Digital control for power supply of a transmitter with variable reference

RF power amplifiers can save much energy if they are supplied with a variable voltage as described in the state of the art. The design of the power supply of these amplifiers is challenging since many requirements have to be accomplished: very low output voltage ripple; wide output voltage variation at kHz frequencies; fast load current steps; etc. A typical solution is the use of a multiphase dc-dc converter based on the buck topology. In this paper, we propose the use of digital control for these power supplies. The main advantage is that current loops are removed. The design of this control circuit and main trade-offs are discussed. The results obtained from a 240 W prototype show the advantages and the limitations of this proposal.