Switching Mode Power Amplifier Concept Combining Multi-Level and Pulse-Width Modulation

This paper presents system simulation results of a digital RF transmitter chain concept using a digital pulse-width and pulse-position modulator (DPWPM) and a multi-level switching mode power amplifier (SMPA). The effect of the limited output bandwidth of a SMPA on the signal quality is discussed, which leads to deteriorating values for the adjacent channel leakage ratio (ACLR) and the code efficiency eta(C). Therefore a new concept by using a 4-level SMPA with four output levels instead of a conventional one with only two output levels is proposed. By using the four-level SMPA (4L-SMPA) with a 256-QAM signal at a symbol rate of 31.25 MBaud on a 2 GHz carrier, the ACLR can be improved from -38 dB to -44 dB in the adjacent channel (ACLR1) and from -36 dB to -45 dB in the alternate channel (ACLR2). Especially the code efficiency can be improved from 63 % to 85 %.