Real-Time Differential Signal Phase Estimation for Space-Based Systems using FPGAs

High performance and reliability are important aspects of space-based systems. In many cases correct system functionality must be continuously monitored to ensure the validity of collected data. In this research we develop a new digital circuit which can detect minute phase differences in time-varying analog signals. These phase shifts can be determined for both a single channel input versus a known model of the signal and across two channels with simultaneously-sampled data. Phase shift data can be used in spaceborne systems to either confirm correct system operation or identify potential problems. Current systems primarily transfer data to the Earth for error checking rather than performing error analysis in real-time. The benefits of our field-programmable gate array (FPGA)-based approach are evaluated using a 3 gigasamples per second (GSamp/s) data acquisition system developed as part of the NASA Surface Water Ocean Topography (SWOT) initiative. Phase calculations with an error of less than 0.021 deg (0.006% of 360 deg) are determined using our adaptive approach. The high accuracy of differential phase detection allows for the real-time monitoring of environmental metrics, such as temperature fluctuations, which affect signal phase.