A Reconfigurable Modulator for Digital Outphasing Transmitters

This paper presents the next development stage of baseband-transparent modulators for digital microwave amplifiers. A modulator, used for encoding the baseband signal into a bitstream suitable for digital outphasing amplification, is presented. Once implemented, it is flexible enough to accommodate a variety of amplifier circuits only by exchanging information stored in a table in memory. This is the first time a complete transmitter chain based on digital outphasing is evaluated with wideband modulated baseband signals. Without an external DPD, measurements of the overall system shows adjacent channel leakage ratios of 57 dB for a 5 MHz wide signal, easily surpassing the 3GPP base-station specification of 45 dB, and reach 44 dB for 20 MHz wide signals at a 900 MHz carrier.