Enhancements of the multiple input buck converter used for Envelope Tracking applications by improved output filter design and multiphase operation

Increasing the efficiency of Radio Frequency Power Amplifiers has growth in importance due to the widespread use of wireless communications. Efficiency enhancement techniques such as Envelope Tracking and Envelope Elimination and Restoration use DC/DC converters to track the envelope of the signals being transmitted. These envelopes often have very high bandwidth and slew rate, challenging the design of fast and efficient tracking converters. Furthermore, traditional second order output filter design techniques applied to tracking converters lead to very high switching frequencies and thus low efficiencies. This paper analyzes the use of higher order filters to improve the dynamic response of tracking converters without increasing the switching frequency, thus maintaining high efficiency operation. This approach can be combined with a multiphase architecture to further increase the achievable bandwidth. Experimental results that demonstrate the effectiveness of the proposed approach are shown using a 2-phase multiple-input buck converter operating in open loop with a fourth order Bessel output filter.