A 24-dBm Tri-Stacked House-of-Cards Doherty Polar Transmitter for NB-IoT with Digital PLL Phase Modulator

This paper presents a digital polar transmitter (DPTX) for narrow-band (NB)-IoT UE applications. It features a 3-fold stacking of House-of-Cards-based voltage-mode Doherty PA and an embedded low-spur fractional-N digital PLL. Realized in $40-\mathrm{nm}$ CMOS, the DPTX prototype covers the 800 MHz-to-1.5 GHz band. It delivers more than 23.9 dBm of peak power and a peak system efficiency of 21.7 % at 1 GHz. The DPTX demonstrates $\mathbf{-42. 1} \mathrm{dB}$ EVM for a 10-MS/s 64-PSK signal. Using a simple memory-less digital pre-distortion, it achieves $\mathbf{-30. 4} \mathbf{d B}$ EVM for a 5 MHz single-carrier 64-QAM signal.