SpecEES:Collaborative Research: Power and Spectral Efficiency enabled by RF Co-Designed Electrically-Adaptive Front Ends

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The rapid growth of wireless communications and sensing demand more efficient use of the precious frequency spectrum, imposing tougher constraints on the radio-frequency hardware. To responds to this challenge, transformative radio front-end designs are needed. This collaborative project proposes new classes of electrically-tuned RF front-ends for efficient, on-demand spectrum access/sharing in spectrally-congested environments. Although 5G networks, devices and communication schemes have been extensively discussed, they are not yet appropriately defined, deployed and fully exploited. The goal of this project is to develop RF front-ends with multiple levels of transfer-function adaptivity enabled by electrically-controlled materials and new types of RF filters that can: (a) arbitrarily define the band of operation; (b) efficiently transmit/receive under dynamic spectrum allocations; and (c) co-exist in unlicensed bands. The co-design of filters with other transceiver components such as antennas, power amplifiers and low-noise amplifiers will increase power efficiency while reducing the size of RF front-end. The multi-level adaptivity and circuit co-design are fundamental methodology advances which will allow transformative improvements in hardware performance. The proposed research will be carried out by a unique multi-institute team from the University of Colorado at Boulder (UCB) and the University of Michigan (UM), with complementary expertise in RF filters, active circuits and microfabrication. The outreach components of this project focus on: (i) broadening the undergraduate experience in practical training and research through NSF Research Experiences for Undergraduates (REU) program, as well as university and industry-funded opportunities for students; (ii) enhancing the UCB/UM curriculum with new class contents integrating the proposed research results; (iii) increasing the participation of underrepresented undergraduate/graduate students by active recruiting through organized events and university scholarship programs; and (iv) outreach efforts for K-12 students through existing infrastructure at UCB/UM such as the well-established Science Discovery Program at UCB.The technical objective of the proposed collaborative research is to investigate new classes of fully-reconfigurable co-designed RF front-ends that will facilitate efficient spectrum access at frequencies below 6 GHz, where the spectrum is most congested. For 5G applications, the millimeter-wave frequency allocations allow for larger bandwidths, but are accompanied by higher atmospheric loss and higher cost. The proposed hardware developments will exploit the multi-functional voltage-controlled properties of barium strontium titanate (BST) as structural materials for bulk acoustic-wave resonators (FBARs) and electrically-tuned reactive elements. This allows for significantly increased functionality through: (1) new filter design methodologies and tuning schemes for continuous and analog RF tuning; (2) high quality factor FBARs with intrinsically-switched transfer function; (3) co-designed RF passive and active circuit elements resulting in miniaturization and reduced loss; and (4) frequency-selective agile harmonic terminations to increase the circuit efficiency and dynamically adapt to RF signals with diverse spectral and spatial content. The collaborative research effort will lead to the development of switchless transmitter/receiver front-end chains with multiple levels of transfer function adaptivity capable of achieving higher efficiency and lower noise than conventional approaches. The proposed tuning speeds on the order of hundreds of ns will allow dynamic frequency coverage in 0.8 - 6 GHz and adaptive multi-band front-end chains.