A Ka-Band Phase-Compensated Variable-Gain CMOS Low-Noise Amplifier

A variable-gain low-noise amplifier implemented in a 65-nm CMOS process for a beamforming front-end chip is presented, of which the phase remains constant during gain variations. The phase compensation characteristic is achieved by introducing a shunt PMOS and a parallel resistor at the differential outputs of common-gate (CG) transistors. This allows the gain to be controlled without phase variation by adjustment of the combined gate voltage of the CG transistor and the shunt PMOS at the same time. The proposed device shows a gain of 20.8 dB and a noise figure of 3.71 dB at 31 GHz. It shows a root-mean-square phase error of less than 3° over the gain control range of 10.6 dB at 30-34.5 GHz.

I. Introduction

The rising demand for various millimeter-wave (mm-wave) frequency band systems including 5G comm- unication, automotive radar, and imaging radar has led to active research of mm-wave transceivers. However, there is a high path loss problem at the mm-wave bands. To overcome this problem, a phased-array technique that uses an antenna array for high antenna gain has been considered.