Signal-Flow-Based Analysis and Design of LMBA

The conventional LMBA theory is derived based on the Z-matrix of quadrature coupler. However, it neither rigorously explains the wideband nature of LMBA nor fully unleashes its design space with a systematic methodology. By revisiting LMBA using signal-flow approach in S-matrix domain, a generalized wideband LMBA theory is established, taking into account the frequency dependence of all components. Moreover, from the signal-flow analysis of LMBA, a frequency-agnostic phase-alignment condition is identified, which enables not only the independent design of balanced amplifier (BA) and control amplifier (CA) but also the use of arbitrary complex matching circuits. This new design methodology addresses the fundamental challenges of carrier-peaking co-design imposed on the active load-modulation PAs, leading to unprecedent design space and nearly unlimited bandwidth that are experimentally validated with developed prototypes.