A 22-to-37.8-GHz Low-Gain-Phase-Error Variable-Gain Amplifier With Impedance-Compensation Technique in 65-nm CMOS Process

This letter presents a wideband variable-gain amplifier (VGA) with an impedance-compensation technique for 5G new radio. To minimize the gain and phase errors of a millimeter-wave VGA in a wide frequency band, a parasitic-capacitance-compensation method based on varactors is proposed to alleviate the input impedance variation of a cross-coupled structure. To extend gain bandwidth and save chip area, compact transformers with various coupling coefficients are employed to design the input, interstage, and output impedance-matching networks. The VGA is demonstrated by using a 65-nm CMOS process. According to the measurement results, the circuit achieves a peak gain of 12 dB with a 3-dB gain bandwidth of 15.8 GHz. Its fractional bandwidth is up to 52.8%. The tested root-mean-square phase and gain errors of the proposed VGA are lower than 1.2° and 0.1 dB across 24–38 GHz, respectively.

I. Introduction

Phased-array systems can significantly improve the equivalent isotropic radiated power (EIRP) of transmitters (TXs) and signal-to-noise ratio (SNR) of receivers (RXs) to achieve large coverage in millimeter-wave (mm-wave) 5G frequency range 2 [1], [2], [3], as well as multiple gigahertz data throughput. To cope with in-band blockers, beam-tapering approaches are usually applied to suppress the sidelobes of radiation patterns of wireless systems [4]. Gain-control modules, such as variable-gain amplifiers (VGAs) and attenuators, are necessary to perform beam tapering in phased-array transceivers [5], [6]. However, mm-wave VGAs face several technical challenges in terms of limited gain tuning range and relatively high gain and phase errors, especially the ones with a large operating bandwidth.