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- Genre: Masters Thesis
- Creators: Arizona State University
- Creators: Chakraborty, Bijeta
- Member of: ASU Electronic Theses and Dissertations
Description
Efficiency of components is an ever increasing area of importance to portable applications, where a finite battery means finite operating time. Higher efficiency devices need to be designed that don't compromise on the performance that the consumer has come to expect. Class D amplifiers deliver on the goal of increased efficiency, but at the cost of distortion. Class AB amplifiers have low efficiency, but high linearity. By modulating the supply voltage of a Class AB amplifier to make a Class H amplifier, the efficiency can increase while still maintaining the Class AB level of linearity. A 92dB Power Supply Rejection Ratio (PSRR) Class AB amplifier and a Class H amplifier were designed in a 0.24um process for portable audio applications. Using a multiphase buck converter increased the efficiency of the Class H amplifier while still maintaining a fast response time to respond to audio frequencies. The Class H amplifier had an efficiency above the Class AB amplifier by 5-7% from 5-30mW of output power without affecting the total harmonic distortion (THD) at the design specifications. The Class H amplifier design met all design specifications and showed performance comparable to the designed Class AB amplifier across 1kHz-20kHz and 0.01mW-30mW. The Class H design was able to output 30mW into 16Ohms without any increase in THD. This design shows that Class H amplifiers merit more research into their potential for increasing efficiency of audio amplifiers and that even simple designs can give significant increases in efficiency without compromising linearity.
ContributorsPeterson, Cory (Author) / Bakkaloglu, Bertan (Thesis advisor) / Barnaby, Hugh (Committee member) / Kiaei, Sayfe (Committee member) / Arizona State University (Publisher)
Created2013
Description
Class D Amplifiers are widely used in portable systems such as mobile phones to achieve high efficiency. The demands of portable electronics for low power consumption to extend battery life and reduce heat dissipation mandate efficient, high-performance audio amplifiers. The high efficiency of Class D amplifiers (CDAs) makes them particularly attractive for portable applications. The Digital class D amplifier is an interesting solution to increase the efficiency of embedded systems. However, this solution is not good enough in terms of PWM stage linearity and power supply rejection. An efficient control is needed to correct the error sources in order to get a high fidelity sound quality in the whole audio range of frequencies. A fundamental analysis on various error sources due to non idealities in the power stage have been discussed here with key focus on Power supply perturbations driving the Power stage of a Class D Audio Amplifier. Two types of closed loop Digital Class D architecture for PSRR improvement have been proposed and modeled. Double sided uniform sampling modulation has been used. One of the architecture uses feedback around the power stage and the second architecture uses feedback into digital domain. Simulation & experimental results confirm that the closed loop PSRR & PS-IMD improve by around 30-40 dB and 25 dB respectively.
ContributorsChakraborty, Bijeta (Author) / Bakkaloglu, Bertan (Thesis advisor) / Garrity, Douglas (Committee member) / Ozev, Sule (Committee member) / Arizona State University (Publisher)
Created2012
Description
Technology is rapidly evolving, and mental health professionals are increasingly using technology in their clinical work. In reaction to this shift, it is important that research examines the ethical implications of online behaviors. The current study examined the online practices of graduate students in the mental health field and generated prediction models for online client searches and best practices in informed consent and online disclosure. The sample consisted of 316 graduate students in counseling, clinical, and school programs. Of those with clinical experience, a third had utilized the Internet to find information about their client. Progress in the participants' program, as measured by credits completed or in progress, and years of social networking experience were positively related to online client searches. The vast majority (over 80%) of individuals who conducted an online search did not obtain informed consent prior to the search. Curiosity was the most frequent reason given for conducting a client search. Previous professional discussions and belief that information online is private were not significant predictors of obtaining informed consent. The final analysis examined disclosure of client information and found that lower scores on ethical decision-making and years of social networking experience predicted online disclosure. This study is an important step in understanding the implications of the intersection of technology use, ethics, and clinical practice of graduate mental health professionals.
ContributorsHarris, Sara Elisabeth (Author) / Robinson Kurpius, Sharon E (Thesis advisor) / Tracey, Terence (Committee member) / Kinnier, Richard (Committee member) / Arizona State University (Publisher)
Created2012
Description
As women enter STEM fields they are often presented with chilly climates. The chilly climate refers to incidents of sexism, isolation, and pressure to prove themselves to peers and higher level academics (Callister, 2006; Hall & Sandler, 1982). For women of color, the status of being a double minority can intensify the psychological distress experienced by students (Joseph, 2012; Ong, 2011; Malcom, Hall, & Brown, 1976). For minority populations in STEM, loneliness is experienced due to lack of belonging and social isolation (Morris & Daniel, 2008; Walton & Cohen, 2007). This study sought to investigate whether social support could serve as a protective factor in the negative relationship between loneliness and psychological well-being (Cohen, 2004; Lawson, 2001; Lazarus & Folkman, 1984) for those who hold a minority status. In addition, this study explored differences in the associations between loneliness, social support, and psychological well being and whether or not the moderation relationships were different for sub-groups based on gender or ethnic minority status. Cross-sectional data from 205 STEM graduate students was collected through an online study. A hierarchical regression analysis was used to test the buffering effects (Barron & Kenny, 1986) of global social support (total support from friends, family, and significant others) and family social support specifically. Model results suggested that global social support buffers the negative associations between loneliness and psychological well-being for less lonely minority participants in the study. Family social support buffered the associations of loneliness on psychological well-being for men with less loneliness. An unexpected finding in the present study revealed that for men and non –minority participants with high loneliness, psychological well-being decreased as family support increased. These results highlight the need for further research exploring through which mechanisms social support works as a buffer against loneliness in the sub-groups within STEM graduate student populations. The findings of this study could inform practices focused on the recruitment and retention of underrepresented STEM graduate students.
ContributorsAnderson, Mercedes (Author) / Bernstein, Bianca L. (Thesis advisor) / Randall, Ashley K. (Committee member) / Tracey, Terence (Committee member) / Arizona State University (Publisher)
Created2017
Description
In this thesis, a digital input class D audio amplifier system which has the ability
to reject the power supply noise and nonlinearly of the output stage is presented. The main digital class D feed-forward path is using the fully-digital sigma-delta PWM open loop topology. Feedback loop is used to suppress the power supply noise and harmonic distortions. The design is using global foundry 0.18um technology.
Based on simulation, the power supply rejection at 200Hz is about -49dB with
81dB dynamic range and -70dB THD+N. The full scale output power can reach as high as 27mW and still keep minimum -68dB THD+N. The system efficiency at full scale is about 82%.
to reject the power supply noise and nonlinearly of the output stage is presented. The main digital class D feed-forward path is using the fully-digital sigma-delta PWM open loop topology. Feedback loop is used to suppress the power supply noise and harmonic distortions. The design is using global foundry 0.18um technology.
Based on simulation, the power supply rejection at 200Hz is about -49dB with
81dB dynamic range and -70dB THD+N. The full scale output power can reach as high as 27mW and still keep minimum -68dB THD+N. The system efficiency at full scale is about 82%.
ContributorsBai, Jing (Author) / Bakkaloglu, Bertan (Thesis advisor) / Arizona State University (Publisher)
Created2015
Description
The demands and expectations of graduate school can be stressful for any student. Graduate students in a romantic relationship, in particular, contend with both individual and dyadic effects of graduate school stress, as stress has been found to be negatively associated with both individual and relational well-being. Asymmetrical graduate student couples, wherein one partner is in graduate school and the other is not, may be particularly vulnerable to relationship strain because of differences in their experience of graduate school. However, non-student partners can help the graduate student cope with stress through dyadic coping. This study sought to examine whether: a) there were associations between graduate school stress on individual (life satisfaction) and relational (relationship satisfaction) well-being, and b) whether these associations were moderated by positive and negative dyadic coping behaviors. Cross-sectional data from 62 asymmetrical graduate student couples were gathered using an online survey. Data were analyzed using Actor-Partner Interdependence Models (Kenny, Kashy, & Cook 2006). Separate models were conducted to examine overall associations between graduate stress and well-being, and additional analyses were conducted to examine potential moderation effects of perceptions of partner dyadic coping (actor effects) and partner self-reported dyadic coping (partner effects) on the overall associations between stress and life- and relationship satisfaction mentioned above. Results for the overall model suggested that graduate stress is associated with both individual- and relational well-being. Surprisingly, and against prior literature, positive dyadic coping did not buffer the negative association between graduate stress and well-being, and negative dyadic coping did not exacerbate the association. Implications of the findings for future research and for mental health counselors are discussed.
ContributorsSegraves, Megan C (Author) / Randall, Ashley K. (Thesis advisor) / Bernstein, Bianca (Committee member) / Kurpius, Sharon (Committee member) / Arizona State University (Publisher)
Created2017
Exploring the Relationship Between Depression and Graduate School Among Life Sciences Ph.D. Students
Description
Depression is one of the top mental health concerns among biology graduate students and has contributed to the “graduate student mental health crisis” declared in 2018. Prominent science outlets have called for interventions to improve graduate student mental health, but few studies have examined the relationship between depression and graduate school among life sciences Ph.D. students. In this coupled set of qualitative interview studies, 50 life sciences Ph.D. students from 28 institutions across the United States were interviewed. The first study explored how research and teaching affect depression in Ph.D. students and how depression in turn also affects students’ experiences in graduate school. Using inductive coding, four overarching aspects of graduate school that influenced student depression were highlighted, (1) structure in teaching and research, (2) positive and negative reinforcement, (3) success and failure, and (4) social support and isolation. The second study explored depression as a concealable stigmatized identity (CSI) by examining (1) to what extent and why graduate students revealed their depression to faculty advisors, graduate students, and undergraduate researchers, and (2) the consequences or benefits that they perceive are associated with revealing one’s depression through a hybrid approach of deductive and inductive coding. Graduate students most commonly revealed their depression to other graduate students; however, most were reluctant to share their depression with undergraduate researchers. These qualitative interview studies provide insights into creating more inclusive life science graduate programs for students with depression.
ContributorsWiesenthal, Nicholas John (Author) / Cooper, Katelyn M (Thesis advisor) / Brownell, Sara E (Committee member) / Maienschein, Jane (Committee member) / Arizona State University (Publisher)
Created2022
Description
Studies suggest that graduate students experience higher rates of anxiety and depression than their peers outside of academia. Studies also show exercise is correlated with lower levels of anxiety and depression among graduate students. However, despite this evidence, nearly half of graduate students do not exercise regularly. Accordingly, I suggest universities consider adding an exercise requirement to promote graduate student well-being. One potential objection to this recommendation is that an exercise requirement is objectionably paternalistic. I answer this objection with two possible replies. First, there are reasons why the exercise requirement might not be paternalistic, and there may be sufficient non-paternalistic reasons to justify the policy. Second, there are reasons why even if the policy is paternalistic, it is not objectionably paternalistic, and may still be justified. I will offer reasons to consider paternalism in a positive light and why the exercise requirement may be an example of a good paternalistic policy. Because the exercise requirement might be justified on paternalistic grounds, there are reasons to consider other paternalistic policies to promote graduate student well-being.
ContributorsArthur, Philip (Author) / de Marneffe, Peter (Thesis advisor) / Portmore, Doug (Committee member) / DesRoches, Tyler (Committee member) / Arizona State University (Publisher)
Created2020