A Buck Converter for 5G NR RF-PA with 400ns Rise- and Fall-Time and Spread Spectrum Switching

RF-PA for 5G NR requires power supply to adjust voltage within 590ns. A buck converter using phase compensation based on displacement current sensing is proposed to achieve robust damping ratio over process corners and operation condition variation. Furthermore, modulation is introduced in switching frequency to spread the spectrum of the switching noise. A pulse filtering latch forces the switching frequency to follow that of the triangular waveform. During a transition step, the switching frequency is raised shortly to improve controllability and reduce over- or under-shoots. Linear analysis of the simplified control loop and implementation details are presented. The prototype buck converter is designed with a 180nm mixed-signal CMOS process and consumes 0.8 mm² silicon area. The buck converter achieves rise- and fall-time less than 400 ns and a peak efficiency of 90.5% with a 470nH coil and a 220nF capacitor.