Fully Integrated 10-GHz Active Circulator and Quasi-Circulator Using Bridged-T Networks in Standard CMOS

A three-port active circulator and an active quasi-circulator (QC) based on bridged-T networks (BTNs) are designed and fabricated in a standard 0.18-mu m CMOS technology. The BTN provides a notch frequency response, and therefore, the circulator is practical by connecting three BTNs in a ring-type configuration. With a power consumption of 18.2 mW, the circulator achieves 6.1 similar to 8-dB insertion loss, better than 25-dB isolation and 18.3-dB transmission ratio from 8.4 to 11.1 GHz. Furthermore, the QC based on one BTN topology can also be obtained by adding an external amplifier. With a power consumption of 18.6 mW, it achieves 7/-2-dB forward transmission gain, better than 17.3-dB isolation, and better than 15.3-dB transmission ratio at 9.9 GHz. The presented designs feature excellent performances in high isolation and transmission ratio compared with other CMOS active circulators or QCs. To the best of our knowledge, the designs are the first demonstration of three-port circulator/QC designs based on the BTN topology, and the design concept is also applicable to an n-port circulator design.