Pseudo-Linear Time-Invariant Magnetless Circulators Based on Differential Spatiotemporal Modulation of Resonant Junctions

TL;DR

This paper introduces a differential spatiotemporal modulation approach to create magnetless circulators that operate with linear time-invariant-like behavior, significantly improving performance metrics and reducing modulation complexity.

Contribution

The paper presents a novel differential architecture for magnetless circulators using spatiotemporal modulation, achieving IM product cancellation and enhanced performance over traditional single-ended designs.

Findings

All intermodulation products are canceled, mimicking LTI circuit behavior.

Significant improvements in insertion loss, bandwidth, and noise figure.

Reduced modulation parameter requirements in frequency and amplitude.

Abstract

In this paper, we present voltage- and current-mode differential magnetless non-reciprocal devices obtained by pairing two single-ended (SE) circulators, each consisting of three first-order bandpass or bandstop LC filters, connected in either a wye or a delta topology. The resonant poles of each SE circulator are modulated in time with 120 deg phase-shifted periodic signals, resulting in synthetic angular-momentum biasing achieved through spatiotemporal modulation (STM). We tailor the two SE circulators to exhibit a constant 180 deg phase difference between their STM biases. Unlike conventional differential time-variant circuits, for which only the even or odd spurs are rejected, we show that the proposed configuration cancels out all intermodulation (IM) products, thus making them operate alike linear time-invariant (LTI) circuits for an external observer. In turn, this property enhances all metrics of the resulting circulator, overcoming the limitations of SE architectures, and improving insertion loss, impedance matching, bandwidth and noise figure. We show that this differential architecture also significantly relaxes the required modulation parameters, both in frequency and amplitude. We develop a rigorous small-signal model to guide the design of the proposed circuits and to get insights into their pseudo-LTI characteristics. Then, we validate the theory with simulations and measurements showing remarkable performance compared to the current state of the art of magnetless non-reciprocal devices.