A 60-GHz Phase-Invariant Variable Gain LNA With T/R Switch and Gain Interpolation Techniques in 65-nm CMOS

This letter presents a three-stage 60-GHz phase-invariant variable gain low-noise amplifier (VG-LNA) with accurate gain tuning step and large gain tuning range. A single-ended cascode amplifier is adopted as the first stage to integrate the transmit/receive (T/R) switch and achieve wideband input matching. Besides, with gain interpolation techniques, by combining three different gain cells, a stacked gain-boosting variable gain amplifier is proposed to realize wide-range and accurate dB-linear gain tuning functions simultaneously, showing the merits of low layout and logic control complexity. Fabricated in a 65-nm CMOS process, the VG-LNA consumes 38.4 mW with a core area of 0.08 mm $^{2}$ . With measurements, the proposed VG-LNA achieves a peak gain of 20 dB with a 3-dB bandwidth over 53–66.5 GHz and a minimum noise figure (NF) of 6.3 dB. Across a 17.5-dB gain tuning range, it realizes an average gain resolution of 0.47 dB, with an rms phase and amplitude error of less than 2.6 $^{\circ}$ and 0.14 dB, respectively.