Jitter enhanced full digital RF transmitter and PWM RFPA for 5G broadband communications

RFPA (radio frequency power amplifier) based on PWM (pulse width modulation) can be perfect linear without using complicated DPD (digital pre-distortion) hardware. However, PWM RFPA need ultra-high PWM time resolution (less than 10 ps) for wide-band 5G, which is limited by CMOS technologies (can reach 40 ps). It limits the complexity of modulation so that PWM RFPA cannot be really commercialized so far in wideband radio/mobile technologies. This paper presents our contribution by introducing jitter into PWM. For the first time, we demonstrate that jitter can improve the PWM time resolution equivalently reaching less than 2.6 ps. Hence PWM RFPA can be used in 5G supporting 256QAM OFDM modulation based on currently available digital CMOS technologies. We demonstrate that jitter can refine the inherent resolution of PWM hardware circuit modulation. The jitter makes the MCS (modulation and coding scheme) of the bandwidth OFDM system improved from 16QAM to 256QAM in the band n28 of 3GPP 38.101. We also verified that 5G 256QAM OFDM modulation is achievable in the 3GPP band n20, Softbank band28 and NTT Docomo band28. The RMS EVM (root mean square error vector magnitude) of 256QAM OFDM modulation is about −44 dB.