The Role of Impedance Transparency of Non-Reciprocal 90° Phase Shifters in the Evolution of Electronic Circulators

This paper presents an impedance transparency property for 90°/-90° non-reciprocal phase shifter (NRPS) circuits which is different from the impedance transformation property of other NRPS-based gyrators such as 0°/180° and 60°/120°. A linear analysis of electronic circulators is proposed and reveals an electrical-balance virtual ground at the isolated port for the respective excitation. Moreover, the effect of the 90°/-90° NRPS transparency in electronic circulators is shown to enable better isolation of the NRPS circuit from the TX voltage and hence higher power handling. To validate the transparency observation, a 90°/-90° 4-path linear periodically time-variant (LPTV) NRPS with shunt parasitic losses compensation was designed in TSMC’s 65nm CMOS. Measurements show that the theoretical transparency prediction can deviate from the ideal lossless model by up to twice the series switch ON resistance.