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- Genre: Masters Thesis
- Creators: Arizona State University
- Creators: Chakraborty, Bijeta
- Creators: Peterson, Cory
- 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
ABSTRACT Much of teacher feedback research is conducted in the L1 and L2 contexts. There is a paucity of research about feedback in the Teaching Chinese as a Foreign Language (TCFL) context. Particularly, little is known about teachers' feedback practices and student views of teacher feedback. The present study was undertaken to fill the research gap by focusing on teachers'written feedback. Student data from surveying 38 students was interpreted with teacher data gained from interviewing three teachers. The findings indicate that teacher written feedback, which occurred in a multiple-draft writing cycle, generally accorded with recommended feedback principles. Students responded favorably to teacher written feedback. The results also reveal discrepancies between teachers' feedback practices and student perceptions of and preferences regarding teacher feedback. The results show that students wanted more written comments from teachers, though most teachers didn't prioritize written comments. Despite teachers' practices and their inclination toward offering coded indirect error correction, students in the study expressed their preferences for direct error correction. Most students are interested in receiving teacher feedback that addresses all aspects of writing rather than primarily focusing on language accuracy. The reasons that may account for the disjuncture are also discussed in the study. The study concludes that it is important for teachers to be aware of student attitudes and expectations regarding teacher feedback. Teachers should be flexible enough to provide individualized feedback. Pedagogical implications are included in the paper in the hope of shedding light on the development of effective and helpful teacher feedback.
ContributorsChen, Jinglin (Author) / Spring, Madeline (Thesis advisor) / Oh, Young (Committee member) / West, Stephen (Committee member) / Arizona State University (Publisher)
Created2012
Description
This case study explores similarities and differences between the instructors' beliefs about oral corrective feedback and their actual practices in a summer Chinese program. This kind of feedback is beneficial for beginning college-level learners of Chinese to improve their speaking accuracy. The researcher conducted face-to-face interviews with two teachers of Chinese, focusing on their beliefs about oral corrective feedback in their language classrooms. In addition, the researcher recorded teacher-student interactions through class observation in order to analyze the teachers' actual practices of oral corrective feedback. The main findings show that the teachers hold similar beliefs on oral corrective feedback and its beneficial role in helping improve learners speaking accuracy. The fact is that they frequently provide oral corrective feedback in classroom, mostly using recasts. Implications are discussed in view of the necessity of using explicit feedback and recasts appropriately. In addition, this study demonstrates the need for specific professional development and teacher training about how to provide efficient corrective feedback.
ContributorsDong, Zhixin (Author) / Spring, Madeline K. (Thesis advisor) / West, Stephen (Committee member) / Oh, Young (Committee member) / Arizona State University (Publisher)
Created2012
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
Research in foreign language (FL) acquisition has shown that connectives, a key linguistic element contributing to cohesion and sentence complexity, pose a great challenge for FL learners at all proficiency levels. In spite of the importance of connectives in foreign language acquisition, little research has been conducted to explore how connectives are taught and presented in foreign language classrooms and textbooks.
The primary purpose of this study is to examine the presentation and introduction of connectives as well as the pedagogical activities provided for learning connectives in Chinese textbooks for novice to intermediate FL learners. To achieve the purpose of the study, three different sets of widely-used Chinese textbooks were selected and compared. The results show that while the amount of coverage varies greatly among the three sets of textbook, the sequence of presenting connectives in each series of textbooks closely follows the ranks suggested in the HSK Grading Standards and Grammar Outline (HSK is the shortened form for Chinese Proficiency Test). As for the activities, although all three textbooks claim to adopt a communicative approach to FL teaching, they differ considerably in the type of activities provided. In addition, it is evident that more traditional form-focused exercises are included in those textbooks than meaning-focused communicative tasks.
The primary purpose of this study is to examine the presentation and introduction of connectives as well as the pedagogical activities provided for learning connectives in Chinese textbooks for novice to intermediate FL learners. To achieve the purpose of the study, three different sets of widely-used Chinese textbooks were selected and compared. The results show that while the amount of coverage varies greatly among the three sets of textbook, the sequence of presenting connectives in each series of textbooks closely follows the ranks suggested in the HSK Grading Standards and Grammar Outline (HSK is the shortened form for Chinese Proficiency Test). As for the activities, although all three textbooks claim to adopt a communicative approach to FL teaching, they differ considerably in the type of activities provided. In addition, it is evident that more traditional form-focused exercises are included in those textbooks than meaning-focused communicative tasks.
ContributorsGuo, Yifan (Author) / Zhang, Xia (Thesis advisor) / Oh, Young K. (Committee member) / Tanno, Koji (Committee member) / Arizona State University (Publisher)
Created2015
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