A 33.5–39 GHz 5-bit variable gain LNA with 4 dB NF and low phase shift

Abstract

A variable gain low noise amplifier (LNA) with low phase shift for a 38 GHz communication system of 5G application is presented in this paper. This design includes a 3-stage LNA and a 5-bit gain-controlled unit. Gm-boosting technique based on transformer is employed in the first stage to realize a good tradeoff between input match and noise figure (NF). Neutralized capacitors are utilized to improve the gain. The increased noise imported by neutralized capacitors is reduced by positive transformers. Gain-controlled unit is based on switched bridge-T/Pi attenuation structures. In order to reduce the phase shift, compensation capacitors are added in shunt branches of bridge-T/Pi attenuation units. The proposed design is fabricated in 65 nm CMOS process. It realizes a gain of 21 dB, NF of 4 dB and input 1dB compression point of -22 dBm at the maximum gain state. It has a gain-controlled range of 31 dB with 1 dB step. The root mean square (RMS) gain error is <;0.8 dB and RMS phase shift is <;5.4° from 33.5 GHz to 39 GHz. The chip size is 1.5 mm × 0.7 mm and power consumption is 28 mW with 1 V supply.