A 39W Fully Digital Wideband Inverted Doherty Transmitter

A high-power fully-digital Doherty transmitter (DDTX) is proposed. It features two segmented LDMOS output switch banks implemented in a custom VT -down-shifted LDMOS technology. A 40 nm CMOS controller digitally activates the individual LDMOS gate segments of the output stage at RF speed. An inverted Doherty power combiner is proposed that features non-short circuited 2nd harmonic conditions for the main and peak switch banks to boost the RF bandwidth. To guarantee smooth output power and efficiency vs. frequency, a 2nd harmonic trap is introduced in the power combiner, yielding an RF bandwidth of > 400 MHz . The realized demonstrator can achieve over 39 W peak output power. Its highest drain and system efficiencies, respectively 60% and 57%, were found at 34.2 W of output power, while in power back-off its peak drain and system efficiencies are 52% and 48% respectively. Over a 25 dB output range, the system efficiency is within 4 percent points of the drain efficiency.