Browsing by Subject "Filters"
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Item Analysis, modeling and simulation of ring resonators and their applications to filters and oscillators(Texas A&M University, 2004-09-30) Hsieh, Lung-HwaMicrostrip ring circuits have been extensively studied in the past three decades. A magnetic-wall model has been commonly used to analyze these circuits. Unlike the conventional magnetic-wall model, a simple transmission-line model, unaffected by boundary conditions, is developed to calculate the frequency modes of ring resonators of any general shape such as annular, square, or meander ring resonators. The new model can be used to extract equivalent lumped element circuits and unloaded Qs for both closed- and open-loop ring resonators. Several new bandpass filter structures, such as enhanced coupling, slow-wave, asymmetric-fed with two transmission zeros, and orthogonal direct-fed, have been proposed. These new proposed filters provide advantages of compact size, low insertion loss, and high selectivity. Also, an analytical technique is used to analyze the performance of the filters. The measured results show good agreement with the simulated results. A compact elliptic-function lowpass filter using microstrip stepped impedance hairpin resonators has been developed. The prototype filters are synthesized from the equivalent circuit model using available element-value tables. The filters are evaluated by experiment and simulation with good agreement. This simple equivalent circuit model provides a useful method to design and understand this type of filters and other relative circuits.Finally, a tunable feedback ring resonator oscillator using a voltage controlled piezoelectric transducer is introduced. The new oscillator is constructed by a ring resonator using a pair of orthogonal feed lines as a feedback structure. The ring resonator with two orthogonal feed lines can suppress odd modes and operate at even modes. A voltage controlled piezoelectric transducer is used to vary the resonant frequency of the ring resonator. This tuned oscillator operating at high oscillation frequency can be used in many wireless and sensor systems.Item High frequency and high dynamic range continuous time filters(Texas A&M University, 2007-09-17) Lewinski Komincz, Artur JuliuszMany modern communication systems use orthogonal frequency division multiplexing (OFDM) and discrete multi-tone (DMT) as modulation schemes where high data rates are transmitted over a wide frequency band in multiple orthogonal subcarriers. Due to the many advantages, such as flexibility, good noise immunity and the ability to be optimized for medium conditions, the use of DMT and OFDM can be found in digital video broadcasting, local area wireless network (IEEE 802.11a), asymmetric digital subscriber line (ADSL), very high bit rate DSL (VDSL) and power line communications (PLC). However, a major challenge is the design of the analog frontend; for these systems a large dynamic range is required due to the significant peak to average ratio of the resulting signals. In receivers, very demanding high-performance analog filters are typically used to block interferers and provide anti-aliasing before the subsequent analog to digital conversion stage. For frequencies higher than 10MHz, Gm-C filter implementations are generally preferred due to the more efficient operation of wide-band operational transconductance amplifiers (OTA). Nevertheless, the inherent low-linearity of open-loop operated OTA limits the dynamic range. In this dissertation, three different proposed OTA linearity enhancement techniques for the design of high frequency and high dynamic range are presented. The techniques are applied to two filter implementations: a 20MHz second order tunable filter and a 30MHz fifth order elliptical low-pass filter. Simulation and experimental results show a spurious free dynamic range (SFDR) of 65dB with a power consumption of 85mW. In a figure of merit where SFDR is normalized to the power consumption, this filter is 6dB above the trend-line of recently reported continuous time filters.Item Implications of Relative Ant Abundance and Diversity for the Management of Solenopsis Invicta Buren with Broadcast Baits(2009-05-15) Calixto, Alejandro AntonioHigher densities of S. invicta in the United States relative to South America are explained mainly by the absence of natural enemies and low interspecific competition (IC). Despite advances in S. invicta management, broadcast insecticide baits remain as the primary tool for effective control. I studied interspecific interactions of ants and the use of baits on the management of S. invicta to test the following hypotheses: 1) relative abundance of native ants increases ~25% for bait treated sites compared to untreated, 2) behavioral dominance by S. invicta decreases ~10% in bait treated sites compared to untreated, and, 3) foraging by S. invicta on insecticide baits is higher ~10% in low native ant densities areas compared to high densities. Experiments were conducted on three sites with different densities of native ants (low, medium, high), but with similar densities of S. invicta. An enhanced BACI (Before/After-Control/Impact) design was used. Experimental units consisted of 0.4 ha plots. Three treatments were randomly assigned to units and replicated four times; 1) Slow acting bait, 2) Fast acting bait, 3) Untreated Control. Samples and observations were collected for several weeks before/after the treatments to account for temporal variation and to determine rates of reinvasion. Ants were monitored using pitfalls and food lures. Interspecific competition was determined by applying placebo bait. Results indicate that different management methods did not impact resident ants when they are at low and medium densities and that S. invicta is greatly affected; at high native ant density, competition for these baits is observed affecting both natives and S. invicta. Reinvasion of S. invicta was reduced in areas of low and medium native ant densities previously treated with baits and native ant abundance increased by ~25%. At high native ant densities, reinvasion of S. invicta was similar to Control sites. I conclude: 1) properly used, baits can help in recovery of native ant species that then compete with S. invicta; however, rote re-treatments may have a negative impact on restored populations. 2) ?bait failures? may be due to interspecific competition when initial native ant densities are high. Preliminary management considerations and recommendations are presented.Item Nonlinearity and noise modeling of operational transconductance amplifiers for continuous time analog filters(Texas A&M University, 2006-08-16) Ramachandran, ArunA general framework for performance optimization of continuous-time OTA-C (Operational Transconductance Amplifier-Capacitor) filters is proposed. Efficient procedures for evaluating nonlinear distortion and noise valid for any filter of arbitrary order are developed based on the matrix description of a general OTA-C filter model . Since these procedures use OTA macromodels, they can be used to obtain the results significantly faster than transistor-level simulation. In the case of transient analysis, the speed-up may be as much as three orders of magnitude without almost no loss of accuracy. This makes it possible to carry out direct numerical optimization of OTA-C filters with respect to important characteristics such as noise performance, THD, IM3, DR or SNR. On the other hand, the general OTA-C filter model allows us to apply matrix transforms that manipulate (rescale) filter element values and/or change topology without changing its transfer function. The above features are a basis to build automated optimization procedures for OTA-C filters. In particular, a systematic optimization procedure using equivalence transformations is proposed. The research also proposes suitable software implementations of the optimization process. The first part of the research proposes a general performance optimization procedure and to verify the process two application type examples are mentioned. An application example of the proposed approach to optimal block sequencing and gain distribution of 8th order cascade Butterworth filter (for two variants of OTA topologies) is given. Secondly the modeling tool is used to select the best suitable topology for a 5th order Bessel Low Pass Filter. Theoretical results are verified by comparing to transistor-level simulation withCADENCE. For the purpose of verification, the filters have also been fabricated in standard 0.5mm CMOS process. The second part of the research proposes a new linearization technique to improve the linearity of an OTA using an Active Error Feedforward technique. Most present day applications require very high linear circuits combined with low noise and low power consumption. An OTA based biquad filter has also been fabricated in 0.35mm CMOS process. The measurement results for the filter and the stand alone OTA have been discussed. The research focuses on these issues.Item Plasmonic properties of subwavelength structures and plasmonic optical devices(2009-08) Wang, Wei; Chen, ShaochenThis thesis proposes a metallic hole array of a rectangular converging-diverging channel (RCDC) shape with extraordinary transmission. We use a three-dimensional (3D) finite element method to analyze the transmission characteristics of two-dimensional metallic hole arrays (2D-MHA) with RCDC. For a straight channel MHA, when the aperture size is reduced, the transmission peaks have a blue-shift. The same result is observed for a smaller gap throat for the RCDC structure. For the rectangular holes with a high length-width ratio, a similar blue-shift in the transmission peaks as well as a narrower full width at half maximum (FWHM) are observed. The asymmetry from the rectangular shape gives this structure high selectivity for light with different polarizations. Furthermore, the RCDC shape gives extra degrees of geometrical variables to 2D-MHA for tuning the location of the transmission peak and FWHM. The tunable transmission property of this structure shows promise for applications in tunable filters, photonic circuits, and biosensors.Item Time domain responses of glassy polymers(2011-05) Subramanian, Shankar; McKenna, Gregory B.; Simon, Sindee L.; Weeks, Brandon L.; Quitevis, Edward L.The properties of glassy polymers are generally studied in the vicinity of the glass transition temperature using frequency and time domain responses. In this work, we primarily focus on studying two time domain responses of glassy polymers namely the dielectric, the structural recovery, and aging responses. A proper understanding of these properties is essential for a better prediction of the performances of polymers. Time domain dielectric measurement provides a powerful means to study the glassy responses in short times (as low as micro seconds) to long times (>200 seconds) in a single measurement device. We built a Time Domain Dielectric Spectrometer (TDS) in our laboratory at Texas Tech to take advantage of this ability. Successful working of TDS was demonstrated by studying the dielectric response of poly (vinyl acetate) in a pulse-probe experiment. We see memory effect and this was in quantitative agreement with linear Boltzmann superposition for small applied fields. However, evidence of breakdown of linearity was observed at relatively larger applied fields. This is an interesting result, as we were able to demonstrate the ability to delineate between linear and nonlinear behaviors in the time domain. We also introduce a filtration tool called Empirical Mode Decomposition (EMD) to improve the data analysis in dielectric and structural recovery experiments whose data are time varying in nature corrupted with nonlinear noise. Structural recovery and aging experiments of glassy polymers are very well understood for temperature formed glasses compared to concentration formed glasses. Previous work from our group has shown that concentration formed glasses qualitatively mimic temperature formed glasses but were quantitatively different. Further, our preliminary work on the structural recovery of epoxy film subjected to CO2 plasticizer jumps showed that the effective retardation time for concentration formed glass and temperature formed glass (subjected to same final condition) do not converge to the same point as equilibrium is approached. Hence, we further investigated this behavior by studying the aging and structural recovery of epoxy film subjected to CO2 plasticizer jumps. The results were surprising and we observe evidence for the existence of a new glassy state.