A Fully Integrated Direct Conversion Transmitter with I/Q-Isolated CMOS PA for Sub-6 GHz 5G NR

This work presents a direct conversion transmitter (DCT) for 5G new radio (NR) that eliminates the RF driver by directly feeding a single stage cascode PA through a baseband buffer amplifier and passive up-conversion mixer. The baseband interface uses Class-AB buffers to hold the output capacitor voltage, enabling accurate sampling at the PA input. A mixer switch is selected for minimal on-resistance variation over the required baseband swing. The PA is designed with separate I and Q voltage inputs and a current summing structure. The PA operates at 2.5 V; other blocks use 1.2 V. Post-layout two-tone simulations at 5 GHz indicate 21 dBm output saturation power and −36.1 dBc of IMD3 at 9 dB PBO power while removing the driver to inter stage matching network of a two-stage design. The results validate a compact, driverless architecture for integrated transmitters.