Experimental Validation of Class F Waveform Engineering in Class C Biasing Condition

In this paper, the experimental verification of suitable input harmonic injection to achieve class F operating conditions in class bfC (under pinch-off) biased active devices is discussed. In detail, it is demonstrated that by generating a third harmonic component V_g, 3 with a proper phase relationship with respect to the fundamental one V_g, 1, it is possible to change the phase of the resulting output harmonic components, and in particular of the third one I_D, 3, thus generating the proper squaring of the output voltage. Experimental results at device level have shown an improvement in terms of output power and efficiency from 2.24W to 3.00W and from 72.2% to 79.3%, respectively. The proposed approach could play a key role in the maximization of the achievable efficiency of Doherty power amplifiers, where the auxiliary branch needs to be biased in class C for a exploitation of the architecture.