Monolithically Integrated Time-Varying Transmission Lines (TVTL) for Tunable and Interference Resilient RF Front Ends
With the development of modern wireless communications, interference has become a primary challenge for spectrum utilization and coexistence. High frequency-selectivity, tunable, low-noise, and high-linearity RF front-end components can greatly help the reception robustness under heavy interference scenarios. In this work, we propose to utilize the parametric mixing and amplification behavior of the time-varying transmission lines (TVTL) to design and implement such devices.TVTLs are reactance-based circuits consisting of passive transmission lines whose inductance or capacitance is modulated by an electromagnetic wave called the “pump”. The single-sideband operation of a TVTL is especially favorable in that it can provide low-noise parametric amplification and frequency conversion with a moderate amount of gain. Moreover, TVTLs are compatible with modern IC technologies and can be realized with small form factors. In this work, an in-depth theoretical study on the time-varying transmission lines (TVTL) in the single-sideband operation is presented. The theory then serves as a guideline to design three configurations of TVTLs on commercially available monolithic microwave integrated circuit (MMIC) processes. These MMIC TVTLs are then applied to design the RF correlator with either the frequency translational approach or the tunable peak amplifier approach to overcome the interference issues faced by modern receivers. Measurements results showed that 0 dB conversion loss was realized in the directly-pumped TVTL frequency translational correlator prototype. >25 dB correlation suppression was also achieved by the same prototype when comparing the reception of the correlated signal with the reception of the uncorrelated (orthogonal) signal. For the tunable peak amplifier approach, experiments indicated that the peak gain of the tunable peak amplifier was >25 dB with a bandwidth <5MHz, and the measured frequency tuning range was >100 MHz. The noise figure of the tunable peak amplifier in both simulation and measurement was <1.8 dB. Lastly, the tunable peak amplifier also exhibited good linearity in the measurement, which was -11.5 dBm in-band IIP3 and 30 dBm out-of-band IIP3.