Modern and future communication and radar systems require highly reconfigurable RF front-ends to realize the vision of Software-Defined Radio (SDR), where a single digitally-enabled radio is able to cover multiple bands and multiple operating standards. However, in the increasingly hostile RF environment, filtering becomes a bottleneck for SDRs as the traditional off-chip filters are fixed frequency and bulky. Therefore, tunable filtering is a critical building block for the reconfigurable RF front-ends and on-chip implementations are needed to meet size and weight constraints. On-chip passive components are lossy, especially inductors, and to fulfill the tunability requirements a number of active circuit techniques, e.g. N-path, Q-enhanced, discrete-time filters etc., have been developed. Most of these active filtering techniques, however, are limited to RF frequency range of few GHz and below. Additionally, these techniques lack or have very limited bandwidth tunability. On the other hand, Q-enhanced tunable LC filtering has the potential to be implemented at Microwave frequencies from 4~20 GHz and beyond.
In this dissertation, a number of Q-enhanced parallel synthesis techniques have been proposed and implemented to achieve high-order, frequency tunable, and wide bandwidth tunable filters. First, a tunable 4th-order BPF was proposed and implemented in Silicon Germanium (SiGe) BiCMOS technology. Along with center frequency tuning, the filter achieves first ever reported 3-dB bandwidth tuning from 2% to 25%, representing 120 MHz to 1.5 GHz of bandwidth at 6 GHz. A new set of design equations were developed for the 4th-order parallel synthesis of BPF. A practical switched varactor control scheme is proposed for large tuning ratio varactors to reduce the nonlinear contribution from the varactor substantially which improves the tunable LC BPF filter linearity. Second, parallel addition and subtraction techniques were proposed to realize tunable dual-band filters. The subtraction technique is implemented in SiGe BiCMOS technology at X and Ku bands with more than 50 dB of out-of-band attenuation. Finally, a true wideband band-reject filter technique was proposed for microwave frequencies using parallel synthesis of two band-pass filters and an all-pass path. The proposed band-reject scheme is tunable and wide 20 dB attenuation bandwidths on the order of 10s of MHz to 100s of MHz can be achieved using this scheme.
The implementation of the proposed parallel synthesis techniques in silicon technology along with measured results demonstrate that Q-enhanced filtering is favorable at higher microwave frequencies. Therefore, such implementations are suitable for future wireless communication and radar systems particularly wide bandwidth systems on the order of 100s of MHz to GHz. Future research includes, high-order reconfigurable band-pass and band-reject filters, automatic tuning control, and exploring the parallel synthesis techniques in Gallium Nitride (GaN) technology for high RF power applications. / PHD / The year is 2017 and the current state of the art smartphone can do amazing things using its wireless technologies including LTE, WiFi, Bluetooth, NFC, FM, GPS etc. Each of these wireless standards requires a hardware receiver and a transmitter, also called radio, so as to receive and transmit the signals over air using their designated frequencies. Often more than a single radio is needed to cover different frequency bands, e.g., LTE requires multiple radios to enable operation with different cellular providers and to be used in different countries in cases where the designated frequencies for LTE differs. In order to further reduce the size and cost of communication devices, including but not limited to smartphone, it is desired to implement a single software controlled hardware radio which can cover all of the aforementioned wireless standards. In doing so, the single radio has to distinguish between the desired signal and unwanted signals, also called interference, from other radios using filters that are needed to be reconfigurable to accommodate different wireless standards and bands. The same reconfigurable requirement is valid for radars as well. Therefore, there is a need for the research and development of cost effective and small size dynamic filters which can be controlled from software to adapt to different wireless standards.
In this dissertation, a number of filtering techniques are presented to make the radio tunable and agile in terms of operating frequency and bandwidth. The proposed techniques employs very large frequency and bandwidth tuning and are implemented in on-chip integrated circuit (IC) silicon technology. By doing so, the proposed on-chip integrated filters become tens to hundreds of times smaller than traditional off-chip filters which occupies majority of the space in small form factor devices. Therefore, the proposed tunable filters implementations are suitable for future wireless communication and radar systems particularly wide bandwidth systems to increase the data rate and radar detection accuracy.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/91481 |
| Date | 23 January 2018 |
| Creators | Amin, Farooq Ul |
| Contributors | Electrical Engineering, Koh, Kwang-Jin, Raman, Sanjay, Safaai-Jazi, Ahmad, Orlowski, Mariusz Kriysztof, Nguyen, Vinh |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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