Ka-Band SiGe HBT Low Phase Imbalance Differential 3-Bit Variable Gain LNA

This letter presents the design and implementation of a differential Ka-band variable gain low noise amplifier (VG-LNA) with low insertion phase imbalance. The VG-LNA is based on a 0.12 mum SiGe heterojunction bipolar transistor process, and the gain variation is achieved using bias current steering. The measured VG-LNA gain at 32-34 GHz is 9-20 dB with eight different linear-in-magnitude gain states, and with a noise figure of 3.4-4.3 dB. The measured rms phase imbalance is < 2.5deg at 26-40 GHz for all gain states and this is achieved using a novel compensating resistor in the bias network. The VG-LNA consumes 33 mW (13.5 mA, 2.5 V) and the input 1-dB gain compression point is -27 dBm. The chip size is 0.13 mm² without pads.