A W-Band Bidirectional RF Front-End in 0.1-μm GaAs pHEMT Technology

This article presents a bidirectional radio frequency (RF) front-end with reduced local oscillator (LO) power requirement, including a bidirectional star mixer and a frequency multiplier-by-six chain. In the W-band, it is difficult to generate LO signals with an output power of more than 18 dBm based on an advanced <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.1~\mu $</tex-math> </inline-formula>m GaAs process, resulting in a low conversion gain (CG) for traditional passive bidirectional mixers. In this article, a star mixer core with adaptive dc bias is proposed, which greatly reduces the LO power requirement of the passive mixer. In order to obtain better harmonic suppression characteristics and sufficient LO output power over W-band, a Marchand-Balun-based doubler core for second-harmonic power enhancement with a quadrature power synthesis tripler core employing power-enhancing microstrip transmission lines (MTLs) to maximize third-harmonic efficiency was proposed. To ensure that the LO chain covers the full W-band, negative feedback and multistage peak gain staggering technology are used to expand the bandwidth. The total chip area is 5.56×1.5mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>, and the current is 140 mA under 3.3 V power supply. The frequency multiplier-by-six chain achieves a measured peak output power of 12 dBm at 90 GHz, and its 3-dB power bandwidth covers 75-110 GHz. The modified bidirectional star mixer achieves a measured peak CG of –9.5 dB (75-108 GHz) in downconversion mode and −7.5 dB (76-102 GHz) in upconversion mode, making it a promising candidate for W-band vector network analyzers (VNAs) extenders and up/down frequency converters.