the LML operates at the output of the nonlinear PA, it can independently target individual IMD tones without affecting the rest.