A Ka-Band Ultrawideband Variable Gain Amplifier With Low Phase Variation for 5G Communications

This letter presents a 23–42.5-GHz Ka-band ultrawideband (UWB) variable gain amplifier (VGA) for 5G applications, realized in TSMC 28-nm bulk CMOS process. The proposed VGA adopts a three-level transistor stack structure, and additional inductors are added to compensate for pole roll-off at high frequencies. A cross-connected gain control structure is used to reduce phase variation by minimizing the impedance variation caused by gain tuning. The proposed UWB VGA has a measured peak gain of 9.6 dB at 26 GHz with a 3-dB bandwidth of 23–42.5 GHz. The measured gain tuning range is 16 dB and the root-mean-square (rms) phase variation is smaller than 2°. The UWB VGA draws 15-mA current from 1.8-V power supply with a core size of 0.21 mm2.