Architecture, Modeling, and Analysis of a Plasma Impedance Probe

Variations in ionospheric plasma density can cause large amplitude and phase changes in the radio waves passing through this region. Ionospheric weather can have detrimental effects on several communication systems, including radars, navigation systems such as the Global Positioning Sytem (GPS), and high-frequency communications. As a result, creating models of the ionospheric density is of paramount interest to scientists working in the field of satellite communication. Numerous empirical and theoretical models have been developed to study the upper atmosphere climatology and weather. Multiple measurements of plasma density over a region are of marked importance while creating these models. The lack of spatially distributed observations in the upper atmosphere is currently a major limitation in space weather research. A constellation of CubeSat platforms would be ideal to take such distributed measurements. The use of miniaturized instruments that can be accommodated on small satellites, such as CubeSats, would be key to acheiving these science goals for space weather. The accepted instrumentation techniques for measuring the electron density are the Langmuir probes and the Plasma Impedance Probe (PIP). While Langmuir probes are able to provide higher resolution measurements of relative electron density, the Plasma Impedance Probes provide absolute electron density measurements irrespective of spacecraft charging. The central goal of this dissertation is to develop an integrated architecture for the PIP that will enable space weather research from CubeSat platforms. The proposed PIP chip integrates all of the major analog and mixed-signal components needed to perform swept-frequency impedance measurements. The design\u27s primary innovation is the integration of matched Analog-to-Digital Converters (ADC) on a single chip for sampling the probes current and voltage signals. A Fast Fourier Transform (FFT) is performed by an off-chip Field-Programmable Gate Array (FPGA) to compute the probes impedance. This provides a robust solution for determining the plasma impedance accurately. The major analog errors and parametric variations affecting the PIP instrument and its effect on the accuracy and precision of the impedance measurement are also studied. The system clock is optimized in order to have a high performance ADC. In this research, an alternative clock generation scheme using C-elements is described to reduce the timing jitter and reference spurs in phase locked loops. While the jitter performance and reference spur reduction is comparable with prior state-of-the-art work, the proposed Phase Locked Loop (PLL) consumes less power with smaller area than previous designs

Fully-Integrated Electronic System for a Plasma Impedance Probe

This paper describes a single-chip electronic system for a Plasma Impedance Probe (PIP) currently being developed for microsatellite instrumentation. The chip integrates all of the major analog and mixed-signal components needed to perform swept-frequency impedance measurements. By integrating these components onto a single chip, the weight and volume of the PIP instrument are drastically reduced. Unlike previous PIP designs, the integrated PIP performs direct voltage/current sampling on the probe’s terminal. A Fast Fourier Transform (FFT) is performed by an off-chip FPGA to compute the impedance of the probe. By performing A-to-D conversion as early as possible in the signal flow chain, the design is made less sensitive to variability in analog components. By using an FFT operation, the instrument is made less sensitive to transient spikes that proved disruptive in previous PIP designs