60-GHz low-noise VGA and interpolation-based gain cell in a 40-nm CMOS technology

This paper presents the design and measurement of an interpolation-based low noise and variable gain cell (IBA-cell) in the 60-GHz band, using a 40-nm CMOS technology. The interpolation-based gain cell is designed for an innovative analog beamforming front end, where the array pattern is not only controlled in the phase domain, but also wins the flexibility in the magnitude domain. The circuit specifications are first derived for the application at 60 GHz. Techniques to combine low noise figure (NF) with variable gain tuning are presented focusing on the NF and linearity (IIP₃) on the example of a 60-GHz low noise amplifier and variable gain amplifier. Subsequently, the design and measurement of the whole gain cell (IBA-cell) integrated into a single chip are reported with the technique of a cross-coupled feedback loop to reduce the phase variations over the gain tuning states and enhance the variations of IIP₃. The IBA-cell achieves 15.8-dB maximum gain and 6.5-dB NF at 57 GHz with the gain tuning range from -2 to 15.8 dB and IIP₃ varying from -11.3 to -16 dBm over the gain control range. The IBA-cell consumes a dc power of maximum 54 mA from 1.1 V.