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Sarah Harriman
Department of Electrical Engineering
Research Advisor: Umran Inan
Time: Friday, February 5 at 1:15pm
Location: Packard 202

Low Noise Integrated Amplifier for Sensing of Magnetic Fields in
Remote Locations

Electronic systems for collecting measurements in harsh, remote
environments face special challenges that often require custom
designs.  These systems must have the power capacity, data storage,
and robustness to record high fidelity data for many months with no
human contact.  In this work, a preamplifier for a magnetic sensor is
designed to satisfy the size, weight, power, temperature, and noise
specifications for deployment in Antarctica.  The magnetic antenna has
a low impedance (1 Ω - 1 mH) requiring a low input impedance amplifier
and operates in the VLF (Very Low Frequency) range (50 Hz – 30 kHz).
At these low frequencies, 1/f noise becomes the dominating issue that
limits performance.  Due to the higher 1/f noise corner of MOSFET
devices, only bipolar-junction transistors (BJTs) must be used in
noise-critical parts of the design.  Because of recent interest in
BJTs for their superior performance at high frequencies in the
gigahertz range, new opportunities are available for integrating low
frequency amplifiers in low noise applications.  A low impedance
custom amplifier is presented that was integrated in National’s
BiCMOS process and meets the impedance and temperature requirements
while achieving 0.6 nA/sqrt(Hz) noise in band and consuming only 5 mW
of power.  This noise corresponds to a field noise of 0.25 fT/sqrt(Hz)
for the loop antenna that is used for this application.  The amplifier
was field tested at the South Pole for a year and successfully
collected data suitable for science research.