Experimental investigation of signal time misalignment in dynamic load modulation amplifiers

The effect of time misalignment between the RF input and tuneable matching network (TMN) control signal in load-modulated PAs is experimentally investigated. A reactively load-modulated low-power GaAs E-pHEMT amplifier is used, operating at 2.3GHz with 20dBm peak output power. The amplifier is first characterised under CW operation and the appropriate functions for maximising PAE are extracted. These are then used to enhance the efficiency of the amplifier under modulated signals. Using multi-tone, as well as, 1.4 and 3MHz LTE signals, the effects of time misalignment between the two paths on output power; PAE and spectral regrowth are explored. As expected, proper alignment of the signals is crucial, but it is shown especially important for minimising ACPR asymmetry, similar to supply modulation architectures. This highlights the underlying tradeoff between synchronisation accuracy and linearisation effort requirement.