Phase-Tunable -3dB 180 degree Hybrid Coupler (in 65nm CMOS)
This project introduces a novel approach to enhancing the performance of a 3 dB 180° hybrid coupler, which is used to split power into two signals—either in sync (common mode) or out of sync (differential mode). In CMOS technology, manufacturing variations can lead to phase imbalances, causing performance issues. While many existing designs address out-of-phase errors, they often overlook in-phase discrepancies.
Our solution features a tunable hybrid coupler that uses only two varactors to correct both in-phase and out-of-phase imbalances, making it ideal for applications requiring precise control in both common-mode and differential-mode operations. This design offers increased versatility and reliability.
Developed using Cadence Virtuoso and simulated with EMX, leveraging the Fast Multipole Method (FMM) for efficient analysis, the coupler has been implemented in TSMC 65nm technology. Automated testing was conducted with a Vector Network Analyzer (VNA) using the VISA protocol.
A 3 dB 180° hybrid coupler serves to bifurcate power either coherently or differentially. This facilitates activation in either common mode or differential mode. In CMOS technology, variations in these phases are foreseeable due to manufacturing disparities. While numerous hybrid couplers concentrate on mitigating out-of-phase disparities by integrating phase tunability mechanisms, they often neglect the rectification of in-phase discrepancies. In scenarios demanding the capability to configure both common-mode and differential-mode operations via the hybrid coupler, it becomes imperative to address both in-phase and out-of-phase imbalances. This study introduces a novel approach by proposing a tunable 3 dB 180° hybrid coupler that uses just two varactors. This coupler enables the correction of both in-phase and out-of-phase discrepancies. It facilitates applications in both common mode and differential mode.
Measured Phase correction by tuning varactors voltage. Angle difference at 0\textdegree{} is calculated by subtracting the phase between S23 amd S34 wheras the angle difference at 180\textdegree{} is calculated by subtracting the phase between S21 and S31.
The figure illustrates the phase tunability of the hybrid coupler under both in-phase (IP) and out-of-phase (OP) conditions across frequencies of 14, 15, and 16 GHz. The tunability range for the IP condition covers 0°, indicating complete phase coverage. However, for the OP condition, deviations from the ideal 180° phase shift are observed. Specifically, at 16 GHz, the tunability range achieves the desired 180° phase shift, while at 14 GHz and 15 GHz, the phase shift deviates by approximately 6.21° and 1.68°, respectively.
