Monolithic Sub-Terahertz SPDT Switches With Low Insertion Loss and Enhanced Isolation

This paper presents two 130-180-GHz single-pole double-throw (SPDT) switches in 65-nm CMOS. A new topology using artificial resonator and auxiliary magnetically coupled-lines is introduced to alleviate the bulky and lossy transmission lines used in conventional SPDT designs. Besides its compact size, the coupled-lines based artificial resonator features lower loss as compared to the transmission lines. First, the small-signal equivalent circuit models of the shunt n-type field-effect-transistor switches and the resonator are developed and investigated. Second, the linearity analysis of the proposed switch is performed. Furthermore, the auxiliary coupled-lines are introduced to control the magnetic coupling strength between main coupled-lines of the artificial resonator, and improve the switch isolation performance. To validate the theoretical analysis, two switch prototypes are designed and fabricated in a 65-nm CMOS technology. It is verified experimentally that the isolation is improved by ~2 dB with almost zero compensation on switch insertion loss, by using auxiliary coupled-lines. The fabricated switch achieves operating frequency of 130-180 GHz, insertion loss of 3.3 dB, and isolation of 23.7 dB. To the authors' best knowledge, the circuit size of 0.0035 mm2is the smallest among SPDT switches with similar operating frequencies.