15-40 GHz Broadband Variable Gain Amplifier with 24.5 dB Linear-in-Decibel Gain Control Range in SiGe BiCMOS

This paper presents a current steering variable gain amplifier (VGA) in SiGe BiCMOS with a gain control circuit and a current mirror with negative feedback to avoid thermal runaway. The gain control circuit exploits a current steering topology, whereas a true exponential relationship between the currents of the emitter-and base-driven transistor is locked by a current mirror for gain compensation of the VGA until the highest gain setting. The VGA achieves a maximum measured gain of 21.5 dB and maximum gain control range (GCR) of 24.5 dB at 27 GHz, with an operation bandwidth from 15 GHz to 40 GHz. Within the bandwidth and full GCR, the measured phase error is 12.7°, and lower phase errors can be achieved for lower GCR, e.g., 4.4° for GCR of 14 dB, depending on the applications. The chip is very compact and occupies only 0.1 mm². Thus, the proposed VGA can cover the entire millimetre-wave (mm-wave) 5G band and is suitable for integrating into phased-array systems due to its performance and compactness.