The aim of this study was to determine which land line telephone and/or mobile/cellular telephone will enable an individual with a cochlear implant to achieve the best speech discrimination scores. Objective measurements and the subjective experience of the individual were used. The literature review provided an overview on the telephone abilities of individuals fitted with cochlear implants. In this study three factors, the quality of the telephone, the speaker's voice and different speech-coding strategies, were discussed and examined, in order to explore and explain the technical difficulties commonly experienced by this population regarding the successful use of a telephone. Data regarding various telephones and the influence different voice-types has on the telecommunication abilities were obtained through the execution of the methodology. Telephone abilities on five different telephones were assessed. Ten participants, four females and six males, fitted with the ESPrit 22, ESPrit 24 and ESPrit 3G Nucleus cochlear implants were used. The Central Institute for the Deaf (CID) open-set sentences were used and data was statistically analysed using a split plot design. Significant differences between different types of telephones were found. The results also suggested that different voice types have an impact on these individual's ability to use a telephone independently. Possible reasons such as different coding strategies, technical interference and quality of voices were discussed. Recommendations for developing rehabilitation programs, to obtain successful telephone competence for these individuals, were made and discussed. The study aimed to empower technologists working in this field to actively take note of the need for development and continuous research regarding various telephones. These telephones should enable more individuals fitted with cochlear implants to receive the maximum speech discrimination with the minimum interference. The findings of this study should encourage future research regarding this topic. A more extensive range of telephones should be used and compared to the findings in this study. / Dissertation (M (Communication Pathology))--University of Pretoria, 2006. / Speech-Language Pathology and Audiology / Unrestricted

Electro-Magnetic Interference(EMI) degrades the perfomance of electronic systems. So, Amplifiers which are the basic building blocks used in the front-end of analog and mixed-signal Integrated Circuits (ICs) must be evaluated for EMI. This work introduces the most intriguing figure of merit, Electro-Magnetic Interference Rejection Ratio (EMIRR) to measure the EMI immunity of precision Instrumentation Amplifiers (INAs) that helps to select the EMI robust INAs for EMI critical applications. In this work, a new EMIRR measurement setup is implemented to measure the immunity of INAs for conducted EMI ranging from 10 MHz to 3 GHz. The shift in the DC offset voltage generated at the output of the INA due to RF rectification, is used to compute EMIRR. As part of the setup, the hardware evaluation board is designed and an automation test software is developed to run EMIRR measurements. Furthermore, EMIRR measurements are performed on several INAs with different specifications to compare and rank them on their EMI immunity levels. Additionally, with the help of EMIRR metric, suitable INAs for developing EMI-sensitive applications are proposed. Finally, the influence of amplifier bandwidth, the input capacitance, 50 Ω termination at the end of RF input trace, INA package parasitics and EMI filter bandwidth on EMIRR is analyzed with the measurement results.

With GaN and SiC switching devices becoming more commercially available, higher switching frequency is being applied to achieve higher efficiency and power density in power converters. However, electro-magnetic interference (EMI) becomes a more severe problem as a result. In this thesis, the switching frequency effect on conducted EMI noise is assessed. As EMI noise increases, the EMI filter plays a more important role in a power converter. As a result, an effective EMI modeling technique of the power converter system is required in order to find an optimized size and effective EMI filter. The frequency-domain model is verified to be an efficient and easy model to explore the EMI noise generation and propagation in the system. Of the various models, the unterminated behavioral model can simultaneously predict CM input and output noise of an inverter, and the prediction falls in line with the measurement around 10 MHz or higher. The DM terminated behavioral model can predict the DM input or output noise of the motor drive higher than 20 MHz. These two models are easy to extract and have high prediction capabilities; this is verified on a 10 kHz-switching-frequency Si motor drive. It is worthwhile to explore the prediction capability of the two models when they are applied to a SiC-based power inverter with switching frequency ranges from 20 kHz to 70 kHz. In this thesis, the CM unterminated behavioral model is first applied to the SiC power inverter, and results show that the model prediction capability is limited by the noise floor of the oscilloscope measurement. The proposed segmented-frequency-range measurement is developed and verified to be a good solution to the noise floor. With the improved impedance fixtures, the prediction from CM model matches the measurement to 30 MHz. To predict the DM input and output noise of the SiC inverter, the DM terminated behavioral model can be used under the condition that the CM and DM noise are decoupled. With the system noise analysis, the DM output side is verified to be independent of the CM noise and input side. The DM terminated behavioral model is extracted at the inverter output and predicts the DM output noise up to 30 MHz after solving the noise floor and DM choke saturation problem. At the DM input side, the CM and DM are seen to be coupled with each other. It is found experimentally that the mixture of the CM and DM noise results from the asymmetric impedance of the system. The mixed mode terminated behavioral model is proposed to predict the DM noise when a mixed CM effect exists. The model can capture the DM noise up to to 30 MHz when the impedance between the inverter to CM ground is not balanced. The issue often happens in extraction of the model impedance and is solved by the curving-fitting optimization described in the thesis. This thesis ends with a summary of contributions, limitations, and some future research directions. / Master of Science

Terminal models have been used for various power electronic applications. In this work a two- and three-terminal black box model is proposed for electro-magnetic interference (EMI) characterization. The modeling procedure starts with a time-variant system at a particular operating condition, which can be a converter, set of converters, sub-system or collection of components. A unique, linear equivalent circuit is created for applications in the frequency domain. Impedances and current / voltage sources define the noise throughout the entire EMI frequency spectrum. All parameters needed to create the model are clearly defined to ensure convergence and maximize accuracy. The model is then used to predict the attenuation caused by a filter with increased accuracy over small signal insertion gain measurements performed with network analyzers. Knowledge of EMI filters interactions with the converter allows for advanced techniques and design constraints to optimize the filter for size, weight, and cost. Additionally, the model is also demonstrated when the operating point of the system does not remain constant, as with AC power systems. Modeling of a varying operating point requires information of all the operating conditions for a complete and accurate model. However, the data collection and processing quickly become unmanageable due to the large amounts of data needed. Therefore, simplification techniques are used to reduce the complexity of the model while maintaining accuracy throughout the frequency spectrum. The modeling approach is verified for linear and power electronic networks including: a dc-dc boost converter, phase-leg module, and a simulated dc-ac inverter. The accuracy of the model is confirmed up to 100 MHz in simulation and at least 50 MHz for experimental validation. / Ph. D.

In this work, a modeling approach is delineated and described in detail; predominantly done in the time domain from low frequency, DC, to high frequencies, 100 MHz. Commercially available computer aided design tools will be used to determine the propagation path in a given structure. Next, an integrated transmission-line filter — fabricated using planar processing technologies — is modeled to accurately predict the EMI characteristics of the system. A method was derived to model the filter's performance in the time-domain while accurately depicting the highly frequency dependant transmission-line properties. A system model of a power factor correction (PFC) boost converter was completed by using active device models for diodes, MOSFETs, and the gate driver. In addition, equivalent circuits were used to characterize high frequency impedances of the passive components. A PFC boost converter was built and used to validate the model. The PFC operated at a peak output power of 1 kW, switching at 400 kHz, with a universal input ranging from 90-270 VRMS with unity power factor. The time-domain and EMI frequency spectrum waveforms are experimentally measured and agree very well with the simulated values; within 5 dB for EMI. The transmission-line filter was also manufactured for model verification, and it is tested for the first time with an operating converter: a PFC at 50 W output and 50 VDC input. The small signal characteristics match the model very well. In addition, impedance interactions between the filter, the converter, and the EMI measurement set-up are discussed, evaluated, measured, and improved to minimize undesired resonances and increase low-frequency EMI attenuation. Experimentally measured attenuation provided by the filter in the range from 100 kHz to 100 MHz was 20-50 dBμV. The simulation also shows a similar attenuation, with the exception of one key resonance not seen in the simulation. / Master of Science