Date of Award

2005

Level of Access

Open-Access Thesis

Degree Name

Master of Science in Electrical Engineering (MSEE)

Department

Electrical Engineering

Advisor

David E. Kotecki

Second Committee Member

John Vetelino

Third Committee Member

Donald Hummels

Abstract

A 3-D microelectronic inductor has been fabricated and characterized for use as a magnetic flux sensor, also known as a telecoil, for a hearing aid application. This telecoil was fabricated in a 0.5pm CMOS process with three metal layers. The 3-D structure is more space efficient than conventional spiral inductors and allows for an optimal number of turns for the space available. The telecoil has an inductance of 80pH, a resistance of 34kR, and a capacitance of 275pF. The integrated telecoil acts as a magnetic flux sensor by picking up the magnetic signal fiom the phone speaker. The integrated telecoil is smaller than commercially available telecoils, which may allow telecoils to be available in all types of hearing aids. The electrical response of the telecoil to a changing magnetic field is linear with respect to the input amplitude. Neglecting the noise associated with lower frequencies, it is shown that the telecoil response is not dependent on frequency, which agrees with theory. The magnitude of the telecoil signal is of the form of A + 5 where r is the distance between the speaker and telecoil, which differs from the theory. The increase in response due to the addition of a permeable core is much lower than expected. When the telecoil is combined with a high-gain low-noise amplifier, it can easily be integrated with existing microelectronic hearing aid designs. Therefore the Cherry Hooper amplifier and a single-ended amplifier were investigated. A single stage Cherry Hooper amplifier design was simulated at a gain of 29 dB, THD of -SO&, and equivalent input noise of 2.01%. A three stage Cherry Hooper design (identical stages) with a filter has a simulated gain of 84 dB, THD of -49dB, and equivalent input noise of 2.01%. The three stage amplifier also has a bandwidth of 3kHz and a driving capacity of 30pF external load capacitance. The complete single-ended amplifier design was simulated at a gain of 67dI3, THD of -48dB, equivalent input noise of 45.3%, and driving capacity of I n . external load capacitance. More research is needed to obtain conclusive experimental parameters of the amplifiers.

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