20.10 A 68.1-to-96.4GHz variable-gain low-noise amplifier in 28nm CMOS

To allow a maximum theoretical data-rate of 25Gb/s over a 1km distance using 64QAM, an E-Band system should feature a 20dBm-output-power TX and an RX with 10dB maximum noise figure (NF) over two bands of 5GHz from 71 to 76GHz and 81 to 86GHz [1]. To minimize the NF of a fully integrated RX front-end and to compensate for the low conversion gain and high noise of the following mixer, a broadband LNA with a gain in excess of 20dB showing a flat NF over more than a 15GHz bandwidth is required. Moreover, a variable-gain LNA design would be beneficial to accommodate environmental variability (e.g. atmospherics condition, rain, etc.). Prior works on CMOS car-radar transceivers have shown the feasibility of low-noise amplifiers at 79GHz. However, the bandwidth of these systems is limited to about 10GHz [2,3], which is not enough. This paper presents a 28nm-bulk-CMOS LNA for E-Band applications that employs transformer-based 4th-order inter-stage matching networks to achieve a 29.6dB gain over a 28.3GHz -3dB bandwidth (BW-3dB), resulting in a GBW product in excess of 0.8THz. The gain is variable from 29.6 to 18dB allowing an input-referred 1dB compression point (ICP1dB) that ranges from -28.1dBm at the highest gain to -12.3dBm at the lowest gain. The measured minimum in-band NF is 6.4dB, and the NF varies by less than 2dB from 68.1 to 90GHz. The LNA covers the two bands from 71 to 76GHz and from 81 to 86GHz with an almost uniform gain and NF and with a wide margin over desired specifications to compensate for PVT variations and model inaccuracy.