A 16.5-dBm D-Band Eight-Way Power Amplifier Utilizing Cascaded Transformers in 40-nm Bulk CMOS

We present a D-band eight-way power amplifier (PA), which achieves the saturated output power ( $P_{\mathrm {sat}}$ ) of 16.5 dBm in 40-nm bulk CMOS. The proposed D-band PA consists of four push-pull PA units with three stages, whose active device sizes are gradually tapered from the output to the input optimal power efficiency. A cascaded transformer-transformer (balun) structure was employed at the output of the PA unit to avoid self-resonance with an improved balun performance at the D-band. The power combiner/splitter is comprised of microstrip transmission lines (MSTLs) to combine the power of the four PA units in the current domain. The fabricated prototype has a chip size of 0.72 mm2 with a core size of 0.46-mm2 excluding pads. The measured PA achieved a power gain of 14.5 dB with the 3-dB gain bandwidth of 18 GHz (121–139 GHz), a peak PAE of 7.2%, and a saturated output power ( $P_{\mathrm {sat}}$ ) of 16.5 dBm, which demonstrates the highest output power among the recently reported D-band PAs in bulk CMOS.