Design of a 2-18 GHz Differential Phase Invariant Low Noise Variable Gain Amplifier in 0.18-μm SiGe BiCMOS Technology

This paper presents a fully integrated differential ultra-wideband low noise variable gain amplifier (LNVGA) for 2-18 GHz applications in HHNEC 0.18-μm SiGe BiCMOS technology. To achieve the broadband response and in-band gain flatness, a resistive feedback loop and a mutual gain compensation technique are adopted in both amplification stages. In addition, a phase invariant method using opposite phase variations cancellation is proposed, analyzed, and implemented in the current-steering VGA blocks to miniaturize the phase shifts in all gain states. The proposed LNVGA exhibits 18-dB gain tuning range and <1dB gain flatness with 2-18 GHz operation bandwidth. The noise figure is 3.2 dB-4.7 dB in all gain states, and the phase variation across different gain states is <3° with a 0.15 mm² compact core area.