A system for automated noise parameter measurements on MR preamplifiers and application to high B(0) fields

Area of Science:

• Electrical Engineering
• Instrumentation and Measurement

Background:

• Accurate noise characterization is crucial for electronic systems, especially in sensitive applications like MRI.
• Existing measurement techniques may face challenges in characterizing devices under extreme conditions, such as strong magnetic fields.

Purpose of the Study:

• To develop and validate a versatile noise figure and noise parameter measurement system.
• To adapt the system for characterizing preamplifiers in high magnetic fields relevant to MRI.

Main Methods:

• Developed a system integrating a spectrum/network analyzer, preamplifier, and noise source.
• Employed the Y-factor method for noise figure calculation with advanced calibration techniques.
• Utilized an electronically controlled tuner to vary source impedance for noise parameter extraction.
• Modified the system to test MRI preamplifiers in static magnetic fields up to 9.4 T.

Main Results:

• The system demonstrated accurate noise figure and parameter measurements for amplifiers at 128 MHz and 200 MHz, correlating with datasheet values.
• Measurements of MRI preamplifiers revealed that magnetic fields reduce gain and increase noise figure.
• Gallium arsenide (GaAs) devices showed higher sensitivity to magnetic fields compared to silicon-germanium (SiGe) devices.

Conclusions:

• The developed system provides a robust platform for noise characterization of amplifiers.
• Magnetic field effects on amplifier noise performance are significant and depend on semiconductor device properties.
• Understanding these effects is critical for designing reliable MRI systems and other sensitive electronic equipment operating in magnetic environments.