Compact mm-Wave Ultra-Wideband and Low-Noise Phase Alternately Distributed Quasi-Circulators

Abstract

This article presents ultra-wideband and low-noise distributed active quasi-circulators (QCs) fabricated using a 28-nm CMOS process. The proposed active QCs use a differ- ential two-stage distributed amplifier (DA) design, where the electrical length of the input and output transmission lines is 90 ◦ at 28 GHz. For the ultra-wideband distributed active QC (UWQC), the differential outputs of the amplifier in the second stage are cross-connected to the differential outputs of the amplifier in the first stage, resulting in ultra-wideband isolation regardless of the frequency. In addition, an interstage inductor is inserted in the amplifiers to maintain the frequency response of the input and output transmission lines identically. For the low-noise distributed active QC (LNQC), the resistive termination at the input transmission line of DA is eliminated by using input-matched amplifiers, resulting in a low antenna (ANT) -to-receiver (RX) noise figure (NF). In addition, the LNQC with the input-matched amplifiers allows a 3-dB higher trans- mitter (TX)-to-ANT gain compared to conventional distributed QC. Moreover, the transistor size and bias condition of the input-matched amplifiers can be selected to achieve low noise and high power handling capability of the QC within a given tradeoff. The measured results demonstrate that the UWQC achieves 20.5−35.5-GHz wideband operating bandwidth with TX-to-ANT gain of 4.5 dB, ANT-to-RX insertion loss of 3.6 dB, and >21-dB TX-to-RX isolation,