image: Figure | Design of the Meta-RTWO resonator. a, The structure of uncrossed spoof SPP TL ( L1, L2, L8, L5, L6, and L4). b, The structure of crossed jumpered spoof SPP TL (L3 and L7). c, The phase-frequency curves of Meta-RTWO and MS-RTWO resonators with different lengths. d, Characteristic impedance extraction of different spoof SPP units that make up the Meta-RTWO resonator.
Credit: Da Yue Yao et al.
Quadrature oscillators are core components of modern wireless transceivers, where the quadrature phase accuracy and FOM directly determine the system performance. The traditional designs struggle to achieve both metrics simultaneously: quadrature voltage-controlled oscillators require quadrature coupling for frequency pulling to achieve high phase accuracy, causing resonant Q-factor degradation and phase noise deterioration, and hence creating an inherent FOM-phase accuracy trade-off; while RTWOs suffer from the current phase misalignment and noise degradation in their negative resistance units due to the Möbius ring resonator constraints in planar chip fabrication.
In a new paper published in Light: Science & Applications, a team led by Professor Tie Jun Cui from the State Key Laboratory of Millimeter Waves have developed a plasmonic meta-RTWO with ultrahigh phase accuracy and FOM. The meta-oscillator is constructed using a Möbius ring resonator with uniformly distributed negative resistance units, where the oscillation frequency is determined by the total resonator length. Multi-phase outputs can be directly extracted by tapping signals from different transmission line nodes. To achieve high phase accuracy and high FOM quadrature signals (perfect oscillation state), RTWOs must strictly satisfy the condition that each transmission line segment of the Möbius ring maintains a phase constant of 90° at the oscillation frequency, ensuring synchronized current phase alignment across the entire resonator. The Chinese scientists noted that: “The proposed Meta-RTWO resonator is composed of three-edge non-crossing spoof SPP transmission lines (TLs) connected end-to-end with single-edge crossing jumper spoof SPP TL. The phase characteristic comparisons demonstrate that four types of spoof SPP TLs exhibit highly overlapping phase curves across 0-100 GHz, where the maximum phase difference is only 0.16° at 25.5 GHz; while the traditional microstrip (MS) lines with equivalent length show significantly dispersed phase responses with the phase difference reaching 2.81° at the same frequency. Adjacent spoof SPP units exhibit the maximum deviation of the characteristic impedance of 2.1Ω at 25.5 GHz, resulting in the reflection energy ratio as low as 0.5%, which is essentially negligible.”
The scientists added: “Our Meta-RTWO chip fabricated using the 65nm CMOS process achieved the measured phase error as low as 0.21° and FOM value of 188.5 dBc/Hz, with the relevant performance metrics superior to the recent comparable designs using advanced 28 nm CMOS processes.”
The scientists predict that “Meta-RTWO technology will provide core support for cutting-edge fields including real-time calibration of antenna arrays in 6G massive MIMO system, subpicosecond synchronization for terahertz quantum communication, and super-resolution beamforming in intelligent sensing network.”
Journal
Light Science & Applications
Article Title
A plasmonic meta-rotary travelling-wave oscillator with ultrahigh phase accuracy and figure of merit