A 210-GHz Magnetless Nonreciprocal Isolator in 130-nm SiGe BiCMOS Based on Resistor-Free Unidirectional Ring Resonators

Nonreciprocal components such as circulators, isolators, and gyrators play vital roles in modern communication systems. However, all of them are limited to 0.1 terahertz (THz) due to their poor performances in terms of linearity, loss, and noise at high frequency, making them not amenable for the potential sub-THz/THz operation. In this letter, a 210-GHz nonreciprocal isolator based on the resistor-free unidirectional ring resonators is implemented in a 130-nm SiGe BiCMOS process ( f
_T
/f
_max
= 300/500 GHz). Thanks to the proposed resistor-free ring resonators, the isolator achieves 1.40-dB loss, 6.7-dB noise figure (NF)/unit, 21.2-dB isolation, and superior linearity. Even compared with the nonreciprocal components operating at a much lower frequency, this structure also exhibits a good performance.