Design and Analysis of Fourth Order ZVS Output Filter for Three-Level Buck Envelope Tracking Power Supply

With the increased data speeds, the bandwidth requirements of communication systems are getting higher and higher, so are the losses associated with the radio frequency (RF) transmitters in base stations. Envelope Tracking (ET) is a power supply modulation technique that improves the efficiency of the lossy linear power amplifier of the transmitter by adjusting the voltage magnitude according to the peak of the signal that is being amplified. This paper presents detailed guidelines to design `zero voltage switching (ZVS) filters' for the multi-phase buck converters in bandlimited ET applications. The results of the proposed filter while tracking a 4G LTE envelope signal are compared with that of the standard Legendre Papoulis filter. The proposed filter design achieves better tracking speed, ZVS turn-on, and maintains current balancing among phases in the multi-phase buck converter. The converter with the proposed filter attains a peak efficiency of 97.5% and efficiencies above 90% for most of the operating range.