Date of Award
Open Access Dissertation
Modern wireless electronic circuit design is continually challenged by the needs to reduce circuit size, and to also function reliably with lower power levels. To that end, two aspects of RFIC circuit design and technology have gained great interest, i.e. RF MEMS switching technology, and RF MEMS passive component development. MEMS (Micro-Electromechanical Systems) technology, originally developed for the defense industry, has been in development since the 1970s, and today enjoys wide range of utilization, from the defense industry to the automotive industry. Spiral inductors used in RFIC circuits, e.g. silicon technology, are ubiquitous in wireless RFIC applications. The tradeoff with low cost fabrication processes are inductors with very low quality factors which greatly affect the losses in RF passive circuits, and hence their performance. Research in the area of RF MEMS inductors has shown promise for components with significantly higher Q, and hence has the potential for wide range of benefits in both tunable and non-tunable applications. Electronic design environments such as Agilent ADS provide automated tools for generating passive circuits, e.g. band-pass filters, based on a specified desired frequency response and circuit topology. However, they typically do not incorporate component Q, which can greatly affect the actual circuit’s performance, into the results of their suggested designs. With this in mind, the development of a systematic approach to predict the relationship between passive circuit component’s Q and its S-parameters can be of great benefit to the RF electronic circuit designer, especially in the area of wireless passive circuits. The first of part of this work develops an analytical approach, using mesh-current analysis to derive the relationship between inductor Q, and the S-parameters of a generalized passive RF circuit. For the analysis, the S-parameters of a 90ᵒ Lumped Element Hybrid coupler are derived in terms of even mode and odd mode coupler responses using mathematical functions that relate the S-parameters of each circuit to their associated even mode Q, and odd mode Q factors The results of this research demonstrate that work can still be done in the area of circuit analysis to extend the capability of common passive circuit design tools to include the effects of component Q on the design results, e.g. filter design tools which commonly utilize simple LC circuits as building blocks for more complicated filters. The second part of this work investigates the performance of different RF switching technologies, i.e. MEMS Switching vs. RF PIN Diode, to a 2-3 GHz quasi-tunable RFIC 90ᵒ Lumped Element Hybrid Coupler design utilizing high Q three-dimensional air-core solenoidal MEMS inductors, and IPD Capacitors. The results of this investigation demonstrated the following: The concept of a tunable RFIC Lumped Element Hybrid coupler in the 2-3 GHz range is feasible, and if implement with high Q inductors, comparable to that of off-the-shelf 90° Hybrid Couplers in terms of return loss and isolation performance, but in a much small area, ~ one fiftieth of the surface area at 2 GHz. RF PIN Diodes at low current levels can be sufficient when only the phase imbalance of the coupler is critical. If either magnitude loss or magnitude balance is critical, then RF MEMS switching may provide a better alternative. RF PIN Diode forward bias resistance approaches that of DC contact switch resistance at higher current levels, e.g. 60 mA, and hence their power consumption becomes the main issue in determining the technology best suited for this application. The concept of a ground switched tapped capacitor bank was developed to maximize the switched capacitor Q. This approach optimized the coupler performance compared to a signal switched design. In the third part of this work, a selectable dual-band 630 MHz and 900 MHz PCB lumped element hybrid coupler is designed, fabricated, and measured. The inductors and capacitors are fabricated with only printed conductors and metal patches respectively on a four-layer PCB. The S-parameters of the measured results and simulations correlated extremely well after adjustment of the substrate dielectric thicknesses used for the simulation of the capacitors. This work demonstrates that lumped element passive components can be cheaply fabricated in PCB technology that are useful in the frequency range of 600 MHZ to 1300 MHZ, partially covering the GSM and LTE bands, that can be used in quasi-tunable wireless PCB applications, e.g. base stations, while also reducing circuit size in place of commonly found in microstrip distributed circuits.
Moss, T. L.(2015). AN INVESTIGATION INTO QUASI-TUNABLE RF PASSIVE CIRCUIT DESIGN. (Doctoral dissertation). Retrieved from http://scholarcommons.sc.edu/etd/3147